Introduction
This description is broken down into the following
parts: Trigger Circuits, Sweep Logic, Miller Integrator.
Timing Circuits, Output Amplifier, Gate Output Amplifier.
and Power Supplies. Refer to Fig. 5-1, Functional Block
Diagram, and the Ramp Generator Schematic Diagram
while reading this description.
Trigger Clrculls
Trigger
Selection.
Switch SlOE (AUTO TRIG) dis
connects a positive voltage level from pin 1 3 of U30,
enabling bright baseline operation. The +SLOPE switch,
S10D, connects a positive voltage level to pin 5 of U30 for
positive-slope triggering. S10A, B, and C select triggering
signals respectively from EXT IN, the line trigger source,
and internally via the Power Module main interface board.
The External and Internal circuits each provide a static
20
kO
impedance at dc, changing to about 10
kO
as the
limiter diodes conduct to Clip the incoming signal. The line
circuit attenuates ac vottage from a secondary winding in
Section 5-RG 501
CIRCUIT
DESCRIPTION
the Power Module, producing a one-volt, line-frequency
trigger signal.
T
r
igg
e
r
Input Circuit.
Emitter-follower 015 is the
current source through Rig, driving pin 4 of the Sweep
Logic IC, U30. The LEVEL control, R27, biases pin 40fU30
to different current levels such thai the IC can trigger at
any point within ±1 V of the Input signal.
Sweep Logic
U30 controls trigger initiation, slope selection, bright
baseline operation, sweep start and stop, and holdoff
timing. See Table 5-1.
Miller Integrator
U50 generates a linear, positive-going ramp, controls
its length and timing, and resets the sweep logic in U30.
See Table 5-2.
TABLE
5-1
Sweep Logic U30
Pin
Function
I ,Reset
Current (logic I , high state) for at least 20 ns ends ramp, regardless of how far the ramp has run up.
No current (logic
O.
low state) allows U30 to operate,
3,Ground
Circuit ground,
4,Trigger Input
Analog input, low impedance. Accepts analog current trigger signal. Trigger threshold: zero
current, ±100 J.l.A.
5,Slope Select
Logic 1 permits trigger to be initiated on the positive slope of the trigger signal. Logic 0 permits
trigger to be initiated on the negative slope of the trigger signal.
6.Not Used
Held at logic 1 .
B.GND. Substrate
Reference ground.
1 1 .Holdol! Timing
Connects timing components which set trigger lockout period after endo' ramp. Holdofl capacitor
discharges when ramp starts and holdoll timing starts at end of ramp as holdoff capacitor charges.
When upper threshold is reached. a new ramp can be started.
12.Bright Baseline
Used in Auto Triggered mode to connect timing components that set the time the bright
Timing/Off
baseline is off lollowing trigger recognition. if triggering.signal is absent or occurring at a rate less
than 20 Hz, capacitor charges 3.S-volt threshold. Above this level. U30 is conditioned to
provide a Iree running sweep at a rate determined by the sweep timing and holdotf RC. As soon asa
trigger arrives at pin 4 of U30, pin 1 2
is
driven to ground and C35 is discharged.
5-1
