Frequency discriminator has five integrated circuit chips interconnected to provide a divide function, exclusive OR function, phase shifting, and holding so that a single binary output signal results. The state of the binary signal indicates which one of the two input signals has a lower frequency than the other

Reid, W. J.

English

NASA Technical Reports Server

May 1970	 Brief 70-10010 
NASA TECH BRIEF C' 
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Digital Frequency Discriminator 
Reference fl..fl
	
I I 
Frequency ave
__________ 
IDivide Shiftl— '	 J	 Reference
Input	 o__•ø j Shaper I I	 Register	 I
— 
I	 Shift	 I 
I	 Register ______
I
I	
I	 HShift
Unknown I
^Id
I	 I ster_put 
Frequency Wave  Discriminator 
Input hlftster [RegI	 I Shift Register 
Phase Shifter Frequency 
Circuit Detector Circuit
A frequency discriminator has been designed to 
use digital logical circuitry and supply a single binary 
output signal. Five integrated circuit chips, each con-I 
sisting of a shift register stage, are interconnected to 
provide a divide function, exclusive OR function, 
phase shifting and holding so that a single binary 
output signal results. When the binary signal is in a 
first state, it indicates that a specific one of the two 
input signals has a lower frequency than the other. In 
the second binary state, the opposite condition is 
indicated; - 
To date, most frequency discriminators have been 
analog in character with the phases of the various 
input signals compared in strictly analog fashion and 
the discriminator output indicating the frequency 
difference. Some digital circuits have been constructed 
for comparing frequencies of two input signals with 
the output as a set of signals that varies according 
to the difference between frequencies. These devices 
are called differential rate circuits and do not, at any 
given instant, indicate whether one input frequency,
and which, is greater than the other but only indicate 
the frequency difference by the average of the output 
signals. In such circuits, the output signal frequency 
varies as the phases of the input signals precess with 
respect to each other. In certain applications it is 
desired that the frequency difference be continuously 
indicated in a binary sense to indicate whether one 
frequency, and which, is greater or less than the other. 
In such situations, the connection factor is the con-
stant. 
A reference frequency and a signal of unknown 
frequency are fed tø the discriminator circuitry after 
first being formed into pulses or square waves by 
wave shapers between these sources and the discrim-
inator. Two of the integrated circuit chips are inter-
connected to form a phase shifter circuit that shifts 
the relative phases of two received input signals, 
each with respect to the other. A second pair of inte -
grated circuit chips provides phase detection plus a 
gating circuit that receives phase-shifted signals from 
the phase shifter and compares them. Output signals 
(continued óverleaf) 
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are supplied to a fifth integrated circuit chip that 
receives and holds the binary information indicative 
of which input signal frequency is the greater. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
-• Huntsville, Alabama 35812 
Reference: TSP70-10010
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclu-
sive 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: W. J. Reid of

Motorola, Inc.

under contract to

Marshall Space Flight Center

(MFS- 14322) 
Brief 70-10010	 Category Ol


Digital frequency discriminator

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