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| Dual Output GSM PA Controller AD8316 FEATURES Complete RF Detector/Controller Function Selectable Dual Outputs 49 dB Range at 0.9 GHz (-47.6 dBm to +1.5 dBm re 50 Accurate Scaling from 0.1 GHz to 2.5 GHz Temperature-Stable Linear-in-dB Response Log Slope of 22 mV/dB True Integration Function in Control Loop Low Power: 23 mW at 2.7 V Power-Down to 11 W ) power control signal is required for each band. The logarithmic amplifier technique provides a much wider measurement range and better accuracy than is possible using controllers based on diode detectors. In particular, multiband and multimode cellular designs can benefit from the temperature-stable (-30C to +85C) operation over all cellular telephony frequencies. Its high sensitivity allows control at low input signal levels, thus reducing the amount of power that needs to be coupled to the detector. The selected output, OUT1 or OUT2, has the voltage range and current drive to directly connect to the gain control pin of most handset power amplifiers; the deselected output is pulled low to ensure that the inactive PA remains off. Each output has a dedicated integrating filter capacitor that allows separate control loop settings for each PA. OUT1 and OUT2 can swing from 125 mV above ground to within 100 mV below the supply voltage. Load currents of up to 12 mA can be supported. The setpoint control input applied to pin VSET has an operating range of 0.25 V to 1.4 V. The input resistance of the setpoint interface is over 100 M, and the bias current is typically 0.5 A. The AD8316 is available in 10-lead MSOP and 16-lead LFCSP packages and consumes 8.5 mA from a 2.7 V to 5.5 V supply. When it is powered down, the sleep current is 4 A. APPLICATIONS Single-Band, Dual-Band, and Triband Mobile Handsets (GSM, DCS, PCS, EDGE) Wireless Terminal Devices Transmitter Power Control GENERAL DESCRIPTION The AD8316 is a complete, low cost subsystem for the precise control of dual RF power amplifiers (PAs) operating in the frequency range 0.1 GHz to 2.5 GHz and over a typical dynamic range of 50 dB. The device is a dual-output version of the AD8315 and intended for use in dual-band or triband cellular handsets and other battery-operated wireless devices where a separate FUNCTIONAL BLOCK DIAGRAM VPOS ENBL BSEL DET RFIN 10dB 10dB 10dB 10dB DET DET DET DET LOW NOISE GAIN BIAS LOW NOISE BAND GAP REFERENCE OUTPUT ENABLE DELAY FLT1 HI-Z 1.35 OUT1 HI-Z 1.35 OUT2 FLT2 OFFSET COMPENSATION COMM INTERCEPT POSITIONING V-I VSET REV. C Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 (c) 2004 Analog Devices, Inc. All rights reserved. AD8316-SPECIFICATIONS (V Parameter OVERALL FUNCTION Frequency Range1 Input Voltage Range Equivalent dBm Range Logarithmic Slope2, 3 Logarithmic Intercept2, 3 Equivalent dBm Level RF INPUT INTERFACE Input Resistance4 Input Capacitance4 OUTPUTS Minimum Output Voltage Maximum Output Voltage General Limit Output Current Drive Output Buffer Noise Output Noise Small Signal Bandwidth Slew Rate Full-Scale Response Time SETPOINT INTERFACE Nominal Input Range Logarithmic Scale Factor Input Resistance Slew Rate ENABLE INTERFACE Logic Level to Enable Power Input Current when Enable High Logic Level to Disable Power Enable Time Disable Time Power-On/Enable Time Power-Off/Disable Time BAND SELECT INTERFACE Logic Level to Enable OUT1 Input Current when BSEL High Logic Level to Enable OUT2 POWER INTERFACE Supply Voltage Quiescent Current Over Temperature Disable Current6 Over Temperature Conditions POS = 2.7 V, TA = 25 C, 52.3 on RFIN, unless otherwise noted.) Min 0.1 -58.6 -45.6 20.5 -68 -55 Typ Max 2.5 -10 +3 24.5 -78 -65 Unit GHz dBV dBm mV/dB dBV dBm k pF 0.25 2.6 VPOS - 0.1 12 25 100 30 20 50 0.25 43.5 100 16 1.5 V V V V mA nV/Hz nV/Hz MHz V/s ns V dB/V k V/s V A V s s s s To Meet All Specifications 1 dB Log Conformance, 0.1 GHz 0.1 GHz 0.1 GHz Pin RFIN 0.1 GHz 0.1 GHz Pins OUT1 and OUT2 VSET 200 mV, ENBL High, RF Input -60 dBm ENBL Low RL > 800 2.7 V VPOS 5.5 V Source RF Input = 2 GHz, 0 dBm, CFLT = 220 pF, fNOISE = 400 kHz 0.2 V to 2.6 V Swing 10%-90%, 250 mV Step (V SET), Open Loop5 FLTR = Open; Refer to TPC 28 Pin VSET Corresponding to Central 50 dB 22.1 -74 -61 2.9 1.0 0.1 2.45 0.15 0.025 Pin ENBL 1.8 20 0.8 Time from ENBL High to V APC within 1% of Final Value, CFLT = 68 pF; Refer to TPC 20 Time from ENBL Low to V APC within 1% of Final Value, CFLT = 68 pF; Refer to TPC 20 Time from VPOS/ENBL Low to V APC within 1% of Final Value, CFLT = 68 pF; Refer to TPC 25 Time from VPOS/ENBL High to V APC within 1% of Final Value, CFLT = 68 pF; Refer to TPC 25 Pin BSEL 1.8 50 0.0 Pin VPOS 2.7 ENBL High -30C TA +85C ENBL Low -30C TA +85C 8.5 3 5.5 10.7 12 10 13 V mA mA A A 1.7 VPOS V A V 7 3 3 4 VPOS NOTES 1 Operation down to 0.02 GHz is possible. 2 Calculated over the input range of -40 dBm to -10 dBm. 3 Mean and standard deviation specifications are in Table I. 4 See TPC 9 for plot of Input Impedance vs. Frequency. 5 Response time in a closed-loop system will depend upon the filter capacitor (C FLT) used and the response of the variable gain element. 6 This parameter is guaranteed but not tested in production. The maximum specified limit on this parameter is the +6 sigma value from characterization. Specifications subject to change without notice. -2- REV. C AD8316 Table I. Typical Specifications at Selected Frequencies at 25C Slope (mV/dB) Frequency (GHz) 0.1 0.9 1.9 2.5 Mean 22.1 22.2 21.6 21.3 Standard Deviation 0.3 0.3 0.3 0.3 Intercept (dBm) Mean -61.0 -62.2 -63.1 -66.0 Standard Deviation 1.5 1.5 1.5 1.6 Dynamic Range Low Point (dBm) Mean -45.6 -47.6 -49.2 -51.5 Standard Deviation 0.7 0.6 0.8 1.1 Dynamic Range High Point (dBm) Mean 3.0 1.5 -4.5 -3.0 Standard Deviation 0.7 0.6 0.8 1.1 Slope and intercept calculated over the input amplitude range of -40 dBm to -10 dBm. ABSOLUTE MAXIMUM RATINGS* Supply Voltage VPOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 V OUT1, OUT2, VSET, ENBL . . . . . . . . . . . . . . . . . . . 0 V, VPOS RFIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 dBm Equivalent Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 V Internal Power Dissipation . . . . . . . . . . . . . . . . . . . . . . . 100 mW JA (MSOP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200C/W JA (LFCSP, Paddle soldered) . . . . . . . . . . . . . . . . . . . . . 80C/W JA (LFCSP, Paddle not soldered) . . . . . . . . . . . . . . . . . 130C/W Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . 125C Operating Temperature Range . . . . