Fixed Differential Gain (MAX4060)

The MAX4060 has an internal fixed gain of 10V/V for its

differential input. This feature simplifies design, reduces

pin count, footprint, and eliminates external gain-setting

resistors.

Adjustable Differential-Gain Setting

The MAX4061/MAX4062 allow the user to alter the gain

to optimize the signal-to-noise ratio (SNR) of their system.

The gain is set by a single external resistor (RG) con-

nected between the G1 and G2 pins, where:

RG = 100kΩ / (AV - 1)

where AV is the required voltage gain.

Hence, an 11.11kΩ resistor yields a gain of 10V/V, or

20dB. Leaving the pins unconnected results in a gain of

1V/V. Gain for the MAX4061/MAX4062 is defined as:

AV = VOUT / (VIN+ - VIN-)

The resistor can be either fixed or variable, allowing the

use of a digitally controlled potentiometer to alter the gain

under software control.

Input Capacitors

The two differential microphone inputs and the sin-

gle-ended auxiliary input of the MAX4060/MAX4061/

MAX4062 have on-chip bias components, allowing the

user to AC-couple any signals onto the input. The input

resistance is 100kΩ (typ), so the capacitor size may be

chosen accordingly to define the LF rolloff desired. This

can be calculated as:

CIN = 1 / (2πfCUTRIN)

This assumes a low source impedance driving the inputs.

A further consideration for the differential input is the

effect of these series input capacitors on low-frequency,

common-mode rejection. Any mismatch in the values of

these two capacitors degrades the CMRR at frequen-

cies where the impedance of the capacitor is significant

compared to the input resistance of the amplifier—this is

usually most noticeable at low frequencies. One way to

avoid the need for matched or tight tolerance capacitors

is to deliberately oversize the values on the differential

BIAS

IN-

IN+

6

5

4

VCC

2.4V TO 5.5V

MAX4060

INT/AUX 1

OUT 2

GND

7

BIAS

3

VBIAS

BIAS

x10

BIAS

8 AUX_IN

x10

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Analog Devices │ 9

MAX4060/MAX4061/

MAX4062

Differential Microphone Preamplifiers with

Internal Bias and Complete Shutdown

Functional Diagram