Electronic circuit using operational amplifiers provides output with constant phase shift amplitude, with respect to sinusoidal input, over wide range of frequencies. New circuit includes field effect transistor, Q, operational amplifiers, A1 and A2, and phase detector

Deboo, G. J.

English

NASA Technical Reports Server

July 1971	 Brief 71-10230 
NASA TECH BRIEF 
A nies Research Center 	 - 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Constant-Amplitude, Frequency-Independent Phase Shifter 
An electronic phase-shifting circuit using opera-
tional amplifiers provides an output with a constant 
phase shift amplitude, with respect to a sinusoidal 
input, over a wide range of frequencies. In conven-
tional electronic phase-shifting circuits, the output 
amplitude and phase angle generally vary with fre-
quency, limiting circuit operation to a narrow band 
of frequencies. In addition, the majority of these cir-
cuits can provide only a fixed phase-shift for a given 
frequency.
Ri	 R2
it) 
The new circuit includes a field effect transistor 
(FET), Q, operational amplifiers, Al and A2, and a 
phase detector. The phase difference between the input 
and output is converted into a voltage which drives 
the electronic components of the circuit in such a way
as to maintain the desired phase shift; i.e., the circuit 
is constantly in a balanced or null condition at a se-
lected input-output phase relationship. 
When the gate voltage of Q is properly varied, the 
phase shift imposed on a signal is held constant as the 
frequency varies, and the amplitude of the phase 
shifted signal also remains constant. The output of 
the phase detector supplies the appropriate gate volt-
age, which is a function of the relative phase difference 
between the signals, V 1
 and V out , applied to its 
input terminals. Potentiometer R5 provides a reference 
voltage which is equal to the output of the phase detec-
tor for a selected phase difference. This voltage is fed 
to the input node of amplifier A2. Since the output of 
the phase detector is also fed to this node, any dif-
ference between the potential at the potentiometer 
wiper arm and the output of the phase detector is 
amplified by A2. The amplified signal is applied to 
the base of Q such that the phase of the output 
sinusoid is shifted and a null at the input node of A2 
is restored. In practice, the loop gain of the circuit 
is maintained large enough so that virtually any de-
viation from the selected phase difference provides a 
strong corrective signal at the gate of Q. Thus, the 
phase difference between input and output signals is 
held constant even though the signal frequency may 
vary. 
Notes: 
1. The circuit can provide phase shifts of only 0 to

rad (0 to 180°); however, two circuits can be

cascaded to provide phase shifts of 0 to 2 ir rad
(0 to 360°), and the output at a selected phase shift

will be of constant amplitude at any frequency. 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use uf the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19710000229 2020-03-17T02:20:28+00:00Z
licenses for its commercial use will be granted by 
NASA. Inquiries concerning license rights should 
be made to:
	 0 
Patent Counsel 
Mail Code 200-1 IA 
Ames Research Center 
Moffett Field, California 94035 
Source: G.J.Deboo
Ames Research Center

(ARC-10269) 
2. Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP71-10230 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive
Brief 71-10230	 Category 02


Constant-amplitude, frequency- independent phase shifter

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