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FEATURES

LT5568-2 GSM/EDGE Optimized, High Linearity Direct Quadrature Modulator DESCRIPTIO
The LT(R)5568-2 is a direct I/Q modulator designed for high performance wireless applications, including wireless infrastructure. It allows direct modulation of an RF signal using differential baseband I and Q signals. It supports GSM, EDGE, CDMA, CDMA2000 and other systems that operate in the 850MHz to 965MHz band. It may be configured as an image reject upconverting mixer, by applying 90 phase-shifted signals to the I and Q inputs. The I/Q baseband inputs consist of voltage-to-current converters that in turn drive double-balanced mixers. The outputs of these mixers are summed and applied to an on-chip RF transformer, which converts the differential mixer signals to a 50 single-ended output. The four balanced I and Q baseband input ports are intended for DC coupling from a source with a common mode voltage level of about 0.5V. The LO path consists of an LO buffer with single-ended input, and precision quadrature generators that produce the LO drive for the mixers. The supply voltage range is 4.5V to 5.25V.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Optimized Image Rejection for 850MHz to 965MHz High OIP3: +22.9dBm at 900MHz Low Output Noise Floor at 5MHz Offset: No RF: -159.4dBm/Hz POUT = 4dBm: -153dBm/Hz Integrated LO Buffer and LO Quadrature Phase Generator 50 AC-Coupled Single-Ended LO and RF Ports 50 DC Interface to Baseband Inputs Low Carrier Leakage: -43dBm at 900MHz High Image Rejection: -52dBc at 900MHz 16-Lead 4mm x 4mm QFN Package
APPLICATIO S

Infrastructure Tx for GSM/Cellular Bands Image Reject Up-Converters for Cellular Bands Low-Noise Variable Phase-Shifter for 700MHz to 1050MHz Local Oscillator Signals RFID Reader
TYPICAL APPLICATIO
850MHz to 965MHz Direct Conversion Transmitter Application
VCC LT5568-2 I-DAC V-I I-CHANNEL 0 EN Q-CHANNEL Q-DAC V-I 90 BALUN 5V 100nF x2 RF = 850MHz TO 965MHz
5
4 EVM (%RMS)
PA
3
2 EVM 1
BASEBAND GENERATOR
55682 TA01
VCO/SYNTHESIZER
0 -10
U
U
U
GSM EVM and Noise vs RF Output Power at 900MHz
-96
-98 NOISE FLOOR AT 6MHz OFFSET (dBc/100kHz)
NOISE
-100
-102
-104
4 -8 -6 -4 -2 0 2 GSM RF OUTPUT POWER (dBm)
6
-106
55682 TA02
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1
LT5568-2 ABSOLUTE
(Note 1)
AXI U RATI GS
BBMQ
GND
BBPQ
Supply Voltage .........................................................5.5V Common Mode Level of BBPI, BBMI and BBPQ, BBMQ .......................................................2.5V Operating Ambient Temperature (Note 2) ............................................... -40C to 85C Storage Temperature Range................... -65C to 125C Voltage on Any Pin Not to Exceed...................... -500mV to VCC + 500mV CAUTION: This part is sensitive to ESD. It is very important that proper ESD precautions be observed when handling the LT5568-2.
BBMI
BBPI
GND
16 15 14 13 EN 1 GND 2 LO 3 GND 4 5 6 7 8 VCC 17 12 GND 11 RF 10 GND 9 GND
UF PACKAGE 16-LEAD (4mm x 4mm) PLASTIC QFN TJMAX = 125C, JA = 37C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT5568-2EUF#PBF TAPE AND REEL LT5568-2EUF#TRPBF PART MARKING 55682 PACKAGE DESCRIPTION 16-Lead (4mm x 4mm) Plastic QFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
VCC = 5V, EN = High, TA = 25C, fLO = 900MHz, fRF = 902MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency = 2MHz, I&Q 90 shifted (upper side-band selection). PRF, OUT = -10dBm, unless otherwise noted. (Note 3)
