HP 5334B Service Manual page 146

8-186. Basically, each short interpolation pulse, from MRC U20, is used to rapidly charge a capacitor via a con-
stant current source. When the pulse ends, the capacitor begins a scaled discharge at about 1/200th the charge
rate. This proportionally expands the interpolator error pulse by a factor of
200X.
This integrated waveshape is
then squared and used to gate the 10 MHz reference signal through an internal NAND gate. In the end, the
MFC outputs two 10 MHz 1 T L pulse streams with
a
time length ranging from 20 to 40 microseconds, depending
on the time differences between the Start and 10 MHz pulses and the Stop and the 10 MHz pulses. See
Figure 86.
+ + k
200+
4
I I I
I I I
I
INTERPOLATOR PULSE
FRavl MRC
I
I I I
I
I I
w t u
Figure 8 6 . E.yanded Interpolator Emor Pulse
8-187. The counters following the Interpolators count the number of pulses in each pulse stream from the
MFC. The resulting data is used by the Measurement MCU to increase accuracy of the measurement by adding
the start time error and subtracting the stop time error. The Interpolator counters, U12 and U13, are dual
Cstage ripple counters which are clocked by the falling edge of each incoming pulse. As a result, the count in
the counters will proportionally reflect the length of each pulse stream coming from the MFC. The output of the
counters is multiplexed and can be read by the Measurement MCU from the Measurement Data Bus.
8-188. Measurement signals are accepted through the three MRC channel inputs (CHA, CHB, and CHC). An
external reference oscillator signal is accepted from the HP 5334B 10 MHz time base or an external source
through the REF input, and external arming signals are received through the EXT input via the MFC. Accord-
ing to the measurement function, selected MRC inputs are channeled to the EVENT and TIME registers where
the input pulses are counted and stored as raw measurement data.
8-189. MRC U20 outputs START and STOP Interpolator pulses to the two MFC interpolator circuits (U14B,
U14C); one accepts the START pulse (STI), and the other accepts the STOP (SPI). The phase difference be-
tween the measurement and reference signals causes a time delay between the EVENT (E) count and the TIME
(T) count. The START pulse represents the time from the opening of the E-gate to the start of the T-count, and
the STOP pulse represents the time from the closing of the E-gate to the stop of the T-count. Prior to each
measurement, the MRC generates 100 and 200 nanosecond pulses to each interpolator to calibrate the ST1 and
SPI pulses.
HP
5334B
-
Service
Manual
8-26