March 17, 1959
woo F, cHow ETAL
2,878,386
STABLE TRANSISTOR OSCILLATOR
Filed Feb. 26, 1957
FlG.l.
15
INVENTORI
WOO F. CHOW ,
DEAL!) A. PAYNTER ,
TH
‘M
TTORNEY
United States Patent 0 "ice
2,878,386
Patented Mar. 17, 1959
2
best be understood by reference to the following descrip
tion taken in connection with the accompanying drawing
in which Fig. l is a circuit diagram illustrating one embod
iment of our invention; Fig. 2 is a circuit diagram similar
to the circuit of Fig. l in a form modi?ed for facilitating
2,878,386
STABLE TRANSISTOR OSCILLATOR
Woo F. Chow and Donald A. Paynter, Syracuse, N. _Y.,
assignors to General Electric Company, a corporation
of New York
Application February 26, 1957, Serial No. 642,429
5 Claims. (Cl. 250-36)
an impedance analysis of the circuit; Fig. 3 is the T-equiv
alent circuit of the transistor shown in Figs. 1 and 2; and
Fig. 4 is a simpli?ed equivalent circuit of the circuit
of Fig. 2.
Referring now to the drawings, in Fig. 1 we have
10
shown an NPN transistor 10 having base electrode l1,_
emitter electrode 12 and collector electrode 13. An emit
ter biasing resistor R, is connected between emitter elec
trode l2 and a common point 14 which may be main
Our invention relates to stable transistor oscillators 15 tained at ground potential as indicated. A base biasing
and more particularly to transistor oscillators employing
resistor R1 is connected between base electrode 11 and
series resonant L-C circuits for stabilization.
common point 14. A load impedance R1, is connected
In the prior art it has been conventional to stabilize
between collector electrode 13 and terminal 15, terminal
oscillators by the use of inductor (L) and capacitor (C)
15 being connected to a source of potential V+, the other
circuits for moderate degrees of stability, and by the use 20 side of which is connected to ground. Dropping or volt
of non-linear components such as crystals where the need
age dividing resistor R, is connected between base elec
for a greater degree of stability justi?es the expense.
trode 11 and terminal 15. An inductor L2 and a capaci~
Both series and parallel L-C circuits have been used
tor C3 are connected in series across emitter biasing re
to stabilize oscillators. Among the circuits employing
sistor R, and an inductor L, and capacitor C1 are con
series L-C resonance is an oscillator described by J. K. 25 nected in series across base biasing resistor R1.
Clapp in his article “An inductance-capacitance oscillator
The circuit of Fig. 1 illustrates one embodiment of the
of unusual frequency stability,” Proceedings of the
tuned emitter, tuned base oscillator of our invention. The
I. R. B, vol. 36, p. 356, March 1948. Various modi?ca
D. C. circuit includes the four resistors R1, R2, R3, and
tions employing series L-C resonant combinations have
R1, and the voltage supply V+. The values of these re
also been devised.
30 sistances can be selected on the basis of standard ampli
In stabilizing the frequency of a transistor oscillator
?er design procedure, subject to the modi?cations which
with L-C combinations it is desirable that the values of
will appear later in the analysis of the oscillator circuit.
the external inductances and capacitances control the
This resistor con?guration is suitable for good D. C. sta
frequency of oscillation to the substantial exclusion of
bilization. The two series tuned L-C networks, compris
variations in the transistor parameters or the oscillator 35 ing inductor L1 and capacitor C1 and inductor L2 and
supply voltage. Since L-C components can be made very
capacitor C, respectively, form the resonant elements of
stable, at high degree of frequency stability can then be
the oscillator network. Oscillation will occur when the
achieved without the use of elaborate non-linear com
negative resistance present from base 11 of transistor 10
pensation techniques.
to the common terminal 14 is sut?cient to cancel the
Accordingly, it is a principal object of our invention 40 losses in the resonant circuit formed by inductor L1 and
to provide a stable transistor oscillator.
Another object of our invention is to provide a tran
capacitor C1.
‘
Turning now to Fig. 2, we have shown the circuit of
Fig. 1 re-drawn to facilitate a mathematical analysis. Re
sistances r; and r, are the internal loss resistances of L;
sistor oscillator having a high degree of stability without
necessitating the use of non-linear circuit elements.
A further object of our invention is to provide a stable 45 and L3 respectively and Rh is given by
transistor oscillator employing series resonant L-C net
works.
