Circuit provides dual function of frequency discriminator/phase detector which reduces frequency acquisition time without adding to circuit complexity. Both frequency discriminators, in evaluated frequency discriminator/phase detector circuits, are effective two decades above and below center frequency

Crow, R. B.

English

NASA Technical Reports Server

August 1974	 B74-10098 
NASA TECH BRIEF 
•	 NASA Pasadena Office 
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. 
Frequency Discriminator/Phase Detector 
The problem: 
Frequency acquisition in phase-locked loops often 
takes too much time. One common circuit used in the 
reduction of the acquisition time is an auxiliary fre-
quency discriminator. The discriminator, however, com-
plicates the loop circuit. 
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The solution: 
A circuit providing the dual function of frequency 
discriminator/phase detector reduces frequency acquisi-
tion time without adding to circuit complexity. 
How it's done: 
Two frequency discriminator/phase detector circuits, 
as shown in Figures 1 and 2, were developed and 
evaluated. Basically both circuits accept sine wave 
inputs, shape them, and control two flip-flops (FF1 and 
F172). In the circuit of Figure 1, the input frequency 
f0
 is higher than input frequency f1 , so that Q (FF1) is 
false most of the time while Q (FF2) is true. These two 
flip-flop outputs are differenced, using an operational 
amplifier to produce a dc signal output that is pro-
portional to the input frequency difference. 
The frequency discriminator characteristic is the same 
for both circuits. Both frequency discriminators are 
effective two decades above and below the center 
frequency. In addition, they are broadband and can be 
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Figure 1. Frequency Discriminator/Phase Detector With Half the 
Linear Range of Circuit Shown in Figure 2.
(continued overleaf) 
	
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https://ntrs.nasa.gov/search.jsp?R=19740000098 2020-03-17T14:05:00+00:00Z
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Figure 2. Frequency Discriminator/Phase Detector. 
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used for reference frequencies from 1 kHz to approxi-
mately 3 MHz. Further bandwidth extension is possible 
by changing the input differentiator circuit. 
When the two signals are of the same frequency, the 
circuits perform as phase detectors The circuit shown 
in Figure 1 has the same detector gain as the one shown 
in Figure 2 but only half the linear range. The former 
has a 1800 phase ambiguity when it is used in a phase-
locked loop. In each case the signal input power can 
be as low as —20 dBm with a negligible reduction in 
output performance. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: T5P74-10098
Patent status: 
Title to this invention, covered by U.S. Patent 
No. 3,750,035 has been waived under the provisions 
of the National Aeronautics and Space Act [42 U.S.C. 
2457(f)], to the California Institute of Technology, 
Pasadena, California 91109.
Source: Robert B. Crow of

Caltech/JPL
NASA Pasadena Office
(NPO-11515) 
B74-10098	 Category 02 0


Frequency discriminator/phase detector

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