Development of apparatus for generating output signal commensurate with information contained in input signa

Cohen, M. F.

English

NASA Technical Reports Server

I t1  PLY TO 
A l l N  OF. G P  
To: 
F ROM t 
SUBJECT: 
NATIONAL AERONAUTICS AND SPACE ADMlNiSTRATlON 
WASHINGTON. D.C. 20546 
USI/Scientif ic & Technical Infomat ion  Division 
Attentions Miss winnio M, Morgan 
G P / O f f i c e  of AssistaQt General Counsel f o r  
Patent  Matters 
Announcement of NASA-Owned U. 8 ,  Patent8 i n  STAR 
4 
I n  accordance with the procedures agreed upon by Code GP 
and C o d e  US18 the attached NASA-owned U. S. Patent  is being 
forwarded E o r  abs t rac t ing  and announcement i n  NASA STAR. 
The following information is prwidedt 
U. S. Patent  N o ,  t 6 
Government o r  &z:2 i z 4 d U r n W A  e*. 
Corporate Employee t 8JJLC, /v Y 
Supplementary Corporate 
Source (if applicable) t 
NASA Patent  C a s e  No. : 
NOTE - If t h i s  pa ten t  covers an invention made by a corporate 
employee of a NASA Contractor,  the following i s  applicable: 
Pur suan t  to Sect ion 305(a) of the National Aeronautics and 
Space A c t ,  the name of the Administrator of NASA appears on 
the first  page of the patent ;  however8 the name of the ac tua l  
inventor (author) appears a t  the heading of Column No. 1 of 
the Specif icat ion,  following the words a. . . w i t b  seepect t o  
Y e s  N o  17 
Elizabeth A. Ca 7 1 - 2 6 1  
N 
0 Enclosure -n 
COPY of Patent  a i t e d  abw 3 
9 
$ 
CJ (NASA CR OR TMX 6 R  AD NUM5EB) 
https://ntrs.nasa.gov/search.jsp?R=19710019662 2020-03-17T03:10:17+00:00Z
ted States Patent 
Inventors Thomas 0. Paine 
Administrator of the National Aeronautics 
and Space Administration with respect to 
an invention of; 
Murray F. Cohen, Roslyn Heights, N.Y. 
Appl. No. 889,478 
Filed Dec. 31,1969 
Patented May 18,1971 
DIGITAL MOP);ULATOR AND DEMODULATOR 
10 Claims, 3 Drawing Figs. 
U.S. CI ........................................................ 332/9R, 
3071234,3071265,328/58,3241106,332110 
Int. C1. ........................................................ H03k 7/08, 
H03k 9108 
Fieldof Search ............................................ 332/9,9 
(T). 10; 3291104,106,126, 1; 328158; 3071234, 
265; 3251142 
References Cited [561 
UNITED STATES PATENTS 
3,3 14,062 411967 Pommerning ................ 307/265X 
3,350,637 1011967 Pochtar ........................ 332/9(T)(UX) 
3,426,296 2/1969 Chrktiansen et al. ........ 328158X 
3,478,170 1 111969 Hanni ........................... 3251142X 
Primary Examiner-Alfred L. Brody 
Attorneys-Howard J. Osborn and William H. King 
ABSTRACT: The modulation index of a pulse width modu- 
lated input signal is determined by employing the input signal, 
as synchronized with a reference signal, to control a gate 
which passes high frequency pulses to an up-down counter. 
The direction of counting of the counter is varied at twice the 
frequency of the input pulse repetition rate and the signal 
which controls counting direction is shifted in phase with 
respect to the reference signal whereby the output of the 
counter will be a positive or negative count having a mag- 
nitude commensurate with the degree of pulse width modula- 
tion of the input signal. 
16’ 
28’ 24 
PATENTED WAY 18 1971 
E ' '  
3,579;146 
llllll 
SQI 
- QO 
I I 
FIG. 3 
INVENTOR 
MURRAY F. COHEN 
ATTORNEYS 
3.579.14 
skilled in the art by reference to the accompanying drawing 
wherein: 
FIG. 1 is a block diagram of a prefetaed embodiment of the 
present invention; 
FIG. 2 is a waveform diagram depicting operation of the 
embodiment of FIG. 1. the identification of the waveforms of 
FIG. 2 being applied to FIG. 1 at the points where the various 
signals appear in the circuitry; and 
FIG. 3 is a waveform diagram which theoretically represents 
10 the operation ofthe present invention. 