SYMBOL RF Output (RF) fRF S22, ON S22, OFF NFloor RF Frequency Range RF Frequency Range RF Output Return Loss RF Output Return Loss RF Output Noise Floor -3dB Bandwidth -1dB Bandwidth EN = High (Note 6) EN = Low (Note 6) No Input Signal (Note 8) POUT = 4dBm (Note 9) POUT = 4dBm (Note 10) POUT/PIN, I&Q 20 * Log (VOUT, 50/VIN, DIFF, I or Q) 1VP-P DIFF CW Signal, I and Q (Note 17) (Note 7) (Notes 13, 14) (Notes 13, 15) -9 0.6 to 1.1 0.7 to 1 -16 -18 -159.4 -153 -152.6 -6.8 -6.8 -2.8 -23 8.6 59 22.9 -3 GHz GHz dB dB dBm/Hz dBm/Hz dBm/Hz dB dB dBm dB dBm dBm dBm
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ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
VCC
GP GV POUT G3LO vs LO OP1dB OIP2 OIP3
Conversion Power Gain Conversion Voltage Gain Absolute Output Power 3 * LO Conversion Gain Difference Output 1dB Compression Output 2nd Order Intercept Output 3rd Order Intercept
2
U
WW
W
PIN CONFIGURATION
TOP VIEW
TYP
MAX
UNITS
LT5568-2 ELECTRICAL CHARACTERISTICS
SYMBOL IR LOFT LO Input (LO) fLO PLO S11, ON S11, OFF NFLO GLO IIP3LO BWBB VCMBB RIN, SE PLO2BB IP1dB VCC ICC, ON ICC, OFF tON tOFF Enable Sleep LO Frequency Range LO Input Power LO Input Return Loss LO Input Return Loss LO Input Referred Noise Figure LO to RF Small Signal Gain LO Input 3rd Order Intercept Baseband Bandwidth DC Common Mode Voltage Single-Ended Input Resistance Carrier Feedthrough on BB Input 1dB Compression Point Supply Voltage Supply Current Supply Current, Sleep Mode Turn-On Time Turn-Off Time Input High Voltage Input High Current Input Low Voltage Input Low Current EN = High EN = 0V EN = Low to High (Note 11) EN = High to Low (Note 12) EN = High EN = 5V EN = Low EN = 0V 1.0 245 0.5 0.01 0.3 1.4 EN = High (Note 6) EN = Low (Note 6) (Note 5) at 900MHz (Note 5) at 900MHz (Note 5) at 900MHz -3dB Bandwidth (Note 4) (Note 4) POUT = 0 (Note 4) Differential Peak-to-Peak (Notes 7, 18) 4.5 80 -10 0.6 to 1.1 0 -15 -2.5 14.7 14.7 -3 380 0.54 47 -38 4.3 5 110 5.25 145 100 5 GHz dBm dB dB dB dB dBm MHz V dBm VP-P, DIFF V mA A s s V A V A PARAMETER Image Rejection Carrier Leakage (LO Feedthrough)
VCC = 5V, EN = High, TA = 25C, fLO = 900MHz, fRF = 902MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency = 2MHz, I&Q 90 shifted (upper side-band selection). PRF, OUT = -10dBm, unless otherwise noted. (Note 3)
CONDITIONS fBB = 100kHz (Note 16) EN = High, PLO = 0dBm (Note 16) EN = Low, PLO = 0dBm (Note 16) MIN TYP -52 -43 -65 MAX UNITS dBc dBm dBm
Baseband Inputs (BBPI, BBMI, BBPQ, BBMQ)
Power Supply (VCC)
Enable (EN), Low = Off, High = On
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: Specifications over the -40C to 85C temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Tests are performed as shown in the configuration of Figure 7. Note 4: On each of the four baseband inputs BBPI, BBMI, BBPQ and BBMQ. Note 5: V(BBPI) - V(BBMI) = 1VDC, V(BBPQ) - V(BBMQ) = 1VDC. Note 6: Maximum value within 850MHz to 965MHz. Note 7: An external coupling capacitor is used in the RF output line. Note 8: At 20MHz offset from the LO signal frequency. Note 9: At 20MHz offset from the CW signal frequency.
Note 10: At 5MHz offset from the CW signal frequency. Note 11: RF power is within 10% of final value. Note 12: RF power is at least 30dB lower than in the ON state. Note 13: Baseband is driven by 2MHz and 2.1MHz tones. Drive level is set in such a way that the two resulting RF tones are -10dBm each. Note 14: IM2 measured at LO frequency + 4.1MHz. Note 15: IM3 measured at LO frequency + 1.9MHz and LO frequency + 2.2MHz. Note 16: Amplitude average of the characterization data set without image or LO feedthrough nulling (unadjusted). Note 17: The difference in conversion gain between the spurious signal at f = 3 * LO - BB versus the conversion gain at the desired signal at f = LO + BB for BB = 2MHz and LO = 900MHz. Note 18: The input voltage corresponding to the output P1dB.
