Differential Microphone Preamplifier with

Internal Bias and Complete Shutdown

8

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book PCs or PDAs. Used correctly, the advantages

over a single-ended solution are:

• Better power-supply noise rejection.

• Less degradation from noise in PC board ground

planes.

• The microphone and preamplifier may be placed

physically further apart, easing PC board layout

restrictions.

Differential-Gain Adjustment

The MAX4063 allows the user to alter the differential

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

system. The gain is set by a single external resistor

Hence, an 11.11k

Ω resistor yields a gain of 20V/V, or

26dB. Leaving the pins unconnected results in a gain of

2V/V. Gain is defined as:

For differential out:

The resistor can be either fixed or variable, allowing the

use of a digitally controlled potentiometer to alter the

gain under software control.

Auxiliary Input-Gain Adjustment

The MAX4063 provides an option to increase the

AUX_IN (see Figure 3). To increase the gain, connect

calculated from the following formula:

R

2M

AV

ADJ

AUX

=

−

Ω

20

()

to increase the gain

A

V

V

VD

OUT

OUT

IN+

IN-

=

−

−

V

V

R

200k

A

G

VD

=

−

Ω

2

BIAS

BIAS

AUX_IN

12

IN-

IN+

10

9

6

2.4V TO 5.5V

MAX4063

2

INT/AUX

8

OUT

OUT

ADJ

4

7

GND

11

SHDN

SHDN

3

BIAS

5

G2

G1

1

14

Functional Diagram