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S:\Hp8960\E1962B CDMA 2000\Pi Release\Reference Guide\Chapters\cdma2000_gen_block_diagram.fm
Block Diagram
The RF Interface module provides two identical RF Source path connections to the In/Out port of the
instrument. There is about 25 dB of isolation between the two source paths. There is about 35 dB of isolation
between the source paths and either receiver path. The RFIO module has nominally 23 dB of insertion loss in
the source path. A temperature sensing circuit facilitates compensation for path loss variation with
temperature.
The sampled input power from the directional bridge can be amplified by as many as two 18 dB range
amplifiers and then can be directed to the fast detector, or the slow detector. The input power to the fast
detector is detected by a diode detector that is part of a feedback loop. The input to the slow detector is
measured in a bridge using a pair of RMS thermal detectors in a feedback loop. Signals from the fast and slow
power detectors are calibrated with Gain DAC’s. Video gain can be applied in 6 dB and 1.5 dB steps.
Signal Downconversion
The test set’s downconversion receiver section has two downconversion modules; a high performance
Measurement Downconversion Module for making measurements, and a Demodulation Downconversion
Module for maintaining the radio link.
Demodulation Downconverter Module The Demodulation Downconverter module is used as part of the
demodulation receiver that maintains the radio link. There are 2 output paths from the Demodulation
Downconverter.
• The GSM, AMPS/136 signals are sent out the IF 1 path to the Analog to Digital Converter, the digital data
then goes to the protocol subsystem.
• CDMA signals are sent out the IF 2 path where the (flexible) Link Subsystem maintains the link.
Measurement Downconverter Module The Measurement Downconverter module provides high quality
(wide dynamic range, spurious free) signals to the Analog To Digital Converter module’s measurement
sampler input. These signals are:
• detected envelope of the Intermediate Frequency signal
• 10 kHz - 6 kHz Intermediate Frequency signal
The Measurement Downconverter module is designed for very high performance operation to ensure accurate
and repeatable measurement results. The Measurement Downconverter module contains two downconversion
stages, two local oscillators, and a logarithmic IF envelope detector . Both first and second LO synthesizers are
tunable. The first LO is used when tuning to the RF input frequency, and the second LO is used when setting
second IF frequency, which is fed to the measurement sampler on the Analog To Digital Converter module.
Link Subsystem The Link Subsystem maintains the radio link for all CDMA formats. The Link Subsystem
has three parts:
• Link Subsystem Analog
• Link Subsystem Digital
• Protocol Processor
The Link Subsystem Analog board processes the signal from the Demodulation Downconverter through a 12
bit DAC. The digital data is sent to the Link Subsystem Digital board and processed into I/Q digital data. The
I/Q digital data is returned to the Link Subsystem Analog board and converted into I/Q analog baseband
signals . The I/Q baseband signals are sent to the I/Q modulator in the RF Source.
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