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LT5568-2 TYPICAL PERFOR A CE CHARACTERISTICS
VCC = 5V, EN = High, TA = 25C, fLO = 900MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90 shifted. fRF = fBB + fLO (upper sideband selection). PRF, OUT = -10dBm (-10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3) RF Output Power vs LO Frequency at 1VP-P Differential Baseband Drive
0 85C -2 RF OUTPUT POWER (dBm) SUPPLY CURRENT (mA) VOLTAGE GAIN (dB) 25C -4 -6 -8 -10 -12 90 4.5 -14 550 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G02 -6 -8 -10 -12 -14 -16 -18 550 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G03 -4
Supply Current vs Supply Voltage
120
110
100
-40C
5 SUPPLY VOLTAGE (V)
Output IP3 vs LO Frequency
26 24 22 20 18 16 14 12 550 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 60 fBB, 1 = 2MHz fBB, 2 = 2.1MHz 70
OP1dB (dBm) 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G05
OIP3 (dBm)
OIP2 (dBm)
LO Feedthrough to RF Output vs LO Frequency
-38 -45
LO FEEDTHROUGH (dBm)
-40 P(2 * LO) (dBm)
P(3 * LO) (dBm)
-42
-44
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G07
-46 550
4
UW
Voltage Gain vs LO Frequency
5.5
55682 G01
Output IP2 vs LO Frequency
10 fIM2 = fBB, 1 + fBB, 2 + fLO fBB, 1 = 2MHz fBB, 2 = 2.1MHz 8
Output 1dB Compression vs LO Frequency
65
6
55
4
50
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G06
45 550
2 550
55682 G04
2 * LO Leakage to RF Output vs 2 * LO Frequency
-45
3 * LO Leakage to RF Output vs 3 * LO Frequency
-50
-50
-55
-55
-60 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C
-60
-65 1.1 1.3
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 1.5 1.7 1.9 2.1 2.3 2 * LO FREQUENCY (GHz) 2.5
55682 G08
-65
-70 1.65 1.95 2.25 2.55 2.85 3.15 3.45 3.75 3 * LO FREQUENCY (GHz) 55682 G09
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LT5568-2 TYPICAL PERFOR A CE CHARACTERISTICS
VCC = 5V, EN = High, TA = 25C, fLO = 900MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90 shifted. fRF = fBB + fLO (upper sideband selection). PRF, OUT = -10dBm (-10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3) LO and RF Port Return Loss vs RF Frequency
0 LO PORT, EN = LOW
Noise Floor vs RF Frequency
-158 fLO = 900MHz (FIXED) NO RF IMAGE REJECTION (dBc) -30
-159 NOISE FLOOR (dBm/Hz)
S11 (dB)
-160
-161 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 650 750 850 950 1050 1150 1250 RF FREQUENCY (MHz)
-163
-163 550
LO Feedthrough to RF Output vs LO Input Power
-38 -40 LO FEEDTHROUGH (dBm) IMAGE REJECTION (dBc) -40 -42 -44 -46 - 48 -50 -20 -35
VOLTAGE GAIN (dB)
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C -16 -12 -8 -4 0 4 LO INPUT POWER (dBm) 8
55682 G13
Output IP3 vs LO Power
25 23 HD2 (dBc), HD3 (dBc) 21 0IP3 (dBm) 19 17 15 13 -20 -10 fBB, 1 = 2MHz fBB, 2 = 2.1MHz -20
85C -40C HD3 85C
25C
-40 -50 -60
-20 25C -40C -30 -40
HD2 (dBc), HD3 (dBc)
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C -16 -12 -8 -4 0 4 LO INPUT POWER (dBm) 8
55682 G16
UW
55682 G10
Image Rejection vs LO Frequency
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C
-35
-10
LO PORT, EN = HIGH, PLO = 0dBm
-40
-20
-45
RF PORT, EN = LOW RF PORT, EN = HIGH, PLO = 0dBm RF PORT, EN = HIGH, No LO
-50 fBB = 100kHz 650 750 850 950 1050 1150 1250 LO FREQUENCY (MHz) 55682 G11
-30 LO PORT, EN = HIGH, PLO = 10dBm 650
-55 550
-40 550
750 850 950 1050 1150 1250 RF FREQUENCY (MHz) 55682 G12
Image Rejection vs LO Input Power
-4 PRF = -10dBm fBB = 100kHz -6 -8 -10 -12 -14
Voltage Gain vs LO Power
-45
-50
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C -16 -12 -8 -4 0 4 LO INPUT POWER (dBm) 8
55682 G14
5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C -16 -12 -8 -4 0 4 LO INPUT POWER (dBm) 8
55682 G15
-55 -20
-16 -20
RF CW Output Power, HD2 and HD3 vs CW Baseband Voltage and Temperature
10 RF 0 -40C -30 25C -10 -20 -30 -40 -50 -60 -70 -80 RF CW OUTPUT POWER (dBm) -10
RF CW Output Power, HD2 and HD3 vs CW Baseband Voltage and Supply Voltage
10 RF 0 5V HD3 5V 5.5V HD2 4.5V -10 -20 -30 RF CW OUTPUT POWER (dBm)
HD2 85C
4.5V -40 -50 -60
-70 -80
-50 -60
1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P, DIFF) HD2 = MAX POWER AT fLO + 2 * fBB OR fLO - 2 * fBB HD3 = MAX POWER AT fLO + 3 * fBB OR fLO - 3 * fBB
0
0
5 1 2 3 4 I AND Q BASEBAND VOLTAGE (VP-P, DIFF)
55682 G18
55682 G17
HD2 = MAX POWER AT fLO + 2 * fBB OR fLO - 2 * fBB HD3 = MAX POWER AT fLO + 3 * fBB OR fLO - 3 * fBB
