Datasheet
MAX4060/MAX4061/MAX4062
Differential Microphone Preamplifiers with
Internal Bias and Complete Shutdown
10 ______________________________________________________________________________________
AUX_IN
9
4
IN-
IN+
7
6
5
V
CC
2.4V TO 5.5V
MAX4062
2
GND
8
V
BIAS
G2
G1
BIAS
R
BIAS
C
BIAS
100k
Ω
OUT
3
INT/AUX
10
1
x10
Figure 1. MAX4062 with Auxiliary Input Configuration
ential inputs and to set the lower 3dB point (f
CUT
) of the
amplifier 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 pro-
viding to any signal applied equally to the IN+ and IN-
inputs. 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
V
IN
as an AC signal:
CMRR(dB) = A
DM
/ A
CM
where A
DM
is the differential gain, A
CM
is the common-
mode gain.
Input voltages are sufficiently small such that the output
is not clipped in either differential or common-mode
application. 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
standard. It features source impedance of greater than
2kΩ, and delivers more than 2V of bias when loaded
with a current of 800μA. This limits operation of this part
to supplies between 4.5V to 5.5V (see Figure 2).