Tektronix WFM601, Service Manual

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Theory of Operation
WFM 601 - Service Manual
3–3
The component analog outputs of the three signal DACs are input to anti-aliasing
Reconstruction Filters. The dc offsets of the component analog (Y, P
B
, P
R
)
outputs, from the filters, are controlled by the Microprocessor and a 16 output
DAC.
The Line Rate Controller dictates the selection of display when color difference
or RGB signals are being displayed. The output of the multiplexer drives the
Flat, Luminance, and Differentiated Step Inputs of the Filter Multiplexer.
The Filter Selection Multiplexer controlled by the Line Rate Controller selects
the input to be displayed.
The calibrator provides a 700 mV, 100 kHz output. Its amplitude is set by a
microprocessor–controlled DAC, and its timing is set by the Line Rate Control-
ler.
The Vertical Amplifier is a variable gain amplifier that has controlling inputs
driven by either Microprocessor or synchronous Line Rate Controller outputs.
Stage gain is controlled by the microprocessor-generated DAC converted control
voltages. Magnification is switched by a signal from the Line Rate Controller.
An offset voltage from the DACs vertically positions the display. When CRT
readout is being processed the gain of the amplifier is changed by the Line Rate
Controller. The differential output of the Vertical Amplifier drives the vertical
output amplifier to normalize signal amplitude and drive the CRT deflection
plates.
The Horizontal Reference Multiplexer selects either the internal video, from the
Input Multiplexer or the External Reference input as the instrument sync
reference. The Multiplexer is controlled by an output from the Line Rate
Controller.
Line and Field Rate signal generators are started and stopped by the retrace
signals from the Line Rate Controller. Sweep ramp run up times (
17 ms for
the field sweep and 64
m
s for the line sweep) are controlled by the Microproces-
sor.
The Horizontal Signal Multiplexer is controlled by the Line Rate Controller to
select a signal to drive the horizontal circuitry.
Input Multiplexer
Filter Selection Multiplexer
Squarewave Calibrator
Vertical Amplifier
Horizontal Reference
Multiplexer and Reference
Switch
Sweep Generators and
Horizontal Signal
Multiplexer