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5
LT5568-2 TYPICAL PERFOR A CE CHARACTERISTICS
VCC = 5V, EN = High, TA = 25C, fLO = 900MHz, PLO = 0dBm. BBPI, BBMI, BBPQ, BBMQ inputs 0.54VDC, Baseband Input Frequency fBB = 2MHz, I&Q 90 shifted. fRF = fBB + fLO (upper sideband selection). PRF, OUT = -10dBm (-10dBm/tone for 2-tone measurements), unless otherwise noted. (Note 3) RF Two-Tone Power (Each Tone), IM2 and IM3 vs Baseband Voltage LO Feedthrough to RF Output Image Rejection and Temperature vs CW Baseband Voltage vs CW Baseband Voltage
-36 PRF,TONE (dBm), IM2 (dBc), IM3 (dBc) 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C -45 10 5V, -40C 5V, 25C 5V, 85C 4.5V, 25C 5.5V, 25C 0 -40C -10 -20 -30 -40 -50 -60 -70 -80 3 IM3 -40C IM2 85C
55682 G21
LO FEEDTHROUGH (dBm)
IMAGE REJECTION (dBc)
-38
-40
-42
-44 0 1 2 3 4 5 I AND Q BASEBAND VOLTAGE (VP-P,DIFF)
55682 G19
RF Two-Tone Power (Each Tone), IM2 and IM3 vs Baseband Voltage and Supply Voltage
10 PRF,TONE (dBm), IM2 (dBc), IM3 (dBc) 0 -10 -20 -30 -40 -50 -60 -70 -80 IM3 IM2 5V 5.5V 4.5V
fBBI = 2MHz, 2.1MHz, 0 fBBQ = 2MHz, 2.1MHz, 90
55682 G22
RF 4.5V 5V, 5.5V PERCENTAGE (%) 5V, 5.5V 4.5V 20
15
PERCENTAGE (%)
1 10 0.1 I AND Q BASEBAND VOLTAGE (VP-P, DIFF, EACH TONE) IM2 = POWER AT fLO + 4.1MHz IM3 = MAX POWER AT fLO + 1.9MHz OR fLO + 2.2MHz
LO Leakage Distribution
40 35 30 PERCENTAGE (%) 25 20 15 10 5 0 < -54 -50 -46 -42 -38 LO LEAKAGE (dBm) -34 -30
55682 G25
-40C 25C 85C PERCENTAGE (%)
6
UW
RF 85C -40C 25C 85C 25C
25C
-50
-55 0
fBB = 100kHz 0.5 1 1.5 2 2.5 I AND Q BASEBAND VOLTAGE (VP-P,DIFF)
fBBI = 2MHz, 2.1MHz, 0 fBBQ = 2MHz, 2.1MHz, 90
55682 G20
10 1 0.1 I AND Q BASEBAND VOLTAGE (VP-P, DIFF, EACH TONE) IM2 = POWER AT fLO + 4.1MHz IM3 = MAX POWER AT fLO + 1.9MHz OR fLO + 2.2MHz
Gain Distribution
25 -40C 25C 85C 35 30 25 20 15 10 5 5 0
Noise Floor Distribution
-40C 25C 85C
10
-9
-8.5
-8
-7.5 -7 -6.5 GAIN (dB)
-6
-5.5
55682 G23
0 -160.4
-159.6 -159.2 -160 NOISE FLOOR (dBm/Hz)
-158.8
55682 G24
Image Rejection Distribution
25 -40C 25C 85C
20
15
10
5
0 < -70
-66
-62 -58 -54 -50 IMAGE REJECTION (dBc)
-46
55682 G26
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LT5568-2 PI FU CTIO S
EN (Pin 1): Enable Input. When the enable pin voltage is higher than 1V, the IC is turned on. When the input voltage is less than 0.5V, the IC is turned off. GND (Pins 2, 4, 6, 9, 10, 12, 15): Ground. Pins 6, 9, 15 and 17 (exposed pad) are connected to each other internally. Pins 2 and 4 are connected to each other internally and function as the ground return for the LO signal. Pins 10 and 12 are connected to each other internally and function as the ground return for the on-chip RF balun. For best RF performance, pins 2, 4, 6, 9, 10, 12, 15 and the Exposed Pad 17 should be connected to the printed circuit board ground plane. LO (Pin 3): LO Input. The LO input is an AC-coupled singleended input with approximately 50 input impedance at RF frequencies. Externally applied DC voltage should be within the range -0.5V to VCC + 0.5V in order to avoid turning on ESD protection diodes. BBPQ, BBMQ (Pins 7, 5): Baseband Inputs for the Q-channel, each 50 input impedance. Internally biased at about 0.54V. Applied voltage must stay below 2.5V. VCC (Pins 8, 13): Power Supply. Pins 8 and 13 are connected to each other internally. It is recommended to use 0.1F capacitors for decoupling to ground on each of these pins. RF (Pin 11): RF Output. The RF output is an AC-coupled single-ended output with approximately 50 output impedance at RF frequencies. Externally applied DC voltage should be within the range -0.5V to VCC + 0.5V in order to avoid turning on ESD protection diodes. BBPI, BBMI (Pins 14, 16): Baseband Inputs for the I-channel, each with 50 input impedance. Internally biased at about 0.54V. Applied voltage must stay below 2.5V. Exposed Pad (Pin 17): Ground. This pin must be soldered to the printed circuit board ground plane.
U
U
U
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LT5568-2 BLOCK DIAGRA W
VCC 8 BBPI 14 BBMI 16 V-I 11 RF 0 90 BBPQ 7 BBMQ 5 V-I BALUN 1 EN 13 LT5568-2 2 4 GND 6 9 3 LO 10 12 15 17
55682 BD
GND
APPLICATIO S I FOR ATIO
The LT5568-2 consists of I and Q input differential voltage-to-current converters, I and Q up-conversion mixers, an RF output balun, an LO quadrature phase generator and LO buffers.