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . . . . . -65C to +150C Lead Temperature Range (Soldering 60 sec) MSOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300C LFCSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240C *Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. PIN FUNCTION DESCRIPTIONS Pin No. PIN CONFIGURATION 10-Lead MSOP 16-Lead LFCSP 14 COMM 16 NC 15 NC 13 NC MSOP LFCSP 1 2 3 4 5 6 7 8 9 10 1 2 3 4 6 7 9 10, 14 11 12 5, 8, 13, 15, 16 ORDERING GUIDE Mnemonic Function RFIN ENBL VSET FLT1 BSEL FLT2 OUT2 COMM OUT1 VPOS NC RF Input. Connect to VPOS for Normal Operation. Connect pin to ground for disable mode. Setpoint Input. Integrator Capacitor for OUT1. Connect between FLT1 and COMM. Band Select. LO = OUT2, HI = OUT1. Integrator Capacitor for OUT2. Connect between FLT2 and COMM. Band 2 Output. Device Common (Ground). Band 1 Output. Positive Supply Voltage: 2.7 V to 5.5 V. No Connection. RFIN 1 ENBL 2 VSET 3 FLT1 4 BSEL 5 10 VPOS AD8316 TOP VIEW (NOT TO SCALE) 9 OUT1 8 COMM 7 OUT2 6 FLT2 RFIN 1 ENBL 2 VSET 3 FLT1 4 12 VPOS AD8316 TOP VIEW (Not to Scale) 11 OUT1 10 COMM 9 OUT2 NC 5 BSEL 6 FLT2 7 NC = NO CONNECT Model AD8316ARM AD8316ARM-REEL7 AD8316-EVAL AD8316ACP-REEL AD8316ACP-REEL7 AD8316ACP-EVAL Temperature Range Package Description -30C to +85C -30C to +85C -30C to +85C -30C to +85C 10-Lead MSOP, Tube MSOP, 7" Tape and Reel MSOP Evaluation Board 16-Lead LFCSP, 13" Tape and Reel LFCSP, 7" Tape and Reel LFCSP Evaluation Board NC 8 Package Option Branding RM-10 RM-10 CP-16-3 CP-16-3 J8A J8A J8A J8A CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD8316 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. REV. C -3- AD8316 -Typical Performance Characteristics -73 1.6 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 -73 4 3 1.9GHz -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 1.4 0.9GHz 1.2 VSET - V 1.9GHz 0.1GHz 2 1.0 0.8 1.9GHz ERROR - dB 2.5GHz 1 0 2.5GHz -1 0.9GHz -2 -3 -4 -60 0.6 0.1GHz 0.4 0.2 -60 -50 -40 -30 -20 -10 INPUT AMPLITUDE - dBm 0 10 -50 -40 -30 -20 -10 0 10 INPUT AMPLITUDE - dBm TPC 1. VSET vs. Input Amplitude TPC 4. Log Conformance vs. Input Amplitude at Selected Frequencies -73 1.6 1.4 1.2 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -30 C -3 4 3 +25 C 2 -73 1.6 1.4 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 4 3 +25 C 1.2 +85 C 2 1 -30 C 0 -1 +85 C -2 -3 +25 C -50 -30 C -40 -30 -20 -10 0 -4 10 +85 C 1.0 +85 C ERROR - dB -30 C 0.8 +25 C 0.6 0.4 0.2 0 -60 -1 -2 -3 -4 10 0 0.8 0.6 0.4 0.2 0 -60 -50 -40 -30 -20 -10 0 INPUT AMPLITUDE - dBm INPUT AMPLITUDE - dBm TPC 2. VSET and Log Conformance vs. Input Amplitude at 0.1 GHz TPC 5. VSET and Log Conformance vs. Input Amplitude at 1.9 GHz -73 1.6 1.4 1.2 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 +85 C -13 -3 4 3 2 -73 1.6 1.4 1.2 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 4 3 2 +25 C ERROR - dB +25 C 1 +85 C ERROR - dB 1.0 VSET - V 1.0 VSET - V 1 0 -30 C -1 -2 -3 +25 C -50 -30 C -40 -30 -20 -10 0 -4 10 0.8 0.6 0.4 0.2 -30 C 0 -1 -2 -3 0.8 0.6 +85 C 0.4 0.2 0 -60 +85 C +25 C 0 -60 -50 -30 C -40 -30 -20 -10 0 -4 10 INPUT AMPLITUDE - dBm INPUT AMPLITUDE - dBm TPC 3. VSET and Log Conformance vs. Input Amplitude at 0.9 GHz TPC 6. VSET and Log Conformance vs. Input Amplitude at 2.5 GHz -4- REV. C ERROR - dB 1 1.0 VSET - V VSET - V AD8316 -73 4 3 2 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 -73 4 3 +85 C 2 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 +85 C ERROR - dB 0 -1 -2 -3 -4 -60 -30 C ERROR - dB 1 1 0 -1 -2 -30 C -3 -4 -60 -50 -40 -30 -20 -10 0 10 -50 -40 -30 -20 -10 0 10 INPUT AMPLITUDE - dBm INPUT AMPLITUDE - dBm TPC 7. Distribution of Error at Temperature after Ambient Normalization vs. Input Amplitude, 3 Sigma to Either Side of Mean, 0.1 GHz TPC 10. Distribution of Error at Temperature after Ambient Normalization vs. Input Amplitude, 3 Sigma to Either Side of Mean, 1.9 GHz -73 4 3 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 -73 4 3 -63 INPUT AMPLITUDE - dBV -53 -43 -33 -23 -13 -3 +85 C 2 ERROR - dB 2 +85 C 0 -1 -30 C -2 -3 -4 -60 ERROR - dB 1 1 0 -1 -2 -30 C -3 -4 -60 -50 -40 -30 -20 -10 0 10 -50 -40 -30 -20 -10 0 10 INPUT AMPLITUDE - dBm INPUT AMPLITUDE - dBm TPC 8. Distribution of Error at Temperature after Ambient Normalization vs. Input Amplitude, 3 Sigma to Either Side of Mean, 0.9 GHz TPC 11. Distribution of Error at Temperature after Ambient Normalization vs. Input Amplitude, 3 Sigma to Either Side of Mean, 2.5 GHz 3100 2800 2500 2200 RESISTANCE - 1900 X (LFCSP) 1600 1300 1000 R (CSP) 700 400 100 0 0.5 1.0 1.5 2.0 FREQUENCY - GHz R (MSOP) R X X (MSOP) FREQ (GHz) 0.1 0.9 1.9 2.5 CHIP-SCALE (LFCSP) R - jX R - jX 3100 - j1220 2630 - j1800 600 - j194 1000 - j270 320 - j134 620 - j130 110 - j86 435 - j110 0 -200 MSOP -400 -600 -800 -1000 -1200 -1400 -1600 -1800 -2000 2.5 REACTANCE - SUPPLY CURRENT - mA 8 6 INCREASING VENBL 4 DECREASING VENBL 2 0 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 VENBL - V TPC 9. Input Impedance vs. Frequency TPC 12. Supply Current vs. VENBL REV. C -5- AD8316 23 -60 +25 C -62 SLOPE - mV/dB 22 +25 C INTERCEPT - dBm -64 -30 C -30 C 21 -66 +85 C +85 C 20 0 0.5 1.0 1.5 2.0 2.5 FREQUENCY - GHz -68 0 0.5 1.0 1.5 2.0 2.5 FREQUENCY - GHz TPC 13. Slope vs. Frequency at Selected Temperatures TPC 16. Intercept vs. Frequency at Selected Temperatures 22.5 -58 -60 22.0 0.1GHz INTERCEPT - dBm SLOPE - mV/dB 0.9GHz 0.1GHz 21.5 -62 -64 1.9GHz -66 2.5GHz 0.9GHz 1.9GHz 21.0 2.5GHz -68 20.5 2.5 3.0 3.5 4.0 VS - V 4.5 5.0 5.5 -70 2.5 3.0 3.5 4.0 VS - V 4.5 5.0 5.5 TPC 14. Slope vs. Supply Voltage TPC 17. Intercept vs. Supply Voltage 50 40 30 20 AMPLITUDE - dB 0 -20 10000 -50dBm NOISE SPECTRAL DENSITY - nV/ Hz -40 -60 PHASE - Degrees -40dBm -25dBm 10 CFLT = 220pF 0 -10 -20 -30 -40 -50 -60 1 10 100 1k 10k 100k FREQUENCY - Hz 1M 10M CFLT = 0pF -80 -100 -120 -140 -160 -180 -200 -210 100M 1000 0dBm -20dBm 100 -10dBm RF INPUT 28dBm 10 100 1k 100k 10k 1M FREQUENCY - Hz 10M 100M TPC 15. AC Response from VSET to OUT1 and OUT2 TPC 18. Output Noise Spectral Density, RL = , CFLT = 220 pF, by RF Input Amplitude -6- REV. C AD8316 3.5 3.3 3.1 2.9 ILOAD 0mA 4mA 2mA 2.8 2.7 2mA 2.6 VOUT - V VOUT - V 2.7 2.5 8mA 2.3 2.1 1.9 2.7 6mA 10mA 12 mA 2.5 6mA 2.4 SHADING INDICATES 2.3 3 SIGMA 2.8 2.9 3.0 3.1 VS - V 3.2 3.3 3.4 3.5 2.2 2.7 2.8 VS - V 2.9 3.0 TPC 19. Maximum OUT Voltage vs. Supply Voltage by Load Current, AD8316 Sourcing TPC 22. Distribution of Maximum OUT Voltage vs. Supply Voltage with 2 mA and 6 mA Loads, 3 Sigma to Either Side of Mean, AD8316 Sourcing AVERAGING = 16 SAMPLES CFLT = 68pF 50mV PER VERTICAL DIVISION CFLT = 220pF GND VOUT BSEL INPUT AVERAGING = 16 SAMPLES VOUT2 10mV PER VERTICAL DIVISION GND VENBL 1V PER VERTICAL DIVISION GND 1V PER VERTICAL DIVISION GND 2 s PER HORIZONTAL DIVISION 2 s PER HORIZONTAL DIVISION TPC 20. ENBL Response Time, Rise/Fall Time = 250 ns TPC 23. BSEL Response Time, ENBL Grounded H-P 8648B SIGNAL GENERATOR RF OUT 0.1GHz 60dBm 2.7V H-P 8110A PULSE GENERATOR PULSE OUT TEK P6204 FET PROBE 0.1 F H-P 8648B SIGNAL GENERATOR RF OUT 0.1GHz -60dBm H-P 8110A PULSE GENERATOR PULSE OUT 2.7V TEK P6204 FET PROBE 0.1 F AD8316 RFIN 52.3 ENBL VSET CFLT 2.7V FLT1 BSEL* VPOS OUT1 COMM OUT2 FLT2 AD8316 RFIN TEK P6204 FET PROBE VPOS OUT1 COMM OUT2 FLT2 CFLT RL 1k TEK P6204 FET PROBE TEK 1103 PWR SUPPLY TEK TDS3054 SCOPE 52.3 ENBL VSET CFLT FLT1 BSEL* RL 1k CFLT TEK 1103 PWR SUPPLY TEK TDS3054 SCOPE *BSEL HIGH BSEL LOW OUT1; OUT2 *BSEL HIGH BSEL LOW OUT1; OUT2 TPC 21. Test Setup for ENBL Response Time TPC 24. Test Setup for BSEL Response Time REV. C -7- AD8316 AVERAGING = 16 SAMPLES CFLT = 220pF VOUT 1V PER VERTICAL DIVISION VOUT AVERAGING = 16 SAMPLES CFLT = 68pF GND VPOS/VENBL 250ns RISE TIME 50mV PER VERTICAL DIVISION GND GND 2V PER VERTICAL DIVISION PULSED RF INPUT 0.1GHz, -3dBm GND 2 s PER HORIZONTAL DIVISION 100ns PER HORIZONTAL DIVISION TPC 25. Power-On and Power-Off Response with VSET Grounded, Rise/Fall Time = 250 ns TPC 28. Pulse Response Time, Full-Scale Amplitude Change, Open Loop, CFLT = 0 pF AVERAGING = 16 SAMPLES VOUT AVERAGING = 16 SAMPLES CFLT = 68pF 1V PER VERTICAL DIVISION 50mV PER VERTICAL DIVISION VOUT CFLT = 220pF GND VPOS/VENBL 1s RISE TIME GND PULSED RF INPUT 0.1GHz, -3dBm GND GND 2V PER VERTICAL DIVISION 2 s PER HORIZONTAL DIVISION 2 s PER HORIZONTAL DIVISION TPC 26. Power-On and Power-Off Response with VSET Grounded, Rise/Fall Time = 1 s TPC 29. Pulse Response Time, Full-Scale Amplitude Change, Open Loop, CFLT = 68 pF H-P 8648B SIGNAL GENERATOR RF OUT 0.1GHz -60dBm AD811 H-P 8110A PULSE GENERATOR PULSE OUT 49.9 EXT TRIG H-P 8648B 10MHz REF OUT SIGNAL GENERATOR PULSE MODE IN 0.1GHz RFOUT 0dBm 3dB PWR DIVIDER PULSE OUT H-P 8110A TRIG OUT PULSE GENERATOR TEK P6204 FET PROBE AD8316 RFIN 52.3 ENBL VSET CFLT FLT1 BSEL* VPOS OUT1 COMM OUT2 FLT2 2.7V 732 TEK P6204 FET PROBE TEK P6204 FET PROBE RL 1k TEK 1103 PWR SUPPLY TEK TDS3054 SCOPE AD8316 0.1 F RFIN VPOS OUT1 COMM OUT2 FLT2 52.3 2.7V 0.4V CFLT 2.7V ENBL VSET FLT1 TEK P6204 FET PROBE RL 1k CFLT TEK 1103 PWR SUPPLY TEK TDS3054 SCOPE CFLT BSEL* *BSEL HIGH BSEL LOW OUT1; OUT2 * BSEL HIGH BSEL LOW OUT1; OUT2 TPC 27. Test Setup for Power-On and Power-Off Response with VSET Grounded TPC 30. Test Setup for Pulse Response Time -8- REV. C AD8316 AVERAGING = 16 SAMPLES VOUT 10mV PER VERTICAL DIVISION 250ns RISE TIME 1s RISE TIME amplifiers. When the band select pin, BSEL, directs one of the controller outputs to servo its amplifier toward the setpoint indicated by the power control pin VSET, the other output is forced to ground, disabling the second amplifier. Each output has a dedicated filter pin, FLT1 and FLT2, that allows the filtering and loop dynamics for each control loop to be optimized independently. Basic Theory VPOS INPUT 2V PER VERTICAL DIVISION 2 s PER HORIZONTAL DIVISION Logarithmic amplifiers provide a type of compression in which a signal with a large range of amplitudes is converted to one of a smaller range. The use of the logarithmic function uniquely results in the output representing the decibel value of the input. The fundamental mathematical form is VOUT = VSLP log VIN VZ TPC 31. Power-On and Power-Off Response with VSET and ENBL Grounded (1) H-P 8648B 0.1GHz SIGNAL -60dBm GENERATOR RFOUT AD811 H-P 8110A PULSE GENERATOR PULSE OUT 49.9 Here VIN is the input voltage and VZ is called the intercept (voltage) because when VIN = VZ the argument of the logarithm is unity, and thus the result is zero; VSLP is called the slope (voltage), which is the amount by which the output changes for a certain change in the ratio (VIN/VZ). Because log amps do not respond to power, but only to voltages, and the calibration of the intercept is waveform dependent and only quoted for a sine wave signal, the equivalent power response can be written as AD8316 RFIN 52.3 ENBL VSET CFLT FLT1 BSEL* VPOS OUT1 COMM OUT2 FLT2 732 TEK P6204 FET PROBE TEK P6204 FET PROBE RL 1k TEK 1103 PWR SUPPLY TEK TDS3054 SCOPE VOUT = VDB (PIN - PZ ) (2) CFLT *BSEL HIGH BSEL LOW OUT1; OUT2 TPC 32. Test Setup for Power-On and Power-Off Response with VSET and ENBL Grounded GENERAL DESCRIPTION AND THEORY The AD8316 is a wideband logarithmic amplifier (log amp) with two selectable outputs suitable for dual-band/dual-mode power amplifier control. It is strictly optimized for power control applications rather than for use as a measurement device. Figure 1 shows its main features in block schematic form. The output pins, OUT1 and OUT2, are intended to be applied directly to the automatic power control (APC) pins of two distinct power where the input power PIN and the equivalent intercept PZ are both expressed in dBm (thus, the quantity in the parentheses is simply a number of decibels), and VDB is the slope expressed as so many mV/dB. When base 10 logarithms are used, denoted by the function log10, VSLP represents V/dec, and since a decade corresponds to 20 dB, VSLP/20 represents the change in V/dB. For the AD8316, a nominal (low frequency) slope of 22 mV/dB (corresponding to a VSLP of 0.022 mV/dB x 20 dB = 440 mV) was chosen, and the intercept VZ was placed at the equivalent of -74 dBV, or 199 V rms, for a sine wave input. This corresponds to a power level of -61 dBm when the net resistive part of the input impedance of the log amp is 50 . However, both the slope and the intercept are dependent on frequency (see for example, TPC 13 and TPC 16). For a log amp with a slope VDB of +22 mV/dB and an intercept at -61 dBm, the output voltage for an input power of -30 dBm is 0.022 x (-30 - [-61]) = 0.682 V. FLT1 HI-Z 1.35 OUT1 LOW NOISE RAIL-TO-RAIL BUFFERS HI-Z VPOS ENBL BSEL LOW NOISE GAIN BIAS LOW NOISE BAND GAP REFERENCE OUTPUT ENABLE DELAY DET RFIN 10dB DET DET DET DET 10dB 10dB 10dB 1.35 OUT2 FLT2 OFFSET COMPENSATION COMM INTERCEPT POSITIONING V-I VSET 325mV TO 1.4V = 49dB Figure 1. Block Schematic of the AD8316 REV. C -9- AD8316 Further details about the structure and function of log amps are provided in data sheets for other log amps produced by Analog Devices. The AD640 and AD8307 include detailed discussions of the basic principles of operation and explain why the intercept depends on waveform, an important consideration when complex modulation is imposed on an RF carrier. The intercept need not correspond to a physically realizable part of the signal range for the log amp. Thus, for the AD8316, the specified intercept is -62 dBm at 0.9 GHz, whereas the lowest acceptable input for accurate measurement (+1 dB error) is -48 dBm. At 2.5 GHz, the +1 dB error point shifts to -52 dBm. This positioning of the intercept is deliberate and ensures that the VSET voltage is within the capabilities of certain DACs, whose outputs cannot swing below 200 mV. Figure 2 shows the 0.9 GHz response of the AD8316; the vertical axis represents the value required at the power control pin VSET to null the control loop rather than the voltage at the OUT1 or OUT2 pins. VIN, dBVIN 100 V 80dBV 1.5V 1mV 60dBV 10mV 40dBV 100mV 20dBV 1V (rms) 0dBV In a device intended for measurement applications, this current would be converted to an equivalent voltage to provide the log(VIN) function shown in Equation 1. However, the design of the AD8316 differs from standard practice in that its output needs to be a low noise control voltage for an RF power amplifier, not a direct measure of the input level. Further, it is highly desirable that this voltage be proportional to the time integral of the error between the actual input VIN and a dc voltage VSET (applied to Pin 3, VSET) that defines the setpoint, that is, a target value for the power level, typically generated by a DAC. This is achieved by converting