RlRa
A still further object of our invention is to provide a
R1+R8
stable transistor oscillator employing series resonant L-C
where R, and R, are the same as indicated in Fig. l. The
networks which will provide a higher degree of stability
than has been heretofore obtainable by the use of such
networks.
In carrying out our invention in one form thereof, a
50 remainder of the circuit differs from the circuit of Fig. 1
transistor having base, emitter and collector electrodes is
connected in common emitter con?guration and provided 55
with proper biasing means in order to establish a stable
D. C. operating point. A series resonant L-C network is
connected from the transistor emitter electrode to a com
only in that the source of voltage is not shown.
The impedance Z; in the base circuit externally between
base electrode 11 and common point 14 is given by
(1)
mon point. The values of inductance and capacitance
in this network are selected in order to insure oscillation 60 The impedance Z, in the emitter circuit between emitter
in the circuit. A second series L-C network is connected
electrode 12 and common point 14 is given by
from the transistor base electrode to the common point.
The combined values of inductance and capacitance in the
two series resonant L-C networks determine the fre
quency of oscillation of the transistor oscillator circuit 66
to the substantial exclusion of variations in supply voltage
and transistor parameters resulting from temperature
changes and other eliects.
Consider the T-equivalent circuit for transistor 10 as
shown in Fig. 3, where n,’ represents the transistor equiv
alent base resistance at high frequencies, ra represents the
in the appended claims. Our invention itself, however, 70 emitter resistance, 2,, represents the collector impedance
together with further objects and advantages thereof, can
and it represents the current gain. Since 2;, of Equation
The novel features which we believe to be charac
teristic of our invention are set forth with particularity
2,878,386
3
4
In order to maintain oscillation
2, is in series with the emitter resistance re the input im
pedance Z; of the common emitter stage is
E l6)z[r.+w.bl+<r.'+r.+r.>(1+1)] (13)
(I)
w
2
was
From Equation 11 we have the frequency of oscillation
(14)
10
(15)
15
Thus, the frequency of oscillation is very nearly the res
onant frequency of the circuit formed by the series con
nection of L1, I4, C1, and C2 and the circuit will oscillate
provided that L2 and C2 are chosen according to the con
20 dition stated in Equation 13.
One set of values for the embodiment shown in Fig. 1
illustrating a typical operational design is as follows:
“a: the low frequency a
R1=R,=R3 ______________________ __ohms__
10K
L1=L3
C3
1;, -----------------------------_______________________________
_________________________ .._llh_._
__d0_____
.._/1,uf__
1
t0 110
frequency at which a is 3 db below its low frequency
C1 _______________________________ "MAL-
510
value :10.
‘1+ ____________________________ __volts__
and
wc=2irfv where f,l is the a cutoff frequency which is the
When the frequency is near the resonant frequency f0 30
of L1><C, and Lgxcg, the e?ect of Rb and R, can be
Transistor
10
_______ .._. _________________ __
20
2N78
1 Variable.
The inductances of inductors L1 and L2 are adjusted
for the desired frequency and the amount of feedback,
as is indicated by good sinusoidal output at the transistor
35 collector 13. The stability with respect to supply voltage
neglected, thus
variations of the above circuit is of the order of 7
parts per million per 12% variation of voltage. This de
gree of stability is a considerable improvement over the
Combining Equations 3, 4, 5, 6 and 8 and simplifying
stability of the above-mentioned Clapp oscillator for in
the result by assuming R1, is of the order of 103 ohms and 40 stance, which in its transistorized form is of the order of
200 to 400 parts per million for a 10% variation in sup
ply voltage as speci?ed by E. Keonjian in his article
“Stable transistor oscillator,” IRE Transactions of
we have
PGCT, vol. CT-3, No. 1, p. 38, March 1956.
The above circuit analysis and comparison with the
45 corresponding Clapp oscillator show that the series—
tuned base, series-tuned emitter transistor-oscillator of
the present invention is capable of producing A. C.
voltages of excellent frequency stability without the use
of non-linear compensation techniques.
(9)
It will be obvious to those skilled in the art that
A simpli?cation of the circuit of Fig. 2 is shown in 50
other biasing configurations can be used employing at the
Fig. 4 from which the loop impedance is
same time the circuitry of our invention.
Thus, while
we have shown a particular embodiment of our invention,
it will be understood, of course, that we do not wish
55 to be limited thereto since many modi?cations may be
made and we therefore contemplate by the appended
(10)
At the resonant frequency of the entire circuit of Fig. 4
80 Patent of the United States is:
1. A series tuned transistor oscillator comprising a
wL1--;1C—l+wL=-;-1@—%(n+r=)=0
transistor having base, emitter and collector electrodes,
or
sL‘1-i+=-,L=--1—=i’-"(r.+rn
wC';
we; a:
claims to cover any such modi?cations as fall within the
true spirit and scope of our invention.
