ISD1400 SERIES
PIN NAME
PIN NO
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 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 on the schematic of section 11,
Figure 5) connected from the AGC pin to V
SSA
analog ground.
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
analog
ground. Nominal values of 470 KΩ and 4.7
µF
give
satisfactory results in most cases.
Analog Input
: The analog input pin transfers its signal to the
chip for recording. For microphone inputs, the ANA OUT pin
should be connected via an external capacitor to the ANA IN
pin. This capacitor value, together with the 3.0 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 fed, 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
MIC REF
18
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
input to 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: November 16, 2005
Revision 1.3
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