Positive/Negative Peak Detectors - Agilent Technologies 8564EC Service Manual

Current source U307C provides twice the current of Q316. Resistor
R145 and current source U307D shift the dc level. Resistor R260
terminates the peak detector inputs in 500 ohms. The unterminated
gain is 1.1. Diode CR114 prevents latchup during positive overdrive
conditions while CR113 protects Q318 during overdrive. Diode CR117
is a 12.7 V zener that limits the output of the peak detector to +1.5 V.
Typically, limiting occurs at +1.1 V.

Positive/Negative Peak Detectors

Refer to function blocks Y and Z of A3 Interface Assembly Schematic
Diagram (sheet 5 of 6) in the
n.
Level Informatio
The following information pertains to the positive peak detector and is
applicable to troubleshooting the negative peak detector.
The positive peak detector consists of an input amplifier (A3U204 and
A3Q210) followed by detector diodes (A3CR203 and A3CR204) and hold
capacitor A3C217. Output amplifier A3Q206, Q211, and Q212 buffers
the hold capacitor. Both the input and output amplifiers have a gain of
one. Each amplifier has local feedback. On the output amplifier the
emitter of Q212 connects to the gate of Q206. On the input amplifier the
feedback goes through Q209 and Q208 back to the base of U204D.
Global feedback occurs from the output amplifier through R223 back to
the input amplifier U204D. The peak detector resets through Q207.
1. Press and set the spectrum analyzer controls as follows:
PRESET
Center frequency ..................................................... 300 MHz
Span ......................................................................... 500 MHz
Resolution bandwidth .................................................. AUTO
Video bandwidth ........................................................... AUTO
Log dB/division ...................................................... 10 dB/DIV
2. If the spectrum analyzer does not meet the conditions in steps a
through e below, the positive and negative peak detectors are
probably faulty. Continue with step 3 to check the detectors.
a. The peak-to-peak deviation of the noise in NORMAL detector
mode should be approximately two divisions. Press
,
TRACE TRACE B
and
DETECTOR MODES
b. Select
DETECTOR POS PEAK
c. Confirm that the noise is about one-third division peak-to-peak.
The noise should also be no higher than the top of the noise level
in NORMAL detector mode.
Chapter 8
8560 E-Series Spectrum Analyzer Component
, ,
CLEAR WRITE B VIEW B
.
mode.
ADC/Interface Section
A3 Assembly Video Circuits
, ,
TRACE A MORE 1 of 3
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