User Guide

PAMS
System Module DB6
NHB–3
Technical Documentation
Original 26/97
Page 4–29
Block Description
The codec has two microphone inputs and two earphone outputs. Handport-
able and external audios can therefore be connected directly to the codec. The
codec has internal switches to select which input or output is used. It also has
microphone amplifier and earphone attenuator. Input/output selection and am-
plification/attenuation can be done with codec register settings. The register
control is done by the MCU.
Handportable microphone and earphone (located on the flex) are connected
directly to the codec‘s differential input and output. External audios are con-
nected single sided. There is 21 dB attenuation in the external microphone line
before the codec to prevent clipping.
Microphone signal is routed to the microphone amplifier. After that it is fed to
the bandpass filter and then to the A/D converter. After the conversion the digi-
tal data is sent to the DSP.
Digital downlink signal from the DSP is fed to the D/A converted. After the con-
verter there is a low pass filter and attenuator before the earphone output. All
these are inside the codec. The ASIC generates the 512 kHz and 8 kHz clocks
for the codec and data transmission between the codec and the DSP.
The audio codec communicates with the DSP (analog speech) through a SIO
(signals: PCMIN, SYNC, CODEC_CLK and PCMOUT) . The MCU controls the
audio codec function through a separate serial bus (signals: PCMCDO,
PCMCDI, PCMCLK and XSELPCMC).
The codec generates DTMF tones (key beeps) to the earphone and in HF
mode to the external speaker. In portable mode the MCU generates ringing
tones and also some warning tones to the buzzer. In HF mode they are gener-
ated by the codec and 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 on the
flex.
External microphone line (MIC_JCONN) is used also to detect if junction box is
connected to the bottom connector. Microphone signal is therefore routed to the
MCU A/D converter.
Also external earphone signal is multiplexed. 100 kohm pull down resistor is
used to turn power on to the HF accessories