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19-0630; Rev 1; 2/09
Ultrasound Variable-Gain Amplifier
General Description
The MAX2035 8-channel variable-gain amplifier (VGA) is designed for high linearity, high dynamic range, and low-noise performance targeting ultrasound imaging and Doppler applications. Each amplifier features differential inputs and outputs and a total gain range of typically 50dB. In addition, the VGAs offer very low output-referred noise performance suitable for interfacing with 10-bit ADCs. The MAX2035 VGA is optimized for less than 0.5dB absolute gain error to ensure minimal channel-to-channel ultrasound beamforming focus error. The device's differential outputs are designed to directly drive ultrasound ADCs through an external passive anti-aliasing filter. A switchable clamp is also provided at each amplifier's outputs to limit the output signals, thereby preventing ADC overdrive or saturation. Dynamic performance of the device is optimized to reduce distortion to support second-harmonic imaging. The device achieves a second-harmonic distortion specification of -62dBc at VOUT = 1.5VP-P and fIN = 5MHz, and an ultrasound-specific* two-tone third-order intermodulation distortion specification of -52dBc at VOUT = 1.5VP-P and fIN = 5MHz. The MAX2035 operates from a +5.0V power supply, consuming only 127mW/channel. The device is available in a 100-pin TQFP package with an exposed pad. Electrical performance is guaranteed over a 0C to +70C temperature range.
Features
8-Channel Configuration High Integration for Ultrasound Imaging Applications Pin Compatible with the MAX2036 Ultrasound VGA Plus CW Doppler Beamformer Maximum Gain, Gain Range, and Output-Referred Noise Optimized for Interfacing with 10-Bit ADCs Maximum Gain of 39.5dB Total Gain Range of 50dB 60nV/Hz Ultra-Low Output-Referred Noise at 5MHz Pin-for-Pin 12-Bit Compatibility Supported By MAX2037/MAX2038 0.5dB Absolute Gain Error Switchable Output VGA Clamp Eliminating ADC Overdrive Fully Differential VGA Outputs for Direct ADC Drive Variable Gain Range Achieves 50dB Dynamic Range -62dBc HD2 at VOUT = 1.5VP-P and fIN = 5MHz Two-Tone Ultrasound-Specific* IMD3 of -52dBc at VOUT = 1.5VP-P and fIN = 5MHz 127mW Consumption per Channel
*See the Ultrasound-Specific IMD3 Specification in the Applications Information section.
MAX2035
Applications
Ultrasound Imaging Sonar
Functional Diagram
VCC VREF
Ordering Information
PART MAX2035CCQ-D MAX2035CCQ-TD MAX2035CCQ+D TEMP RANGE 0C to +70C 0C to +70C 0C to +70C 0C to +70C PIN-PACKAGE 100 TQFP-EP 100 TQFP-EP 100 TQFP-EP 100 TQFP-EP
MAX2035
VG_CTL+ VG_CTLVG_IN1+ VG_IN1* * * ** ** **
-10.5dB TO +39.5dB VG_CLAMP_MODE VGA 50 VG_OUT1+ VG_OUT1* * *
MAX2035CCQ+TD
EP = Exposed pad.
50
* * *
VG_IN8+ VG_IN8-
VGA
50
VG_OUT8+ VG_OUT8-
+Denotes a lead(Pb)-free/RoHs-compliant package. -Denotes a package containing lead(Pb). T = Tape and reel. D = Dry packing.