DESCR5'TION OF THE PREFERRED EMBODIMENT 
W i l e  not limited thereto in its utility, the present invention 
15 has been found to be particularly well suited for use in the en- 
vironment of an approach guidance planet tracker. Ac- 
cordingly, the invention will be described below in connection 
with a system wherein the informationcontaining input signal 
comprises a pulse wave indicative of position; Le., a pulse train 
20 wherein information provided by a suitable sensor is employed 
to modulate the width of the input signal pulses. 
With reference now to FIG. 1, a high frequency clock cir- 
cuit is indicated at 10. The clock 10 may, for example, com- 
prise an astable multivibrator which provides a square wave 
25 output. The clock circuit output signals are indicated at A in 
FIG. 2 and the same indicia has been applied to FIG. 1. 
The clock output pulses are applied to a first input of an 
AND gate 12 which in the manner to be described below, 
3o functions as a chopper gate. The clock output pulses are also 
applied to a first frequency division circuit 14. In a typical ex- 
ample, where the clock output frequency was at 102.4 kH,, 
the division circuit 14 provided an output at 12.8 kH, or one- 
eighth of the clock frequency. The division circuits 14,16 and 
35 18 may, for example, comprise binary flip-flops or bistable 
multivibrators whereby a pair of output signals at the desired 
frequency but shifted 90°in phase are obtained. 
The output signals from the division circuit 14 are applied 
as inputs to respective further division circuits 16 and 18. In a 
40 preferred embodiment, the division circuit 16 provides an out- 
put signal at one-half the frequency of the input applied 
thereto. In the example being described, therefore, the output 
of the division circuit 16 was a square wave signal at 6.4 kH,. 
One of the phase-related outputs of the division circuit 14 is 
45 applied as a toggling input to division circuit 18. The circuit 18 
providbs a pair of output signals which are 180" out-of-phase 
with one another and at one-half the frequency of the input 
signal to the division circuit 18. The output signals from the 
circuit 18, which are employed in the manner to be described 
50 below, are at the same frequency as the output from division 
circuit 16 and are related in phase thereto. As a typical exam- 
ple, the negative going pulses which comprise the Q, signal 
from circuit 18 lead the square wave signal from circuit 16 by 
90" while the positive going pulses which comprise the Q, 
The output of the division circuit 16 is applied to a further 
division circuit 20 which again divides by 2 to provide an out- 
put signal at one-half the frequency of the output signals from 
6o the division circuits 16 and 18. Thus, in the example being 
described, the output of circuit 20 would be at 3.2 kH,. The 
circuit 20 may be identical to the circuit 16. 
The output of the division circuit 20 is applied to a triangu- 
lar wave form generator 22 which provides a linear sweep 
65 voltage B as may be seen from FIG. 3. The sweep voltage 
generator 22 may comprise a standard operational amplifier 
conftgured as an integrator. 
The triangular scanning voltage generated by the sweep 
voltage generator 22 is applied as a first input to a pulse width 
70 modulator 24. The modulator %! may, for example, comprise 
a pulsed switching circuit. Also applied to the pulse width 
modulator 24, as the modulating signal, is the information- 
bearing input signal from the condition sensing or scanning 
device 28. The modulating signal applied to the modulator 24 
75 may comprise a pulse wave wherein the duty cycle is the 
5 
55 signal from circuit 18 lag the signal from circuit 16 by 90". 
 AT^^ 
ORIGIN OF T;HE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is subject to the 
provisions of Section 305 of the National Aeronautics and 
Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 
U.S.C. 2457). 
BACKGROUNI) QF TWE INVENTION 
1. Field of the Invention 
The present invention is directed to apparatus for generat- 
ing an output signal commensurate with information con- 
tained in an input signal. More specifically, the present inven- 
tion relates to the digital processing of pulse Width modulated 
wave trains. Accordingly, the general objects of the present in- 
vention are to provide novel and improved apparatus and 
methods of such character. 