the difference between the sum of the detector outputs (still in current form) and an internally generated current proportional to VSET to a single-sided current-mode signal. This, in turn, is converted to a voltage (at FLT1 or FLT2, the low-pass filter capacitor nodes) to provide a close approximation to an exact integration of the error between the power present in the termination at the input of the AD8316 and the setpoint voltage. Finally, the voltages developed across the ground referenced filter capacitors CFLT are buffered by a special low noise amplifier of low voltage gain (x1.35) and presented at OUT2 or OUT1 for use as the control voltage for the appropriate RF power amplifier. This buffer can provide rail-to-rail swings and can drive a substantial load current, including large capacitors. Note: The RF power delivered by the power amplifier is assumed to increase monotonically with an increasingly positive voltage on its APC control pin. Band selection in the AD8316 relies on the fact that dual-band/ dual-mode amplifier systems require only one active amplifier at a time. This allows both amplifier outputs to share the RF input of the AD8316 (Pin 1, RFIN) as long as the inactive amplifier is disabled, i.e., it is not delivering RF power. In this case, power control is directed solely through the selected amplifier. The AD8316 ensures that the output control pin associated with the unselected amplifier pulls its APC pin to ground. It is assumed that the amplifier is essentially disabled when its APC pin is grounded. Control Loop Dynamics 1.408V AT +2dBm 1.0V VSET PE O SL = dB V/ m 22 ACTUAL 0.5V 0.308V AT -48dBm IDEAL 0 -62dBm -67dBm -47dBm -27dBm PIN -7dBm +13dBm Figure 2. Basic Calibration of the AD8316 at 0.9 GHz Controller-Mode Log Amps The AD8316 combines the two key functions required for the measurement and control of the power level over a moderately wide dynamic range. First, it provides the amplification needed to respond to small signals with a chain of four amplifier/limiter cells, each with a small signal gain of 10 dB and a bandwidth of approximately 4 GHz (see Figure 1). At the output of each of these amplifier stages is a full-wave rectifier, essentially a square-law detector cell that converts the RF signal voltages to a fluctuating current having an average value that increases with signal level. A passive detector stage is added ahead of the first stage. These five detectors are separated by 10 dB, spanning 50 dB of dynamic range. Their outputs are in the form of a differential current, making summation a simple matter. It is readily shown that the summed output can closely approximate a logarithmic function. The overall accuracy at the extremes of the total range, viewed as the deviation from an ideal logarithmic response, that is, the law-conformance error, can be judged by referring to TPC 4, which shows that errors across the central 40 dB are moderate. Other performance curves show how conformance to an ideal logarithmic function varies with supply voltage, temperature, and frequency. To understand how the AD8316 behaves in a complete control loop, it is necessary to develop an expression for the current in the integration capacitor as a function of the input VIN and the setpoint voltage VSET. Refer to Figure 3. VSET 3 SETPOINT INTERFACE ISET = VSET / 4.15k VSET RFIN 1 VIN LOGARITHMIC RF DETECTION SUBSYSTEM IDET IDET = ISLP log10 (VIN/VZ) FLT1 4 IERR CFLT 1.35 VOUT1 9 Figure 3. Behavioral Model for the AD8316 with OUT1 Selected First, write the summed detector currents as a function of the input: IDET = ISLP log10 (VIN /VZ ) (3) where IDET is the partially filtered demodulated signal, whose exact average value will be extracted through the subsequent integration step; ISLP is the current-mode slope, and has a value of 106 mA per decade (that is, 5.3 mA/dB); VIN is the input in REV. C -10- AD8316 volts rms; and VZ is the effective intercept voltage, which, as previously noted, is dependent on waveform but is 199 V rms for a sine wave input. Now, the current generated by the setpoint interface is simply point for understanding the more complex situation that arises when the gain control law is less than ideal. This idealized control loop is shown in Figure 4. With some manipulation, it is found that the characteristic equation of this system is VOUT (s ) = (VSET VGSC )/VSLP - VGSC log10 (kGO VCW /VZ ) 1 + sTO ISET = VSET / 4.15 k (4) IERR, the difference between this current and IDET, is applied to the loop filter capacitor CFLT. It follows that the voltage appearing on this capacitor, VFLT, is the time integral of the difference current VFLT ( s ) = ( I SET - I DET ) / sCFLT = VSET / 4.15 k - I SLP log10 (VIN / VZ ) sCFLT (10) (5) (6) where k is the voltage coupling factor from the output of the power amplifier to the input of the AD8316 (e.g., x0.1 for a 20 dB coupler) and TO is a modified time constant (VGSC/VSLP)T. This is quite easy to interpret. First, it shows that a system of this sort will exhibit a simple single-pole response, for any power level, with the customary exponential time domain form for either increasing or decreasing step polarities in the demand level VSET or the carrier input VCW. Second, it reveals that the final value of the control voltage VOUT will be determined by several fixed factors VOUT (t = ) = (VSET VGSC )/VSLP - VGSC log10 (kGO VCW /VZ )(11) The control output VOUT is slightly greater than this, since the gain of the output buffer is x1.35. Also, an offset voltage is deliberately introduced in this stage, but this is inconsequential, since the integration function implicitly allows for an arbitrary constant to be added to the form of Equation 6. The polarity is such that VOUT will rise to its maximum value for any value of VSET greater than the equivalent value of VIN. In practice, the output will rail to the positive supply under this condition unless the control loop through the power amplifier is present. In other words, the AD8316 seeks to drive the RF power to its maximum value whenever it falls below the setpoint. The use of exact integration results in a final error that is theoretically zero, and the logarithmic detection law would ideally result in a constant response time following a step change of either the setpoint or the power level, if the power amplifier control function were likewise "linear-in-dB." This latter condition is rarely true, however, and it follows that the loop response time will, in practice, depend on the power level, and this effect can strongly influence the design of the control loop. Equation 6 can be clarified by noting that it can be restated in the following way V - VSLP log10 (VIN /VZ ) VOUT (s ) = SET sT (7) DIRECTIONAL COUPLER VRF RF PA VCW RF DRIVE: UP TO 2.5GHz VIN = kVRF VSET AD8316 CFLT VOUT1 RESPONSE-SHAPING OF OVERALL CONTROL LOOP (EXTERNAL CAP) Figure 4. Idealized Control Loop for Dynamic Analysis, OUT1 Selected Example where VSLP is the volts-per-decade slope from Equation 1, having a value of 440 mV/dec, and T is an effective time