User's Manual

Eclipse2 Technical Manual, 3-Aug-12 Page 12 of 17
The clock of ADC, DDC and DSP is derived from the system interface board.
Interface (Main) board
The Interface (Main) board provides the interfaces among the Processor (main) board, RF modules
an
d
external equipment. The function of the Interface board can be described as following sub
sections.
Audio signal processing
External audio signals from/to the base station are processed in this section.
The balanced audio input from RJ45 E/M Line connector or D25 system connector is passed, after
line matching transformer (T1) coupling, to a Trans-conductance amplifier (U11), the gain of the
amplifier is controlled by the RISC processor. The output of this amplification stage is then
amplitude limited, attenuated and filtered before send to the channel 1 of the CODEC (U12). The
CODEC encodes the analog audio to digital PCM signal send to the DSP via the serial bus.
The Microphone input from front panel RJ45 connector is amplified by op-amplifier (U16),
amplitude limited and attenuated then fed to the cannel 2 of the CODEC (U12). The CODEC
encodes the analog audio to digital PCM signal send to the DSP via the serial bus.
The AUX input signal from D25 system connector is DC coupled, filtered and amplitude limited by
the op-amplifier (U16), then fed into a 16-bit ADC (U17) to convert to the digital signal. The
digitized signal is send to the DSP via the serial bus. This AUX input is useful for low frequency
(down to 0Hz DC) signals, the DC offset of input signal is 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.
I/O and Controls
The RISC processor uses serial buses and GPIO to control the base station.
A 1
0-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 use.
A 10-bit 8-channel DAC (U6) converts data from the RISC processor serial bus to analog voltage
for following functions: