Solid state circuit for switching alternating current input signal as function of direct current gating transisto

Chapman, C. P.

Rupnik, D. R.

English

NASA Technical Reports Server

REPLY TO 
ARNOF: G p  
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
November 6, 1970 
TO : USI/Scientific P Technical Information Division 
Attention2 M i s s  Winnie I%. Morgan 
FROIvin GP/Office of Assiqtaqt General Counsel for  
Patent Matters 
SUBJECT: Announcement of NASA-Owned U. S. Patents i n  STAR 
In accordance with the procedures agreed upon by C o d e  GP 
and Code U S I ,  the attached NASA-awned U. S. Patent is being 
forwardea fo r  abstracting and announcement in NASA STAR. 
The following information is provided8 
U. S. Patent No. g 3,501,648 
Government or 
Corporate Employee Pasadena, California 91109 
Supplementary Corporate 
Source (if applicable) Jet .Propulsion Laboratory 
California Ins t i t u t e  of Technology 
NASA Patent C a s e  No. 3 XNP-06505 
NOTE - I f  t h i s  patent covers an invention made by a corporate 
employee of a NASA Contractor, the following is  applicable: 
Pursuant t o  Section 305 (a) of the National Aeronautics and 
Space Act, the name of the Administrator of NASA appxr s  on 
the first page of the patent; however, the name of the actual 
inventor (author) appears a t  the heading of Column No,  1 of 
Yes N O 0  
' - t h e  Specification, following 
Elizabeth A. C a r t e r  
Copy of Patent aited abws 2 
c 
Enclosure N 
g 
(NASA CR OR TMX OR AD NUMBER) 
https://ntrs.nasa.gov/search.jsp?R=19710015323 2020-03-17T02:58:09+00:00Z
SWITCHINO CIRCUIT 
Filed June 29, 1966 
i I 
- 2 0 v  
atesated 
3,501,648 
SWITCHING CIRCUIT 
James E. Webb, Administrator of the National Aero- 
nautics and Space Administration with respect lo  an 
invention of Carl P. Chapman, La &rewenti?, Calif., and 
Donald R. Rupnik, Snnland, Calif. 
Filed June 29. 1966, Ser. No. 562,933 
Int. CI. H03k 17/00 
PIS. CI. 307-254 4 elairas 
ABSIIZACF OF THE DISCLOSURE 
A solid state switching circuit is disclosed in which AC 
signals at an input terminal are switched to an output 
terminal through a gating transistor, as a function of the 
transistor's state of conduction. The state of conduction 
is controlled by controlling the DC potential difference 
between its emitter and base and by means of a pair of 
control transistors, forming part of a DC control circuit. 
The relative states of conduction of the control transistors 
which produce the potential difference are controlled as 
a function of the amplitude of a DC control signal. 
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 Aero- 
nautics and Space Act of 1958, Public Law 85-568 ( 7 2  
Stat. 435; 42 USC 2457). 
This invention relates to switching circuitry and, more 
particularly, to a solid state circuit for switching AC 
(alternating current) signals between input and output 
terminals as a function of Ix' (direct current) controlline 
signals. 
Generally. herebefore. DC control signals or voltage? 
have been used Io control or switch DC voltages to an 
appropriate DC load. I t  is a primary object o f t h e  pres- 
ent invention therefore to provide a novel circuit in which 
DC control voltages are used lo control the switching 
of AC signals. 
Another object of the present invention is to provide a 
stable solid state switching circuit for AC signals. 
A further object of the present invention is the pro- 
vkion of a solid state circuit employing transistors in 
which AC signals are switched in response to a DC con- 
trol signal or voltage. 
Still a further object of the present invention is to 
provide a simple relatively inexpensive transistorized 
rwitching circuit in which AC signals are switched in re- 
sponse to a DC control voltage of a selectable amplitude. 
These and other objects of the present invention are 
achieved by probiding a circuit in which the switching of 
AC signals. supplied to an input terminal. is controlled as 
a function of the \late of conduction of a conducting de- 
vice, such a$ a tramistor. When the transistor is i n  a 
nonconducting \late, the input AC signals, at the input 
terminal, are inhibited from beinc impressed or supplied 
to the output terminsl. However. when the transistor is in 
a conducting state, the input AC signals are impressed at 
the output terminal. The state of conduction of the tran- 
si5tor is controlled by a pair of transistors, the state of 
conduction of which is in turn controlled by the con- 
trolling DC control voltage. In the absence of a DC con- 
trol voltage of the desired amplitude, both transistors are 
substantially the same state of conduction, so that the 
transistor connected between the input and output termi- 
nals is in a nonconducting state. However. when a DC 
control signal of the desired amplitude is supplied to the 
pair of transi\tors, one of the transistors is in a state of 
conduction different from that of the other transistor, re- 
sulting in a potential difierence. which is impressed be- 
tween the base and emitter of the transistor connected 
between the input and output terminals. Conseqtlently, 
the latter transistor is switched to its conducting state, 
resulting in the input AC signals being impressed at the 
output terminal of the circuit. Thus, the switching of the 
AC signals between the input and output terminals is con- 
trolled by the DC control signal. 
The novel features that are considered characteristic 
of this invention are set forth with particulnrity in the 
10 appended claims. The invention itself both as to its or- 
ganization and method of operation, as wcll a s  additional 
objects and advantages thereof, will best be understood 
from the following description when read in connection 
with the accompanying drawing, which is a schematic 
15 diagram of the switching circuit of the present invention. 
Referring to the figure, there is shown a first seniicon- 
ductor device such as a PNP transistor 11 having its 
emitter l l e  connected to an input terminal 12 and its 
collector I l c  connected to an output terminal .13 and 
20 through a resistor R1 to a source of negative potential 
such as -20 volts. The emitter and collector may also 
be connected to the input and output terminals respec- 
tively through coupling capacitors C1 and C2 (or trans- 
formers). In addition, a variable resistor R2 may be 
25 placed hetween the emitter l l e  and the input terminal 12 
in order to control the gain produced by transistor 12. 
The transistor also includes a base l l b ,  which together 
with the emitter l l e ,  are connected to a scmiconductor 
control circuit, generally designated by numeral 15. 
In accordance with the teachings of the present inven- 
tion, AC signals supplied to input terminal 12 are alter- 
nately 1r:insferred to the output terminal 13 when tran- 
sistor 11 is in a conductive stale, which is in turn con- 
trolled by the potential difference between the base Plh 
35 and emitter l l r ,  produced by the control circuit IS. As 
seen from thc figure. circuit 15 comprises a pair of NPN 
transistors 16 and 17, each having its respective base 
16h, 176, collector 16c, 17c, and emitter 16e, P7e. Col- 
4o Iectors 16c and 17c are connected lo a source of posi- 
tive potential such as +20 volts, through resistors R3 
and R4, respectively. Also. collector 16c is connected to 
the emitter l l e  of transistor 11. The emitters 16e and 17e 
are connected to opposite ends of a resistor R5.'In the 
preferred embodiment of the invention, resistor RS com- *' prises a variable resistor, the movable arm of which is 
connected to a constant current source 20. The function 
of the latter circuit is to provide constant emitter cur- 
rent to the emitters of transistors I6 and 17, in order to 
stabilize the operation of the switching circuit hereinde- 
scribed. In one embodiment of the invention, the constant 
current source 20 comprised an NPN transi\tor 21 hav- 
ing its collector 21c connected lo the movable arm of 
reristor R5. with the emitter Zle being connected 'to the 
65 source of -20 volts through a rrsibtor R6. The base Ztb 
of transistor 21 was connected through a resistor R7 to 
a reference potential such as ground. with a 7mer diode 
Z1 being connected hetwcen the b a e  Zlh and the - 2 0  
volt source. Thc ba\e 166 of tran\istor 16 was connected 
through serially connected resistors R8 and R9. forming 
a voltage divider, to the ground potential. while the base 
17h of transistor 17 was connected to the junction point 
hetween the two resistors. comprising the voltage divider. 
The DC control voltage is supplied to an input terminal 
85 25 which i s  directly connected to the base 16h of 
transistor 16. 
From the foregoing description, and from the figure, 
it should be appreciated by those familiar with the art 
that in the absence of a DC control voltage of an am- 
70 plitude sufficient to produce large enough a potential 
difference between the base 1Pb and emitter l l r  of tren- 
sistor 11 In switch the trlrnsistor to its conductive stale. 
30 
3,501,648 
3 
the input AC signals at terminal 12 are inhibited from 
being impressed at output terminal 13. For example. with 
the moving arm in the middle of resistor R5, in the 
absence of a DC control voltage, transistors 16 and 17 
will be in the same state or level of conduction. The 
collector voltage of each transistor will be approximately 
12 volts DC with respect to ground potential. Thus the 
potential difference between the base and emitter of tran- 
sistor il will be substantially zero, maintaining the tran- 