LT5568-2 RF VCC = 5V C BALUN FROM Q LOMI LOPI
R1A 25 BBPI 12pF
R1B 23 CM R3 VREF = 540mV R4
R2B 23
BBMI
55682 F01
GND
Figure 1. Simplified Circuit Schematic of the LT5568-2 (Only I-Half is Drawn)
8
U
R2A 25
W
U
U
External I and Q baseband signals are applied to the differential baseband input pins, BBPI, BBMI, and BBPQ, BBMQ. These voltage signals are converted to currents and translated to RF frequency by means of double-balanced up-converting mixers. The mixer outputs are combined in an RF output balun, which also transforms the output impedance to 50. The center frequency of the resulting RF signal is equal to the LO signal frequency. The LO input drives a phase shifter which splits the LO signal into inphase and quadrature LO signals. These LO signals are then applied to on-chip buffers which drive the up-conversion mixers. Both the LO input and RF output are single-ended, 50-matched and AC coupled. Baseband Interface The baseband inputs (BBPI, BBMI), (BBPQ, BBMQ) present a differential input impedance of about 100. At each of the four baseband inputs, a first-order lowpass filter using 25
12pF
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LT5568-2 APPLICATIO S I FOR ATIO
and 12pF to ground is incorporated (see Figure 1), which limits the baseband bandwidth to approximately 330MHz (-1dB point). The common mode voltage is about 0.54V and is approximately constant over temperature. It is important that the applied common mode voltage level of the I and Q inputs is about 0.54V in order to properly bias the LT5568-2. Some I/Q test generators allow setting the common mode voltage independently. In this case, the common mode voltage of those generators must be set to 0.27V to match the LT5568-2 internal bias, because for DC signals, there is no -6dB source-load voltage division (see Figure 2).
50 0.27VDC 0.54VDC GENERATOR 50 50 0.54VDC 0.54VDC GENERATOR 0.54VDC LT5568-2
55682 F02
+ -
+ -
Figure 2. DC Voltage Levels for a Generator Programmed at 0.27VDC for a 50 Load and the LT5568-2 as a Load
C3 1nF VCC = 4.5 TO 5.25V R7 200 R9 249 3 C1 1.2nF 0mA to 20mA DAC 0mA to 20mA R6 53.6 R8 200 R10 249 R5 53.6 2 7 VCC 0.54V 6 R11 249 0.54V R13 499 R12 249 6 0.54V R15 50 C5 10nF R14 50 0.54V RF = 1.2dBm, GSM C LOMI BALUN LT5568-2 FROM Q LOPI
U2 LT1818
GND 7 VCC
2 C2 1.2nF C4 3 1nF
-
U3 LT1818 4V SS
+
VSS = -2V to -5.25V
Figure 3. LT5568-2 GSM Baseband Interface with 3rd Order Lowpass Filter and Ground Referenced DAC (Only I-Channel is Shown)
U
48
+
-
W
U
U
+ -
The baseband inputs should be driven differentially; otherwise, the even-order distortion products will degrade the overall linearity severely. Typically, a DAC will be the signal source for the LT5568-2. Reconstruction filters should be placed between the DAC output and the LT5568-2's baseband inputs. In Figure 3, a typical baseband interface schematic for GSM is drawn. It shows a ground referenced DAC output interface followed by a 3rd order active OpAmp RC lowpass filter with a 400kHz cutoff frequency (-3dB). The DAC in this example sources a current from 0mA to 20mA, with a voltage compliance range of at least 0V to 1V. This interface is DC coupled, which allows adjustment of the DAC's differential output current to minimize the LO feedthrough. The voltage swing at the LT5568-2 baseband inputs is about 2VP-P,DIFF, which results in a 1.2dBm GSM RF output power at 900MHz with noise floor of -154.3dBm/Hz at 6MHz offset (= -104.3dBm/100kHz). The RMS EVM is about 0.6%. The LT1819, which houses two LT1818s, can be used instead of U2 and U3. The total current in the positive supply is about 157mA and the current in the negative supply is about 40mA.
4V SS
GND BBPI C6 10nF BBMI 0.54V
R1 45 CM R3 33 VREF = 540mV
R2 45 R4 33 16mA U1
55682 F03
GND
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LT5568-2 APPLICATIO S I FOR ATIO
LO Section The internal LO input amplifier performs single-ended to differential conversion of the LO input signal. Figure 4 shows the equivalent circuit schematic of the LO input.
VCC 20pF LO INPUT
51
5568 F04
Figure 4. Equivalent Circuit Schematic of the LO Input
The internal, differential LO signal is then split into in-phase and quadrature (90 phase shifted) signals that drive LO buffer sections. These buffers drive the double balanced I and Q mixers. The phase relationship between the LO input and the internal in-phase LO and quadrature LO signals is fixed, and is independent of start-up conditions. The internal phase shifters are designed to deliver accurate quadrature signals. For LO frequencies significantly below 650MHz or above 1.25GHz, however, the quadrature accuracy will diminish, causing the image rejection to degrade. The LO pin input impedance is about 50, and the recommended LO input power is 0dBm. For lower LO input power, the gain, OIP2, OIP3 and noise floor at PRF = 4dBm will degrade, especially for PLO below -2dBm and at TA = 85C. For high LO input power (e.g., +5dBm), the image rejection will degrade with no improvement in linearity or gain. Harmonics present on the LO signal can degrade the image rejection because they can introduce a small excess phase shift in the internal phase splitter. For the second (at 1.8GHz) and third harmonics (at 2.7GHz) at -20dBc, the resulting signal at the image frequency is about -61dBc or lower, corresponding to an excess phase shift of much less than 1 degree. For the second and third LO harmonics at -10dBc, the introduced signal at the image frequency is about -51dBc. Higher harmonics than the third will have less impact. The LO return loss typically will be better than 11dB over the 700MHz to 1.05GHz range. Table 1 shows the LO port input impedance vs frequency.
