ISD1200 SERIES
PIN NAME
MIC REF
PIN NO.
18
FUNCTION
Microphone Reference:
The MIC REF input is the inverting
input to the microphone preamplifier. This provides a noise-
canceling or common-mode rejection input to the device when
connected to a differential microphone.
Automatic Gain Control (AGC):
The AGC input dynamically
adjusts the gain of the preamplifier to compensate for the wide
range of microphone input levels. The AGC allows the full
range of sound, from whispers to loud sounds, to be recorded
with minimal distortion. The “attack” time is determined by the
time constant of a 5 KΩ internal resistance and an external
capacitor (C6 of Figure 5 in Section 11) connected from the
AGC pin to V
SSA
. The “release” time is determined by the time
constant of an external resistor (R5) and an external capacitor
(C6) connected in parallel between the AGC pin and V
SSA
pin.
Nominal values of 470 KΩ and 4.7
µF
give satisfactory results
in most cases. Tying this to ground gives maximum gain,
while tying it to V
CCA
gives minimum gain for the AGC
amplifier.
Analog Input:
The ANA IN transfers an input signal to the
chip for recording. For microphone usage, this ANA IN pin
should be connected via an external capacitor to the ANA
OUT pin. This capacitor value, together with the 3 KΩ input
impedance of ANA IN, is selected to give additional cutoff at
the low-frequency end of the voice passband. If the desired
input is derived from a source other than a microphone, the
signal can be capacitively coupled into the ANA IN pin directly.
Analog Output:
This pin provides the preamplifier output to
the user. The voltage gain of the preamplifier is determined by
the voltage level at the AGC pin.
Playback, Level-Activated
: When this input signal is held
LOW, a playback cycle is initiated, and playback continues
AGC
19
ANA IN
20
ANA OUT
21
PLAYL
[2]
23
until
PLAYL
is pulled HIGH, or an EOM marker is detected.
The device automatically powers down and enters into
standby mode upon completion of a playback cycle.
PLAYE
[2]
24
Playback, Edge-Activated
: When a LOW-going transition is
detected on this pin, a playback cycle begins. Taking
PLAYE
HIGH during a playback cycle will not terminate the current
cycle. Playback continues until an EOM is encountered. Upon
completion of a playback cycle, the device automatically
powers down and enters into standby mode.
-7-
Publication Release Date: April 21, 2005
Revision 1.1
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