User's Manual

12 68P80801H45-1 1/20/2002
Base Radio Exciter EBTS System Manual - Vol 2
QUAD Channel 900 MHz Exciter
900 MHz QUAD Channel Exciter Theory of Operation
Table 4 describes the basic circuitry of the Exciter. Figures 9 show the QUAD
Carrier Exciter’s functional block diagram.
Memory Circuitry
The memory circuitry is an EEPROM on the Controller portion of the Exciter/
Controller module. The Controller performs memory read and write operations
over the parallel bus. The memory device stores the following data...
❐ kit number
❐ revision number
❐ module specific scaling and correction factors
❐ serial number
❐ free form information (scratch pad)
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
Table 4 900 MHz Exciter Circuitry
Circuit Description
LNODCT 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 LNODCT IC for the second
up-conversion and first down-conversion of the feedback
signal from the PA
1025 MHz VCO (900 MHz BR) Provides a LO signal to the LNODCT IC, for up-conversion
to the transmit frequency
90.3 MHz VCO (900 MHz BR) Provides a LO signal to LNODCT 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