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Table 1. LO Port Input Impedance vs Frequency for EN = High and PLO = 0dBm
Frequency MHz 500 600 700 800 900 1000 1100 1200 Input Impedance 47.5 + j12.1 59.4 + j8.4 66.2 - j1.14 67.2 - j13.4 61.1 - j23.9 53.3 - j26.8 48.2 - j26.1 42.0 - j27.4 S11 Mag 0.126 0.115 0.140 0.185 0.232 0.252 0.258 0.297 Angle 95.0 37.8 -3.41 -31.7 -53.2 -68.7 -79.4 -90.0
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If the part is in shutdown mode, the input impedance of the LO port will be different. The LO input impedance for EN = Low is given in Table 2.
Table 2. LO Port Input Impedance vs Frequency for EN = Low and PLO = 0dBm
Frequency MHz 500 600 700 800 900 1000 1100 1200 Input Impedance 33.6 + j41.3 59.8 + j69.1 140 + j89.8 225 - j62.6 92.9 - j128 39.8 - j95.9 22.8 - j72.7 16.0 - j57.3 S11 Mag 0.477 0.539 0.606 0.659 0.704 0.735 0.755 0.763 Angle 85.4 49.8 19.6 -6.8 -29.6 -45.5 -65.6 -79.7
RF Section After up-conversion, the RF outputs of the I and Q mixers are combined. An on-chip balun performs internal differential to single-ended output conversion, while transforming the output signal impedance to 50. Table 3 shows the RF port output impedance vs frequency.
Table 3. RF Port Output Impedance vs Frequency for EN = High and PLO = 0dBm
Frequency MHz 500 600 700 800 900 1000 1100 1200 Input Impedance 22.0 + j5.7 28.2 + j12.5 38.8 + j14.8 49.4 + j7.2 49.3 - j5.1 42.5 - j11.1 36.7 - j11.7 33.0 - j10.3 S22 Mag 0.395 0.317 0.206 0.072 0.051 0.143 0.202 0.238 Angle 164.2 141.3 117.5 90.6 -94.7 -117.0 -130.7 -141.6
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LT5568-2 APPLICATIO S I FOR ATIO
The RF output S22 with no LO power applied is given in Table 4.
Table 4. RF Port Output Impedance vs Frequency for EN = High and No LO Power Applied
Frequency MHz 500 600 700 800 900 1000 1100 1200 Input Impedance 22.7 + j5.6 29.7 + j11.6 40.5 + j11.6 47.3 + j2.2 44.1 - j6.7 38.2 - j9.8 34.0 - j9.4 31.5 - j7.8 S22 Mag 0.381 0.290 0.164 0.037 0.094 0.171 0.218 0.245 Angle 164.0 142.0 121.9 139.6 -126.9 -133.9 -143.1 -151.6
For EN = Low the S22 is given in Table 5.
Table 5. RF Port Output Impedance vs Frequency for EN = Low
Frequency MHz 500 600 700 800 900 1000 1100 1200 Input Impedance 21.2 + j5.4 26.6 + j12.5 36.6 + j16.6 49.2 + j11.6 52.9 - j2.0 46.4 - j11.2 39.3 - j13.2 34.4 - j12.1
VCC 21pF RF OUTPUT
S22 Mag 0.409 0.340 0.241 0.116 0.034 0.121 0.188 0.231 Angle 164.9 142.5 118.1 87.4 -33.1 -101.1 -120.6 -133.8
7nH
1pF
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51
Figure 5. Equivalent Circuit Schematic of the RF Output
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Note that an ESD diode is connected internally from the RF output to ground (see Figure 5). For strong output RF signal levels (higher than 3dBm), this ESD diode can degrade the linearity performance if the 50 termination impedance is connected directly to ground. To prevent this, a coupling capacitor can be inserted in the RF output line. This is strongly recommended during a 1dB compression measurement. Enable Interface Figure 6 shows a simplified schematic of the EN pin interface. The voltage necessary to turn on the LT5568-2 is 1V. To disable (shut down) the chip, the enable voltage must be below 0.5V. If the EN pin is not connected, the chip is disabled. This EN = Low condition is assured by the 75k on-chip pull-down resistor. It is important that the voltage at the EN pin does not exceed VCC by more than 0.5V. If this should occur, the supply current could be sourced through the EN pin ESD protection diodes, which are not designed to carry the full supply current, and damage may result.
VCC EN 75k 25k
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Figure 6. EN Pin Interface
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LT5568-2 APPLICATIO S I FOR ATIO
Evaluation Board Figure 7 shows the evaluation board schematic. A good ground connection is required for the exposed pad. If this is not done properly, the RF performance will degrade. Additionally, the exposed pad provides heat sinking for the part and minimizes the possibility of the chip overheating.
