Simoco SRP8000 SERIES, Руководство по обслуживанию

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3.10 TP0332/2
The analogue control interfaces are as follows:
(1) The processor generates and controls various analogue voltages for receiver and transmitter
purposes. IC605 is a triple 10-bit DAC which the processor controls via a 3-wire serial bus. Two of
the DAC outputs are used for receiver front-end tuning (RX_TUNE1, RX_TUNE3) and the third for
TCXO XL400 frequency trimming.
(2) The processor has two pulse width modulator (PWM) outputs which are used as additional analogue
control voltages. These are RX_TUNE2 and RX_TUNE4 for receiver front-end tuning.
The processor has several ADC inputs for monitoring analogue voltages. These are used for:
(a)
Monitoring battery voltage (VBAT) for indicating battery status on the LCD display and
detecting low battery voltage condition
(b) Reading the position of the rotary control ROT_CTRL1 for setting loudspeaker volume
(c) Reading RSSI level from the discriminator IC201 in receive mode and the transmitter
temperature monitored by the thermistor R247 in transmit mode. These two voltages share
the same processor input RSSI_TX_TEMP.
BASEBAND AUDIO AND SIGNALLING
All of the baseband audio and signalling functions are carried out by the baseband chip IC701
(SC11372CQ). The device operates in half-duplex mode and many of the analogue paths are common
between receive and transmit modes of operation. The device is controlled via the IIC serial bus lines SCL
and SDA.
Clock Generation
All the microprocessor and signalling timing is derived from the crystal oscillator formed by TR700,
XL700 and associated components. The oscillator runs at 11,0592MHz ±80ppm. The oscillator runs at its
normal frequency when both the transmitter and receiver supplies are enabled by the processor. In this
case RX_ON and TX_ON are both high and TR702 is conducting. The oscillator operates at a ‘pulled’
frequency when only the receiver supply is enabled. In this case TX_ON is low and TR702 is off. The
transmit supply is inhibited from being turned on when the receiver is on and allows the ‘pulling’ feature to
be used.
The oscillator output from TR700 drives the XIN pin on the baseband chip IC701. The baseband
derives all of its internal signalling clocks from this input clock and also generates a buffered clock CLK for
the processor on the CLKOUT pin. The processor clock frequency is also 11,0592MHz.
Receive Audio Path
Refer to Figure 3.8 on page 3.11.
The discriminator audio signal RX_AF from IC201 enters the baseband chip on the RX_IN pin. The
internal path in receive mode is shown in Figure 3.8 on page 3.11. The path consists of:
(1) A stage of amplification (GC2)
(2) De-emphasis filter (F1)
(3) 300Hz High-pass CTCSS Filter (F5)
(4) 3kHz Low-pass Filter (F8)
(5) Audio Volume Control (GC7, GC10, GC11).
Signalling detection is described in a later section.
Transmit Audio Path
Audio from the smart interface and the internal microphone enter the baseband chip on MIC1_IN
and MIC2_IN respectively. The internal path in transmit mode through to the TX modulator is shown in
Figure 3.9 on page 3.11 and consists of:
(1) MIC1_IN/MIC2_IN Audio Source Selection
(2) Amplification Stage (GC0)
(3) Pre-emphasis Filter (F6)
(4) Automatic Level Control (ALC)
(5) 300Hz High-pass Filter (F5)
(6) Limiter
(7) 3kHz Low-pass Filter (F8)
(8) Transmit Modulation Level Control (GC7, GC8, GC9).