HP 8340A Service Manual page 76

Integrating Amplifier
Q4 is a differential input pair which together with QS and Q6
forms a high gain amplifier.
to make an integrating amplifier.
so for the amplifier to remain linear,
by virtue of the entire phase-lock loop.
VCXO Divider and Buffers
A 100 MHz signal from A30 VCXO is applied to counter U3 which
.divides by S,
are buffered by U4 to be used as reference frequencies by other
assemblies in the instrument.
drive the Phase Lock Sampler
Fourty Five Degree Phase Lead Amplifier G and Fourty Five Degree
Phase Lag Amplifier H
The.4S degree phase shift buffers are used to provide two
signals which are 90 degrees apart in phase. The purpose of these
signals is explained in Lock Indicator Sampler
4S degree phase shift in
in H it is done by RS9 and C38.
Lock Indicator Sampler
The lock indicator sampler functions the same as the phase lock
sampler D.
shifted in phase.
sampler to be a maximum negative voltage when the loop is locked.
Phase Lock Detector
The output of the lock indicator sampler is compared to -0.S volt
by US. When the output voltage becomes closer to
volt, US switches its output to TTL high to indicate to the AS9
Digital Interface that the loop is unlocked.
8-100
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Model 8340A - Service
E
F
then by 2. Its outputs are
G is accomplished with C3S and RS3,
I
The only difference is that the
This causes the output of the lock indicator
J
Scans by HB9HCA and HB9FSX
Feedback is added with C32 and R49
C32 provides ac feedback only,
de feedback is accomplished
10 MHz and
The other 10 MHz output is used to
D and Lock Indicator Sampler
10 MHz is 90 degrees
20 MHz which
I.
10 MHz
I description.
while
O than to -0.S
the