U.S. patent application number 09/800305 was filed with the patent office on 2001-09-06 for microwave oscillation circuit using a dielectric resonator.
Invention is credited to Kose, Yasushi, Ogisou, Akihiro.
Application Number | 20010019293 09/800305 |
Document ID | / |
Family ID | 18579570 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019293 |
Kind Code |
A1 |
Kose, Yasushi ; et
al. |
September 6, 2001 |
Microwave oscillation circuit using a dielectric resonator
Abstract
In a microwave oscillation circuit using a dielectric resonator,
a bias resistor for determining a bias voltage supplied to a base
terminal of a transistor is located in the neighborhood of a
connection point between a feedback circuit side stub for the
dielectric resonator and the base terminal of the transistor. The
bias resistor has a resistance which basically determines a bias
voltage supplied to the base terminal of the transistor and which
is enough to make high the impedance of a bias voltage supplying
circuit including the bias resistor, viewed at the input terminal
of the transistor. Thus, a stable oscillation can be maintained
independently of variation in a load impedance.
Inventors: |
Kose, Yasushi; (Tokyo,
JP) ; Ogisou, Akihiro; (Tokyo, JP) |
Correspondence
Address: |
HELFGOTT & KARAS, P.C.
EMPIRE STATE BUILDING
60TH FLOOR
NEW YORK
NY
10118
US
|
Family ID: |
18579570 |
Appl. No.: |
09/800305 |
Filed: |
March 2, 2001 |
Current U.S.
Class: |
331/99 ;
331/117D; 331/117FE; 331/117R |
Current CPC
Class: |
H03B 5/1864
20130101 |
Class at
Publication: |
331/99 ;
331/117.00R; 331/117.0FE; 331/117.00D |
International
Class: |
H03B 005/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2000 |
JP |
2000-59068 |
Claims
1. A microwave oscillation circuit comprising a dielectric
resonator located on a dielectric substrate, a first high frequency
transmission line formed on said dielectric substrate and having
one end coupled to said dielectric resonator at a resonation
frequency, and a second high frequency transmission line formed on
said dielectric substrate and having one end coupled to said
dielectric resonator at said resonation frequency, and a transistor
mounted on said dielectric substrate and having an input terminal
connected to the other end of said first high frequency
transmission line and an output terminal connected to the other end
of said second high frequency transmission line, so that when said
transistor is driven with a DC voltage, said transistor oscillates
so that an oscillation output is outputted from said output
terminal of said transistor, the microwave oscillation circuit
further includes a bias resistor located in the neighborhood of a
connection point between said other end of said first high
frequency transmission line and said input terminal of said
transistor, said bias resistor having a resistance which basically
determines a bias voltage supplied to said input terminal of said
transistor and which is enough to make high the impedance of a bias
voltage supplying circuit including said bias resistor, viewed at
said input terminal of said transistor.
2. A microwave oscillation circuit claimed in claim 1, wherein said
bias resistor is located in a range of a distance of not greater
than .lambda.g/6 from said connection point between said other end
of said first high frequency transmission line and said input
terminal of said transistor, where .lambda.g is a wavelength at
said dielectric substrate of said resonation frequency.
3. A microwave oscillation circuit claimed in claim 2, wherein said
transistor is a bipolar transistor, so that said input terminal of
said transistor is a base terminal of the bipolar transistor, and
said output terminal of said transistor is a collector terminal of
the bipolar transistor, an emitter terminal of the bipolar
transistor being connected to ground.
4. A microwave oscillation circuit claimed in claim 2, wherein said
transistor is a field effect transistor, so that said input
terminal of said transistor is a gate terminal of the field effect
transistor, and said output terminal of said transistor is a drain
terminal of the field effect transistor, a source terminal of the
bipolar field effect being connected to ground.
5. A microwave oscillation circuit claimed in claim 2, further
including a DC voltage supplying conductor pattern laid out on said
dielectric substrate, a fine-adjusting bias resistor located on
said dielectric substrate and having one end connected to said DC
voltage supplying conductor pattern, a bias voltage supplying
conductor pattern laid out on said dielectric substrate and having
one end connected to the other end of said fine-adjusting bias
resistor, said bias voltage supplying conductor pattern extending
near to said input terminal of said transistor, said bias resistor
having one end connected to the other end of said bias voltage
supplying conductor pattern and the other end connected to said
first high frequency transmission line in the neighborhood of said
connection point between said other end of said first high
frequency transmission line and said input terminal of said
transistor.
