User's Manual

The 10/100Mbps Ethernet Physical Layer single chip transceiver (U10) provides the

interface between RISC processor and the Ethernet. A serial ATA cable is used for

connecting between the Master board and System interface board.

The DSP (U2) is a 32-bit fixed-point digital signal processor, it provides the base band

processing such as: modulation, demodulation, RSSI/SINAD calculation, sub-tone

encoding/decoding and audio processing of the base station. The DSP software is

modularized, the modulator, demodulator, pre-emphasis, de-emphasis, filters and gain

are individual modules, user can connect the disconnect any module by the Service Kit

software for different applications. The DSP also controls the frequencies of the PLL

chips in the RF modules. The digitized audio signal interfaced to the CODEC of the

system interface board is via the DSP serial port.

The digital IF receiver consists an ADC (analog to digital converter, U4) and a DDC

(digital down converter, U3). The pre-filtered analog IF signal from the receiver module

is fed to ADC, converted to the digital IF and passed to the DDC via the parallel bus, the

DDC mixes the incoming digital IF with the internal Numerically Controlled Oscillator

(NCO) frequency signal to produce the 0Hz IF, the DDC also provides decimating and

further filtering for the IF signal. The output from the DDC is in complex I/Q format, sent

to the DSP for demodulating via the serial bus.

The clock of ADC, DDC and DSP is from the system interface board.

2.3.2 Interface (Main) board

The Interface (Main) board provides the interfaces among the Processor (main) board ,

RF modules and external equipment. The function of the Interface board can be

described as following sub sections.

2.3.2.1 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