HP 8133A Service Manual page 153

Variable Pulse Width Generation
The Pulseformatter
The Output Amplifier
The delayed output signal of the Timing Board (single ended,
squarewave) is the input signal to the Width Board. This board
generates the variable pulse width and contains the Output Amplifier.
The input signal split into two signals. One of these signals
is
delayed by about 4ns with a fixed delay line (semi-rigid cable). The
other signal fed through a delay block that consists of two different
is
hybrids (Variable Width Hybrid, Switched Width Hybrid) and two
refresh amplifiers (Shaper Amplifier). The two hybrids and the refresh
amplifiers are described in the section "Timing Board
two signals with the same frequency are generated: One with a fixed
delay of 4ns, the other one with
(4ns is the minimum delay of the delay block). In the pulse mode, the
delay of the second signal is limited to 4ns plus actual period value by
the instrument software.
The delayed and undelayed signals are fed to the Pulseformatter. The
Pulseformatter is a full-custom bipolar IC packaged on a thickfilm
hybrid. It is a high-speed EXOR gate generating an output signal of
a pulse width equal to the delay between the two input signals, at
twice the input frequency. Initially, the frequency of the input signals
an
is divided by two by on-chip flip-flop, and they are now
original frequency through the action of the EXOR gate. An additional
EXOR gate gives a choice between Normal Mode and Complement
Mode, depending on the control voltage at the appropriate input. The
Pulseformatter can be switched between the Pulse Mode (Normal
mode), described above, or the Complement Mode (Square Mode) by
the control voltage.
In Square Mode, the input signal with the programmable delay
is connected to the input of the Pulseformatter. Thus, the width
capability can be switched off, producing an additional Ons - lOns
delay capability instead. This is particularly useful in
Instrument not fitted with the delay block on the Timing Board.
A t switch-on the Pulseformatter always starts running in the Normal
Mode (self-initialization). The Pulseformatter works from DC to
produce Pulse
has a fully differential output
transition time of approximately 80ps.
The differential output of the Multiplexer provides the input signals
to the Output Amplifier. Voltage and current sources, some of them
programmable via the device bus interface, are used for biasing and
programming the output amplitude and high level. Two voltage
sources anti two current sources are programmable to adjust the pulse
performance over frequency and temperature.
The amplifier consists of 2 identical, full-custom GaAs ICs packaged
on a thickfilm hybrid. All voltage and current sources needed for the
amplifier are located on the PC-Board and are decoupled by capacitors
on the PC-board, in addition to printed bypass capacitors on the
hybrid.
-
a
a
as as 120ps or less. It
widths narrow
a swing of 500mV and a typical
with
Theory
is
at
the
Standard
of 7-21
Operation