6. A microwave oscillation circuit claimed in claim 5, further
including a second bias resistor located near to said DC voltage
supplying conductor pattern and having one end connected to said DC
voltage supplying conductor pattern, and a drive voltage supplying
conductor pattern laid out on said dielectric substrate and having
one end connected to the other end said second bias resistor, said
drive voltage supplying conductor pattern extending to a connection
point between said other end of said second high frequency
transmission line and said output terminal of said transistor, for
supplying a drive voltage to said output terminal of said
transistor.
7. A microwave oscillation circuit claimed in claim 6, further
including an open stub formed on said dielectric substrate to
extend from said drive voltage supplying conductor pattern and to
function as a capacitor for making high the impedance of a drive
voltage supplying circuit including said drive voltage supplying
conductor pattern, viewed from said second high frequency
transmission line.
8. A microwave oscillation circuit claimed in claim 2, further
including a DC voltage supplying conductor pattern laid out on said
dielectric substrate, a second bias resistor located near to said
DC voltage supplying conductor pattern and having one end connected
to said DC voltage supplying conductor pattern, and a drive voltage
supplying conductor pattern laid out on said dielectric substrate
and having one end connected to the other end said second bias
resistor, said drive voltage supplying conductor pattern extending
to a connection point between said other end of said second high
frequency transmission line and said output terminal of said
transistor, for supplying a drive voltage to said output terminal
of said transistor.
9. A microwave oscillation circuit claimed in claim 8, further
including an open stub formed on said dielectric substrate to
extend from said drive voltage supplying conductor pattern and to
function as a capacitor for making high the impedance of a drive
voltage supplying circuit including said drive voltage supplying
conductor pattern, viewed from said second high frequency
transmission line.
10. A microwave oscillation circuit claimed in claim 1, wherein
said transistor is a bipolar transistor, so that said input
terminal of said transistor is a base terminal of the bipolar
transistor, and said output terminal of said transistor is a
collector terminal of the bipolar transistor, an emitter terminal
of the bipolar transistor being connected to ground.
11. A microwave oscillation circuit claimed in claim 1, wherein
said transistor is a field effect transistor, so that said input
terminal of said transistor is a gate terminal of the field effect
transistor, and said output terminal of said transistor is a drain
terminal of the field effect transistor, a source terminal of the
bipolar field effect being connected to ground.
12. A microwave oscillation circuit claimed in claim 1, further
including a DC voltage supplying conductor pattern laid out on said
dielectric substrate, a fine-adjusting bias resistor located on
said dielectric substrate and having one end connected to said DC
voltage supplying conductor pattern, a bias voltage supplying
conductor pattern laid out on said dielectric substrate and having
one end connected to the other end of said fine-adjusting bias
resistor, said bias voltage supplying conductor pattern extending
near to said input terminal of said transistor, said bias resistor
having one end connected to the other end of said bias voltage
supplying conductor pattern and the other end connected to said
first high frequency transmission line in the neighborhood of said
connection point between said other end of said first high
frequency transmission line and said input terminal of said
transistor.
13. A microwave oscillation circuit claimed in claim 12, further
including a second bias resistor located near to said DC voltage
supplying conductor pattern and having one end connected to said DC
voltage supplying conductor pattern, and a drive voltage supplying
conductor pattern laid out on said dielectric substrate and having
one end connected to the other end said second bias resistor, said
drive voltage supplying conductor pattern extending to a connection
point between said other end of said second high frequency
transmission line and said output terminal of said transistor, for
supplying a drive voltage to said output terminal of said
transistor.
14. A microwave oscillation circuit claimed in claim 13, further
including an open stub formed on said dielectric substrate to
extend from said drive voltage supplying conductor pattern and to
function as a capacitor for making high the impedance of a drive
voltage supplying circuit including said drive voltage supplying
conductor pattern, viewed from said second high frequency
transmission line.
