Circuit limits the positive and negative peaks of a random-noise signal. It accurately establishes a known limiting level relative to any given RMS value of the random-noise signal input

Woodbury, R. C.

English

NASA Technical Reports Server

R4 
Input 
J-1 
4 
September 1969
	 Brief 69-10349 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Automatic Gaussian Random-Noise Limiter 
R  1 
This circuit has been designed to limit the positive 
and negative peaks of a random-noise signal. Limit-
ing is held to a value not exceeding 3 times the rms 
value of the random-noise signal. The circuit can be 
used to limit the peak acceleration automatically and 
continuously during random-noise vibration testing 
to a value no greater than 3 times the rms acceleration 
level.
The advantage of this circuit is that it accurately 
establishes a known limiting level relative to any given 
rms value of the random-noise signal input. The 
feature that achieves this result lies in the method of 
back-biasing diodes by means of an operational rec-
tifier that establishes the conduction point of the 
diodes with respect to the instantaneous random-
signal level. Fixed-level limiters, which have pre-
(continued overleaf) 
AMk
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000348 2020-03-16T18:12:19+00:00Z
viously been used, cannot establish the maximum 
limiting level reference to all possible rms values of 
the random-noise signal. 
The random-noise signal is normally applied to 
input J-1 of the Automatic Noise Limiter (ANL); 
the gain of the overall system, from J-1 to J-2 (the 
output) is unity. All six amplifiers used in the system 
are standard linear operational amplifiers (op-amp) 
provided with one inverting input designated (—) and 
one noninverting input designated (+); each amplifier 
has overall negative feedback applied externally to 
fix or adjust the gain of each amplifier. The input 
signal is fed through Cl and Ri to op-amp Al on 
through C3, R6, R15 and op-amp A4 to the output 
jack J-2. Cl, C2, and C3 provide dc isolation. R6 
is a sensing resistor to provide a signal indication 
whenever diodes D3 or D4 conduct; this signal is 
monitored via op-amp A3 used as a differential ampli-
fier. The output of A3 is coupled to Ti, a line to grid 
transformer to provide isolation between the ANL 
and the oscilloscope. R6 provides sufficient resistance 
between op-amp Al and the op-amp A4 to permit 
proper limiting action of diodes D3 and D4, hence 
effecting higher signal current through R6 when the 
diodes conduct. The gain of op-amp A4 is adjusted 
by R16 to effect unity gain from J-1 through J-2,. with 
diodes D3 and D4 disconnected from the circuit, and 
op-amp Al having a fixed gain or amplification of 
10 from J-1 through C3. (Note: After adjustment, 
the gain of op-amp A4 may' be as low as 0.1.) The 
output of op-amp Al is coupled through C2 and the 
feed forward resistor R3 to op-amp A2 of the limiter 
circuit. The output of A2 is capacitively coupled to 
diodes Dl and D2 to, in effect, gate the positive and 
negative going portion of the signal to a voltage 
divider (RiO, R12, and R20); the divided signal is 
• placed in a negative feedback loop via R4 to compen-
sate for diode nonlinearities in the conduction mode. 
Diodes Di and D2 are referred to as operational rec-
tifiers. The half-wave signal at the junction of D2 
and R12 is fed into an averaging network R13 and 
C7; R14 feeds the negative dc signal from the averag-
ing network to op-amp A5; A5 inverts the signal to 
provide a back bias to D3. A5 also feeds, via R18, 
a positive signal to op-amp A6, which inverts the 
signal and provides a back bias to D4. (NoteA6 has 
a fixed gain of unity.)
The circuit is calibrated by applying Gaussian noise 
between 0.1 and 1.0 volt rms to the input J-1 and 
establishing a known rms level at the output J-2. A 
probability density analyzer is connected to output 
J-2. The gain of amplifier A5 is adjusted by resistance 
R17 to back-bias the diodes D3 and D4 to a value 
that permits forward conduction when positive and 
negative noise peaks exceed the back-bias voltage. 
This voltage is determined by the required signal-
limiting level, which is confirmed by the probability 
density analyzer. The normal sigma limiting range 
is adjustable by the resistor R17 from 1.75 to 3 sigma. 
The limiting point is established by the ratio of the 
rms noise voltage at the output of amplifier Al and 
the rectified dc voltage at the output of amplifier AS. 
The limiting point depends only on the ratio of these 
two voltages and not on their magnitudes. 
Limiting occurs when diode D3 or diode D4 con-
ducts because of the voltage divider created by re-
sistance R6 and the forward conduction impedance 
of diode D3 or diode D4. During limiting, the cur-
rent through resistor R6 creates a voltage across re-
sistor R6 which is amplified by differential amplifier 
A3. This voltage is applied to an oscilloscope to 
indicate the occurrence of limiting. 
Notes: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10349 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, non-exclusive 
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should 
be made to NASA, Code GP, Washington, D.C. 
20546.
Source: Raymond C. Woodbury of
Jet Propulsion Laboratory
under contract to 
NASA Pasadena Office
(NPO-10169)
. 
Brief 69-10349	
0	 Category 01


Automatic Gaussian random-noise limiter

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server