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OVERVIEW: Digital Section
1.5.5 Transmit Paths
The average human voice signal has an audible frequency band of approximately 300 - 3400 Hz.
Low pass filters are utilized to provide the optimum voice signal response on the mic signal line by
filtering out unnecessary and potentially disruptive higher frequencies. The mic signal is then
amplified by the Roadrunner's internal op-amp and then converted from analog to digital in the
ADC. The digital mic signal is then digitally filtered, transferred to the DSP for necessary
processing, and then sent to SLEDGEHAMMER. Lastly, the data is sent to JANUS and
transmitted.
1.5.6 Receive Paths
The received voice signal is first converted to digital by SLEDGEHAMMER and then sent to the
DSP for necessary processing. The DSP sends the processed voice signal to the CODEC, where it
is converted from digital to analog in its internal DAC. The output of the DAC is then band-pass
filtered to attenuate any out-of-band noise.
Next, depending on the audio mode of operation and state of the High/Low Speaker key and audio
jack detect circuit, the speaker signal is either sent to the Roadrunner amplifier to drive the earpiece
speaker, the external 0.5W amplifier to drive the high audio speakers, or the audio jack output.
1.6
Digital Section
This section includes the Zeus which is a Dual Core Baseband Processor associated and
external memories. The Zeus controls the transmit, receive, and synthesize operations of the
integrated circuits located in the RF section.
The digital section contains the following (see Figure 1-8):
• Zeus Dual Core Baseband Processor
• Host memories (NAND flash and DDR)
• iDEN Power Management
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Figure 1-8: iDEN Digital Block Diagram
6880401P59-O
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