Nokia Mobile Phones NSE-5 Series Service Manual page 48

NSE–5
System Module
PCMDClk
PCMSClk
PCMTxData
PCMRxData
The output for the internal earphone is a dual ended type output capable
of driving a dynamic type speaker. The output for the external accessory
and the headset is single ended with a dedicated signal ground SGND.
Input and output signal source selection and gain control is performed
inside the COBBA_GJP asic according to control messages from the
MAD2PR1. Keypad tones, DTMF, and other audio tones are generated
and encoded by the MAD2PR1 and transmitted to the COBBA_GJP for
decoding. MAD2PR1 generates two separate PWM outputs, one for a
buzzer and one for vibra (internal and external via BTEMP).
Speech Processing
The speech coding functions are performed by the DSP in the MAD2PR1
and the coded speech blocks are transferred to the COBBA_GJP for
digital to analog conversion, down link direction. In the up link direction the
PCM coded speech blocks are read from the COBBA_GJP by the DSP.
There are two options for the PCM interface between MAD2PR1 and
COBBA_GJP. The 4 pin solution and a one pin solution. The four pin serial
interface between MAD2PR1 and COBBA_GJP includes transmit and
receive data, clock and frame synchronisation signals. It is used to
transfer the PCM samples. The frame synchronisation frequency is 8 kHz
which indicates the rate of the PCM samples and the clock frequency is 1
MHz. COBBA_GJP generates both clocks. NSE–5 uses the 4–pin
solution.
Alert Signal Generation
A buzzer is used for giving alerting tones and/or melodies as a signal of
an incoming call. Also keypress and user function response beeps are
generated with the buzzer. The buzzer is controlled with a BuzzerPWM
output signal from the MAD2PR1. A dynamic type of buzzer is used since
the supply voltage available can not produce the required sound pressure
for a piezo type buzzer. The low impedance buzzer is connected to an
output transistor that gets drive current from the PWM output. The alert
volume can be adjusted either by changing the pulse width causing the
level to change or by changing the frequency to utilize the resonance
frequency range of the buzzer.
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