HP (Hewlett-Packard) HP 85660B ユーザーズマニュアル

 amplifies the output of the 

 M/N VCO in two different paths. One path is

amplification and buffering to drive the mixer in the M/N phase-lock loop. The other path
drives a divide by two which, after further amplification, goes to the 

 Sampler.

The integrating loop amplifier which generates the tuning voltage for the M/N VCO is also

included on 

Q5 is a common-emitter amplifier followed by a resistive pad to increase reverse isolation. 

is a common-base amplifier which is broadly tuned by L2, 

 and associated capacitances.

 is another common-emitter amplifier which is followed by a 400 MHz low-pass filter.

U2 is an ECL divide-by-2 Integrated Circuit. U2 generates the M/N output frequency which

is one-half that of the M/N VCO. For frequency spans of greater than 5 MHz, the M/N

control line (LMNE) goes to a TTL high during the sweep. This disables U2, switching off
the M/N output to the 

 Sampler. At the beginning of each sweep, U2 is turned back

on and the M/N VCO is phase-locked to give the correct start frequency. During multi-band
sweeps, U2 is turned on at the beginning of each band, but is turned off during the actual
sweep.

 is connected as an integrating amplifier and generates -5 V to -35 V for tuning the M/N

VCO. Cl3 is the integrating capacitor; Cl2 and Cl5 compensate 

 to guarantee stability.

R33, R34, C14, and R15 compensate the entire phase-lock loop. The 200 

 low pass filter

rejects the sampling frequency (20 MHz divided by N) and its harmonics which are generated
in the phase detector. CR6, R42, and R41 form an impedance breakpoint that increases the
loop gain by approximately 5 

 when the tune voltage goes below approximately -7 V. This

helps to make the varactor tuning curve linear.

For instruments with 

 M/N Output Assembly, part number 85660-60267, power for

integrating amplifier 

 is provided by an additional 

 V connection (Pl-9, P24) and

by 

 which generates -15 V from the -40 V supply. The output of 

 is buffered by

common-base amplifier 

 and by emitter-follower buffer 

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