constant for the integration, being equal to (4.15 k x CFLT)/1.35; the resistor value comes from the setpoint interface scaling Equation 4 and the factor 1.35 arises as a result of the voltage gain of the buffer. So the integration time constant can be written as T = 3.07 x CFLT Assume that the gain magnitude of the power amplifier runs from a minimum value of x0.316 (-10 dB) at VOUT = 0 to x100 (40 dB) at VOUT = 2.5 V. Applying Equation 9, we find GO = 0.316 and VGSC = 1 V. Using a coupling factor of k = 0.0316 (that is, a 30 dB directional coupler) and recalling that the nominal value of VSLP is 440 mV and VZ = 199 V for the AD8316, we will first calculate the range of values needed for VSET to control an output range of +32 dBm to -17 dBm. Note that, in the steady state, the numerator of Equation 7 must be zero, that is VSET = VSLP log10 ( kVPA VZ ) (12) (in s when CFLT is expressed in nF ) (8) To simplify understanding of the control loop dynamics, begin by assuming that the power amplifier gain function actually is linear-in-dB; for now, we will also use voltages to express the signals at the power amplifier input and output. Let the RF output voltage be VPA and its input be VCW; further, to characterize the gain control function, this form is used VPA = GO VCW 10( V OUT when VIN is expanded to kVPA, the fractional voltage sample of the power amplifier output. Now, for +32 dBm, VPA = 8.9 V rms, this evaluates to VSET (max) = 0.44 log10 (281 mV/ 199 V ) = 1.39V (13) /V GSC ) (9) For a delivered power of -17 dBm, VPA = 31.6 mV rms, where GO is the gain of the power amplifier when VOUT = 0 and VGSC is the gain scaling. While few amplifiers will conform so conveniently to this law, it nevertheless provides a clearer starting VSET (min) = 0.44 log10 (1.0 mV/ 199 V ) = 0.310 V (14) Note: The power range is 49 dB, which corresponds to a voltage change of 49 dB x 22 mV/dB = 1.08 V in VSET. REV. C -11- AD8316 The value of VOUT is of interest, although it is a dependent parameter inside the loop. It depends on the characteristics of the power amplifier, and the value of the carrier amplitude VCW. Using the control values derived above, that is, GO = 0.316 and VGSC = 1 V, and assuming that the applied power is fixed at -7 dBm (so that VCW = 100 mV rms), Equation 11 shows VOUT (max ) = (VSETVGSC ) VSLP - log10 (kGOVCW VZ ) 0.0316 x 0.316 x = (1.39 x 1) 0.44 - log10 0.1 / 199 V = 3.2 - 0.7 = 2.5 V VOUT (min) = ( SETVGSC ) VSLP - log10 (kGOVCW VZ ) V 0.0316 x 0.316 x = (0.31 x 1) 0.44 - log10 0.1 / 199 V = 0.7 - 0.7 = 0 (15) is not. For example, 224 mV rms is always -13 dBV, with one further condition of an assumed sinusoidal waveform; see the AD640 data sheet for more information about the effect of waveform on logarithmic intercept. This corresponds to a power of 0 dBm when the net impedance at the input is 50 . When this impedance is altered to 200 , however, the same voltage corresponds to a power level that is four times smaller (P = V2/R), or -6 dBm. A dBV level may be converted to dBm in the special case of a 50 system and a sinusoidal signal simply by adding 13 dB. 0 dBV is then, and only then, equivalent to 13 dBm. PRF V2, P2 (16) 33dBm 23dBm Both results are consistent with the assumptions made about the amplifier control function. Note that the second term is independent of the delivered power and is a fixed function of the drive power. Finally, the loop time constant for these parameters, using an illustrative value of 2 nF for the filter capacitor CFLT, evaluates to 13dBm 3dBm TO = ( GSC / VSLP )T V Practical Loop -7dBm VOUT1 V1, P1 -47dBm -27dBm -7dBm +13dBm = (1 / 0.44) x 3.07 s x 2(nF ) = 13.95 s (17) -67dBm Figure 5. Typical Power Control Curve At the present time, power amplifiers, or VGAs preceding such amplifiers, do not provide an exponential gain characteristic. It follows that the loop dynamics (the effective time constant) will vary with the setpoint, since the exponential function is unique in providing constant dynamics. The procedure must therefore be as follows. Beginning with the curve usually provided for the power output versus APC voltage, draw a tangent at the point on this curve where the slope is highest (see Figure 5). Using this line, calculate the effective minimum value of the variable VGSC, and use it in Equation 17 to determine the time constant. (Note that the minimum in VGSC corresponds to the maximum rate of change in the output power versus VOUT.) For example, suppose it is found that, for a given drive power, the amplifier generates an output power of P1 at VOUT = V1, and P2 at VOUT = V2. Then, it is readily shown that VGSC = 20( 2 - V1 ) / (P2 - P1 ) V (18) Therefore, the external termination added ahead of the AD8316 determines the effective power scaling. This often takes the form of a simple resistor (52.3 will provide a net 50 input), but more elaborate matching networks may be used. The choice of impedance determines the logarithmic intercept, that is, the input power for which the VSET versus PIN function would cross the baseline if that relationship were continuous for all values of VIN. This is never the case for a practical log amp; the intercept (so many dBV) refers to the value obtained by the minimum-error straight-line fit to the actual graph of VSET versus PIN (more generally, VIN). Where the modulation is complex, as in CDMA, the calibration of the power response needs to be adjusted; the intercept will remain stable for any given arbitrary waveform. When a true power (waveform independent) response is needed, a mean-responding detector, such as the AD8361, should be considered. The logarithmic slope, VSLP in Equation 1, which is the amount by which the setpoint voltage needs to be changed for each decade of input change (voltage or power) is, in principle, independent of waveform or termination impedance. In practice, it usually falls off somewhat at higher frequencies, because of the declining gain of the amplifier stages and other effects in the detector cells (see TPC 13). Basic Connections This should be used to calculate the filter capacitance. The response time at high and low power levels (on the "shoulders" of the curve shown in Figure 5) will be slower. Note also that it is sometimes useful to add a zero in the closed-loop response by placing a resistor in series with CFLT. A Note About Power Equivalency Users of the AD8316 must understand that log amps fundamentally do not respond to power. For this reason, dBV (decibels above 1 V rms) are included in addition to the commonly used metric dBm. The dBV scaling is fixed, independent of termination impedance, while the corresponding power level Figure 6 shows the basic connections for operating the AD8316 and Figure 7 shows a block diagram of a typical application. The AD8316 is typically used in the RF power control loop of dual mode and trimode mobile handsets where there is more than one RF power control line. -12- REV. C AD8316 R1 52.3 RFIN +VS VSET CFLT1 VBSEL AD8316 1 RFIN 2 ENBL 3 VSET 4 FLT1 5 BSEL C1 0.1 F +VS 2.7 TO 5.5V VOUT1 VPOS 