15. A microwave oscillation circuit claimed in claim 1, further
including a DC voltage supplying conductor pattern laid out on said
dielectric substrate, a second bias resistor located near to said
DC voltage supplying conductor pattern and having one end connected
to said DC voltage supplying conductor pattern, and a drive voltage
supplying conductor pattern laid out on said dielectric substrate
and having one end connected to the other end said second bias
resistor, said drive voltage supplying conductor pattern extending
to a connection point between said other end of said second high
frequency transmission line and said output terminal of said
transistor, for supplying a drive voltage to said output terminal
of said transistor.
16. A microwave oscillation circuit claimed in claim 15, further
including an open stub formed on said dielectric substrate to
extend from said drive voltage supplying conductor pattern and to
function as a capacitor for making high the impedance of a drive
voltage supplying circuit including said drive voltage supplying
conductor pattern, viewed from said second high frequency
transmission line.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a microwave oscillation
circuit, and more specifically to a microwave oscillation circuit
using a dielectric resonator.
[0002] Referring to FIG. 2, there is shown a simplified circuit
layout pattern diagram of a microwave oscillation circuit of the
type which uses a dielectric resonator and which is used at a low
gain at an operating frequency. The shown microwave oscillation
circuit includes a dielectric resonator 53 mounted on a not-shown
dielectric substrate, a pair of stubs 51 and 52 each formed on the
not-shown dielectric substrate and located adjacent to the
dielectric resonator 53 to be coupled with the dielectric resonator
53 at a resonation frequency, a bipolar transistor or a field
effect transistor 54 located on the not-shown dielectric substrate
and electrically connected to the pair of stubs 51 and 52,
respectively, and an oscillation output terminal 56 connected to
the stub 52. The transistor 54 is driven with DC voltages supplied
from a biasing circuit 55 including bias resistors.
[0003] The dielectric resonator 53 is formed of a solid body of
dielectric material having a large dielectric constant sufficient
to operate as a resonator. The stub 52 and the dielectric resonator
53 constitute a microwave resonating circuit, and the stub 51 and
the dielectric resonator 53 constitutes a feedback circuit for the
transistor 54.
[0004] The oscillation circuit is constituted of the transistor 54,
the stubs 51 and 52 and the dielectric resonator 53. An oscillation
signal generated in the oscillation circuit thus formed is picked
out from the oscillation output terminal 56. Therefore, the
transistor 54, the stubs 51 and 52, the dielectric resonator 53,
and the oscillation output terminal 56 constitutes a high frequency
circuit (microwave circuit).
[0005] As mentioned above, the transistor 54 is formed of either a
bipolar transistor or a field effect transistor. When the
transistor 54 is formed of the bipolar transistor, an emitter
terminal of the bipolar transistor is connected to ground. A base
terminal and a collector terminal of the bipolar transistor are
connected to the stub 51 and the stub 52, respectively. On the
other hand, when the transistor 54 is formed of the field effect
transistor, a source terminal of the field effect transistor is
connected to ground. A gate terminal and a drain terminal of the
field effect transistor are connected to the stub 51 and the stub
52, respectively. The biasing circuit 55 supplies necessary DC
voltages to the base (or the gate) and the collector (or the drain)
of the transistor 54, respectively, and therefore is constituted
independently of the high frequency circuit as mentioned above.
[0006] For only convenience, the following description will be
described under the assumption that the transistor 54 is formed of
the bipolar transistor, but it should not be forgotten that as
mentioned above, the transistor 54 can be formed of either a
bipolar transistor or a field effect transistor.
[0007] In the above mentioned microwave oscillation circuit having
the above mentioned construction, if the impedance of a load
connected to the oscillation output terminal 56 varies, the
impedance of the stub 52 correspondingly varies, with the result
that the oscillation characteristics varies, and simultaneously, an
operation stability at the side of the stub 51 becomes
deteriorated. Specifically, when the impedance of the load varies,
the oscillation output level becomes unstable, and in an extreme
case, the oscillation stops.
