LeCroy DDA 7 Zi series, Руководство оператора

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WavePro 7Zi
147
WP700Zi-OM-E-RevA
5. Select Interpolate from the Filter submenu.
6. Touch the Interpolate tab in the mini setup dialog to the right of the main dialog.
7. Touch inside the Algorithm field and select an interpolation type.
8. Touch inside the Upsample by [Upsampling is the factor by which sampling is increased.] field and enter a
value, using the pop-up numeric keypad, if you want to enter a specific value. Otherwise, use the Up/Down
buttons to increment the displayed value in a 1-2-5 sequence.
Demodulation
The DMOD math function adds seven new processing functions:
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Amplitude Demodulation - For a given bandwidth, the instantaneous magnitude or amplitude of a specific
carrier frequency sinusoid.
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Complex Demodulation - For a given bandwidth, the instantaneous complex vector (Cartesian) of a
specific carrier frequency sinusoid.
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Frequency Demodulation -This is based on the phase of the sequential vectors compared with the
expected phase since the last vector (the derivative of the phase error) or the rate of phase movement (in
Hz).
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Imaginary Component Demodulation - “Quadrature-phase” component "Q".
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Phase Demodulation - This is based on the phase of sequential vectors, as compared to the “expected
ideal” phase. Closely related to Time Interval Error, but with a change in sign since positive phase error
implies early edge arrival (negative TIE).
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Real Component Demodulation - the “In-phase” component "I".
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Wideband AM - Wideband amplitude demodulation
These demodulated waveforms are useful for many purposes:
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Analyzing FM or PM modulated signals
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Studying unwanted variations in any of these domains (frequency or phase “noise” analysis)
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Studying unwanted systematic “pickup” or interference on either transmitted RF, or on oscillators, phase-
locked loops etc.
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Studying instantaneous power
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Studying envelopes of amplitude modulated signals with variable bandwidth.
Only two of the result types are rescalable, Frequency (FM) and Phase (PM), since the magnitudes of these
projections cannot be known beforehand. All of the other results are scaled on the vertical scale of the original
digitized carrier waveform.
There are no parameters specific to the Demodulation math function.
Theory of Operation
The basic procedure is a localized (by windowing) complex finite impulse response (FIR), which amounts to no
less than a local (windowed) discrete complex Fourier “term” (or sum) at the carrier frequency.
The length of the complex FIR is determined by the selection of Bandwidth. The result of each convolution with
the FIR at a given time offset is then translated into a single complex vector, defining the instantaneous phase
and amplitude of the modulated carrier. The user selects one of several “views” on this vector (including its
amplitude, phase, rate of change, real, imaginary, or complex). The appropriate values from the vector constitute
the samples of the resulting processed waveform.
Using the same window and bandwidth criteria, there is also a “wide-band” AM demodulation function. This
function doesn’t produce a complex vector for each data point of the resulting function, but simply uses the
instantaneous rms signal to produce a scaled output. Basically there is no complex FIR, only the window. The
scaling is such as to show (for practically any carrier frequency) an envelope of the same magnitude as the
sinusoid.
Setting Up Demodulation
1. Touch Math Math Setup on the menu bar.
2. Touch a Math function tab F1 to F8 .
3. Touch inside the Source1 field and select an input waveform from the pop-up menu.
4. Touch inside the Operator1 field and select Demodulate from the pop-up menu.
5. Touch the Demodulate tab in the right-hand dialog.