Rainbow Electronics MAX9860 - Manual (Page 28)

MAX9860
Microphone Inputs
The MAX9860 provides two differential microphone
inputs and a low-noise 1.55V microphone bias for power-
ing the microphones. In typical applications, the left
microphone is used to record a voice signal and the
right microphone is used to record a background noise
signal. In applications that require only one microphone,
use the left microphone input and disable the right ADC.
The microphone signals are amplified by two stages of
gain and then routed to the ADCs. The first stage offers
selectable 0dB, 20dB, or 30dB settings. The second
stage is a programmable gain amplifier (PGA) adjustable
from 0dB to 20dB in 1dB steps. Zero-crossing detection
is included on the PGA to minimize zipper noise while
making gain changes. See Figure 5 for a detailed dia-
gram of the microphone input structure.
16-Bit Mono Audio Voice Codec
28 ______________________________________________________________________________________
MICLN
MICLP
MICBIAS
AGC
PGA
PGA
-
PREAMP
MICRN
ADC
L
ADC
R
MICRP
REG 1.55V
0/20/30dB
0dB to +20dB
0dB to +20dB
V CM
V CM
0/20/30dB
MICGND
PREAMP
MAX9860
Figure 5. Microphone Input Block Diagram