[0008] Furthermore, since the oscillation circuit is of the
feedback type, an isolation between the base and the collector of
the transistor 54 (between the gate and the drain in the case of
the field effect transistor) is not so good, so that variation on
the output side is transferred to the base (or the gate), with the
result that the unstability becomes large.
BRIEF SUMMARY OF THE INVENTION
[0009] Accordingly, it is an object of the present invention to
provide a microwave oscillation circuit using a dielectric
resonator, which has overcome the above mentioned problems of the
prior art.
[0010] Another object of the present invention is to provide a
microwave oscillation circuit using a dielectric resonator, capable
of maintaining a stable oscillation independently of variation in a
load impedance.
[0011] The above and other objects of the present invention are
achieved in accordance with the present invention by a microwave
oscillation circuit comprising a dielectric resonator located on a
dielectric substrate, a first high frequency transmission line
formed on the dielectric substrate and having one end coupled to
the dielectric resonator at a resonation frequency, and a second
high frequency transmission line formed on the dielectric substrate
and having one end coupled to the dielectric resonator at the
resonation frequency, and a transistor mounted on the dielectric
substrate and having an input terminal connected to the other end
of the first high frequency transmission line and an output
terminal connected to the other end of the second high frequency
transmission line, so that when the transistor is driven with a DC
voltage, the transistor oscillates so that an oscillation output is
outputted from the output terminal of the transistor, the microwave
oscillation circuit further includes a bias resistor located in the
neighborhood of a connection point between the other end of the
first high frequency transmission line and the input terminal of
the transistor, the bias resistor having a resistance which
basically determines a bias voltage supplied to the input terminal
of the transistor and which is enough to make high the impedance of
a bias voltage supplying circuit including the bias resistor,
viewed at the input terminal of the transistor.
[0012] With this arrangement, since the bias resistor for basically
determining the bias voltage supplied to the input terminal of the
transistor is located in the neighborhood of the connection point
between the input terminal of the transistor and the other end of
the first high frequency transmission line, although the microwave
oscillation circuit behaves as a distributed parameter circuit, the
impedance of the bias voltage supplying circuit viewed at the input
terminal of the transistor becomes high by action of the resistance
of the bias resistor. As the result, a high-frequency impedance of
a microwave circuit at an input terminal side of the transistor is
stabilized, and the amplitude modulation of the bias voltage
supplied to the input terminal of the transistor, caused by the
oscillation component, is avoided. Therefore, the oscillation
stability is improved, and the oscillation output level are
stabilized. Therefore, it is possible to completely avoid the stop
of the oscillation caused by a variation in the impedance of the
load.
[0013] The above and other objects, features and advantages of the
present invention will be apparent from the following description
of preferred embodiments of the invention with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a circuit layout pattern diagram of one embodiment
of the microwave oscillation circuit in accordance with the present
invention of the type using a dielectric resonator; and
[0015] FIG. 2 is a simplified circuit layout pattern diagram of a
conventional microwave oscillation circuit of the type using a
dielectric resonator.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Referring to FIG. 1, there is shown a circuit layout pattern
diagram showing one embodiment of the microwave oscillation circuit
in accordance with the present invention, which is constituted by
using a microstrip line.
[0017] In FIG. 1, the reference number 100 designates a dielectric
substrate. The microwave oscillation circuit includes a stub (first
high frequency transmission line) 1 and a stub (second high
frequency transmission line) 2 formed on the dielectric substrate
100 each to form a microstrip line optimum to an oscillation
frequency of the microwave oscillation circuit. A dielectric
resonator 3 is located on the dielectric substrate 100 between one
end 1A of the stub 1 and one end 2A of the stub 2, so that the
dielectric resonator 3 is coupled with the stubs 1 and 2 at a
resonation frequency f.sub.o. The dielectric resonator 3 is formed
of a solid body of dielectric material having a large dielectric
constant sufficient to operate as a resonator. A transistor 4,
which is a discrete component and which is constituted of either a
bipolar transistor or a field effect transistor, is located on the
dielectric substrate 100 to be electrically connected to the other
end 1B of the stub 1 and the other end 2B of the stub 2,
respectively. In this construction, the one end 1A of the stub 1
and the one end 2A of the stub 2 have an infinite impedance.
