Linear sawtooth voltage wave generator with transistor timing circuit having capacitor and zener diode feedback loop

Green, E. D.

Woolfson, M. G.

English

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REPLY TO 
ATTN OF: 
TO : 
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SUBJECT: 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASIIINGTON. D C .  20546 
October 15, 1970 
USI /Sc ien t i f ic  & Technical Information Div is ion  
At ten t ion :  M i s s  Winnie M. Morgan 
GP/Office of A s s i s t a n t  General 
Counsel f o r  P a t e n t  Mat te rs  
Announcement of NASA-Owned 
U.S .  P a t e n t s  i n  STAR 
I n  accordance wi th  t h e  procedures contained i n  t h e  Code GP 
t o  code U S 1  memorandum on t h i s  s u b j e c t ,  dated June 8, 1970,  
t h e  a t t ached  NASA-owned U.S.  p a t e n t  is being forwarded f o r  
a b s t r a c t i n g  and announcement i n  NASA STAR, 
The fol lowing information i s  provided: 
U.S.  Pa t en t  No, : 3,302,040 
Corporate Source : Westinghouse Elec t r ic  Corp. 
Supplementary 
Corporate Source 
NASA Pa ten t  C a s e  No,: XMS-01315 
Please note  t h a t  t h i s  p a t e n t  covers  an  invent ion  made b y  an 
employee of a NASA c o n t r a c t o r .  Pursuant t o  Sec t ion  305(a) of 
t h e  Nat ional  Aeronautics and Space A c t ,  t h e  name of t h e  
Adminis t ra tor  of NASA appears  on t h e  f i r s t  page of t h e  p a t e n t ;  
however, t h e  name of t h e  a c t u a l  i nven to r  (au thor )  appears  a t  
t h e  heading of Column No. 1 of t h e  S p e c i f i c a t i o n ,  fol lowing t h e  
words e . wi th  respect t o  an inven t ion  of .  e . .'I 
Gdyle Parker 
Enclosure: 
Copy of Pa ten t  
https://ntrs.nasa.gov/search.jsp?R=19700032359 2020-03-17T02:12:17+00:00Z
Jan, 31, 1967 HUGH L. DRYDEN 3,302,040 DEPUTY ADMINISTRATOR OF THE NATIONAL 
AERONAUTICS AND SPACE ADMINISTRATION 
COMBINATION FEEDBACK 
LINEAR SAWTOOTH VOLTAGE-WAVE GENERATOR EMPLOYING TRANSISTOR 
TIMING CIRCUIT HAVING CAPACITOR-ZENER DIODE 
Filed Feb. 24. 1964 
8+ 
481 
1 T 32 T 3 6  -- 
24 
24 
- 
FIG. 2 
I h Vb.h 1 OR& 
lbsrson €3. Green 
Mortin G. Woolfson \ 
3,302,04 nited States Patent Office patented Jan. 31, 1969 
1 2 
diode is connected to the other side of the charging re- 
3,302,040 sistor. Also connected to the emitter in a second feed- 
LFNEAR SAWTOOTH VOLTAGE-WAVE GENERA- back path is a capacitor, the other side of which is con- 
TOR EMPLOYING TRANSISTOR TIMING CIR- nected to a current limiting resistor. The current limit- 
CUIT HAVING CAPAC~oR-ZENERDIODECOM- 6 ihg resistor has its other side connected to the cathode 
BINATkON FEEDBACK 
Dryden, Deputy Adminisbator of the National of the zener diode. Further, the junction of the feed- 
AeronauGcs and Space Administration with respect to back capacitor and current limiting resistor is connected 
an invention of Elberson D. Green and Madin G. to a source of positive potential through a diode. The 
Woolfson resultant combination of two feedback paths results in a 
10 substantially lincar output sawtooth voltage. 
The advantages of this invention, both as to its con- 
struction and mode of operation, wkll be readily appreci- 
This invention relates in general to  electric wave gen- ated as the same become better understood by reference to 
eralors and more particularly to an improved generator the following dctailcd description when considered in con- 
for providing i~ linear sawtooth voltage wave shape. 16 nection with the :rccompanying drawings in which like 
In  high precision sweep or delay circuits, the slight ex- referenced numerals designatc like parts ihrough the fig- 
ponential curvature of a sawtooth voltage waveform is urcs, and wherein: 
highly undesirable and methods of conipensation must FIG. 1 is a circuit diagram of a presently known wave 
be employed Io produce the necessary degree of linearity. shape generator which is shown to .assist in an under- 
The most direct method of producing a linear sawtooth 20 standing of the invention, and 
voltage is by increasing the source of potential used to FIG. 2 is a circuit diagram of the novel wave shape 
charge a capacitor so that during the time the capacitor generator in accordance with this invention. 
is charged it will charge linearly. However, there is a Referring now to the drawings, there is shown in FIG. 
definite practical limit to the magnitude of the source of 1 a well-known transistorized waveshape generator for 
potential. Further, if transistors are to be used in the 26 generating a sawtooth voltage. A source of pulses are 
circuit, high voltages become extremely impractical. applied to  an input terminal 12 connected to the base 14 
A more satisfactory manner to produce a linear saw- of a switching transistor 16. Connected across the col- 