50 BIAS CIRCUITRY
PD
GND
EXT_RES
________________________________________________________________ Maxim Integrated Products
1
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Ultrasound Variable-Gain Amplifier MAX2035
ABSOLUTE MAXIMUM RATINGS
VCC, VREF to GND .................................................-0.3V to +5.5V Any Other Pins to GND...............................-0.3V to (VCC + 0.3V) VGA Differential Input Voltage (VGIN_+ - VGIN_-)...........8.0VP-P Analog Gain-Control Input Differential Voltage (VG_CTL+ - VG_CTL-)...................................................8.0VP-P Continuous Power Dissipation (TA = +70C) 100-Pin TQFP (derated 45.5mW/C above +70C).........................3636.4mW Operating Temperature Range...............................0C to +70C Junction Temperature ......................................................+150C JC (Note 1) .....................................................................+2C/W JA (Note 1) ...................................................................+22C/W Storage Temperature Range .............................-40C to +150C Lead Temperature (soldering, 10s) .................................+300C
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(Figure 2, VCC = VREF = 4.75V to 5.25V, VCM = (3/5)VREF, VGND = 0, PD = 0, no RF signals applied, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, TA = +25C, unless otherwise noted.) (Note 2)
PARAMETER Supply Voltage Range VCC External Reference Voltage Range Total Power-Supply Current VCC Supply Current VREF Current Current Consumption per Amplifier Channel Differential Analog Control Voltage Range Differential Analog Control Common-Mode Voltage Analog Control Input Source/Sink Current LOGIC INPUTS CMOS Input-High Voltage CMOS Input-Low Voltage VIH VIL 2.3 0.8 V V VCM IVCC IREF Refers to VCC supply current Minimum gain Maximum gain 2.85 SYMBOL VCC VREF (Note 3) Refers to VCC supply current plus VREF current PD = 0 PD =1 CONDTIONS MIN 4.75 4.75 TYP 5 5 204 27 192 12 24 +2 -2 3.0 4.5 3.15 5 MAX 5.25 5.25 231 33 216 15 27 UNITS V V mA mA mA mA VP-P V mA
2
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Ultrasound Variable-Gain Amplifier
AC ELECTRICAL CHARACTERISTICS
(Figure 2, VCC = VREF = 4.75V to 5.25V, VCM = (3/5)VREF, VGND = 0, PD = 0, no RF signals applied, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, TA = +25C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS Differential output capacitance is 10pF, capacitance to GND at each single-ended output is 60pF, RL = 1k No capacitive load, RL = 1k Differential Input Resistance Input Effective Capacitance Differential Output Resistance Maximum Gain Minimum Gain Gain Range TA = +25C, -2.0V < VG_CTL < -1.8V, VREF = 5V Absolute Gain Error VGA Gain Response Time Input-Referred Noise TA = +25C, -1.8V < VG_CTL < +1.2V, VREF = 5V TA = +25C, +1.2V < VG_CTL < +2.0V, VREF = 5V 50dB gain change to within 1dB final value VG_CTL set for maximum gain, no input signal VG_CTL set for +20dB of gain No input signal VOUT = 1.5VP-P, 1kHz offset -55 RIN CIN ROUT fRF = 10MHz, each input to ground 170 MIN TYP MAX UNITS
MAX2035
Large-Signal Bandwidth
f-3dB
VOUT = 1.5VP-P, 3dB bandwidth, gain = 20dB
17 MHz
22 200 15 100 39.5 -10.5 50 0.6 0.5 1.2 1 2 60 120 nV/Hz s nV/Hz dB 230 pF dB dB dB
Output-Referred Noise
Second Harmonic
HD2
VG_CLAMP_MODE = 1, VG_CTL set for +20dB of gain, fRF = 5MHz, VOUT = 1.5VP-P VG_CLAMP_MODE = 1, VG_CTL set for +20dB of gain, fRF = 10MHz, VOUT = 1.5VP-P VG_CLT set for +20dB of gain, fRF1 = 5MHz, fRF2 = 5.01MHz, VOUT = 1.5VP-P, VREF = 5V (Note 4)
-62 dBc -62
Third-Order Intermodulation Distortion
IMD3
-40
-52
dBc
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3
Ultrasound Variable-Gain Amplifier MAX2035
AC ELECTRICAL CHARACTERISTICS (continued)
(Figure 2, VCC = VREF = 4.75V to 5.25V, VCM = (3/5)VREF, VGND = 0, PD = 0, no RF signals applied, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, TA = +25C, unless otherwise noted.) (Note 2)
PARAMETER Channel-to-Channel Crosstalk Maximum Output Voltage at Clamp ON Maximum Output Voltage at Clamp OFF SYMBOL CONDITIONS VOUT = 1VP-P differential, fRF = 10MHz, VG_CTL set for +20dB of gain VG_CLAMP_MODE = 0, VG_CTL set for +20dB of gain, 350mVP-P differential input VG_CLAMP_MODE = 1, VG_CTL set for +20dB of gain, 350mVP-P differential input MIN TYP -80 MAX UNITS dB VP-P differential VP-P differential
2.2
3.4
Note 2: Specifications at TA = +25C and TA = +70C are guaranteed by production test. Specifications at TA = 0C are guaranteed by design and characterization. Note 3: Noise performance of the device is dependent on the noise contribution from the supply to VREF. Use a low-noise supply for VREF. VCC and VREF can be connected together to share the same supply voltage if the supply for VCC exhibits low noise. Note 4: See the Ultrasound-Specific IMD3 Specification section.
