Tektronix 1730 Series, Instruction Manual

Page: 95 / 258

1730–Series Theory of Operation
4–11
linearity and reduce the thermal distortions introduced by Q383. In addition,
negative feedback increases the input impedance. A series compensation
network consisting of R384 and C384 provides improved bandwidth and
stability.
The combination of Q385 and Q387 form a shunt-feedback amplifier, identical
to Q383 and Q382. The signal current for this amplifier is input through R485.
Signal current through Q387 is equal in value and opposite in phase to the
current change in Q382. The Limit Center, R489, balances the bias current
flowing in Q382 and Q387. R387 and C387 form another series compensation
to improve bandwidth and stability. R486 and C389 provide high-frequency
peaking to improve the flat response; R385 and C385 improve low-frequency
transient response.
Q280 and Q289 are common-base stages that couple the complementary signal
currents to the non-inductive CRT load resistors, R184 and R186. The resulting
signal voltages drive the CRT vertical deflection plates. R183 and R187 shunt
the load resistors to provide the proper load resistance for the high-bandwidth
output signal. L180 and L190 are adjustable shunt-peaking coils to increase the
vertical bandwidth and allow precise adjustment of flat response.
The Picture Monitor Output Amplifier consists of U978 and Q877. The
amplifier is driven from pin 2 of U978D by the SIG 2 input from Diagram 1.
The output, that drives a 75
W
load, is the emitter of U978A (pin 7). R883 and
R884, on the amplifier input, develop the signal voltage 0.554V (1 mA * 554
W
).
The overall gain for this non-inverting amplifier is set by feedback divider
resistors R975 and R876. The signal amplitude at the emitter of U978A is 2 V
(0.554 * (1+3570/1400)). Q973 adds an offset to the video, for LINE SELECT
operation, that provides the bright-up (or strobe) pulse. The amount of the offset
is set by the value of R870.
Timing
Diagram 3
Composite sync from the Sync Separator (Diagram 1) is used to time the
Horizontal and Vertical Sync Generators. Outputs from these generators are used
to develop line and field rate signals that are used to display selected lines or
fields of information. The Clamp Pulses used to time the vertical amplifier DC
Restorers are generated by a Back Porch Generator driven by the Horizontal
Sync Generator.
The input Staircase for the RGB/YRGB parade display is input to an operational
amplifier through the rear-panel REMOTE connector. The compensatable (dc
level and transient response) RGB Amplifier is enabled (RGB ENABLE) by a
TTL low.
Pix Monitor