10 OUT1 9 COMM 8 OUT2 7 FLT2 6 VOUT2 CFLT2 Figure 6. Basic Connections (Shown with MSOP Pinout) level and the level corresponding to the setpoint voltage will be corrected by the selected output, OUT1 or OUT2, which drives the gain control terminal of the PAs. This restores a balance between the actual power level sensed at the input of the AD8316 and the demanded value determined by the setpoint. This assumes that the gain control sense of the variable gain element is positive; that is, an increasing voltage from OUT1 or OUT2 will tend to increase gain. The outputs can swing from 100 mV above ground to within 100 mV of the supply rail and can source up to 12 mA. (A plot of maximum output voltage versus output current is shown in TPC 19.) OUT1/OUT2 are capable of sinking more than 200 A. Range on VSET and RF Input RX1 ANT RX2 TX1 TX2 PWR AMP GAIN CONTROL VOLTAGES RFIN2 RFIN1 DIRECTIONAL COUPLER ATTN R1 52.3 OUT1 OUT2 RFIN FLT1 CFLT1 VSET BSEL FLT2 CFLT2 BAND SELECT DAC Figure 7. Block Diagram of Typical Application A supply voltage of 2.7 V to 5.5 V is required for the AD8316. The supply to the VPOS pin should be decoupled with a low inductance 0.1 F surface-mount ceramic capacitor close to the device. The AD8316 has an internal input coupling capacitor, which negates the need for external ac coupling. This capacitor, along with the device's low frequency input impedance of approximately 3.0 k, sets the minimum usable input frequency to around 20 MHz. A broadband 50 input match is achieved in this example by connecting a 52.3 resistor between RFIN and ground (COMM). A plot of input impedance versus frequency is shown TPC 9. Other matching methods are also possible (see the Input Coupling Options section). In a power control loop, the AD8316 provides both the detector and controller functions. A number of options exist for coupling the RF signal from the power amplifiers (PA) to the AD8316 input. Because only one PA output is active at any time, a single RF input on the AD8316 is sufficient in all cases. Two directional couplers can be used directly at the PA outputs. The outputs of these couplers would be passively combined before being applied to the AD8316 RF input (in general, some additional attenuation will be required between the coupler and the AD8316). Another option involves using a dual-directional coupler between the PA and T/R switch. This device has two inputs/outputs and a single-coupled output so that no external combiner is required. A third option is to use a single broadband directional coupler at the output of the transmit/receive (T/R) switch (the outputs from the two PAs are combined in the T/R switch). This is shown in Figure 7. This provides the advantage of enabling the power at the output of the T/R switch to be precisely set, eliminating any errors due to insertion loss and insertion loss variations of the T/R switch. The relationship between RF input level and the setpoint voltage follows from the nominal transfer function of the device (see TPCs 2, 3, 5, and 6). At 0.9 GHz, for example, a voltage of 1 V on VSET indicates a demand for -17 dBm (-30 dBV) at RFIN. The corresponding power level at the output of the power amplifier will be greater than this amount due to the attenuation through the directional coupler. For setpoint voltages of less than approximately 200 mV and RF input amplitudes greater than approximately -50 dBm, VOUT will remain unconditionally at its minimum level of approximately 250 mV. This feature can be used to prevent any spurious emissions during power-up and power-down phases. Above 250 mV, VSET will have a linear control range up to 1.4 V, corresponding to a dynamic range of 49 dB. This results in a slope of 22.2 mV/dB or approximately 45.5 dB/V. Transient Response The time domain response of power amplifier control loops, using any kind of controller, is only partially determined by the choice of filter which, in the case of the AD8316, has a true integrator form 1/sT, as shown in Equation 7, with a time constant given by Equation 8. The large signal step response is also strongly dependent on the form of the gain control law. Nevertheless, some simple rules can be applied. When the filter capacitor CFLT is very large, it will dominate the time domain response, but the incremental bandwidth of this loop will still vary as VOUT traverses the nonlinear gain control function of the PA, as shown in Figure 5. This bandwidth will be highest at the point where the slope of the tangent drawn on this curve is greatest--that is, for power outputs near the center of the PA's range--and will be much reduced at both the minimum and the maximum power levels, where the slope of the gain control curve is lowest, due to its S-shaped form. Using smaller values of CFLT, the loop bandwidth will generally increase, in inverse proportion to its value. Eventually, however, a secondary effect will appear, due to the inherent phase lag in the power amplifier's control path, some of which may be due to parasitic or deliberately added capacitance at the OUT1 and OUT2 pins. This results in the characteristic poles in the ac loop equation moving off the real axis and thus becoming complex (and somewhat resonant). This is a classic aspect of control loop design. The lowest permissible value of CFLT needs to be determined experimentally for a particular amplifier and circuit board layout. For GSM and DCS power amplifiers, CFLT will typically range from 150 pF to 300 pF. In many cases, some improvement in the worst-case response time can be achieved by including a small resistance in series with CFLT; this generates an additional zero in the closed-loop transfer function, which will serve to cancel some of the higher-order A setpoint voltage is applied to VSET from the controlling source, generally a DAC. Any imbalance between the RF input REV. C -13- AD8316 3.5V 4.7 F 1F TO T/R SWITCH LDC15D190A0007A 1 7 8 5 2 6 R7 4 49.9 3 GSM RF OUTPUT +35.5dBm MAX PCS/DCS RF OUTPUT +33dBm MAX RF3108 GSM RF IN +6dBm DCS/PCS RF IN +6dBm DCS/PCS VAPC GND GSM/DCS 16.5dBm/19dBm 21.5dB ATTENUATOR R5 54.9 R4 576 ENABLE 0V/+VS R3 1k CFLT1 220pF R1 52.3 C1 0.1 F AD8316 1 RFIN VPOS 10 OUT1 9 COMM 8 OUT2 7 FLT2 6 2 ENBL 3 VSET 4 FLT1 5 BSEL +VS 2.7V TO 5.5V 8-BIT RAMP DAC 0V 2.55V R2 600 R8 (R5, R6 OPTIONAL) (SEE TEXT) R6 (R2, R3 OPTIONAL) (SEE TEXT) CFLT2 220pF BAND SELECT 0V/+VS GSM/(DCS/PCS) Figure 8. Dual-Mode (GSM/DCS) PA Control Example (Shown with AD8316 MSOP Pinout) poles in the overall loop. A combination of main capacitor CFLT shunted by a second capacitor and resistor in series will also be useful in minimizing the settling time of the loop. Mobile Handset Power Control Example a 2.7 V supply, the voltage on OUT1/OUT2 can come to within approximately 100 mV of the supply rail. This will depend, however, on the current draw (see TPC 19). During initialization and completion of the transmit sequence, VOUT should be held at its minimum level of 250 mV by keeping VSET below 200 mV. In this example, VSET is supplied by an 8-bit DAC that has an