tooth voltage would be to charge the capacitor from a lector 18 and emitter 22 of the transistor 16 is a charging 
constant current source. One method of obtaining a capacitor 24. One side of the charging capacitor is con- 
constant current is by use of a feedback circuit commonly SO nected to a source of reference potential and the other 
called a “bootstrap sweep circuit.” In one such bootstrap side is connected to a charging resistor 26. The charging 
sweep circuit the desired constant current source is ob- resistor 26 is connected to a source of positive potential 
tained by using a capacitor in the feedback path. How- through a current limiting resistor 28. 
ever, the feedback capacitor will discharge and thereby The collector 18 is also connected to the base 32 of a 
prevent a constant voltage from being maintained across 36 second transistor 34. The collector 36 of the second 
the charging resistor during the charging time. The saw- transistor 34 is connected to a source of positive poten- 
tooth voltage obtained by this method will be nonlinear. tia], and the emitter 38 is connected to a source of nega- 
Another method of obtaining a sawtooth voltage utiliz- tive potential through a current limiting resistor 42. Out- 
ing a bootstrap sweep circuit would be by use of a zener put signals are taken from a terminal 44 Connected to the 
diode in the feedback path. The charging current in such 40 emitter 38. Further, a feedback path containing a zener 
a citcuit is equal to the zener voltage divided by the charg- diode 46 has its anode connected to the emitter 38 and its 
ing resistance and is substantially constant. However, the cathode connected to the junction of the charging resistor 
theoretical maximum sweep voltage for the bootstrap 26 and the current limiting resistor 28. The arrangement 
sweep circuit is the value Of the source Of potential. for the transistor 34 will be readily recognized as an 
Another drawback to the latter-mentioned circuit is that 45 emitter-follower circuit. 
the current through the zener diode is a function of the At time rl, when a pulse 48 is applied to the base 14, the 
sweep voltage So that the voltage across the zener diode transistor 16 is rendered conductive, thereby causing the 
changes due to its finite resistance. capacitor 24 to discharge. At time ti, when the transistor 
In order to overcome the attendant disadvantages in the is again rendered nonconductive, the capacitor 24 begins 
Prior art Sweep circuits, the sweep circuit of the Present 6o to charge through the charging resistor 26 and resistor 28 
invention utilizes a pair of feedback loops. The first loop towards a Further, due to the 
contains a zener diode which maintains a relatively con- emitter-follower arrangement of the transistor 34, the 
stant charging current. The second loop contains a ca- output voltage 50 appearing at the output terminal 44 pacitor which allows the zener diode current to remain 66 will 
relatively constant during the generation of the sweep The output voltage 50 appearing at terminal 44 is also 
voltage while further allowing a charging capacitor to fed back to  the junction of the resistors 26 and 28 through charge to a relatively high voltage level. the zener diode 46, so that the voltage across the resistor 
More ParticU1arly, the circuit comprises an input t e p  26 tends to remain constant. Thus, the net result is a mina* for a source Of to the base Of a substantially constant voltage across the resistor 26 result- 
switching transistor. A charging capacitor is connected 60 ing in a constant charging current to the capacitor 24. 
The circuit of FIG. 1, however, has two drawbacks. across the collector-emitter circuit of the transistor. The 
emitter of the transistor is grounded and the collector is First, the peak sweep va~tage is limited to a theoretical 
connected to one side of a charging resistor. The side 
of the charging capacitor connected to the collector is also where 
Ep=B+- (E,S-iRae) connected to the base of a second transistor connected in 08 emitter-follower fashion. The collector of the second 
transistor is connected to a source of positive potential, where &=the voltage drop across the diode 46, and iRaa 
whereas the emitter is connected to a source of negative is equal to  the voltage drop across the resistor 28. At the 
potenti.al through a resistor. The output terminal of the maximum sweep voltage the current through the zener 
circuit is connected to the emitter of the second tran- 70 diode will reduce to zero and the zener diode cuts off. 
sistor. An anode of a zener diode is also connected to the The second drawback to the circuit of FIG. 1 is that 
second transistor emitter .and the cathode of the zener since the current through the zener diode is a function of 
Filed Feh. 24,1964, Ser. No. 347,101 
2 Claims. (CI. 307-88.5) 
approaching B+. 
the voltage acrOSS the capacitor 24. 
