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A20
A20
Main
Coil
Driver,
Circuit
Description
The A20 Main Coil Driver produces a tuning current proportional to the tuning voltage input
from the A19 DAC and applies it to the
AllA
YTO. Th’
is
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
AllA
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.
Input
Amplifier
@
Transistors
QS
through
Ql2
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
Ql,
Q4, and Q5 which supply the YTO Main Coil current. For frequency spans greater
than 5 MHz, LYSP
(1
ow
= YTO span) turns on (closes) switch
Q2
allowing a current flow
through R19. This is done to improve sweep linearity for wide spans
(>5
MHz).
Phase
Lock
Amplifier
@
Phase Lock Amplifier
UlB
provides a current proportional to the low-frequency error voltage
input (YTO TUNE 2). Th’
is
error voltage input is from the
AllA
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.
Coil
Driver
@
Transistors
Ql,
Q4, and Q5 provide drive current to the main coil of the
AllA
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 mA.
Shaping
Network
@J
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,
Rl6,
and R25 sense the current output of the Coil Driver. R25 is used to fine tune the YTO to
6.15 GHz.
Offset Reference
6~
The Offset Reference composed of
UlA
and associated circuitry provides a fixed voltage to
Phase Lock Amplifier
UlB.
This voltage provides the current necessary to fine tune the YTO
to 2.3 GHz.
A20 1