output range from 0 V to 2.55 V or 10 mV per bit. This sets the control resolution of VSET to 0.4 dB/bit (0.04 dB/mV 10 mV). If finer resolution is required, the DAC's output voltage can be scaled using two resistors as shown. This converts the DAC's maximum voltage of 2.55 V down to 1.6 V and increases the control resolution to 0.25 dB/bit. Two filter capacitors (CFLT1/CFLT2) must be used to stabilize the loop for each band. The choice of CFLT will depend to a large degree on the gain control dynamics of the power amplifier, something that is frequently poorly characterized, so some trial and error may be necessary. In this example, a 220 pF capacitor is used. The user may want to add a resistor in series with the filter capacitor. The resistor adds a zero to the control loop and increases the phase margin, which helps to make the step response of the circuit more stable when the slope of the PA's power control function is the steepest. In this example, the two filter capacitors are equal values; however, this is not a requirement. A smaller filter capacitor can be used by inserting a series resistor between VOUT and the control input of the PA. A series resistor will work with the input impedance of the PA to create a resistor divider and will reduce the loop gain. The size of the resistor divider ratio depends upon the available output swing of VOUT and the required control voltage on the PA. This technique can also be used to limit the control voltage in situations where the PA cannot deliver the power level demanded by VOUT. Overdrive of the control input of some PAs causes increased distortion. REV. C Figure 8 shows a complete power amplifier control circuit for a dual-mode handset. The RF3108 (RF Micro Devices), dualinput, trimode (GSM, DCS, PCS) PA is driven by a nominal power level of 6 dBm at both inputs and has two gain control lines. Some of the output power from the PA is coupled off using a dual-band directional coupler (Murata part number LDC15D190A0007A). This has a coupling factor of approximately 20 dB for the GSM band and 15 dB for DCS and an insertion loss of 0.38 dB and 0.45 dB, respectively. Because the RF3108 transmits a maximum power level of approximately 35 dBm for GSM and 32 dBm for DCS/PCS, additional attenuation of 20 dB is required before the coupled signal is applied to the AD8316. This results in peak input levels of -5 dBm (GSM) and -3 dBm (DCS). While the AD8316 gives a linear response for input levels up to +3 dBm, for highly temperature-stable performance at maximum PA output power, the maximum input level should be limited to approximately -3 dBm (see TPC 3 and TPC 5). This does, however, reduce the sensitivity of the circuit at the low end. The operational setpoint voltage, in the range 250 mV to 1.4 V, is applied to the VSET pin of the AD8316. This will typically be supplied by a DAC. The desired output is selected by applying a high or low signal to the BSEL pin (HI = OUT1, LO = OUT2). The selected output directly drives the level control pin of the power amplifier. In this case a minimum supply voltage of 2.9 V is required and VOUT reaches a maximum value of approximately 2.6 V while delivering about 5 mA to the PA's VAPC input. For power amplifiers with lower VAPC input ranges, a corresponding low power supply to the AD8316 can be used. For example, on -14- GSM VAPC AD8316 Enable and Power-On The AD8316 may be disabled by pulling the ENBL pin to ground. This reduces the supply current from its nominal level of 8.5 mA to 3 A at 2.7 V. The logic threshold for turning on the device is at 1.8 V at 2.7 V. A plot of the enable glitch is shown in TPC 20. Alternatively, the device can be completely disabled by pulling the supply voltage to ground; ENBL would be connected to VPOS. The glitch in this mode of operation is shown on TPC 25 and TPC 26. If VPOS is applied before the device is enabled, a narrow glitch of less than 50 mV will result. This is shown in TPC 31. In both situations, the voltage on VSET should be kept below 250 mV during power-on and power-off, preventing any unwanted transients on VOUT. Input Coupling Options Figure 9c shows a third method for coupling the input signal into the AD8316, applicable where the input signal is larger than the input range of the log amp. A series resistor, connected to the RF source, combines with the input impedance of the AD8316 to resistively divide the input signal being applied to the input. This has the advantage of very little power being tapped off in RF power transmission applications. Using the Chip Scale Package On the underside of the chip scale package, there is an exposed paddle. This paddle is internally connected to the chip's ground. For better electrical performance, this paddle should be soldered down to the printed circuit board's ground plane, even though there is no thermal requirement to do so. EVALUATION BOARD The internal 5 pF coupling capacitor of the AD8316, along with the low frequency input impedance of 3 k, result in a high-pass input corner frequency of approximately 20 MHz. This sets the minimum operating frequency. Figure 9 shows three options for input coupling. A broadband resistive match can be implemented by connecting a shunt resistor to ground at RFIN. This 52.3 resistor (other values can also be used to select different overall input impedances) combines with the input impedance of the AD8316 (3 k 1 pF) to give a broadband input impedance of 50 . While the input resistance and capacitance (CIN and RIN) will vary by approximately 20% from device to device, the dominance of the external shunt resistor means that the variation in the overall input impedance will be close to the tolerance of the external resistor. This method of matching is most useful in wideband applications or in multimode systems where there is more than one operating frequency and those frequencies are quite far apart. A reactive match can also be implemented as shown in Figure 9b. This is not recommended at low frequencies because device tolerances will vary the quality of the match dramatically because of the large input resistance. For low frequencies, Option 9a or Option 9c is recommended. In Figure 9b, the matching components are drawn as generic reactances. Depending on the frequency, the input impedance at that frequency, and the availability of standard value components, either a capacitor or an inductor will be used. As in the previous case, the input impedance at a particular frequency is plotted on a Smith chart and matching components are chosen (shunt or Series L, shunt or Series C) to move the impedance to the center of the chart. Figures 10 and 11 show the schematics of the AD8316 MSOP and LFCSP evaluation boards. Note that uninstalled components are marked as open. The layout and silkscreen of the MSOP evaluation board are shown in Figures 12 and 13. Apart from the slightly smaller device footprint and number of pins, the LFCSP evaluation board is identical to the MSOP board. The boards are powered by a single supply in the 2.7 V to 5.5 V range. The