Typical Operating Characteristics
(Figure 2, VCC = VREF = 4.75V to 5.25V, VGND = 0, PD = 0, VG_CLAMP_MODE = 1, fRF = 5MHz, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, VCM = 3.0V, TA = +25C, unless otherwise noted.)
OVERDRIVE PHASE DELAY vs. FREQUENCY
MAX2035 toc01
POWER-SUPPLY MODULATION RATIO
MAX2035 toc02
TWO-TONE ULTRASOUND-SPECIFIC IMD3 vs. GAIN
-10 -20 VOUT = 1VP-P DIFFERENTIAL GAIN = 20dB
MAX2035 toc03
5.0 4.5
OVERDRIVE PHASE DELAY (ns)
-30 -40 -50 VOUT = 1.5VP-P DIFFERENTIAL VMOD = 50mVP-P, fCARRIER = 5MHz, GAIN = 20dB
0
4.0 3.5
VIN1 = 35mVP-P DIFFERENTIAL VIN2 = 87.5mVP-P DIFFERENTIAL GAIN = 20dB
PSMR (dBc)
IMD3 (dBc)
3.0 2.5 2.0 1.5 1.0 0.5 0 0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 FREQUENCY (MHz)
-30 f = 10MHz -40 -50 -60
-60 -70 -80 -90 0 25 50 75 100 125 150 175 200 FREQUENCY (kHz)
-70 -80 -15 -5
f = 2MHz, 5MHz
5
15 GAIN (dB)
25
35
45
4
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Ultrasound Variable-Gain Amplifier
Typical Operating Characteristics (continued)
(Figure 2, VCC = VREF = 4.75V to 5.25V, VGND = 0, PD = 0, VG_CLAMP_MODE = 1, fRF = 5MHz, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, VCM = 3.0V, TA = +25C, unless otherwise noted.)
SECOND-HARMONIC DISTORTION vs. GAIN
MAX2035 toc04
MAX2035
THIRD-HARMONIC DISTORTION vs. GAIN
-10 -20 -30 HD3 (dBc) f = 12MHz VOUT = 1VP-P DIFFERENTIAL
MAX2035 toc05
0 -10 -20 -30 HD2 (dBc) -40 -50 -60 -70 -80 -90 -100 -15 -5 5 15 GAIN (dB) 25 35 f = 2MHz f = 12MHz f = 5MHz VOUT = 1VP-P DIFFERENTIAL
0
-40 -50 -60 -70 -80 -90
f = 5MHz
f = 2MHz
45
-100 -15 -5 5 15 GAIN (dB) 25 35 45
OVERLOAD RECOVERY TIME
MAX2035 toc06
OVERLOAD RECOVERY TIME
MAX2035 toc07
f = 5MHz
DIFFERENTIAL INPUT 200mV/div
f = 5MHz DIFFERENTIAL INPUT 200mV/div
DIFFERENTIAL OUTPUT 500mV/div
DIFFERENTIAL OUTPUT 500mV/div
OUTPUT OVERLOAD TO 1VP-P
OUTPUT OVERLOAD TO 100mVP-P
CHANNEL-TO-CHANNEL CROSSTALK vs. GAIN
MAX2035 toc08
CHANNEL-TO-CHANNEL CROSSTALK vs. FREQUENCY
-40 -50 CROSSTALK (dB) -60 -70 -80 -90 -100 -110 VOUT = 1VP-P DIFFERENTIAL GAIN = 20dB, ADJACENT CHANNELS
MAX2035 toc09
-60 -65 -70 CROSSTALK (dB) -75 -80 -85 -90 -95 -100 -15 -5 5 15 GAIN (dB) 25 35 VOUT = 1.5VP-P DIFFERENTIAL f = 10MHz, ADJACENT CHANNELS
-30
45
1
10 FREQUENCY (MHz)
100
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5
Ultrasound Variable-Gain Amplifier MAX2035
Typical Operating Characteristics (continued)
(Figure 2, VCC = VREF = 4.75V to 5.25V, VGND = 0, PD = 0, VG_CLAMP_MODE = 1, fRF = 5MHz, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, VCM = 3.0V, TA = +25C, unless otherwise noted.)