J1 BBMI J2 BBPI VCC 16 VCC EN LO IN R1 100 1 2 J4 3 4 EN GND LO GND LT5568-2 15 14 13 GND RF GND GND 12 11 10 9 17 J3 RF OUT C2 100nF
BBMI GND BBPI VCC
GND BBMQ GND BBPQ VCC 5 J5 BBMQ GND 6 7 8
C1 100nF
J6 BBPQ
BOARD NUMBER: DC1178A
Figure 7. Evaluation Circuit Schematic
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R1 (optional) limits the EN pin current in the event that the EN pin is pulled high while the VCC inputs are low. In Figures 8 and 9 the silk screens and the PCB board layout are shown.
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Figure 8. Component Side of Evaluation Board
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Figure 9. Bottom Side of Evaluation Board
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LT5568-2 APPLICATIO S I FOR ATIO
Application Measurements The LT5568-2 is recommended for base-station applications using various modulation formats. Figure 10 shows a typical application. Figure 11 shows the ACPR performance for CDMA2000 using 1- and 3-carrier modulation. Figures 12 and 13 illustrate the 1- and 3-carrier CDMA2000 RF spectrum. To calculate ACPR, a correction is made for the spectrum analyzer noise floor. If the output power is high, the ACPR will be limited by the linearity performance of the part. If the output power is low, the ACPR will be limited by the noise performance of the part. In the middle, an optimum ACPR is observed.
VCC 8, 13 14 I-DAC 16 V-I I-CHANNEL EN 1 Q-CHANNEL V-I 0 90 7 Q-DAC 5 BALUN 11 LT5568-2
PA
ACPR, AltCPR (dBc)
BASEBAND GENERATOR
2, 4, 6, 9, 10, 12, 15, 17
3 VCO/SYNTHESIZER
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Figure 10. 850MHz to 965MHz Direct Conversion Transmitter Application
-30 -40 POWER IN 30kHz BW (dBm) -50 -60 -70 -80 UNCORRECTED SPECTRUM -100 -110 -120 -90
DOWNLINK TEST MODEL 64 DPCH POWER IN 30kHz BW (dBm)
CORRECTED SPECTRUM
SPECTRUM ANALYSER NOISE FLOOR -130 896.25 897.75 899.25 900.75 902.25 903.75 RF FREQUENCY (MHz)
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Figure 12. 1-Carrier CDMA2000 Spectrum
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Because of the LT5568-2's very high dynamic range, the test equipment can limit the accuracy of the ACPR measurement. See Application Note 99. Consult the factory for advice on the ACPR measurement, if needed. The ACPR performance is sensitive to the amplitude match of the BBPI and BBMI (or BBPQ and BBMQ) inputs. This is because a difference in AC current amplitude will give rise to a difference in amplitude between the even-order harmonic products generated in the internal V-I converter. As a result, they will not cancel out entirely. Therefore, it is important to keep the currents in those pins exactly
-50 -125
5V 100nF x2 RF = 850MHz TO 965MHz
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DOWNLINK TEST MODEL 64 DPCH 1-CH. ACPR
-60 3-CH. ACPR
-135
NOISE FLOOR AT 30MHz OFFSET (dBm/Hz)
-70 3-CH. AltCPR
-145
-80 3-CH. NOISE
1-CH. AltCPR
-155
1-CH. NOISE -90 -30 -165 -25 -15 -10 -5 -20 RF OUTPUT POWER PER CARRIER (dBm)
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Figure 11. ACPR, AltCPR and Noise CDMA2000 Modulation
-30 -40 -50 -60 -70 -80 -90 -100 -110 -120 -130 894 CORRECTED SPECTRUM 896 UNCORRECTED SPECTRUM
DOWNLINK TEST MODEL 64 DPCH
SPECTRUM ANALYSER NOISE FLOOR 906
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900 902 904 898 RF FREQUENCY (MHz)
Figure 13. 3-Carrier CDMA2000 Spectrum
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LT5568-2 APPLICATIO S I FOR ATIO
the same (but of opposite sign). The current will enter the LT5568-2's common-base stage, and will flow to the mixer upper switches. This can be seen in Figure 1 where the internal circuit of the LT5568-2 is drawn. After calibration when the temperature changes, the LO feedthrough and the image rejection performance will
-50 LO FEEDTHROUGH (dBm), IR (dBc)
CALIBRATED WITH PRF = -10dBm PRF (dBm), LOFT (dBm), IR (dBc) IMAGE REJECTION
-60
-70
LO FEEDTHROUGH
-80 EN = High fLO = 900MHz VCC = 5V fRF = fBB + fLO fBBI = 2MHz, 0 PLO = 0dBm fBBQ = 2MHz, 90 -90 40 20 0 80 60 -40 -20 TEMPERATURE (C) 55682 F14
-90
0
1 3 4 5 2 I AND Q BASEBAND VOLTAGE (VP-P, DIFF) fLO = 900MHz fRF = fBB + fLO PLO = 0dBm
Figure 14. LO Feedthrough and Image Rejection vs Temperature after Calibration at 25C
fBBI = 2MHz, 0 fBBQ = 2MHz, 90 VCC = 5V EN = High
Figure 15. LO Feedthrough and Image Rejection vs Baseband Drive Voltage after Calibration at 25C
5
-96
4 EVM (%RMS)
-98 NOISE FLOOR AT 6MHz OFFSET (dBc/100kHz)
3
NOISE
-100
2 EVM 1
-102
-104
0 -10
4 -8 -6 -4 -2 0 2 GSM RF OUTPUT POWER (dBm)
6
-106
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Figure 16. GSM EVM and Noise vs RF Output Power at 900MHz
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change. This is illustrated in Figure 14. The LO feedthrough and image rejection can also change as a function of the baseband drive level, as is depicted in Figure 15. In Figure 16 the GSM EVM and noise performance vs RF output power is drawn.
