Agilent Technologies 8960, Справочное руководство

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S:\Hp8960\E1962B CDMA 2000\Pi Release\Reference Guide\Chapters\cdma2000_gen_block_diagram.fm
Block Diagram
Audio 1 Path The Audio 1 path provides analog baseband signals used for frequency modulation of the test
set’s RF sources. Up to four separate audio sources may be summed together in any combination to provide the
composite Audio 1 output. These include the external FM input, internal direct digital synthesis (DDS,)
regenerated SAT, and audio echo input.
The external FM input accepts an externally supplied audio signal with a peak voltage between 0.25 and 2 V
peak.
The internal DDS generates low distortion audio signals from DC to 20 KHz with 0.1 Hz resolution. One to
four signals may be generated and internally summed, with independent level control of each waveform.
The SAT regeneration circuit outputs a signal which is phase-locked to a received SAT signal. This is useful
for testing situations where the test set needs to emulate a mobile station.
The audio echo input is used for retransmitting the received audio after a selectable time delay, to check both
radio transmit and receive paths simultaneously.
For most applications, only one or two of these Audio 1 path sources are enabled at any given time.
Audio 2 Path The Audio 2 path provides a secondary means for sending analog baseband signals to the FM
modulator. Audio 2 contains only one source, a DDS similar to that used for Audio 1.
Typically, the Audio 2 path DDS is used for cases where multiple signals must be summed together with the
lowest possible distortion. Another potential use of Audio 2 would be to obtain higher output levels than Audio
1 is capable of (up to twice as much), assuming the two outputs are set to the same frequency and phase, and
then summed together at the Baseband Generator module.
Audio 2 is rarely used in practice because the DDS used for Audio 2 is the same DDS that is used for the front
panel audio output.
Audio Out Path Any one of four inputs may be coupled to the front panel audio output connector. These
include a 4 channel DDS (shared with Audio 2), receiver discriminator audio from the Demodulation
Downconverter module, audio echo from the Analog To Digital Converter module, and audio vocoder.
The front panel output is capable of providing signal levels up to 9 V peak into > 600 ohm loads, and up to 0.8
V peak into an 8 ohm load (e.g. speaker). The output level is calibrated for all modes except discriminator
audio,
The discriminator audio has an uncalibrated volume control provided due to the high tolerances involved.
Typically the DDS mode is used to feed the MIC input of a radio, or it may simply be used as a general purpose
low distortion function generator.
Audio echo can be selected to route the received audio to the front panel audio output connector.
RF Sources
The test set can contain two identical RF sources. The RF sources are used to provide analog or digitally
modulated RF carriers for use in parametric testing of mobile stations encompassing a variety of cellular radio
formats. In general, the sources have a frequency range of 292 MHz to 2.7 GHz and an amplitude range of -10
dBm to -127 dBm.
The RF sources consist of a Synthesized Signal Generator module followed by a Vector Output module and an
RF Attenuator module. Baseband modulation information is supplied to the RF sources from a Baseband
Generator module preceded by an Audio Section module. The various components which make up the test set
source system are described in the following sections.