power supply is decoupled by a single 0.1 F capacitor. Table II details the various configuration options of the evaluation boards. For operation in controller mode, both jumpers, LK1 and LK2, should be removed. OUT1 and OUT2 can be selected with SW3 in Position A and Position B, respectively. The setpoint voltage is applied to VSET, RFIN is connected to the RF source (PA output or directional coupler), and OUT1 or OUT2 is connected to the gain control pins of each PA. When the AD8316 is used in controller mode, a capacitor and a resistor must be installed in C4, C6, and R10, R11 for loop stability. For GSM/DCS handset power amplifiers, this capacitor should typically range from 150 pF to 300 pF. The series resistor improves the system phase margin at low power levels, which in turn improves the step response in the circuit. Typically, this resistor value should be about 1.5 k. A quasi-measurement mode (in which the AD8316 delivers an output voltage that is proportional to the log of the input signal) can be implemented to establish the relationship between VSET and RFIN with the installation of two jumpers, LK1 and LK2. This mimics an AGC loop. To establish the transfer function of the log amp, the RF input should be swept while the voltage on VSET is measured, that is, the SMA connector labeled VSET acts as an output. This is the simplest method for validating operation of the evaluation board. When operated in this mode, a large capacitor (0.01 F or greater) must be installed in C4 or C6 (set R10/R11 to 0 ) to ensure loop stability. REV. C -15- AD8316 ANTENNA RFIN RSHUNT 52.3 CC AD8316 X1 RFIN X2 CC AD8316 STRIPLINE RFIN RATTN CC AD8316 CIN RIN CIN RIN CIN PA RIN a. Broadband Resistive b. Narrow-Band Reactive Figure 9. Input Coupling Options c. Series Attenuation J1 INPUT VPOS A B SW1 R1 0 R2 52.3 C1 0.1 F AD8316 1 RFIN 2 ENBL 3 VSET VPOS 10 OUT1 9 COMM 8 OUT2 7 FLT2 6 C6 (OPEN) R11 (OPEN) R12 0 R9 (OPEN) VPOS R3 0 C2 (OPEN) C7 (OPEN) OUT1 (A) SW3 OUT2 (B) R4 (OPEN) J2 OUT1 J4 OUT2 J3 VSET C4 (OPEN) R10 (OPEN) VPOS OUT1(A) OUT2(B) LK1 C5 0.1 F SW2 4 FLT1 5 BSEL VPOS R7 16.2k C3 0.1 F R8 10k LK2 AD8031 R6 17.8k R5 10k Figure 10. Schematic of Evaluation Board (MSOP) J1 INPUT VPOS A B J3 VSET C4 (OPEN) R10 (OPEN) SW1 R1 0 R2 52.3 NC NC 16 1 RFIN 2 ENBL 15 14 NC 13 VPOS 12 OUT1 11 C1 0.1 F VPOS R3 0 C2 (OPEN) R9 (OPEN) C7 (OPEN) OUT1 (A) SW3 OUT2 (B) R4 (OPEN) J2 OUT1 J4 OUT2 AD8316 BSEL 3 VSET 4 FLT1 5 COMM 10 COMM FLT2 R12 0 OUT2 9 8 6 7 NC NC = NO CONNECT VPOS OUT1 (A) OUT2 (B) SW2 VPOS C5 0.1 F NC C6 (OPEN) R11 (OPEN) LK1 R7 16.2k C3 0.1 F R8 10k LK2 AD8031 R6 17.8k R5 10k Figure 11. Schematic of Evaluation Board (LFCSP) -16- REV. C AD8316 Table II. Evaluation Board Configuration Options Component TP1, TP2 SW1 Function Supply and Ground Vector Pins. Device Enable. When in Position A, the ENBL pin is connected to VPOS and the AD8316 is in operating mode. In Position B, the ENBL pin is grounded, putting the device into power-down mode. Band Select. When in Position A (OUT1), the BSEL pin is connected to VPOS and the AD8316 OUT1 is in operation mode. In Position B (OUT2), the BSEL pin is grounded and the AD8316 OUT2 is in operation while OUT1 pin is shut down. Input Interface. The 52.3 resistor in Position R2 combines with the AD8316's internal input impedance to provide a broadband input impedance of around 50 . A reactive match can be implemented by replacing R2 with an inductor and R1 (0 ) with a capacitor. In addition, the RF microstrip line has been provided with a clean mask ground plane to provide additional matching. Note that the AD8316's RF input is internally ac-coupled. Output Interface. R4 and C2, R9 and C7 can be used to check the response capacitive and resistive loading, respectively. R3/R4 and R12/R9 can be used to reduce the slope of OUT1 and OUT2. Power Supply Decoupling. The nominal supply decoupling consists of a 0.1 F capacitor. Filter Capacitors/Resistors. The response time of OUT1, OUT2 can be modified by placing the capacitors between FLT1, FLT2 and resistors R10, R11 to ground. Measurement Mode. A quasi-measurement mode can be implemented by installing LK1 and LK2 (connecting an inverted OUT1 or OUT2 to VSET) to yield the nominal relationship between RFIN and VSET. In this mode, a large capacitor (0.01 F or greater) must be installed in C4 and C6 and a 0 resistors to ground in R10 and R11. To select OUT1 or OUT2, SW3 must be in the OUT1 position or the OUT2 position, respectively. Measurement Mode Output Select. When in measurement mode, output 1 or output 2 can be selected by positioning SW3 to the OUT1 position or the OUT2 position, respectively. Default Condition Not Applicable SW1 = A SW2 SW2 = OUT1 R1, R2 R2 = 52.3 (Size 0603) R1 = 0 (Size 0402) R3, R4, R12, R9, C2, C7 C1, C5 C4, C6, R10, R11 LK1, LK2 R4 = C2 = Open (Size 0603) R9 = C7 = Open (Size 0603) R3 = R12 = 0 (Size 0603) C1 = C5 = 0.1 F (Size 0603) C4 = C6 = Open (Size 0603) R10 = R11 = Open (Size 0603) LK1, LK2 = Installed SW3 SW3 = OUT1 REV. C -17- AD8316 Figure 12. Silkscreen of Component Side (MSOP) Figure 13. Layout of Component Side (MSOP) -18- REV. C AD8316 OUTLINE DIMENSIONS 16-Lead Lead Frame Chip Scale Package [LFCSP] 3 mm 3 mm Body (CP-16-3) Dimensions shown in millimeters 0.50 0.40 0.30 PIN 1 INDICATOR 16 1 3.00 BSC SQ 0.45 PIN 1 INDICATOR TOP VIEW 0.60 MAX 13 12 BOTTOM VIEW 2.75 BSC SQ 0.50 BSC 9 8 1.65 1.50 SQ* 1.35 5 4 0.25 MIN 12 MAX 1.00 0.85 0.80 SEATING PLANE 0.30 0.23 0.18 0.80 MAX 0.65 TYP 0.05 MAX 0.02 NOM 0.20 REF 1.50 REF *COMPLIANT TO JEDEC STANDARDS MO-220-VEED-2 EXCEPT FOR EXPOSED PAD DIMENSION 10-Lead Mini Small Outline Package [MSOP] (RM-10) Dimensions shown in millimeters 3.00 BSC 10 6 3.00 BSC 1 5 4.90 BSC PIN 1 0.50 BSC 0.95 0.85 0.75 0.15 0.00 0.27 0.17 1.10 MAX 8 0 0.80 0.60 0.40 SEATING PLANE 0.23 0.08 COPLANARITY 0.10 COMPLIANT TO JEDEC STANDARDS MO-187BA REV. C -19- AD8316 Revision History Location 1/04-Data Sheet changed from REV. B to REV. C. Page Changes to FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Updated ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Edit to Figure 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3/03-Data Sheet changed from REV. 0 to REV. A. C02192-0-1/04(C) 12/03-Data Sheet changed from REV. A to REV. B. Addition of LFCSP package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Universal Edits to SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Edits to ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Edits to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Edits to TPC 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 TPC 9 replaced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Edit to TPC 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Edits to Example section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Edits to Input Coupling Options section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Addition of new Figure 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 -20- REV. C |
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