Rainbow Electronics APR9600 - Manual (Page 9)

INTEGRATED CIRCUITS INC.
- APR9600
http://www.aplusinc.com.tw Page / 17 Ver2.1 9
An internal oscillator provides the APR9600 sampling clock. Oscillator frequency can be
Changed by changing the resistance from the OscR pin to GND.
Table 2 summarizes resistance values and the corresponding sampling frequencies, as
well as the resulting input bandwidth and duration.
Table 2 Resistance Values & Sampling Frequencies
Resistance
Sampling
Frequency
Input
Bandwidth
Duration
84 K 4.2 kHz 2.1 kHz 60 sec
38 K 6.4 kHz 3.2 kHz 40 sec
24 K 8.0 kHz 4.0 kHz 32 sec
3.5 Automatic Gain Control (AGC) :
The APR9600 device has an integrated AGC. The AGC affects the microphone input
but does not affect the ANA_IN input. The AGC circuit insures that the input signal is
properly amplified. The AGC works by applying maximum gain to small input signals and
minimum gain to large input signals. This assures that inputs of varying amplitude are
recorded at the optimum signal level. The AGC amplifier is designed to have a fast attack
time and a slow decay time.
This timing is controlled by the RC network connected to pin 19. A value of 220K and 4.7uF
has been found to work well for the English language. Be aware that different languages,
speakers from different countries, and music may all require modification of the
recommended values for the AGC RC network.
3.6 Sampling Application :
The following reference schematics are included as examples of how a recording system
might be designed. Each reference schematic shows the device incorporated in one of its
three main modes: Random Access, Tape mode – Normal option, and Tape mode – Auto
Rewind option. Note that in several of the applications either one or all of the /BUSY,
/STROBE,or /M7_END pins are connected to LEDs as indicators of device status.
This is possible because all of these pins and signals were designed to have timing
compatible with both microprocessor interface and manual LED indication.
A bias must be applied to the electret microphone in order to power its built-in circuitry. The
ground return of this bias network is connected to the /Busy.
This configuration saves power when record mode.Both pins 18 and 19, MicIn and MicRef,
must be AC coupled to the microphone network in order to block the DC biasing voltage.
Figure 3 shows the device configured in random access mode. The device is using eight
Message segments, the maximum available, in this mode. Note that message trigger pins
that are not used, for modes with less than eight segments, can be left unconnected with
the exception of pin /M8_OPTION which should be pulled to VCC through a 100k resistor.