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Al6 Assembly Fast ADC Circuits (Option 007)
The fast ADC consists of video signal scaling and limiting amplifiers, an 8-bit flash ADC,
peak/pit detection of the digitized video signal, a 32 K-byte RAM, and the fast ADC control
circuitry.
Video
Input
Scaling
Amplifiers
and
Limiter
Refer to function block L of the Al6 fast ADC assembly schematic diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
The video input scaling amplifiers help provide scaling (10 dB/div, 5
dB/div,
2
dB/div,
or
1 dB/div) and buffer the flash video output. When the GAINX2 control line is low, switch
U44D is open and switch U44C is closed. Thus, the scaled video at TP26 virtually follows
the video input (0
-
1 V). When the GAINX2 control line is high, switch U44C is open and
switch U44D is closed. Amplifier U43 then provides a gain of
2(Vi,)
-1 V. Voltage clamp
CR4 prevents the scaled video input to amplifier U45 from going more negative than -0.35 V
or more positive than
t1.25
V.
Note
When measuring voltages or waveforms on the Al6 fast ADC assembly,
connect the ground (or common) lead to the ground-plane trace on the Al6
assembly. This digital ground plane is totally isolated from the chassis.
1. Press
(PRESET)
on the Option 007 spectrum analyzer and set the controls as follows:
Centerfrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...300 MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
Reference level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -10
dBm
Log/division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dB/DIV
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 ms
2. Connect the CAL OUTPUT to the INPUT
500
connector.
3. Adjust the Option 007 spectrum analyzer reference level to place the signal at the top
graticule line on the CRT display.
4. Measure the dc level at TP25. If the voltage measured is not
+l.O
f0.15 V, troubleshoot
the A3 interface assembly.
5. Measure the dc level at TP26. The level should be approximately the same as the level
measured at TP25. If not, suspect switch U44.
6. Set the Option 007 spectrum analyzer scale to 5dB per division.
7. Adjust the Option 007 spectrum analyzer reference level to place the signal at the top
graticule line on the CRT display.
8. Measure the dc level at TP25 and TP26. The level should be i-1.0 f0.25 V. If the level
measured at TP26 differs from the level measured at TP25 by more than 0.25 volts,
troubleshoot U43 and associated circuitry.
9. Disconnect the CAL OUTPUT signal from the INPUT
500
connector.
10. The level at TP26 should drop to -0.35 Vdc. If the level is less (more negative) than
-0.35 Vdc, replace voltage clamp CR4.
ADC/lnterface
Section 8-31