Capacitive integrator circuit using Silicon Controlled Switches /SCS/ insures output voltage linearly proportional to input pulse width. This circuit provides high input impedance and relatively low output impedance

Newcomb, A. L., Jr.

English

NASA Technical Reports Server

June 1965	 Brief 65-10159 
NASA TECH BRIEF rLNFA 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia, 22151. 
Solid-State Switching Used to Speed Up Capacitive Integrator 
B+ 
The problem: Where the width of variable electric 
pulses is of interest, as in a control system that indi-
cates certain parameter changes by Changes in pulse 
width, a method of converting the pulses to an analog 
voltage is needed in order to measure such pulse 
width. Conventional capacitive integrators that per-
form this conversion use relays for switching the ca-
pacitors. Relays have limited operating lifetime, draw 
appreciable power, and cannot be switched in much 
less than two milliseconds.
The solution: A capacitive integrator that uses sili-
con controlled switches (SCS's) to steer each input 
pulse to the proper capacitor (Ci or C2) in a sequence 
of charge, discharge, and read. The circuit has a re-
sponse time in microseconds. 
How it's done: The silicon transistors Si and S2 are 
alternately biased on by the bistable multivibrator 
formed by Q  and Q2, which is triggered by the trail-
ing edge of each input pulse. At the end of each pulse, 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19650000157 2020-03-11T17:23:34+00:00Z
the capacitor that is next to be charged is unloaded of 
its previous charge by a shunted silicon controlled 
switch (S3 or S4) that is also triggered by the multi-
vibrator. Blocking diodes Di and D2 prevent dis-
charge of the capacitors (Cl and C2) through the 
charge components. Capacitors Ci and C2 are 
charged by the constant current circuit Q, Z i, Z2, 
Ri, and R2. This circuit insures an output voltage 
that is linearly proportional to the input pulse width. 
Maximum linear output voltage level is determined by 
the zener voltage of Zi and Z2 and the magnitude of 
the input pulse since: V 0 t = V - V0 = VB+ 
—2Vz. Capacitors Cl and C2 are connected to the 
base of the combined emitter follower Q4 through D3 
and D4. This circuit exhibits an output equal in mag-
nitude to the highest voltage appearing on either Cl 
or C2. It also provides a high input impedance (500K 
ohms) to prevent transient discharge of the capacitors, 
while maintaining a relatively low output impedance. 
System output can be considered as an integral 
function of the input on a single pulse basis, or as an 
RMS (root mean square) equivalent of a series of 
evenly spaced pulses.
Notes:	 - 
1. A modified version of this circuit has been used 
successfully for over eight months to integrate the 
output of an infrared horizon scanner for space 
exploration. 
2. The circuit can be used to integrate either high or 
low duty cycle pulses with repetition rates ranging 
from I pulse per second to over 10,000 pulses per 
second with negligible ripple factors. 
3. Inquiries concerning this innovation may be di-
rected to: 
Technology Utilization Officer 
Langley Research Center 
Langley Station 
Hampton, Virginia, 23365 
Reference: B65-l0l 59 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taihing rights for its commercial use may be made to 
NASA,Code AGP, Washington, D.C., 20546. 
Source: Arthur L. Newcomb, Jr. 
(Langley-104) 
Brief 65-10159	 Category No. 01


Solid-state switching used to speed up capacitive integrator

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