Tektronix WFM 601A, Service Manual

Page: 59 / 368

Block Diagram Descriptions
3–4
WFM 601A, WFM 601E, & WFM 601M Service Manual
The Line Rate Controller selects the signal from the Horizontal Signal Multiplex-
er to drive the Horizontal Amplifier circuit.
The Horizontal Amplifier is a variable gain amplifier with controlling inputs
from the microprocessor and Line Rate Controller. Stage gain is controlled by the
DAC output voltages. The Line Rate Controller selects the magnification gain.
An offset voltage horizontally positions the display. The amount of offset
required for the Waveform mode is significantly greater than that required for the
other display modes. During processing of the CRT readout, the Line Rate
Controller changes the gain of the amplifier as necessary.
The differential output of the Horizontal Amplifier drives the horizontal output
amplifier which powers the CRT deflection plates.
An additional amplifier stage within the Horizontal Amplifier provides a
differential output that controls the intensity for the Picture Monitor mode. The
microprocessor controls the Picture Monitor contrast.
The Blanking Logic is a multiplexer, which is controlled by the Line Rate
Controller. The Blanking Logic selects the blanking/unblanking signals that drive
the Z-Axis Amplifier, which drives the CRT control grid.
Block Diagram 2, Component
The Y, P
b
, P
r
Reconstruction Filters drive the input selection matrix. The
coprocessor picks either the component channels or blanking levels for output.
Switch output is buffered and becomes the input to the Color Difference to GBR
Transcoder, Bypass Switching, and Component display mode switching.
The three component signals enter three mixers that produce GBR signals
according to the SMPTE format. An adjustable offset is added to each signal as
required for display.
The Switch Control Buffers select either the color difference input signals or the
transcoded GBR signals to drive the Picture Monitor Output amplifiers.
The Gamut Limit Comparator includes separate circuits to compare the GBR
signals and the component signals to the user selected gamut limits. The two
comparators generate separate GBR and composite gamut alarm signals. When
the signal exceeds the GBR gamut limits, the Monitor output flashes. A gamut
inhibit signal causes the 2 Hz blink rate. The Monitor Out display can be either
Horizontal Amplifier
Blanking Logic
Component Blanking
Switching
Color Difference to GBR
Transcoder
Bypass Switching
Gamut Limit Comparator
and Monitor Out
Amplifiers