User's Manual

© RF Technology 2007
shifted by the bias circuit which is controlled by the RISC processor to give the
maximum dynamic range for the ADC.
The CODEC has two identical channels, the output of channel 1 is used for line output.
PCM signal from the DSP is decoded to analog audio, and amplified, buffered by op-
amplifier U10, coupling through the line matching transformer (T2), and sent to the RJ45
E/M Line connector and the D25 system connector.
The channel 2 output of the CODEC is used for monitor speaker, PCM signal from the
DSP is decoded to analog audio, amplified by a Trans-conductance amplifier (U11), this
amplifier is used as the speaker volume control. The power amplifier (U13) provides
additional power gain to drive the internal and external speaker.
A 16-bit DAC (U14) converts the digital output from the DSP to analog signal, the signal
is filtered and buffered by op-amplifier (U10), then sent to the D25 system connector.
The amplifier is DC coupled, the DC offset can be set by the bias circuit which is
controlled by the RISC processor. This output is useful for low frequency application
such as sub-tone, and NRZ digital signals.
2.3.2.2 I/O and Controls
The RISC processor uses serial buses and GPIO to control the base station.
A 10-bit 11-channel ADC (U7) senses the following signals and passes the data to the
RISC processor via serial bus:
Channel 0: exciter PLL tuning voltage
Channel 1: exciter forward power of the power amplifier
Channel 2: exciter reverse power of the power amplifier
Channel 3: receiver PLL tuning voltage
Channel 4: Interface board temperature
Channel 5: Input power supply voltage
Channel 6: receiver power supply voltage
Other channels are reserved for future usage.
A 10-bit 8-channel DAC (U6) converts data from the RISC processor serial bus to
analog voltage for following functions:
Channel 0: monitor speaker volume control
Channel 1: 600 ohm audio Line input gain control
Channel 2: exciter reverse power of the power amplifier
Channel 3: AUX audio input bias setting
Channel 4: AUX audio output bias setting
Channel 5: receiver IF amplifier gain control (not used in release1 RX module)
Channel 6: exciter RF output power control
Channel 7: exciter VCO bias setting
Channel 8: receiver VCO bias setting
The op-amplifiers (U4, U28) are used for converting DAC output to proper voltage which
is required by the system hardware.