Phase locked phase modulation system with voltage controlled oscillator for final phase linearit

Sivley, J. B.

Vaughan, G. R.

English

NASA Technical Reports Server

NATIONAL 
'c -_ - 
REPLY TO 2 
ATTN OF. y. 
>- =L 
2 5 (NASA CR OR TMX OR AD NUMBER) 
AERONAUTICS AND SPACE ADMINISTRATION 
WASIIINGTON. D C 20540 
March 30, 1971 
(CATEGORY) 
TO : USI/Scientific &Technical Information Division 
Attention: Miss Winnie M. Morgan 
FROM: GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
U.S. Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code US1 memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U.S. patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U.S. Patent No. 3,393,380 
Corporate Source : Westinghause Electric Corporation 
Supplementary 
Corporate Source 
NASA Patent Case No. : XMP-05382 
Please note that this patent covers an invention made by an 
employee of a NASA contractor. Pursuant to Section 305(a) of 
the National Aeronautics and Space Act, the name of the 
Administrator of NASA appears on the first page of the patent; 
however, the name of the actual inventor (author) appears at 
the heading of Column No. 1 of the Specification, following the 
words 'I. . e with respect to an invention of. . . . ' I  
Gayle Parker 
Enclosure : 
Copy of Patent 
https://ntrs.nasa.gov/search.jsp?R=19710014068 2020-03-17T03:03:32+00:00Z
July 16, 1968 JAMES E WEBB 3,393,380 
ADMINISTRATOR OF THE NATIONAL AERONAUTICS 
AND SPACE ADMINISTRATION 
PHASE LOCKED PHASE MOD‘JLATOR INCLUDING A 
VOLTAGE CONTROLLED OSCILLATOR 
Filed March 15, 1966 
cp 
-\ 
N -r- * 
0 
Z L T  
w w  
= 0  
w *  a- &= 
0-  -)z i 
I 
qx 
0 
CD 
, l q - ’ ,  
JAMESB.SI V LEY 
2 
divided down phase modulated carrier (which is divided 
down to the frequency of the reference frequency) and 
the reference frequency is combined with the incoming 
modulating signal. The result obtained by the addition of 
these two signals is applied through a low pass filter to  
a voltage controlled oscillator. The output of the voltage 
controlled oscillator comprises a carrier having the phase 
Filed Mar. 15,1966, Ser. No. 536,217 information thereon. This i s  both transmitted and applied 
5 Claims. (Cl. 332-19) to the frequency divider to be divided down and there- 
10 after applied to the linear phase detector. 
Origin of the invention The novel features that are considered characteristic 
The invention described herein was made in the per- of this invention are set forth with particularity in the 
formance of work under a NASA contract and is subject appended Claims. The invention itself both as to  its organ- 
to the provisions of Section 305 of the National A ~ ~ ~ -  ization and method of operation, as well as additional 
nautics and Space Act of 1958, Public L~~ 85-568 (72 15 objects and advantages thereof, will best be understood 
Stat. 435; 42 USC 2457). from the following description, when read in connection 
This invention relates to phase modulator systems, and with the accompanying drawing, which is a block sche- 
more particularly to improvements therein. matic diagram of an embodiment of this invention. 
With the advent of space communications, there has Referring now to the drawing, it is desired to transmit 
come an increased utilization of communication tech- '20 by phase modulation, the information in a modulating 
niques employing phase modulated carriers and phase co- signal, VIII derived from a modulating signal source 10. 
herent receivers. The reason for the popularity is because These are applied through a first-resistor 12 as one input 
with presently known techniques of coherent phase detec- to an inverting amplifier 14. The amplifier has a feedback 
tion, successful communication is obtainable Over inter- resistor 16 connected between its output and its input. A 
planetary distances with minute quantities of transmitted 26 second input to the amplifier is the output of a linear phase 
power. detector 18. This is applied through a third resistor 20 
The earliest phase modulators included a reactance tube to the amplifier input to be added to the input received 
arranged so that the reactance formed a portion of the from the 
total circuit impedance. It was well known that the re- may be any One Of the 
actance tube output reacted as a function of the drive volt- 30 well known circuits which are capable of providing a 
age. Therefore, the phase response of the reactance tube voltage output which varies linearly with the phase dif- 
circuit was a function of the drive or modulating voltage. f ~ ~ c e  of its two inputs. This may be for example a flip- 
AS voltage sensitive capacitors (varactor diodes) became flop circuit wherein one input drives the flip-flop to its 
available, the reactance tube was gradually replaced with set state and the other input drives the flip-flop to its 
this. However, both devices yield an output carrier whose 35 reset state. Both outputs of the flip-flop circuit are applied 
phase is a function of the modulating voltage. Unfortu- to a low Pass filter 24. The output of the low pass filter 