OUTPUT-REFERRED NOISE VOLTAGE vs. GAIN
MAX2035 toc10
GAIN vs. DIFFERENTIAL ANALOG CONTROL VOLTAGE (VG_CTL)
MAX2035 toc11
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
45 40 VOUT = 1.5VP-P DIFFERENTIAL VG_CTL = -2VP-P DIFFERENTIAL
MAX2035 toc12
80 OUTPUT-REFERRED NOISE VOLTAGE (nV/Hz) f = 5MHz 70
45 f = 5MHz 35 25 GAIN (dB)
50
GAIN (dB)
60
35 30 25 20
15 5
50
40
-5 -15 -15 -5 5 15 GAIN (dB) 25 35 45 -2.5 -1.5 -0.5 0.5 1.5 2.5 VG_CTL (VP-P DIFFERENTIAL)
15 10 0.1 1 10 FREQUENCY (MHz) 100 1000
30
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
MAX2035 toc13
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
25 20 GAIN (dB) GAIN (dB) 15 10 5 0 -5 -10 VOUT = 1.5VP-P DIFFERENTIAL VG_CTL = +0.2VP-P DIFFERENTIAL
MAX2035 toc14
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
15 10 5 0 -5 -10 -15 -20 VOUT = 1.5VP-P DIFFERENTIAL VG_CTL = +1.2VP-P DIFFERENTIAL
MAX2035 toc15
40 35 30 GAIN (dB) 25 20 15 10 5 0 0.1 1 10 FREQUENCY (MHz) 100 VOUT = 1.5VP-P DIFFERENTIAL VG_CTL = -0.8VP-P DIFFERENTIAL
30
20
1000
0.1
1
10 FREQUENCY (MHz)
100
1000
0.1
1
10 100 FREQUENCY (MHz)
1000
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
MAX2035 toc16
LARGE-SIGNAL BANDWIDTH vs. FREQUENCY
MAX2035 toc17
HARMONIC DISTORTION vs. DIFFERENTIAL OUTPUT VOLTAGE
-10 HARMONIC DISTORTION (dBc) -20 -30 -40 -50 -60 -70 -80 -90 -100 SECOND HARMONIC THIRD HARMONIC f = 5MHz, GAIN = 20dB
MAX2035 toc18
10 5 0 GAIN (dB) VOUT = 1.5VP-P DIFFERENTIAL VG_CTL = +1.7VP-P DIFFERENTIAL
0 -5 -10 GAIN (dB) -15 -20 -25 -30 -35 -40 VOUT = 1VP-P DIFFERENTIAL VG_CTL = +2VP-P DIFFERENTIAL
0
-5 -10 -15 -20 -25 -30 0.1 1 10 100 FREQUENCY (MHz) 1000
0.1
1
10 100 FREQUENCY (MHz)
1000
0
0.5
1.0
1.5
2.0
2.5
3.0
DIFFERENTIAL OUTPUT VOLTAGE (VP-P)
6
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Ultrasound Variable-Gain Amplifier
Typical Operating Characteristics (continued)
(Figure 2, VCC = VREF = 4.75V to 5.25V, VGND = 0, PD = 0, VG_CLAMP_MODE = 1, fRF = 5MHz, capacitance to GND at each of the VGA differential outputs is 60pF, differential capacitance across the VGA outputs is 10pF, RL = 1k, TA = 0C to +70C. Typical values are at VCC = VREF = 5V, VCM = 3.0V, TA = +25C, unless otherwise noted.)