What we claim as new and desire to secure by Letters
(11>
In order to produce oscillation a‘ncg‘ative resistance in
the impedance 2, must exist. Thus
biasing means connected to said transistor electrodes for
establishing a stable direct current operating point for
65 said transistor, a series tuned inductance-capacitance
network connected from said emitter to a common point,
a load impedance connected from said collector elec
trode through a source of potential to said common point,
said load impedance being small compared with the out
70 put impedance of said transistor, and a series tuned in
ductance-capacitance network connected from said base
electrode to said common point, whereby the frequency
of oscillation of said oscillator will be substantially de
termined by said series tuned inductance-capacitance net
works.
2,878,886
5
6
minal; a load impedance connected between said col‘
lector electrode and the other terminal of said source,
transistor having base, emitter and collector electrodes,
said load impedance being small compared with the out~
biasing means connected to said transistor electrodes for
put impedance of said transistor; a voltage dividing re
establishing a stable direct current operating point for
sistor connected between said base electrode and said
said transistor, a series tuned inductance-capacitance net
other terminal; a series tuned inductance-capacitance
work connected from said emitter electrode to a common
network connected across said base biasing resistor; and
point, said inductance-capacitance network providing a
a series tuned inductance-capacitance network connected
capacitive reactance which is large at the frequency of
across said emitter biasing resistor, said emitter induct
oscillation compared with its inductive reactance and the
ance-capacitance network providing a capacitive react
10
input resistive components of said transistor, 21 load im
ance which is large at the frequency of oscillation com
pedance connected from said collector electrode through
pared with its inductive reactance and the input resistive
a source of potential to said common point, said load im
components whereby the values of the two series tuned
2. A series tuned transistor oscillator comprising a
pedance being small compared with the output impedance
inductance-capacitance networks determine the frequency
of said transistor and a series tuned inductance-capaci
tance network connected from said base electrode to 15 of oscillation to the substantial exclusion of the variation
in transistor parameters.
said common point whereby the effect of variations of
5. A series tuned transistor oscillator comprising a
transistor parameters on the frequency of oscillation of
transistor having base, emitter, and collector electrodes,
said oscillator are minimized, said frequency being sub
stantially determined by said series tuned inductance
a source of direct current potential, resistance means
transistor having base, emitter and collector electrodes,
connected between said transistor electrodes and said
source for establishing a stable direct current operating
point for said transistor, a load impedance connected
biasing means connected to said transistor electrodes for
establishing a stable direct current operating point for
said transistor, a ?rst inductor and a ?rst capacitor con
nected in series from said emitter electrode to a common
capacitance network connected from said emitter to said
common point, said emitter network proportioned to
capacitance networks.
3. A series tuned transistor oscillator comprising a
from said collector electrode through a source of po
tential to said common point, a series tuned inductance
have a net capacitive reactance so as to present a nega
point, said ?rst capacitor being small enough to provide
tive input resistance between said base and said common
a capacitive reactance which is large at the frequency of
point, a series tuned inductance-capacitance network
oscillation compared to the combined impedance of said
?rst inductor and the input resistive components of said 30 connected from said base to said common point so as
to oscillate in conjunction with said negative input re
transistor, a load impedance connected from said collec
sistance, the inductance-capacitance values of said series
tor electrode through a source of potential to said com
tuned circuits determining the frequency of oscillation to
mon point, said load impedance being small compared
the substantial exclusion of variations in transistor pa
with the transistor output impedance, and a second in
ductor and a second capacitor connected in series from 35 rameters.
said base electrode to said common point whereby the
References Cited in the ?le of this patent
combined values of said inductors and capacitors deter
mine the frequency of oscillation of said oscillator.
UNITED STATES PATENTS
4. A series tuned transistor oscillator comprising a
transistor having base, emitter and collector electrodes;
a source of direct current potential; a base biasing re
sistor connected between said base electrode and one ter
minal of said source; an emitter biasing resistor con
nected between said emitter electrode and said one ter
40
1,896,781
2,382,954
Llewellyn ____________ __ Feb. 7, 1933
Beaudoin ____________ __ Aug. 21, 1945
2,438,382
2,750,508
Born _______________ __ Mar. 23, 1948
Waldhaur ___________ __ June 12, 1956