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MAX2037CCQ-TD

Ultrasound Variable-Gain Amplifier

Maxim Integrated 

Ultrasound Variable-Gain Amplifier

Applications Information

External Compensation

External compensation is required for bypassing inter-

nal biasing circuitry. Connect, as close as possible,

individual 4.7µF capacitors from each pin EXT_C1,

EXT_C2, and EXT_C3 (pin 13, 14, 15) to ground.

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 7.5kΩ resistor from EXT_RES (pin 38) to

ground.

Analog Input and Output Coupling

In typical applications, the MAX2037 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 MAX1436 octal ADC). The

differential input impedance of the MAX2037 is typically

200Ω. The differential outputs are capable of driving a

differential load resistance of 1000Ω. The output

impedance is 100Ω differential. The differential outputs

have a common-mode bias of approximately 3.0V. AC-

couple these differential outputs if the next stage has a

different common-mode input range.

Ultrasound-Specific IMD3 Specification

Unlike typical communications specs, the two input

tones are not equal in magnitude for the ultrasound-

specific IMD3 two-tone specification. In this measure-

ment, f1 represents reflections from tissue and f2

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.

Board Layout

The pin configuration of the MAX2037 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 paddle (EP) of the MAX2037’s TQFP-EP

package provides a low thermal-resistance path to the

die. It is important that the PC board on which the

MAX2037 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.

ULTRASOUND

IMD3

-25dB

f1 - (f2 - f1)

f1

f2

f2 + (f2 - f1)

Figure 1. Ultrasound IMD3 Measurement Technique

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