[0018] For only convenience of explanation, the following
description will be made under the assumption that the transistor 4
is constituted of a bipolar transistor. In the case that the
transistor 4 is constituted of a field effect transistor, the
following description should be read while replacing a base, a
collector and an emitter by a gate, a drain and a source,
respectively, as will be apparent to persons skilled in the art.
Furthermore, it should be understood in the specification that, the
term "an input terminal of the transistor" means a base terminal of
the bipolar transistor in an emitter grounded transistor circuit,
and a gate terminal of the field effect transistor in a source
grounded transistor circuit, and the term "an output terminal of
the transistor" means a collector terminal of the bipolar
transistor in the emitter grounded transistor circuit, and a drain
terminal of the field effect transistor in the source grounded
transistor circuit.
[0019] A base terminal of the transistor 4 is electrically
connected to the other end 1B of the stub 1, and a collector
terminal of the transistor 4 is electrically connected to the other
end 2B of the stub 2. An emitter terminal of the transistor 4 is
electrically connected to a grounded conductor pattern 16 laid out
on the dielectric substrate 100, in the proximity of the other end
of each of the stubs 1 and 2.
[0020] Furthermore, oscillation outputting conductor patterns 6 and
17 are formed on the dielectric substrate 100 to form a microstrip
line optimum to the oscillation frequency of the microwave
oscillation circuit. The oscillation outputting conductor pattern 6
extends from the other end 2B of the stub and 2. The oscillation
outputting conductor pattern 17 extends toward an edge of the
dielectric substrate 100 from a position slightly apart from an
outer end of the oscillation outputting conductor pattern 6. An
output load capacitor 15 is electrically connected between the
outer end of the oscillation outputting conductor pattern 6 and an
inner end of the oscillation outputting conductor pattern 17.
[0021] In the above mentioned construction, the stub 2 and the
dielectric resonator 3 constitute a microwave resonating circuit,
and the stub 1 and the dielectric resonator 3 constitutes a
feedback circuit for the transistor 4. The stubs 1 and 2 and the
dielectric resonator 3 functions as a positive feedback circuit for
the transistor 4, so that the stubs 1 and 2, the dielectric
resonator 3 and the transistor 4 constitute an oscillation circuit.
An oscillation outputted generated in the oscillation circuit is
picked up through the oscillation outputting conductor pattern 6,
the output load capacitor 15 and the oscillation outputting
conductor pattern 17.
[0022] The above mentioned construction constitutes a microwave
circuit. Now, a DC voltage supplying circuit for driving the
transistor 4 will be described.
[0023] A DC voltage supplying conductor pattern 5 is laid out on
the dielectric substrate 100, and a base bias voltage supplying
conductor pattern 9 is laid out on the dielectric substrate 100 to
extend from a position slightly apart from the DC voltage supplying
conductor pattern 5 to bypass the dielectric resonator 3 and to
reach a position slightly apart from a connection point between the
other end 1B of the stub 1 and the base terminal of the transistor
4. A fine-adjusting base bias resistor 7 is connected between the
DC voltage supplying conductor pattern 5 and one end of the base
bias voltage supplying conductor pattern 9, and a main base bias
resistor 8 is connected between the other end of the base bias
voltage supplying conductor pattern 9 and the stub 1 at a position
in the neighborhood of the connection point between the other end
of the stub 1 and the base of the transistor 4.
[0024] In addition, a collector voltage supplying conductor pattern
11 is laid out on the dielectric substrate 100 to extend from
another position slightly apart from the DC voltage supplying
conductor pattern 5 to reach a connection point between the stub 2
and the oscillation outputting conductor pattern 6. A collector
bias resistor 10 is connected between the DC voltage supplying
conductor pattern 5 and one end of the collector voltage supplying
conductor pattern 11. An open stub 12 is formed on the dielectric
substrate 100 and a base end of the open stub 12 is connected to
the collector voltage supplying conductor pattern 11. This open
stub 12 can be either in the form of a sector as shown in FIG. 1 or
in the form of an elongated rectangle.