10 0 -10 -20 -30 -40 -50 -60 -70 -80 25C 25C -40C 85C LOFT -40C IR 85C PRF -40C 25C 85C
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LT5568-2 PACKAGE DESCRIPTIO U
UF Package 16-Lead Plastic QFN (4mm x 4mm)
(Reference LTC DWG # 05-08-1692)
0.72 0.05 PACKAGE OUTLINE 0.30 0.05 0.65 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW--EXPOSED PAD 4.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 2.15 0.10 (4-SIDES) 0.75 0.05 R = 0.115 TYP PIN 1 NOTCH R = 0.20 TYP OR 0.35 x 45 CHAMFER 15 16 0.55 0.20 1 2
(UF16) QFN 10-04
4.35 0.05 2.15 0.05 2.90 0.05 (4 SIDES)
0.200 REF 0.00 - 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.30 0.05 0.65 BSC
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Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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LT5568-2 RELATED PARTS
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High Linearity, Low Power Downconverting Mixer Single-Ended 50 RF and LO Ports, 17.6dBm IIP3 at 1900MHz, ICC = 28mA High Linearity, Low Power Downconverting Mixer 3V to 5.3V Supply, 16.5dBm IIP3, 100kHz to 2GHz RF, NF = 11dB, ICC = 28mA, -65dBm LO-RF Leakage 400MHz to 3.7GHz High Signal Level Downconverting Mixer 1.5GHz to 2.4GHz High Linearity Direct Quadrature Modulator 400MHz to 3.8GHz, 3.3V, Very High Linearity Downconverting Mixer 600MHz to 1100MHz High Linearity Direct Quadrature Modulator Ultra-Low Power Active Mixer 700MHz to 1050MHz High Linearity Direct Quadrature Modulator 1.5GHz to 2.5GHz High Linearity Direct Quadrature Modulator 800MHz to 2.7GHz High Linearity Direct Conversion Quadrature Demodulator RF Power Detectors with >40dB Dynamic Range 100kHz to 1000MHz RF Power Detector 300MHz to 7GHz RF Power Detector 300MHz to 3GHz RF Power Detector 300MHz to 7GHz Precision RF Power Detector 300MHz to 7GHz Precision RF Power Detector 300MHz to 7GHz Precision RF Power Detector 50MHz to 3GHz Log RF Power Detector with 60dB Dynamic Range IIP3 = 23.5dBm and NF = 12.5dB at 1900MHz, 4.5V to 5.25V Supply, ICC = 78mA 21.8dBm OIP3 at 2GHz, -159.3dBm/Hz Noise Floor, 50, 0.5VDC Baseband Interface, 4-Ch W-CDMA ACPR = -66dBc at 2.14GHz IIP3 = 24.7dBm at 1.9GHz, 23.5dBm at 3.5GHz, Conversion Gain = 2.9dB at 1.9GHz, 3.3V at 82mA, -3dB LO Drive 22.4dBm OIP3 at 900MHz, -158dBm/Hz Noise Floor, 3k, 2.1VDC Baseband Interface, 3-Ch CDMA2000 ACPR = -70.4dBc at 900MHz 10mA Supply Current, 10dBm IIP3, 10dB NF, Usable as Up- or Down-Converter 22.9dBm OIP3 at 850MHz, -160.3dBm/Hz Noise Floor, 50, 0.5VDC Baseband Interface, 3-Ch CDMA2000 ACPR = -71.4dBc at 850MHz 21.6dBm OIP3 at 2GHz, -158.6dBm/Hz Noise Floor, High-Ohmic 0.5VDC Baseband Interface, 4-Ch W-CDMA ACPR = -67.7dBc at 2.14GHz 28dBm IIP3 and 13.2dBm P1dB at 900MHz, 60dBm IIP2 and 12.7dB NF at 1900MHz 300MHz to 3GHz, Temperature Compensated, 2.7V to 6V Supply 100kHz to 1GHz, Temperature Compensated, 2.7V to 6V Supply 44dB Dynamic Range, Temperature Compensated, SC70 Package 36dB Dynamic Range, Low Power Consumption, SC70 Package Precision VOUT Offset Control, Shutdown, Adjustable Gain Precision VOUT Offset Control, Shutdown, Adjustable Offset Precision VOUT Offset Control, Adjustable Gain and Offset 1dB Output Variation over Temperature, 38ns Response Time
RF Power Detectors LTC(R)5505 LTC5507 LTC5508 LTC5509 LTC5530 LTC5531 LTC5532 LT5534 LTC5536 LT5537
Precision 600MHz to 7GHz RF Detector with Fast 25ns Response Time, Comparator Reference Input, Latch Enable Input, -26dBm to Comparator +12dBm Input Range Wide Dynamic Range Log RF/IF Detector Low Frequency to 800MHz, 83dB Dynamic Range, 2.7V to 5.25V Supply
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16 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0307 * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2007

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