value of 
3,302,040 
3 
the sweep voltage, the voltage across the zener diode will 
vary to a limited extent due to its finite resistance R,, thus 
preventing the voltage across the resistor 26 from remain- 
ing constant. 
In order to overcome the drawbacks of the circuit of 
FIG. 1 there is shown a modified version thereof in 
FIG. 2. A second bootstrap feedback circuit containing 
a capacitor 52 is ccffim'rtted befWeh the emitter 38 and 
resistor 28. Connected to the junctbn bf the resistor 28 
and capacitor 52 is a diode 54 having its anode connected 
to a first source of positive potential (B+), while the col- 
lector 36 is connected to a second source of positive po- 
tential (B++). 
Operation of the device of FIG. 2 is similar to that 
of FIG. 1, However, the second feedback path containing 
the capacitor 52 allows the output voltage 56 a t  the ter- 
minal 44 to be also feed back to the junction of the 
resistor 28 and diode 54. Thus, the potential at the 
junction of the resistor 28 and diode 54 can rise to  a value 
greater than the value of the first source of positive poten- 
tial because of the additional voltage being fed back 
through the capacitor 52. When the voltage at the junc- 
tion of capxitor 52 and diode 54 rises to  a value above 
that of the first source of positivc potential, the diode 54 
will act iis a switch and cut the first source of positive 
potential out of the circuit. Also, due to the increased 
voltage in the circuit caused by the capacitor feedback, 
the zener diode no longer cuts off, as the sweep voltage 
can now rise to a value greater than the source of refer- 
ence potential. Therefore, due to the voltage applied by 
the feedback capacitor 52, any change in the slope of the 
sweep voltage caused by the voltage drop across the zener 
diode will be minimized. 
Thus, the modified circuit of FIG. 2 maintains the ad- 
vantage of FIG. 1 in that the zener diode still allows EL 
a substantially constant charging current through the re- 
sistor 26 which is substantially independent of changes 
in the positive potential. However, the circuit is no 
longer limited to a maximum sweep voltage as was 
FIG. 1. 
While the invention has been shown utilizing NPN 
type transistors it will be readily recognized by those 
skilled in the art that with minor modifications to  the 
circuit PNP, as well as other types of transistors, may be 
employed in the circuit with the proper polarity applied 
to the elements without departing from the spirit and 
soope of this invention. 
It should be further understood that the foregoing dis- 
closure relates only to preferred embodiments of the in- 
vention, and that it is intended to cover all changes and 
modifications of the examples of the invention herein 
chosen for the purpose of the disclosure which do not con- 
4 
stitute departures from the spirit and scope of the in- 
vention. 
What is claimed and desired to be seoured by Letters 
Patent is: 
1. A sawtooth voltage wave generator for producing 
sawtooth waveforms of increased linearity comprising: 
a switching transistor having a base, emitter, and c01- 
lector; 
an output transistor having a base, emitltir, aid cot- 
lector and biased for emitter follower operation; 
a charging capacitor connected between said switching 
transistor collector and emitter; 
means coupling said switching transistor collector to 
said output transducer base; 
a first diode connected with its anode to  a source of 
voltage; 
first resistor coupled at one side t o  the cathode of 
said first diode; 
a sewnd resistor connected between the other side of 
said first resistor and said switching transient col- 
lector; 
a diode means connected between said output transistor 
emitter and the junction of said first resistor and 
said second resistor for maintaining a constant cur- 
rent for said charging capacitor; and 
a capacitor connected between said one side of said 
first resistor and said switching transistor emitter and 
cooperating with said diode means to provide an in- 
creased period of response for said diode means 
whereby sawtooth waveforms of increased linearity 
are provided. 
2. A sawtooth voltage wave generator in accordance 
with claim 1 wherein said diode means is a zener diode. 
References Cited by the Examiner 
UNITED STATES PATENTS 
2,998,532 811961 Smeltzer _ _ _ _ _ _ _ _ _ _ _  307-88.5 
Waveforms by Chance et al., published by McGraw- 
5 
10 
I5 
20 
25 
30 
35 
40 OTHER REFERENCES 
Hill Book Co. (1949), pp. 269-270. 
46 
2,957,090 1011960 
3,001,086 911961 Martinez. 
50 3,031,583 4/1962 Murphy. 
ARTHUR GAUSS, Primary Examiner. 
J. S. HEYMAN, Assistant Examiner. 


Linear sawtooth voltage-wave generator employing transistor timing circuit having capacitor-zener diode combination feedback Patent

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