nately, the phase response of these systems is quite non- is a signal which has an amplitude dependent upon the 
linear for other small phase deviations. The usual accept- phase relationship O f  its two inputs. One of the two inputs 
able linear phase deviation of either the reactance tube to the linear phase detector comprises the output signals 
or varactor is plus or minus 0.1 radians. Since the ranging '*' from a source of reference frequency signals 20. The other 
system of current space communication systems demands input to t h e h e a r  phase detector is derived from a fre- 
phase deviations up to plus or minus 4 radians, in order quency divider 22- 
to increase the phase deviation obtained, a phase modu- The output of the amplifier consisting of the amplified 
lator typically is followed by frequency multipliers with sum of its two inputs, is applied to a low pass filter 24. 
multiplication factors that bridge the gap between the 45 The low Pass filter should be one which i s  capable of 
modulator capabilities and the final required deviation. passing the highest frequency of the modulating signal 
Such a system is not without problems. The informa- received from the source 10. The output of the low pass 
tion transmitted is carried in the phase of the carrier. filter is applied to a voltage controlled OSCillatOr 26. The 
Therefore, the phase linearity of all subsequent multi- 50 voltage controlled oscillator may be any of the well known 
pliers, amplifiers and mixers is paramount. Further, a vco circuits wherein the frequency of its output may be 
meaningful analysis of the final phase linearity and group varied in well known manner in response to the voltage 
delay of this system, as a function of the individual cas- applied to its input. The output of the voltage controlled 
caded nonlinearity is an impossible task. The usual pro- oscillator is transmitted and is also fed back to the fre- 
cedure is to build d l  components as linear as possible and quency divider to be divided down by an amount N. Since 
to hope for the bqst. 55 phase deviation information may be derived from fre- 
An object of this invention is to provide a phase modu- WencY shift inforKIation, the OutPUt Of the voltage con- 
lating arrangement which provides a linear phase devia- trolled cscillator 26 therefore is phase modulated with 
tion over a much larger range than presently available the modulating voltage V m  which may be detected using 
systems. any of the well known phase detection receivers. In order to understand the operation of the invention, 
an improved phase modulator system which provides the aS*ume at the outset that no modulating signal V, is 
required phase deviation without using multipliers, ampli- being applied from the modtrlating signal source 10. 
fiers and mixers to the extent employed in presently known The Output of the voltage controlled oscillator 26 Pro- 
phase modulators. vides an output at some frequency, assume for illustra- 
Yet another object of this invention is the provision 65 tion, that this is 50 megacycles. The frequency divider 
of a novel and useful phase modulation system. will divide this by N, which will be assumed to be 4. 
These and other objects of the invention may be The 12% megacycle output of the frequency divider is 
achieved in a system wherein a reference frequency is pro- applied to the linear phase detxtor. Assume that the 
vided. This is applied to  a linear phase detector to which source Of reference frequency and phase signals provides 
there is also applied the divided down output of the phase an output consisting of a 12.5 mc. signal having a constant 
modulator carrier. Any difference in phase between this phase and frequency. If the output of the VCO is equal 
3,393,380 
PHASE LQCKED PHASE RWL?JDING 
James E. Webb, Administrator of the National Aeronau- 
R. Vaughan, J&thicum, and J~~~~ 
A VOLTAGE CON 
tics and space Administration, with 
vention of 
B. Sivley, Laurel, Md. 
to an in- 5 
source. 
The linear phase detector 
Another object of the present invention is to provide 6o 
3,393,380 
3 
in frequency and phase to the output of the source 20, 
then no correcting signal is generated at the output of 
the linear phase detector. However, if for somc cause What is claimed is: 
there is a deviation in the output of the VCO from the 1. A phase locked phase modulator comprising volt- 
output of the source 20, the linear phase detector will 5 age controlled oscillator means for producing output 
provide an output signal having an amplitude representa- signals whose frequency is determined by the voltage of 
tive thcreof. With no modulating signal being applied, an input signal applied thereto, means for generating ref- 
the output of the linear phase detector is applied to altor erence signals having a stable phase and frequency, means 
the VCO output to change its frequency in a manner to for comparing the phase of said output signals with said 
reduce the linear phase detector output to zero. Thus, the reference signals to produce error signals representative 
