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

The A20 Main Coil Driver produces a tuning current proportional to the tuning voltage input

from the A19 DAC and applies it to the 

 YTO. Th’  provides coarse tuning of the

YTO frequency and sweep. Fine tuning is performed by summing a current proportional to
the low-frequency error voltage from the 

 YTO Phase Detector (via the A21 FM Coil

Driver) with the tuning current from the A19 DAC. Additional fine tuning is done by the A21
FM Coil Driver using the current proportional to the high-frequency error voltage component.

Transistors 

 through 

 form a discrete noninverting operational amplifier whose output

is proportional to the tuning voltage input (YTO TUNE 1). This output is applied to Coil

Driver 

 Q4, and Q5 which supply the YTO Main Coil current. For frequency spans greater

than 5 MHz, LYSP (1ow = YTO span) turns on (closes) switch 

 allowing a current flow

through 

 This is done to improve sweep linearity for wide spans 

 MHz).

Phase Lock Amplifier 

 provides a current proportional to the low-frequency error voltage

input (YTO TUNE 2). Th’  error voltage input is from the 

 YTO Phase Detector and

is indicative of the YTO frequency error. The current output of the Phase Lock Amplifier is
summed with the current output controlled by the Input Amplifier in the Coil Driver.

Transistors 

 Q4, and Q5 provide drive current to the main coil of the 

 YTO to set

the frequency and amount of sweep of the YTO. YTO main coil sensitivity is approximately
25 mA/GHz. The Coil Driver output is between approximately 50 and 150 

Compensation network U2 provides linearity shaping of the current output of the Coil Driver.
The components of the network are factory selected to match the YTO. Resistors R24, 
and R25 sense the current output of the Coil Driver. R25 is used to fine tune the YTO to
6.15 

The Offset Reference composed of 

 and associated circuitry provides a fixed voltage to

Phase Lock Amplifier 

 This voltage provides the current necessary to fine tune the YTO

to 2.3