sistor in the nonconducting slate. 
Furthermore, by unbalancing resistor R5, it is posiblc 
0 maintain transistor 16 at  a lower state of conduction b an that of transistor 17 without a DC control voltage, 
in which case the base 116 is at a higher potential than 
the emitter lle. However as long as the potential dif- 
ference is not negative during a complete cycle of the 
input AC signals, the base llb remains positive with 
respect to the emitter lle, no output signal is provided at 
output terminal 13. For example, resistor RS may be 
unbalanced so that the potential at 16c and 116 is + I O  
v. DC and that at 17c and lie is +I4 v. DC. However 
as long as the peaks of the AC signals do not exceed 4 
volts, no AC signal is provided at output termihal 13. 
However, by providing a DC control voltage of a suf- 
ficient amplitude at control terminal 25, due to the voltage 
dividing action of resistors RE and R9, the voltage at 
base 17b is less than that at base 16b. Consequently, 
transistor 16 is at a higher state of conduction than that 
of transistor 17 so that collector 16c and base Ilb con- 
nected thereto are at a lower voltage than interconnected 
collector 17c and base lle, resulting in transistor 11 being 
switched to a conducting state over the complete cycle 
of each input AC signal. Thus output AC signals are 
impressed at output terminal 13. It should again be 
pointed out that by adjusting R5, the amplitude of the DC 
control voltage necessary to provide the AC switching is 
controllable. 
In one actual reduction to practice of the novel switch- 
ing circuit of the present invention, the following list 
of component values and types were used. It should be ap- 
preciated that the list is presented for explanatory pur- 
poses only rather than as a limitation on the teachings 
disclosed herein. 
Component: Type or value 
11 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  2N328. 
16 and 17 2N2480. 
21-_______--~_______-_________ 2N1613. 
R l - - _ - - _ _ - _ - - _ _ _ _ _ - _ _ - - - - - - - - -  47K. 
R2 _____.______________________ IOOK variable. 
R3 ____________________________  lOOK ghw. 
, R4 ____._______________________ IOOK %w. 
RS .___________________________ IK variable. 
,' R6 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  33K :hW.  
R7 _.__________________________ 33K 1hw. :I R8 ____________________________  1K thw. 
R9 ____________________________  1K 'hw. 
Zl_-__________________________  Zener 6.2 v. 
C 1  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  1 mfd. 
C2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  1 mfd. 
. . In the aforementioned embodiment actually reduced 
to practice, the resistor R2 was adjusted so that the gain 
of transistor 11 was unity. The output of transistor 11 was 
found to be flat within +3 db in the frequency range 
between 6 cycles per second to 21.5 kc. By adjusting the 
variable resistor R5, the amplitude of the direct current 
signal at terminal 25 necessary to produce the AC switch- 
ing was made a variable between the limits of 0.1 v. 
DC and 5 v. DC. 
There has accordingly been shown and described herein 
a novel circuit for switching AC signals between input and 
output terminals us a function of the amplitude of a direct 
current control signal. The circuit of the invention incor- 
porates solid state semiconductor components which in- 
clude a first semiconductor transislor used to provide a 
4 
path for the AC signals bctwecn input and output terminals 
when it is switched to its conducting state, while inhibiting 
the flow of signals therebetween when being in the noncon- 
ductive state. The state of conduction of the particular 
transistor is controlled by a pair of transistors, which in the 
absence of a DC control signal of sufficient amplitude, 
maintains the transistor in a nonconductive state. How- 
ever, when the amplitude of the DC control signal reaches 
a selected amplitude, the two controlling transistors ark. 
switched to different states of conduction, because of the 
voltage divider RE, R9, providing a potential difference be- 
tween the base and emitter of the transistor connected be- 
tween the input and output terminals. Consequently, the 
latter transistor is switched to the conductive state and 
15 thereby provides a path for the AC signals from the input 
terminal to be supplied to the output terminals. 
It is appreciated that those familiar with the art may 
make modifications and/or substitute equivalents in the 
specific arrangements hereinbefore described for explana- 
20 tory purposes, without departing from the true spirit of the 
invention. Therefore, all such modifications and/or equiva- 
lents are deemed to fall within the scope of the invention 
as defined in the appended claims. 