output of the linear phase detector alone can change the of the difference of these, a source of modulating signals, 
frequency of the VCO to cornpensat,: for deviations f:om meam for combining said error signals with modulating 
the frequency and phase of the source of reference fre- signals from said source, and means applying said com- 
quency and phase signals. bined signals to said voltage controlled oscillator for con- 
Considering now a modulating signal Vm being present 15 trolling the frequency of the output signals of said volt- 
and the output of the linear phase detector, as an error age controlled oscillator means. 
correcting signal, then this error correcting signal is corn- 2. Apparatus as recited in claim 1 wherein the fie- 
bined with the modulating signal Vm to produce a result- WencY of signals generated by said means for generating 
ant signal which varies the frequency of the VCO by Reference Signals iS 1 /N times the frequency of said out- 
an amount required to both correct for frequency and 20 put signals of said voltage controlled oscillator means in 
phase deviation as related to the reference source 20 and the absence Of an input signal applied thereto and there is 
also to represent the modulating signal. included means for dividing the frequency of said output 
Included in the drawing are notations indicative of loop signals by an amount 1/N connected between the output 
scale factors and transfer functions expressed in Laplace of said voltage controlled oscillator means and said means 
notation. Thus expressing the transfer of output phase as 25 for comparing the phase of said output signals and said 
a function of the baseband modulation, the following reference Signals. 
equation may be derived using the standard servo-loop 3. Apparatus as recited in claim 1 wherein said means 
relationships : for comparing the phase of said reference frequency sig- 
nals and said output signals comprises a linear phase de- 
4. A system for phase modulating a carrier with modu- 
K" E'ds)  ( 1 )  lating signals from a source of modulating signals com- 
prising a source of reference signals having a fixed fre- 
quency and phase, voltage controlled oscillator means for 
35 producing output signals at a frequency determined by 
input voltage control signals, the frequency of said output 
signals in the absence of input voltage control signals 
being N times higher than the fmwencY of said refer- 
ence signals, frequency divider means for dividing the 
40 frequency of said output signals of said voltage controlled 
osciflator by N, phase detecting means for detecting the 
difference in phase between said output signals and the 
output of said frequency divider and producing an error 
signal representative thereof, means for combining said 
45 error signal with modulating signals from said source of 
signals, and means for applying the output of said means 
voltage controlled oscillator means. 
5. A system as recited in claim 4 wherein said means 
for combining as 
frequency was 12" and the oscillator means includes low pass filter means for pass- 
a novel, useful and unique apparatus for the phase modu- 
lation of a signal on a carrier. 
- 30 tector. 1 Ods) = N . 
Vrn Kd s ( a / w l + 1 )  1 
where 
IC, = 1 K q  Kdr RVCO 
It will be seen from the drawing that Kd, K, and Kvco 
are all respectively constants of the linear phise detector, 
the amplifier, and the voltage controlled oscillator. N is 
the division factor of the divider. 
The equation indicates that the output phase e, (3) 
is a linear function of the baseband modulation voitage 
V, if 
SlK,. 5 S I  + I  >>1 
Fi(s) 
at least Over the frequency range of the baseband modula- for combining as signa1s to said 
tion voltage V,. 
In an actual embodiment of the invention which was 5o for applying the output of said 
constructed and successfully operated, where the refer- input voltage control signals to said .voltage controlled 
'ho Output Of the vCo was 50 mega- ing signals up to the frequency of said modulating signals, cycles, with the modulating voltage comprising the am- 
plitude modulation of a 1.5 megacycle sigaal, with N .5.5 
equal to 4, a linear phase deviation at the carrier fre- 
quency of 50 megacycles was obtained which was on the 
order of plus or minus 4 radians. This is a wider linear 2,661,214 12/1953 Hugenholtz _ _ _ _ _ _ _ _ _  332-19 
phase deviation than has been obtainable from presently 3,046,496 7/1962 Trevor _ _ _ _ _ _ _ _ _ _ _ _ _  332-19 
known devices. GO 3,118,117 1/1964 King et al. _ _ _ _ _ _ _ _ _ _  332-22 
The receiver for detecting a transmission generated by 3,142,806 7/1964 Fernandez _ _ _ _ _ _ _ _  332-19 X 
apparatus of this invention may be a standard phase 3,277,3901 10/1966 McLin _ _ _ _ _ _ _ _ _ _ _ _ _ _  331-25 
detector receiver. 
There has accordingly been described and shown herein 
References Cited 
UNITED STATES PATENTS 
ALFRED L. BRODY, Primary Examiner. 


Phase locked phase modulator including a voltage controlled oscillator Patent

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server