HARMONIC DISTORTION vs. DIFFERENTIAL OUTPUT LOAD RESISTANCE
MAX2035 toc19
MAX2035
HARMONIC DISTORTION vs. DIFFERENTIAL OUTPUT LOAD CAPACITANCE
MAX2035 toc20
HARMONIC DISTORTION vs. FREQUENCY
-10 HARMONIC DISTORTION (dBc) -20 -30 -40 -50 -60 -70 -80 -90 -100 SECOND HARMONIC VOUT = 1VP-P DIFFERENTIAL GAIN = 20dB THIRD HARMONIC
MAX2035 toc21
-40 -45 HARMONIC DISTORTION (dBc) -50 -55 -60 -65 -70 -75 -80 -85 -90 -95 -100 200 500 800 1100 1400 1700 SECOND HARMONIC THIRD HARMONIC VOUT = 1VP-P DIFFERENTIAL f = 5MHz, GAIN = 20dB
-40 -45 HARMONIC DISTORTION (dBc) -50 -55 -60 -65 -70 -75 -80 -85 -90 -95 -100 SECOND HARMONIC THIRD HARMONIC VOUT = 1VP-P DIFFERENTIAL f = 5MHz, GAIN = 20dB
0
2000
5
25
45
65
85
105
0
10
20
30
40
50
DIFFERENTIAL OUTPUT LOAD ()
DIFFERENTIAL OUTPUT LOAD (pF)
FREQUENCY (MHz)
TWO-TONE ULTRASOUND-SPECIFIC IMD3 vs. FREQUENCY
MAX2035 toc22
GAIN ERROR HISTOGRAM
45 40 35 % OF UNITS 30 25 20 15 10 SAMPLE SIZE = 188 UNITS fIN_ = 5MHz, GAIN = 20dB
MAX2035 toc23
0 -10 -20 IMD3 (dBc) -30 -40 -50 -60 -70 0 5 10 15 20 VOUT = 1VP-P DIFFERENTIAL GAIN = 20dB
50
5 0 25 FREQUENCY (MHz) -4.50 -3.00 -1.50 0.75 2.25 3.75 -3.75 -2.25 -0.75 1.50 3.00 4.50 GAIN ERROR (dB)
OUTPUT COMMON-MODE OFFSET VOLTAGE vs. GAIN
MAX2035 toc24
DIFFERENTIAL OUTPUT IMPEDANCE MAGNITUDE vs. FREQUENCY
180 160 ZOUT () 140 120 100 80 60
MAX2035 toc25
100 75 OFFSET VOLTAGE (mV) 50 25 0 -25 -50 -75 -100 -15 -5 5 15 GAIN (dB) 25 35
200
45
0.1
1
10
100
FREQUENCY (MHz)
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7
Ultrasound Variable-Gain Amplifier MAX2035
Pin Description
PIN 1, 2, 5, 6, 7, 10, 11, 12, 19, 20, 21, 24, 25, 26, 29, 30, 31, 34, 35, 36, 41, 43, 44, 45, 47, 48, 51, 55, 58, 59, 64, 65, 66, 69, 73, 76, 79, 80, 81, 83, 84, 85, 88-92, 96, 97, 98 3 4 8 9 13 14 15 16, 39, 42, 46, 54, 72, 82, 87 17 18 22 23 27 28 32 33 NAME FUNCTION
GND
Ground
VGIN3VGIN3+ VGIN4VGIN4+ EXT_C1 EXT_C2 EXT_C3 VCC VGIN5VGIN5+ VGIN6VGIN6+ VGIN7VGIN7+ VGIN8VGIN8+
VGA Channel 3 Inverting Differential Input VGA Channel 3 Noninverting Differential Input VGA Channel 4 Inverting Differential Input VGA Channel 4 Noninverting Differential Input External Compensation. Connect a 4.7F capacitor to ground. External Compensation. Connect a 4.7F capacitor to ground. External Compensation. Connect a 4.7F capacitor to ground. 5V Power Supply. Bypass each VCC supply to ground with 0.1F capacitors as close to the pins as possible. VGA Channel 5 Inverting Differential Input VGA Channel 5 Noninverting Differential Input VGA Channel 6 Inverting Differential Input VGA Channel 6 Noninverting Differential Input VGA Channel 7 Inverting Differential Input VGA Channel 7 Noninverting Differential Input VGA Channel 8 Inverting Differential Input VGA Channel 8 Noninverting Differential Input 5V Reference Supply. Bypass to GND with a 0.1F capacitor as close to the pins as possible. Note that noise performance of the device is dependent on the noise contribution from the supply to VREF. Use a low-noise supply for VREF. VCC and VREF can be connected together to share the same supply voltage if the supply for VCC exhibits low noise. External Resistor. Connect a 7.5k resistor to ground. Power-Down Switch. Drive PD high to set the device in power-down mode. Drive PD low for normal operation. VGA Channel 8 Noninverting Differential Output VGA Channel 8 Inverting Differential Output VGA Channel 7 Noninverting Differential Output VGA Channel 7 Inverting Differential Output VGA Channel 6 Noninverting Differential Output VGA Channel 6 Inverting Differential Output VGA Channel 5 Noninverting Differential Output
