inputs and to set the lower 3dB point (fCUT) of the ampli-

fier by sizing the output capacitor appropriately.

The input impedance matching on the differential input

is typically 1%, allowing input capacitor matching to be

effective at improving low-frequency PSRR.

Common-Mode Rejection Ratio

The common-mode rejection ratio (CMRR) refers to the

amount of rejection that the amplifier is capable of provid-

ing to any signal applied equally to the IN+ and INinputs.

In the case of amplifying low-level microphone signals in

noisy digital environments, it is a key figure of merit. In

audio circuits, this is generally measured for VIN as an

AC signal:

CMRR(dB) = ADM / ACM

where ADM is the differential gain, ACM is the common-

mode gain.

Input voltages are sufficiently small such that the output is

not clipped in either differential or common-mode applica-

tion. The topology used in the MAX4061/MAX4062 means

that the CMRR actually improves at higher differential

gains—another advantage of using differential sensing.

Auxiliary Input

The auxiliary input is a single-ended input intended to be

used with a jack-socket-type microphone input (Figure 1).

Internal DC-bias components (as on the main inputs) allow

the input signal to be AC-coupled. Mechanically switched

jack sockets can be used in conjunction with the INT/AUX

select pin, allowing the auxiliary microphone input to be

automatically selected when a jack socket is inserted.

Microphone Bias Voltage

MAX4060

The MAX4060 has a microphone bias voltage designed

to comply with the Microsoft/Intel PC99/2001 audio stan-

dard. It features source impedance of greater than 2kΩ,

and delivers more than 2V of bias when loaded with a cur-

rent of 800μA. This limits operation of this part to supplies

between 4.5V to 5.5V (see Figure 2).

Figure 1. MAX4062 with Auxiliary Input Configuration

AUX_IN

9

4

IN-

IN+

7

6

5

VCC

2.4V TO 5.5V

MAX4062

2

GND

8

VBIAS

G2

G1

BIAS

RBIAS

CBIAS

100kΩ

OUT 3

INT/AUX

10

1

x10

www.analog.com

Analog Devices │ 10

MAX4060/MAX4061/

MAX4062

Differential Microphone Preamplifiers with

Internal Bias and Complete Shutdown