Phase-locked loop with photoresistive control, which provides both sine and cosine outputs for subcarrier demodulation, serves as a telemetry demodulator signal conditioner with a second harmonic signal for synchronization with the locally generated code

Crow, R. B.

English

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September 1969	 Brief 69-10383 
____  
NASA TECH BRIEF 
TT ±	 i	 ___ 
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. 
Wide-Band Doubler and Sine Wave Quadrature Generator 
Control Voltage V 
sin (wt)
	 cos(wt)	 SIN (2 t) 
Reference 
B	 T	 0deg 
Input	
Integrator	
Voltage- 
Controlled ______  
Phase Shifter
90 deg 
Second Harmonic 
Input/Output Phase Relationship 
The problem: 
To provide a telemetry demodulator signal condi-
tioner having sine and cosine outputs for data sub-
carrier demodulation from 100 Hz to 100 kHz and 
a second harmonic signal for synchronization with 
the locally generated code.
The solution: 
A unique-phase locked loop with photoresistive 
control, which provides both sin (w t) and cos (w t), 
and multiplies these two functions together in the 
loop phase detector. The difference frequency is 
used as the error signal to keep the two signals 
A
m(continued overleafl 
NW
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 Uniteçl 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=19690000378 2020-03-16T18:14:19+00:00Z
phase-locked while the multiplier sum frequency 
yields the second harmonic of the input frequency. 
This solution to the doubling application yields the 
proper zero degree input/output phase relationship. 
How it's done: 
The simplified block diagram illustrates that the 
phase relationship between the input and output is 
achieved by having two series R-C phase shifters 
controlled so that the output is phase-locked 90 deg 
from the input signal, i.e., the output is cos (w t) 
for sin (w t) input. This is accomplished by using a 
photoresistor (not shown) as the variable resistor in 
the R-C circuit. An error voltage is generated at the 
output of a digital multiplier that is integrated using 
an operational amplifier and applied to a light source 
that controls the resistance of the photoresistor. 
In a loop analysis, the steady-state phase error be-
tween the sin (w t) input and cos (w t) output will be 
zero, providing (dR)/(dv) of the photoresistor is not 
zero at the operating point. This condition (viz., (dR)/ 
(dv) 5,-- 0) holds for the particular device used for in-
put frequencies of from 0.1 to 100 kHz. Further, the 
loop response is one of the first order and is always 
stable. 
One unusual problem was encountered in building 
the first model. The desired control voltage ranged 
from —2 to —10 Vdc to control the lamp properly 
which in turn causes the photoresistor to change its 
resistance. In checking the prototype it was found, 
however, that decade step changes in frequency could 
shoëk the integrator so that the control voltage (V) 
momentarily became positive. When this occurred, 
the loop no longer had control (the lamp being 
equally sensitive to either polarity control), and the 
integrator would continue integrating because of the 
reversal of K until the operational integrator saturated. 
This problem was solved by designing an acquisition
circuit that sensed when the loop no longer had control 
(i.e., when the light was off and the cos (w t) signal 
disappeared) and then applying a discrete command 
to make the control voltage (V) the approximate cor-
rect negative voltage; the loop was again active and 
could lock onto the input signal. 
This wide-band quadrature generator has an output 
that is 90 degrees displaced from the input (and a 
square wave second harmonic of the input) over a 
frequency range of 0. 1 to 100 kHz. Operation is auto-
matic and independent of frequency (over the specified 
limit) and operator controlled. 
Notes: 
1. This information should interest research personnel 
in the telemetry and communications industries. 
2. Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-10383 
Patent status: 
This invention is owned by NASA, and a patent

application has been filed. Royalty-free, nonexclusive

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: Robert B. Crow of

Caltech/JPL
under contract to

NASA Pasadena Office

(N PO- 1 1133)
.. 
Brief 69-10383	 Category 01


Wide-band doubler and sine wave quadrature generator

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