B Sweep Gate; Sweep Control Integrated Circuit - Tektronix 465 Instruction Manual

Circuit Description-465
signal at the collector of 0862 is connected to the AZ Axis
Gate Circuit to control CRT blanking and to generate the +
A GATE signal. The signal at the collector of 0864 is
connected to the emitter of the Sweep Disconnect Ampli-
fier stage (01024) in the A Sweep Generator Circuit to
initiate A Sweep generation.
B Sweep Gate
0812 and 0814 compose the B Sweep Gate Circuit.
They also form an emitter-coupled stage where only one
transistor can be conducting at any time. The input signal
to the stage is the positive-going trigger signal from the B
Fire Trigger TD in the B Trigger Generator Circuit. The
signal at the collector of 0812 is connected to the B Z Axis
Gate Circuit to control CRT blanking and to generate the+
B GATE signal. The signal at the collector of 0814 is
connected to the emitter of the Sweep Disconnect Ampli-
fier stage (01084) in the B Sweep Generator Circuit to
initiate B Sweep generation.
Sweep Control Integrated Circuit
U870 is the Sweep Control Integrated Circuit. Several
functions are performed in this stage, depending on the
mode of operation of the instrument sweep generators. The
following is a brief explanation of the function associated
with each pin of the IC.
Pin 1. This is the positive Auto Sense input. The signal
connected here comes from the A Fire Trigger TD.
Pin
2. This is the negative Auto Sense input. A fixed DC
level established by R871 and R872 is connected here.
Pin 3. This is the + auto gate terminal. In the AUTO
mode of operation, if no trigger signals are applied to pin 1
of U870 during the ~100 ms following the end of holdoff
the gate level at pin 3 steps LO to turn 0864 on which
initiates a sweep.
Pin 4.
Not used in this application.
Pin 5. Input terminal for negative voltage supply.
Pin 6.
This is the auto gate timing terminal. R879 and
C879 determine the amount of time between the end of
holdoff and the generation of the auto gate.
3-12
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Pin 7.
This terminal lights the TRIG'D light when a
triggered gate has occurred.
Pin
8. This is the holdoff timing terminal. The R/C
connected to this terminal (selected by the TIME/DIV
switch) determines the length of holdoff time.
Pin
9. Ground terminal.
Pin 10. This is the Holdoff output terminal. The gate
level present here is LO during sweep holdoff time and HI
otherwise.
Pin
11. This terminal lights the READY light when
operating in the single sweep mode.
Pin
12. This is the single sweep mode terminal. When +5
volts is applied to this terminal the sweep operates in the
single sweep mode; when the terminal is left open or
grounded the sweep operates in the repetitive mode.
Pin
13. Not used in this application.
Pins 14 & 15.
Single sweep reset terminals. Pushing the
PUSH TO RESET button prepares the single sweep
circuitry to respond to the next one triggering event. Also
causes the READY light to be lit.
Pin 16. This is the holdoff start input terminal. The HI
sweep reset gate pulse from the sweep generators is applied
here to initiate sweep holdoff.
Pin
17. This is the sweep disable output terminal. The
gate level at this terminal is HI during holdoff and LO
otherwise.
Pin 18.
Sweep lockout input. +5 volts applied to this
terminal disables all sweep action.
Pin 19. Auto mode terminal. Grounding this terminal
enables auto sweep operation.
Pin 20.
Input terminal for positive voltage supply.
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