Image Processing Reference
In-Depth Information
acquire eight or more offset sources at frequency
f . Seven under test signals, denoted
frequency
xi fi
,
1,2,3...
, are down-converted to sinusoidal beat-frequency signals at
nominal frequency
f by mixing them with the offset sources at frequency
f . The signal
flow graph is showed in figure 6.
Fig. 6. Block Diagram of the Multi-Channel Digital Frequency Stability Analyzer
The channel zero is calibrating channel, which input the reference source running at
frequency f to test real time noise floor of the DFSA, and then can calibrate systematic
errors of the other channels. The calibrating can be finished depending on the relativity
between the input of channel zero and the output of OG. Because both signals come from
one reference oscillator, they should have strong relativity that can cancel the effect of
reference oscillator noise.
The Digital Signal Processing module consists of multi-channel Data Acquisition device
(DAQ), personal computer (PC) and output devices. The Measurement Frequency (MF)
software is installed in PC to analyze data from DAQ. The beat frequency signals, which are
output from the MBFG that are connected to channels of analog-to-digital converter
respectively, are digitized according to the same timing by the DAQ that are driven by a
clock with sampling frequency N . Then, MF software retrieves the data from buffer of
DAQ, maintains synchronization of the data stream, carries out processing of measurement
(including frequency, phase difference, and analyzing stability), stores original data to disk,
and manages the output devices.
The MBFG output must be sinusoidal beat frequency signals, because processing beat
frequency signal make use of the property of trigonometric function. It has the obvious
difference with traditional beat frequency method using square waveform and Zero Crosser
Assembly.
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