Tektronix 1730 Series, Инструкция по эксплуатации

Страница: 86 / 258

1730–Series Theory of Operation
4–2
Front-panel mode switching is accomplished by a series of push-button switches
whose status is being constantly polled by a Microprocessor. In turn, the
Microprocessor controls switching functions and circuit gains so that the
instrument can perform as a monitor or be used to make specific measurements.
The Microprocessor is an 8051 type.
The Low Voltage Power Supply is a high-efficiency switching type. The High
Voltage Power Supply provides 13 kV acceleration potential.
Block Diagram
The Block Diagram for the 1730-Series Waveform Monitor is located on a
foldout in Section 9 of this manual. The following functional description uses
the diagram as its illustration. The numbers on the circuit blocks correspond to
the schematic diagram where that circuit block is detailed.
Vertical — Color-encoded video signals are input through the bridging Channel
A and Channel B inputs. The input amplifiers are shunted by sample-and-hold-
type clamps, that are timed by a Back Porch Sample from the Back Porch
Generator. This clamped signal, prior to any filtering, is also the rear-panel
Picture Monitor Output. In LINE SELECT modes, a strobe, that acts as a
bright-up pulse, is added to the Picture Monitor Output to identify the selected
line (or block of lines in 15 Line). Switching at the output of the amplifiers
provides for display of either input signal or a combination of both in all sweep
modes. In the combination mode, the Channel A signal is displayed on the left
of the CRT with the Channel B following.
Front-panel switching can select a Flat (unfiltered), a Low Pass, or a Chroma
filtered signal for display. The low pass filtered signal can be displayed with a
Flat (unfiltered signal) as part of the dual filter mode. In dual filter mode, the
low pass filtered signal is displayed to the left with the unfiltered (flat) signal
following. When the calibrator signal is selected (from the front-panel switch-
ing), a 1 volt, 100 kHz signal is applied to the input of the Gain Cell instead of
input video. The calibrator signal is used to set up both Vertical Gain (Volts Full
Scale) or Horizontal Gain (Sweep rate) from a common, self-contained source.
Signal amplitude can be adjusted at the Gain Cell using either the front-panel
V GAIN or VARIABLE gain control. The output signal from the Gain Cell
drives another clamped amplifier. This second clamped amplifier has a
loop-compensated sample-and-hold circuit to provide the fast clamping required
for the Fast DC Restorer. Clamping, as with the first clamp, occurs at back
porch time.
The Vertical Positioning voltage, along with the conditioned video signal, is
input to a Switchable Gain Amplifier, to provide X5 vertical magnification.
Both amplifier gain and positioning range can be increased by a factor of 5 when
Circuit Blocks