User's Manual

8 68P80801E35-A 9/1/2001
Base Radio Exciter EBTS System Manual - Vol 2
Low Noise 800 MHz Exciter
Low Noise Exciter Theory of Operation
Table 3 describes the basic circuitry of the Low Noise Exciter. Figures 9 show the
Low Noise Exciter’s functional block diagram.
Memory Circuitry
The memory circuitry is loaded on an EEPROM on the Exciter. The EBRC
performs memory read and write operations via the SPI bus. Information stored
in this memory device includes the kit number, revision number, module-specific
scaling, and correction factors, operations, parameters, and free-form information
(scratch pad) kit number
A/D Converter Circuitry
Analog signals from various areas throughout the Exciter board enter the A/D
converter (A/DC). The A/DC converts these analog signals to digital form. Upon
request of the BRC, A/DC output signals enter the BRC via SPI lines. The
Controller periodically monitors all signals.
Some of the monitored signals include amplifier bias and synthesizer signals.
Table 3 Exciter Circuitry
Circuit Description
Low Noise IC • Up-converts baseband data to the transmit frequency
• Down-converts the PA feedback signal to baseband
• Uses a baseband Cartesian feedback loop system, necessary
to obtain linearity from the transmitter and avoid
splattering power into adjacent channels
• Performs training functions for proper linearization of the
transmitter
Memory & A/D Converter Serves as the main interface between the synthesizer, Tranlin
IC, A/D, and EEPROM on the Exciter, and the BRC via the
SPI bus
Frequency Synthesizer
Circuitry
• Consists of a phase-locked loop and VCO
• Provides a LO signal to the Low Noise IC for the second
up-conversion and first down-conversion of the feedback
signal from the PA
970 MHz VCO (800 MHz BR) Provides a LO signal to the Low Noise IC, for up-conversion
to the transmit frequency
90.3 MHz VCO (800 MHz BR) Provides a LO signal to Low Noise IC, for the up-conversion
and for the down-conversion of the feedback signal.
The mixed output becomes the LO signal for Transmit signal
up- and down- conversion
Regulator Circuitry Provides a regulated voltage to various ICs and RF devices
located on the Exciter
Linear RF amplifier Stages Amplifies the RF signal from the Exciter IC to an appropriate
level for input to the PA