HP 54710A User's Reference Manual page 21

How the Oscilloscope Works
Hardware Architecture
Hybrid Behind each plug-in slot in the mainframe is a hybrid. The
hybrid contains the following:
•
A quad, 500-MSa/s, 2-GHz bandwidth, bipolar, sampling IC
•
Four, 6th order, low-pass, thickfilm, IF filters
•
Two, dual, 500 MSa/s, bipolar, ADC ICs
•
Two, dual, 4K, FISO, memory ICs.
The signal is sampled by the 500-MSa/s sampler, converted to a digital signal,
and then stored into the 4K FISO (fast-in-slow-out) memory.
In the real-time sampling mode the four 500-MSa/s sampling paths are
interleaved to achieve a 2-GSa/s sampling rate with 16K of memory behind
each plug-in slot on the A model mainframes (64K on the D model
mainframes). However, the HP 54721A plug-in, for example, uses two slots
which interleaves two hybrids in time to give you a 4-GSa/s sample rate and
32K (128K on the D models) of memory. The HP 54722A plug-in uses four
slots which interleaves four hybrids in time to give you 8-GSa/s sample rate
and 64K (256K on the D models) of memory.
In the equivalent-time sampling mode, the 500-MSa/s samplers are
synchronized and the voltage reference of the ADCs is shifted in voltage by
one-quarter of a least significant bit to achieve higher vertical resolution.
This process results in 500 MSa/s and 16K (64K on the D models) of memory
behind each plug-in slot. In this mode, the HP 54721A plug-in, for example,
gives you a 500-MSa/s sample rate and 32K (256K on the D models) of
memory.
When viewing a signal that happens either once or infrequently, the preferred
acquisition mode is the real-time sampling mode because the higher sampling
rate gives a higher single-shot bandwidth. When viewing signals that occur
repetitively, the equivalent-time sampling mode is the preferred choice
because of the higher system bandwidth and vertical resolution.
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