What is claimed is: 
I. A signal switching circuit comprising: 
an input terminal for receiving alternating current input 
an output terminal; 
a first transistor having conductive and nonconductive 
states, coupled between said input and output termi- 
nals, for switching said input signals from said input 
terminal to said output terminal when said first tran- 
sistor is in said conductive state, said transistor having 
a base electrode, an emitter electrode coupled to said 
input terminal, and a collector electrode coupled to 
said output electrode; and 
semiconductor control means including second and third 
transistors respectively coupled to the base electrode 
and to the emitter electrode of said first transistor for 
selectively controlling the potential difference between 
the base and emitter electrodes of said first transistor 
in the absence of input signals to he a function of the 
relative conductive states of said second and third 
transistors. said potential difference including a 
selected potential difference of a fint polarity whereby 
said first transistor is in a nonconductive state so that 
an output signal is present a t  said output terminal 
only when the input signal a t  said input terminal has 
an amplitude above said selected potential difference 
and of a second polarity opposite said first polarity, 
said semiconductor control means further including 
means responsive to a directcurrent control signal for 
controlling the relative conduction states of said 8ec- 
ond and third transistors as  a function of a t  least the 
amplitude of said directcurrent control signal. 
25 
signals; 
30 
35 
40 
45 
50 
55 
2. A switching circuit comprising: 
an input terminal for receiving alternating current sig- 
an output terminal; 
a first source of reference potential; 
a first transistor having emitter, collector and base elec- 
trodes, said transistor being switchable between con- 
ductive and nonconductive states; 
means coupling the emitter and collector of said first 
transistor to said input and output terminals respec- 
tively; 
first resistive means coupled between said collector and 
said first source of reference potential; 
a control terminal for receiving a direct current control 
control means coupled to said control terminal and the 
emitter and base. electrodes of said first transistor for 
controlling the direct-current potential difference be- 
tween said emitter and base electrodes said control 
means including means for selectively controlling the 
nals; 
60 
65 
70 signal; and 
75 
3,501,648 
5 6 
p0teiili;il dilfercnce in the ahxncc of \aid direct ciir- 
rent control \ignal at said contriil terniind. tu bc o f  ii 
lirst pol;irity. wherehy stid firs! transislor is in a min- 
contliiclive sliitc. with said current signah which have 
;In amplitidc below >aid tirst potentiul dilfercnce he- 
ing inhihiled from being switched to  said output lei- 
niinal. 
3. The circuit defined in claim 2 wherein said control 
means include second and third transiston respectively 
coupled to the base and emitter electrodes of said first tran- 
sistor, and circuit means coupled to said first and second lo 
transistors and to raid cootrol terminal for  controlling said 
second and third transistors to be in selected states of con- 
duction so as to firovide a selected directturrent potential 2,979625 4/1961 Bothwell et ------- 307-239 
difference between the base and emitter electrodes of said 15 3*054*910 9/1962 Bothwell ------------ 307-23s 
first transistor when the amplitude of said control signal i s  3'173'023 3/1965 3,365,566 1/1968 Billings _ _ _ _ _ _ _ _ _ _ _ _  307-235 above a selected level. 
said third transistor to the emilter electrode of said first 
trmsistor. mentially adjtistuble conlrol tiie:ins for provid- 
ing the emitter electrodes of said second and third triinsiu- 
lory with controlluhle emitter ciirrenls, iind metins con- 
nected to wid wntrol terminal for conlrollinp the relalivL 
pcitentiitl~ at the colleclor electrodes of said second and 
lhird transistors as a function of the potentials at the edit- 
ter electrodes of said second and third transistors ~d the 
amplitudes of said control signal. 
i 
References Cited 
UNITED STATES PATENTS 
4. The circuit defined in claim 3 wherein each of said 
second and third transistors includes a base electrode, an 
emitter electrode and a collector electrode, said control 20 B. '. 
,oHN s, H E Y ~ A ~ ,  pimary ~~~~i~~~ 
Assistant Examiner 
means including means for coupling the collector electrode 
of said second transistor to the base electrode of said first 
transistor, means for coupling the collector electrode of 
US. C1. X.R. 
307-235, 237; 330-30 


Switching circuit Patent

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