37, 93
VREF
38 40 49 50 52 53 56 57 60
EXT_RES PD VGOUT8+ VGOUT8VGOUT7+ VGOUT7VGOUT6+ VGOUT6VGOUT5+
8
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Ultrasound Variable-Gain Amplifier
Pin Description (continued)
PIN 61 62 63 67 68 70 71 74 75 77 78 86 94 95 99 100 -- NAME VGOUT5VG_CTLVG_CTL+ VGOUT4+ VGOUT4VGOUT3+ VGOUT3VGOUT2+ VGOUT2VGOUT1+ VGOUT1VGA Analog Gain-Control Inverting Input VGA Analog Gain-Control Noninverting Input VGA Channel 4 Noninverting Differential Output VGA Channel 4 Inverting Differential Output VGA Channel 3 Noninverting Differential Output VGA Channel 3 Inverting Differential Output VGA Channel 2 Noninverting Differential Output VGA Channel 2 Inverting Differential Output VGA Channel 1 Noninverting Differential Output VGA Channel 1 Inverting Differential Output FUNCTION VGA Channel 5 Inverting Differential Output
MAX2035
VGA Clamp Mode Enable. Drive VG_CLAMP_MODE low to enable VGA clamping. VGA output VG_CLAMP_MODE will be clamped at typically 2.2VP-P differential. Drive VG_CLAMP_MODE high to disable VGA clamp mode. VGIN1VGIN1+ VGIN2VGIN2+ EP VGA Channel 1 Inverting Differential Input VGA Channel 1 Noninverting Differential Input VGA Channel 2 Inverting Differential Input VGA Channel 2 Noninverting Differential Input Exposed Pad. Internally connected to GND. Solder the exposed pad to the ground plane using multiple vias.
Detailed Description
The MAX2035's VGAs are optimized for high linearity, high dynamic range, and low output-noise performance, making this component ideal for ultrasoundimaging applications. The VGA paths also exhibit a channel-to-channel crosstalk of -80dB at 10MHz and an absolute gain error of less than 0.25dB for minimal channel-to-channel focusing error in an ultrasound system. Each VGA path includes circuitry for adjusting analog gain, an output buffer with differential output ports (VGOUT_+, VGOUT_-) for driving ADCs, and differential input ports (VGIN_+, VGIN_-) that are ideal for directly interfacing to the MAX2034 quad LNA. See the Functional Diagram for details. The VGA has an adjustable gain range from -10.5dB to +39.5dB, achieving a total dynamic range of typically 50dB. The VGA gain can be adjusted with the differential gain-control input VG_CTL+ and VG_CTL-. Set the differential gain-control input voltage at -2V for maximum gain and +2V for minimum gain. The differential analog control common-mode voltage is typically 3.0V.
VGA Clamp
A clamp is provided to limit the VGA output signals to avoid overdriving the ADC or to prevent ADC saturation. Set VG_CLAMP_MODE low to clamp the VGA differential outputs at 2.2VP-P. Set the VG_CLAMP_MODE high to disable the clamp.
Power Down
The device can also be powered down with PD. Set PD to logic-high for power-down mode. In power-down mode, the device draws a total supply current of 27mA. Set PD to a logic-low for normal operation
Overload Recovery
The device is also optimized for quick overload recovery for operation under the large input signal conditions that are typically found in ultrasound input buffer imaging applications. See the Typical Operating Characteristics for an illustration of the rapid recovery time from a transmit-related overload.
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9
Ultrasound Variable-Gain Amplifier MAX2035
Applications Information
External Compensation
External compensation is required for bypassing internal biasing circuitry. Connect, as close as possible, individual 4.7F capacitors from each pin EXT_C1, EXT_C2, and EXT_C3 (pin 13, 14, 15) to ground.
