Tektronix Webcam 070-8030-01 ユーザーズマニュアル
Theory of Operation
3–90
1780R-Series Service Manual
Diff Gain/Phase Alternate Mode Switch. U425 implements a Switchable Polarity
Amplifier, which outputs a differential current. Pin 4 is the signal input;
transconductance gain is set by R422. The pin 6 output drives the + input of a
Differential Operational Amplifier and pin 12 drives the – input. Levels at pin 8
and pin 10 dictate the polarity of the output from the Differential Amplifier.
When pin 10 is high, there is no inversion between the pin 4 input and the Alt
Demod signal. If pin 8 is high, the Alt Demod output is inverted. The gain is
unity between pin 4 and the Alt Demod signal, which goes back to the Waveform
Monitor Diff Amp and Video Filters (Diagram 5).
Amplifier, which outputs a differential current. Pin 4 is the signal input;
transconductance gain is set by R422. The pin 6 output drives the + input of a
Differential Operational Amplifier and pin 12 drives the – input. Levels at pin 8
and pin 10 dictate the polarity of the output from the Differential Amplifier.
When pin 10 is high, there is no inversion between the pin 4 input and the Alt
Demod signal. If pin 8 is high, the Alt Demod output is inverted. The gain is
unity between pin 4 and the Alt Demod signal, which goes back to the Waveform
Monitor Diff Amp and Video Filters (Diagram 5).
DAC. An Offset DAC, U325, provides a variable level for dG measurements
(from measurements knob setting, through the Microprocessor). For dP
measurements the DAC outputs a fixed level, corresponding to center range.
DAC current output is converted to a voltage by U221A and B (operational
amplifiers). R322 calibrates the gain to ensure that 750 mV is equal to 7% or 7
(from measurements knob setting, through the Microprocessor). For dP
measurements the DAC outputs a fixed level, corresponding to center range.
DAC current output is converted to a voltage by U221A and B (operational
amplifiers). R322 calibrates the gain to ensure that 750 mV is equal to 7% or 7
_
(5% or 5
_ PAL). R315 sets the DC level to center the DAC in its range and
compensate for the DC level out of the demodulator.
Data Latch. U330 is an octal, D-type flip-flop that latches data from the Micro-
processor Data Bus. All communication from the Processor to the Oscillator and
Recursive Filter circuit boards is through this latch. U243 is a TTL 3- to 8-line
decoder/de-multiplexer used to decode the memory mapped Oscillator circuit
board addresses. Clock signal for the Data Latch is from the Y3 output of U243.
processor Data Bus. All communication from the Processor to the Oscillator and
Recursive Filter circuit boards is through this latch. U243 is a TTL 3- to 8-line
decoder/de-multiplexer used to decode the memory mapped Oscillator circuit
board addresses. Clock signal for the Data Latch is from the Y3 output of U243.