MAX4063
Differential Microphone Preamplifier with
Internal Bias and Complete Shutdown
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mode application. The topology used in the MAX4063
means that the CMRR actually improves at higher dif-
ferential 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
On the MAX4063 thin QFN package, connect the
exposed paddle (backside of PRS) to the ground
plane. The MAX4063 has an integrated low-noise, low-
output impedance bias voltage. An optimum electret
bias resistor can be set externally. This gives a low-
noise, flexible solution that can run from 2.4V to 5.5V,
which is suitable for hand-held devices such as PDAs
that typically have audio power supplies in the 3V
region (Figure 2).
Output
DC Bias
In shutdown mode, the bias voltage is disabled. OUT
and OUT have a low-noise, DC-bias voltage indepen-
dent of the power supplies, resulting in superior PSRR
performance. The MAX4063 outputs are high imped-
ance when the part is in shutdown mode.
Differential Output
The MAX4063 features a differential output stage (OUT
and OUT), allowing optimum performance when con-
nected to ADCs and CODECs with differential inputs.
This differential output is particularly useful in designs
where the microphone preamplifier is mounted some
distance away from the CODEC/ADC, as the low-imped-
ance, differential line provides excellent noise rejection
and immunity (Figure 4).
Applications Information
Shutdown Mode
The MAX4063 features a low-power, complete shut-
down mode. When SHDN goes low, the supply current
drops to 0.3µA, the output enters a high-impedance
state, and the bias current to the microphone is
switched off. Driving SHDN high enables the amplifier.
SHDN should not be left unconnected.
Power Supplies and Layout
The MAX4063 operates from a 2.4V to 5.5V single sup-
ply. Bypass the power supply with a 0.1µF capacitor to
ground. In systems where analog and digital grounds
are available, the MAX4063 should be connected to the
analog ground.
