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Earpiece
6.6.2
6.6.2
The earpiece is driven directly from IC27 AOUTP(#94) and AOUTN(#93) pins. The
gain is controlled by the DSP software element within IC27. The earpiece is
located in the handset front panel, and the signals are routed to it via two
connection pads on the front of the logic board.
RXI and RXQ signals from IC300 (PMB2410) are fed to IC27 #77-80 (Superchip)
where they are amplified and then A/D converted. The I and Q samples are stored
in lots of 32 before the DSP part of Superchip (IC27) is interrupted to process
them. The DSP will carry out error detection and correction, and assemble the
speech data into a form acceptable to the D/A converter in the CSP section. After
D/A conversion the signal is output on IC27 #93/94) - earpiece - and / or #95/96)
- RXAF.
Hands-Free Interface
6.6.3
6.6.3
The audio out (RXAF+/-) to the hands-free kit consists of a pair of differential
signals from IC27's auxiliary outputs (#95-96), which are tracked down the board
to the system connector (P5) at the base of the handset.
The audio in (TXAF+/-) from the hands-free is converted to a single signal using
the op-amp (IC13). The bias voltage VREF from IC27 #3 is used as a reference
voltage for this amplifier. The TXAF signal is then input to the AUXIN (#99) of IC27.
The DC level of the signal is supplied to the AUXOUT pin.
Buzzer Driver
6.6.4
6.6.4
The buzzer or alerter is a piezo-electric transducer which is driven by a pulse-width
modulated square wave from the PWMOUT output of NELL (#M14). TR4 and
TR11 amplify the signal in order to achieve the specified loudness of 100dBa.
See Figure:6E. Audio and Miscellaneous Interfaces.
Battery Charging
6.6.5
6.6.5
The battery is charged via a constant 850mA current source, which is plugged into
the DC jack in the system connector P5 #2. Charge control is implemented in
software using the analogue to digital converter in NELL. It then determines the
type and capacity of the battery connected by reading the battery ID resistor
(BATID), on an A/D converter port, from which it determines the charging
algorithm. When an external charging source is connected via the P5 connector
an interrupt signal EXTCHG is sent to NELL #N4. When NELL receives this
interrupt it initiates the charger enable signal CHGEN, this action switches on
TR28 which activates FET –TR3. When TR3 is conducting it allows the battery to
be charged. Battery charging current is measured by means of a fixed loop
stripline or "shunt" which is mounted internally within the layers of the PCB. When
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