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SECTION 1
THEORY OF OPERATION
1-1. PA-227 BOARDd. Clamp circuit, Blanking circuit
IC3, IC4, IC5 and their peripheral circuits comprise the
The light that passes through the camera lens impingesfeedback clamp circuit. Set the DC level of the video
upon the chip surface of the CCD (IC1) on the PA-227signal output from Pin 3 of IC2 to the specified output
board, converted to electrical signals, and output from Pinlevel of approx. 0 V using R22, R43 and R23. To
8 of the CCD.amplify a video signal whose signal level has been
The signal from the CCD is input to the CDS IC (IC2) vialowered by a resistive division, the AMP of IC3 is set
the Q1 buffer amplifier, and a signal amplified to roughlyso that roughly double the gain can be obtained. The
triple the strength of the input signal is output from there.capacity of the clamp is determined by C25, and the
The signal output from IC2 is input to the PR boaDC level of the clamp should be adjusted to 0 V usingrd via the
Q2 buffer amplifier.RV4.
The blanking circuit consists of Q9, IC6 and its
1-2. PR-247 BOARDperipheral circuits. The DC level of blanking should be
adjusted to 0 V using RV5.
This board consists of the processing section, where the
video signal output from the PA board is processed, ande. White clip circuit, video signal driver circuit
the power supply section, where various power voltagesThe white clip circuit consists of Q11 and its peripheral
are generated for various circuits.circuits, and the clip level is adjusted to 1150 mV using
The processing section contains the following circuits a toRV6.
e:The video signal driver circuit consists of IC7, which
has a roughly two-fold gain, and its peripheral circuits.
a. Pre clip circuit
This circuit consists of IC8, for removing unnecessaryf. Power circuit
components in the processing section during SVRThe voltages necessary for CCDs and various circuits
operation, and of the Q4 peripheral circuits, forare generated by the PU1, DC-DC converter and IC9.
adjusting DC level with the processing section.The input voltage to PU1 is 12 V DC (fixed) and three
trains of voltage +15 V, _7 V, and +5 V are output.
b. Fixed gain circuitIC9 is a regulator that generates _5 V used only by the
This circuit consists of the Q5 and Q6 fixed-gainPR board, and _7 V is input and _5 V is output there.
amplifiers, which amplify the signal attenuated at the
input section, and of several circuits (Q8, Q12, etc.)
that adjust the input DC bias of IC2.
c. Gain adjustment circuit
The level of the video signal input to Pin 1 of IC2 can
be varied by the DC voltage input to Pin 2 of IC2 in the
range of ?6 dB.
The standard status of the video signal output from the
camera should be set as follows:
(1) Set the video signal (TP1) input to IC2 to 500 mV
using the lens iris.
(2) Adjust the gain of IC2 using RV3.
CVC-1000
1-1 |
ACEC
