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iO1000 Detailed Service Manual - THEORY OF OPERATION
The GCAP II consists of active RC filters, digital filters, variable attenuators, an
analog-to-digital converter (ADC), a digital-to-analog converter (DAC), and a
microphone amplifier.
The average voice signal has a frequency band of approximately 300-3400 Hz.
Low-pass filters are set up to provide the optimum response to the signal while fil-
tering out high-level frequencies. Input signals from the microphone are amplified
by the GCAP II internal op-amp and this amplified signal is converted from ana-
log to digital in the ADC. These signals are then digitally filtered and transferred
to the DSP core for further processing.
Received analog signals are converted to digital signals by the ADDAG, then sent
to the DSP for processing. The DSP then sends the processed signals to the
CODEC, where they are converted from digital to an analog audio signal in the
DAC. The DAC output is low-pass filtered to attenuate any out-of-band noise.
From this point, the audio signal is sent to the GCAP II output ampli-fier A4 - the
external audio output.
Figure 4 indicates the circuitry path of the audio components.
The iO1000 accepts audio input from the external microphone and sends the
received audio to the external audio output.
Figure 12. iDEN Audio Circuitry Path
MCORE
DSP
MDI
ESSI1
QSPI Bus
Inbound Audio
Int.
Mic
Ext.
Audio
Out
Ext.
Audio
In
AUXMIC
MICIN
GCAP-II
Reg 00
Reg 06
CODEC
A/D
CODEC
D/A
CDC_EN
AUDOG
AUDIG
AUDOS
AUDIS
EXTOUT
A1
A4
A3
A5
PGA
PGA