Art 
in its utility, the present invention 
is r use in the demodulation of pul- 
sating signals wherein the duty cycle of the signal is the infor- 
mation desired. Thus, for example, the present invention may 
be empIoyed in a control system wherein an operational 
parameter or condition is monitored and a train of pulses hav- 
ing widths indicative of instantaneous position or condition is 
generated. 
There have, in the prior art, been several schemes proposed 
of a pulse width modulated 
r purposes of display or other 
use. These prior art demodulation schemes have, however, 
been characterized by a slow response to changes in the 
modulation index and have been relatively inaccurate in that 
they are insensitive to small changes in puke width. As a 
general rule, the prior art circuits for generating a signal com- 
mensurate with the modulation index of a train of input signal 
pulses may be characterized as analog approaches in that they 
provide output signals having a magnitude or pulse width com- 
mensurate with modulation index. The inaccuracies inherent 
in such analog approaches are well known to those skilled in 
the art. 
OF THE INVENTION 
The present invention overcomes the foregoing and other 
disadvantages of the prior art by providing for the digital 
processing of information-bearing input signals. In acwm- 
plishing the foregoing, the present invention employs a 
chopper gate, controlled by the input signal or a signal com- 
mensurate therewith, to trigger an updown counter. The up- 
down counter totalizes pulses from a high frequency clock, the 
clock pulses being passed by the chopper gate when ener- 
gized. Before being applied to the chopper gate, the input 
signal is mixed with a scanning signal at a reference frequency. 
The scanning signal may be generated, via suitable frequency 
division circuitry, from the clock output. 
Counter control signals at double the scanning signal 
frequency are also generated, typically through the use of 
frequency division circuitry, from the clock output and are 
shifted in phase with relation to the scanning signal whereby 
chopper gate control pulses commensurate with the input 
signal information control the application of clock pulses to 
the counter and the counter will alternately count, under com- 
mand o€ its control signals, up and down with the counting in 
one direction bemg synchronized with the midpoint of the 
control pulses applied to the chopper gate. Accordingly, the 
output ofthe counter will be a positive or negative count hav- 
ing a magnitude commensurate with the degree of pulse width 
modulation or other information contained in the input signal. 
BRIEF DESCRWTION OFTHE DRAWING 
The present invention may be better understood and its nu- 
merous objects and advantages will become apparent to those 
3,579,146 
sensed information or, as depi d in FIG. 3 at C, the input in- rence signal for generating 
formation may be in the form of a )w: signal having a mag- counter control signals having a preselected phase and 
nitude commensurate with the information. In either event, frequency relationship to said pulse width modulated 
the input signal modulates the sweep voltage to provide the signals whereby the direction of counting of reference 
pulse width modulated pulses D as shown in FIG. 3. The pulses 5 signal pulses passed by said gate means may be varied 
D are, accordingly, characterized by width commensurate during each cycle of said pulse width modulated signal; 
with the infomation contained in the input signal; either in and 
the form of magnitude or puke width. means applying said counter control signals to said counter 
The pulse width modulated signals D from the modulator 24 means whereby the totalized count will be commensurate 
are applied as gating signals to the AND gate 12 and thus con- 10 with the infopation. 
trof the transmission of clock pulses A to an up-down counter 2. The apparatus of claim 1 wherein said counter control 
26 via the gate 12. Restated, gate 12 is enabled by the pulse Signals are in the form Of Pulses 90" OUt-Of-Phase With said 
width m d u l a a  output sign& from the modulator and pulse width modulated signals whereby the middle of each 
will pass clock pulses to the counter 26 only when a pulse D is Puke Of the Pulse width modulated gating Signal is 
applied at h e  input thereto. ne updown counter 24 may l 5  synchronized with the middle of one of said counter control 
comprise a chain of binary flip-flops or a bistable multivibra- 
3. The apparatus of claim 2 wherein said pulse width modu- tor with appropriate gating. 
The direction of counting of the counter 
scanning signal generator means responsive to said the Q, and Q, signals from the frequency 
reference signal for providing a linear sweep voltage; and The counting direction control signals, as may clearly be seen 
from 3%. 3, are related in phase and frequency to the sweep pulse responsive to the Output Of 
said scanning signal generator and to said input signals. voltage B. In the embodiment being described this phase rela- 
tionship results in the midpoint of the a, or command 4. The apparatus of claim 3 wherein said scanning signal 
the pulses which contain the desired infoma- frequency divider means connected between said reference 
signal generating means and said scanning signal genera- 
tor whereby the pulse width modulated signal is at a fust tion. Accordingly, as may be seen from a simultaneous con- 
frequency lower than the frequency of said reference sideration of the various wave forms of FIG. 3, when clock pulses are passed via the gate 12 to the counter 26, the 30 signal. 
