Tektronix 80A00, Техническое описание

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Optical Sampling Modules
In terms of voltage, and resistance, the bandwidth is expressed as:
where V
f
is the RMS of the voltage swing response at the bandwidth frequency
and V
DC
is the RMS voltage swing response at a frequency approaching DC.
Further math yields that V
f
= 0.707 × V
DC
. The expression is simpli fi ed by
the cancellation of the R and the movement of the squared term inside the log
expression to a multiple outside the log expression:
therefore at
In the DSA8300, the vertical units displayed for an optical module are not in
voltage, but are in watts, which is a unit of power. The O/E converter inside
the module outputs a voltage swing whose amplitude is linearly dependent on
the incoming optical power swing. In this condition the voltage applied at the
electrical sampler already represents Optical Power in its linear form (as opposed
to having to square the voltage and divide by R). For the optical sampling
modules, then, the bandwidth where the displayed optical power is one half that
approaching DC is:
The V
f
in such a system is one half (0.5) the V
DC
as opposed to 0.707. The optical
bandwidth, therefore, corresponds to the traditional electrical bandwidth at –6 dB.
During testing of optical modules via impulse testing, the resulting impulse
waveform is converted to frequency via Fourier transform, and the bandwidth
is de
fi ned as:
This de fi nition is used for 2.3 GHz, 2.5 GHz, 12.5 GHz, 20 GHz, 30 GHz,
40 GHz, 50 GHz, 65 GHz, and 80 GHz bandwidth settings.
During reference receiver curve calculation, however, the de fi nition is changed to
match the industry standard de fi nition, which was authored assuming electrical
bandwidths where:
This de fi nition is used for all NRZ reference receiver settings in all the modules.
DSA8300 Performance Veri fi cation 223