PCB Layout
The pin configuration of the MAX2035 is optimized to facilitate a very compact physical layout of the device and its associated discrete components. A typical application for this device might incorporate several devices in close proximity to handle multiple channels of signal processing. The exposed pad (EP) of the MAX2035's TQFP-EP package provides a low thermal-resistance path to the die. It is important that the PCB on which the MAX2035 is mounted be designed to conduct heat from the EP. In addition, provide the EP with a low-inductance path to electrical ground. The EP MUST be soldered to a ground plane on the PCB, either directly or through an array of plated via holes.
External Bias Resistor
An external resistor at EXT_RES is required to set the bias for the internal biasing circuitry. Connect, as close as possible, a 7.5k resistor from EXT_RES (pin 38) to ground.
Analog Input and Output Coupling
In typical applications, the MAX2035 is being driven from a low-noise amplifier (such as the MAX2034) and is typically driving a discrete differential anti-alias filter into an ADC (such as the MAX1434 octal ADC). The differential input impedance of the MAX2035 is typically 200. The differential outputs are capable of driving a differential load resistance of 1k. The output impedance is 100 differential. The differential outputs have a common-mode bias of approximately 3V. AC-couple these differential outputs if the next stage has a different common-mode input range.
-25dB
ULTRASOUND IMD3
Ultrasound-Specific IMD3 Specification
Unlike typical communications specs, the two input tones are not equal in magnitude for the ultrasoundspecific IMD3 two-tone specification. In this measurement, f 1 represents reflections from tissue and f 2 represents reflections from blood. The latter reflections are typically 25dB lower in magnitude, and hence the measurement is defined with one input tone 25dB lower than the other. The IMD3 product of interest (f1 - (f2 - f1)) presents itself as an undesired Doppler error signal in ultrasound applications. See Figure 1.
f1 - (f2 - f1)
f1
f2
f2 + (f2 - f1)
Figure 1. Ultrasound IMD3 Measurement Technique
10
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Ultrasound Variable-Gain Amplifier MAX2035
ZIN CONTROL D2, D1, D0 SINGLE CHANNEL
MAX2034
SINGLE CHANNEL +V VG_CTL+ VG_CTL18nF 100nF 100nF VGIN_+ VGIN_100nF VGA 50 50 100nF VG_OUT_+ VG_OUT_100nF TO A SINGLE CHANNEL OF
MAX2035
VIN
MAX1434 ADC
100nF -V
Figure 2. Typical per-Channel Ultrasound-Imaging Application
Pin Configuration
TOP VIEW VGIN2+ GND VGIN1+ VGIN1VREF VGIN2GND GND VG_CLAMP_MODE VGOUT1VGOUT1+ 78 77
GND GND
GND GND GND
GND
GND
GND
GND GND VCC
100 99 98
97
96
95
94
93
92
91
90
89
88
87
GND VCC
86
85
84
83
82
81
80
79
GND GND VGIN3VGIN3+ GND GND GND VGIN4VGIN4+ GND GND GND EXT_C1 EXT_C2 EXT_C3 VCC VGIN5VGIN5+ GND GND GND VGIN6VGIN6+ GND GND
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
+
76
GND
75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52
VGOUT2VGOUT2+ GND VCC VGOUT3VGOUT3+ GND VGOUT4VGOUT4+ GND GND GND VG_CTL+ VG_CTLVGOUT5VGOUT5+ GND GND VGOUT6VGOUT6+ GND VCC VGOUT7VGOUT7+ GND
MAX2035
*EP
51
26 27 28
29
30
31
32 33 34 35
36
37 38 39
40
41
42
43
44
45
46
47 48 GND
49
EXT_RES VCC
PD GND VCC
GND GND GND VCC
*EP = EXPOSED PAD
TQFP (14mm x 14mm)
______________________________________________________________________________________
GND VGOUT8+ VGOUT8-
VGIN7+ GND GND GND VGIN8VGIN8+ GND
GND VGIN7-
GND GND VREF
50
11
Ultrasound Variable-Gain Amplifier MAX2035
Chip Information
PROCESS: Silicon Complementary Bipolar
PACKAGE TYPE 100 TQFP-EP
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE CODE C100E+3 DOCUMENT NO. 21-0116
12
______________________________________________________________________________________
Ultrasound Variable-Gain Amplifier
Revision History
REVISION NUMBER 0 1 REVISION DATE 10/06 2/09 Initial release Updated various sections DESCRIPTION PAGES CHANGED -- 1-7, 9, 12
MAX2035
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13
(c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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