Rainbow Electronics ISD5216 - Manual (Page 48)

I5216 SERIES
Advanced Information
PRELIMINARY
Publication Release Date: November 30, 2001
- 48 Revision A1
ANALOG I/O PINS
MIC+, MIC- (Microphone Input +/-)
The microphone input transfers the voice signal to the on-chip AGC preamplifier or directly to the
CODEC A/D INPUT MUX, depending on the selected path. The AGC circuit has a range of 45 dB in
order to deliver a nominal 694 mV p-p into the storage array from a typical electric microphone output
of 2 to 20 mV p-p. The input impedance is typically 20 kΩ differential and 13.3 kΩ differential when the
CODEC INPUT MUX MICIN path is selected.
MICROPHONE INPUT
AGC
MIC+
MIC -
AGCCAP
MIC IN
1
(AGPD)
2.2V Voltage
reference
MICBS
2
1
CODEC INPUT MUX
IN
P-
IN
P+
SU
M
2
-
SU
M
2
+
CODEC ADC IN
1.5k Ω
1.5k Ω
Electret Microphone
WM-54B Panasonic
Ra=10k Ω
Rc=40k Ω
( )
CDI1
CDI0
(AGPD)
. 1 µ F
. 1 µ F
4.7 µ F
ACAP (AGC Capacitor)
This pin provides the capacitor connection for setting the parameters of the microphone AGC circuit. It
should have a 4.7 µF capacitor connected to ground. It cannot be left floating. This is because the
capacitor is also used in the playback mode for the AutoMute circuit or when signal compression is
chosen (AMT0 is set to ONE). This circuit reduces the amount of noise present in the output during
quiet pauses. Tying this pin to ground gives maximum gain. Tying it to V
CCA
gives minimum gain for the
AGC amplifier, but cancels the AutoMute function.
COUPLE
dB
C Ra
f
⋅ ⋅ ⋅
=
−
π
2
1
3