[0025] Furthermore, another grounded conductor pattern 14 is laid
out on the dielectric substrate 100 near to the DC voltage
supplying conductor pattern 5. A low frequency parasite oscillation
preventing capacitor 13 is electrically connected between the DC
voltage supplying conductor pattern 5 and the grounded conductor
pattern 14.
[0026] In the above mentioned arrangement, for example, DC 5V is
supplied to the DC voltage supplying conductor pattern 5. The base
bias resistors 7 and 8 and the base bias voltage supplying
conductor pattern 9 determines a base bias voltage which is applied
to the base of the transistor 4 so as to determine a collector
current of the transistor 4. Here, assuming that the base bias
resistor 7 has the resistance Rb2, the base bias resistor 8 has the
resistance Rb1, and the resistance of the base bias voltage
supplying conductor pattern 9 is negligible, it is in an ordinary
case that the resistance {Rb1+Rb2} is on the order of 5k.OMEGA. to
15k.OMEGA.. In addition, the resistors 7, 8 and 10 and the
capacitors 13 and 15 are ordinarily constituted of chip components.
In this case, a coarse resistance adjustment is carried out by the
base bias resistor 8 and a fine resistance adjustment is carried
out by the base bias resistor 7.
[0027] The base bias resistor 8 is located in the extreme
neighborhood of a connection point between the other end of the
stub 1 and the base of the transistor 4. Ordinarily, the base bias
voltage supplying conductor pattern 9 has a conductor width of
about 50 .mu.m to 100 .mu.m, although it is in now way limited to
these values.
[0028] The collector bias resistor 10 and the collector voltage
supplying conductor pattern 11 constitutes a collector voltage
supplying circuit for the transistor 4. The open stub 12 connected
to the collector voltage supplying conductor pattern 11 functions
as a capacitor to cause the collector voltage supplying circuit to
have a high impedance when it is viewed from the microwave circuit
(namely, when it is viewed from the stub 2), so that the
oscillation output is prevented from leaking to the DC voltage
supplying conductor pattern 5 from the microwave circuit.
[0029] In the microwave circuit, since a substantial current flows
through the collector of the transistor, a resistor having a high
resistance cannot be inserted for realizing a high impedance in the
collector voltage supplying circuit. In this case, the open stub is
often connected to a position apart from a connection point between
a microwave circuit line and a collector voltage supplying line by
.lambda.g/4 (where .lambda.g is a wavelength at the dielectric
substrate of the resonation frequency), in order to cause the
collector voltage supplying circuit to have a high impedance when
it is viewed from the microwave circuit. However, since the open
stub itself is well known to persons skilled in the art, a further
description will be omitted. On the other hand, the open stub 12 is
not necessarily indispensable, if it is possible to cause the
collector voltage supplying circuit to have a high impedance by any
other means, or it is not necessary to cause the collector voltage
supplying circuit to have a high impedance.
[0030] The capacitor 13 is provided for preventing a parasite
oscillation at a low frequency. The capacitor 15 is provided for
blocking a DC component while allowing passage of the oscillation
output.
[0031] In operation, if for example DC 5V is applied to the DC
voltage supplying conductor pattern 5, the transistor 4 is driven
with an appropriate base bias and an appropriate collector voltage.
As a result, the shown circuit oscillates by action of the
resonating circuit composed of the stub 2 and the dielectric
resonator 3 and the feedback circuit composed of the dielectric
resonator 3 and the stub 1. In this oscillation operation, the base
bias voltage and the collector voltage of the transistor vibrate by
the oscillation power, and are greatly influenced by the impedance
of a peripheral circuit connected to the oscillation circuit.
[0032] In order to obtain a stable oscillation in the microwave
oscillation circuit, it is necessary that the voltages applied to
the transistor 4 are stable without being influenced by the high
frequency power, and the impedance of the peripheral circuit is
stable.
[0033] As mentioned above, the oscillation output is picked up from
the collector of the transistor. However, the stability against to
a variation in a load impedance can be realized by constituting a
L-type or .pi.-type attenuator at the output terminal of the
oscillation circuit.
[0034] On the other hand, since the base side of the transistor 4
has no external interface, it is necessary that any means for
obtaining a stable oscillation operation is provided in an
oscillation circuit block, namely, on the dielectric substrate 100.