counter will f i t  count up, will then count down and will again 6. The apparatus of claim wherein said scanning signal 
count up during the duration of the pulse D from the modula- generator comprises a triangular 
7. The apparatus of claim 6 wherein said counter control tor 24. Referring to wave form E of FIG. 3, it may be seen that the signal generating pulses passed to the counter 26 second frequency divider means connected between said 
ample cycle of the sweep voltage provided by the waveform reference signal generating means and said means for ap- 
generator 22 will be a negative count and this count will be in- plying counter control signals to said counter, said 
dicative d both direction and magnitude of a. deviation of the frequency divider means providing a pair of output 
sensed condition from a normal value. Restated, the totalized signals at twice said first frequency. 
count at the end of each cycle of the output of the triangular 4O . A digital dem&ulator comprising: 
wave form generator 22 is axmnensurate with modulation 
index and may be an indication of magnitude and direction of 
error. 
The theory of operation of the present invention will be 
clearly understood from a consideration of FIG. 2 which illus- 45 
traks the instant technique for the digital processing of the 
means responsive to said 
lated signal generating means comprises: 
pdse w i g  synchronized wia  the midpoint of the positive 25 generatorcomprisesatriangular wave form generator' 
portions of the sc-inp voltage and thus wi& the midpoint of s* The Of 'Iaim comprising: 
generator, 
comprises: 
Of the an ex- 35 
clock means for generating a pulsating reference signal; 
means connected to said clock and responsive to said 
reference signal for generating control signals at a first 
rence signal, 
ctively lead- 
to said con- 
trol signal generating means and responsive to said third 
control signal for generating a linear sweep voltage 
synchronized with said third control signal, said sweep 
voltage being at a second frequency which is one-half said 
fmt frequency; 
modulator means connected to said scanning voltage 
generating means and responsive to said sweep voltage 
and information bearing input signals for providing a gat- 
ing signal having pulses which vary in width with the in- 
formation contained in said input signals; 
gate means connected to said clock means and to said 
modulator meam, said gate means passing reference 
signal pulses when enabled by said gating signals; and 
bidirectional counter means responsive to reference signal 
pulses passed by said gate means, said counter means 
being connected to said control signal generating means 
and counting in the direction commanded by said first 
and second control signals. 
3. The apparatus of claim wherein said scanning voltage 
generatingmeanscomprises: 
first frequency divider means for providing a signal at one- 
sweep voltage generator means responsive to the output 
PO. The apparatus of clsnn 9 wherein said control signal 
50 pling process; this implies that the individual pulses are modu- 
lated symmetricaliy about the midduration point of the 
scanning voltage provided by the generator 22. In the usual in- 
stance this is insured by employing the scanning voltage from 
the generator 22 
scanning or sensing device 28. In FIG. %, a square wave modu- 
lator output pulse D is shown at a frequency F with a counter 
control signal at 2P and displaced by 90". It is to be noted that 
the area appearing in the positive portions of the counter con- 
trol signal is equal to the area contained in the negative par- 60 
tions in the FIG. 2 example; the depicted condition typically 
being indicative of no error in the sensed condition. 
with information con&ed in an input signal comprising: 
a means for driving or COntrOrh the 55 
1 claim: 
1. Apparatus for generating an output signal commensurate 
means for generating a pulsating reference signal, 
means responsive to said reference signal and the informa- 
tiqn-bearing input signal for generating a pulse width 
modulated gating control signal characterized by pulses 
having widths commensurate with the information; half the frequency of said third control sign& and 
gate means responsive to said gating signal and to said pul- 
sating reference signal for selectively passing said provided by said first frwuency generator means. 
reference signal, 
means; 75 second frequency divider means. 
65 
70 
up-down counter means connected to the output of gate generatingmeanscomprises: 


Digital modulator and demodulator Patent

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server