After Sales
Technical Documentation
RAE/RAK–1N
Baseband
Page 2–34
Original, 08/96
The codec generates DTMF tones (key beeps) to the earphone and in
PHF mode to the PHF speaker. When an external audio accessory is
used, the DTMF tones are directed to the external audio output. In
handportable and PHF modes the codec generates ringing tones and also
some warning tones to the PHF speaker. In external HF mode they are
driven to the external speaker line. Some tones come also from the
network.
One codec output pin is used to switch on/off the microphone bias circuit.
Both microphones are biased simultaneously regardless of which one is
actually used.
External microphone line is used also to detect if the junction box is
connected to the bottom connector. Microphone signal is therefore
low–pass filtered and routed to the MCU A/D converter named as the
JCONN signal.
Also external earphone signal is multiplexed. 100 kohm pull down resistor
is used to turn power on to the HF accessories.
Main components
– Audio codec ST5090
Contains e.g. PCM codec, audio routing switches, 3 differential
microphone input channels, 2 differential earpiece output chan-
nels, ringing tone and DTMF generators. Physically the codec
is inside MCM2.
– Power amplifier LM4861 (N400)
Used as the booster amplifier for Personal Hands–Free.
– Transistors BC859C (V380) and BC849C (V381)
Used for implementing the microphone bias switch.
ASIC
Introduction
The ASIC takes care of the following functions:
– interface between MCU and UIF
– interface between MCU, DSP and RFI
– hardware accelerator functions to DSP
– clock generation and disable/enable
– RF controls
– UIF interface
– Timers
– MBUS or RBUS activity detection
– SIM interface
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