Tektronix WFM 601A, Service Manual

Page: 58 / 368

Block Diagram Descriptions
WFM 601A, WFM 601E, & WFM 601M Service Manual
3–3
The Half Band filters (HBF) use interpolation to double the number of data
values in order to ensure a smoother product from the DACs. Data timing signals
are 13.5 MHz for luminance and 6.75 MHz for color difference. The HBFs are
clocked at 27 MHz for luminance (Y) and 13.5 MHz for P
b
and P
r
signals. Data
out of the HBFs are input to three DACs. The DAC outputs are the component
analog signals, Y, P
b
, and P
r
. Their gain and DC offset is set by the microproces-
sor through a Daculator on the Component board, diagram 12.
The three separate Reconstruction Filters are bandpass filters that provide
adjustments for matching the delay through the three HB filters, DACs and
Reconstruction filters. An adjustable offset is added to each signal as required for
display.
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, which is 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 Controller.
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 DAC output voltages. The Line Rate Controller
selects and enables vertical magnification.
An offset voltage from the DACs vertically positions the display. When CRT
readout processing occurs, the Line Rate Controller changes the gain of the
amplifier. The differential output of the Vertical Amplifier drives the vertical
output amplifier, which powers the CRT deflection plates.
The Horizontal Reference Multiplexer selects either the COMPSYNC signal
from the coprocessor or the External Reference input as the instrument sync
reference. The front-panel REF switch controls the multiplexer.
Line and Field Rate signal generators are started and stopped by the retrace
signals from the Line Rate Controller. The microprocessor controls the Sweep
ramp times, which are
17 ms for the field sweep and 64
m
s for the line sweep.
Y, P
b
and P
r
Reconstruction Filters
Input Multiplexer
Filter Selection
Multiplexer
Square Wave Calibrator
Vertical Amplifier
Horizontal Reference
Multiplexer and Reference
Switch
Sweep Generators and
Horizontal Signal
Multiplexer