On the other hand, it is difficult to stabilize the impedance of
the feedback circuit by only the infinite impedance of the free end
1A of the stub 1, because the base bias voltage supplying conductor
pattern 9 connected to the stub 1 behaves as a distributed
parameter circuit in a microwave band. In the shown embodiment, the
base bias resistor 8 connected to the stub 1 is located in the
neighborhood of the connection point between the other end of the
stub 1 and the base terminal of the transistor 4. Since the base
bias resistor 8 has the resistance on the order of 10k.OMEGA., the
impedance of the base bias voltage supplying circuit becomes
sufficiently high when it is viewed from the oscillation circuit
(namely, the microwave circuit) which is constituted to have the
characteristic impedance of for example 50k.OMEGA.. As the result,
a high-frequency impedance of a microwave circuit at a base
terminal side of the transistor (namely, at a side of the stub 1)
is stabilized, and the amplitude modulation of the base bias
voltage caused by the oscillation component is avoided. Therefore,
the oscillation stability is improved, and the oscillation output
level are stabilized. Therefore, it is possible to completely avoid
the stop of the oscillation caused by a variation in the impedance
of the load.
[0035] Here, it is to be noted that in a microwave band,
particularly in a frequency band of not less than 2 GHz, the
circuit behaves as a distributed parameter circuit. Therefore, when
the base bias resistor is connected, the impedance of the base bias
voltage supplying circuit viewed from the oscillation circuit is
different dependently upon the position to which the base bias
resistor is connected. In the present invention, therefore, in
order to make high the impedance of the base bias voltage supplying
circuit viewed from the oscillation circuit, it is indispensable to
locate the base bias resistor 8 in the neighborhood of the
connection point between the other end of the stub 1 and the base
terminal of the transistor 4. Preferably, the base bias resistor 8
is located at a position within the distance of not greater than
.lambda.g/6 from the connection point between the other end of the
stub 1 and the base terminal of the transistor 4.
[0036] Incidentally, in the shown embodiment, even if the load
impedance is infinite so that a total reflection is realized, the
oscillation never stops for all phases. In addition, even in the
worst load varying condition of the total reflection and the
all-phase, it is possible to improve the variation width of the
oscillation output by 2 dB to 3 dB, without increasing the number
of components included in the whole oscillation circuit.
[0037] Accordingly, the shown embodiment can elevate the
oscillation stability against the variation in the load impedance
without increasing the number of components.
[0038] Furthermore, since the base bias resistor 8 for basically
determining the base bias voltage is located in the neighborhood of
the connection point between the stub (constituting the feedback
circuit) and the base terminal of the transistor, the amplitude
modulation of the base bias voltage caused by the oscillation
component is avoided, with the result that it is possible to
minimize the oscillation output level against the variation in the
output load impedance.
[0039] In the above mentioned embodiment, the fine-adjusting base
bias resistor 7 can be omitted, since the base bias voltage is
fundamentally determined by the base bias resistor 8, if the
fine-adjusting is not necessary, or if not only the coarse
adjustment but also the fine-adjusting can be realized by only the
base bias resistor 8. As mentioned hereinbefore, however, the base
bias resistors 7 and 8 are formed of chip resistors in many
practical cases. Since the resistance of the chip resistors is
actually discrete, it is preferable to combine the fine-adjusting
base bias resistor 7 having a small resistance and the base bias
resistor 8 having a large resistance on the order of 10k.OMEGA., in
order to obtain a desired base bias voltage.
[0040] In addition, the position of the fine-adjusting base bias
resistor 7 is in no way limited to the position near to the DC
voltage supplying conductor pattern 5. Even if fine-adjusting base
bias resistor 7 is located at any position along the base bias
voltage supplying conductor pattern 9 from the DC voltage supplying
conductor pattern 5 to the base bias resistor 8, the advantage of
the present invention can be obtained with no deterioration.
[0041] The invention has thus been shown and described with
reference to the specific embodiments. However, it should be noted
that the present invention is in no way limited to the details of
the illustrated structures but changes and modifications may be
made within the scope of the appended claims.
* * * * *