Push-push oscillator having in-phase and anti-phase output combining circuits

A push-push oscillator including a resonator having a transmission line and a capacitance connected to the transmission line in parallel; an oscillating circuit responsive to the resonator for oscillating and for producing first and second outputs having an antiphase relation therebetween; an in-phase combining circuit for summing the first and second outputs of said oscillating circuit to produce a summed signal; and an antiphase combining circuit responsive to two components from the resonator having an antiphase relation for producing a differential signal in accordance with a difference between the two components. Alternatively, the in-phase combining circuit is connected to the resonator and the antiphase combining circuit is connected to the oscillating circuit. The antiphase combining circuit outputs a fundamental wave component of the resonator. The in-phase combining circuit outputs a second harmonic wave component. When this push-push oscillator is used in a PLL circuit to form a frequency synthesizer, a high frequency output is obtained with a low power consumption.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a push-push oscillator, and particularly to a 
push-push oscillator for high-frequency radio, communication, and 
measuring apparatus. 
2. Description of the Prior Art 
A prior art TEM mode resonator is frequently used for a high-frequency 
miniaturized resonator comprising an open-end half-wave resonator and 
U-shaped resonator. FIG. 15 shows an example of a prior art open end 
half-wave resonator comprising a resonating transmission line 101. FIG. 16 
shows a prior art resonator 102 formed into U-shape by bending the 
resonating transmission line. 
A prior art push-push oscillator using the above-mentioned resonator as a 
high-frequency oscillator is frequently used, which is described in U.S. 
Pat. No. 4,763,084. 
FIG. 17 shows a schematic circuit diagram of such prior art push-push 
oscillator. The push-push oscillator comprises a resonating portion 103, 
an oscillating portion 104 including two symmetric oscillators such as a 
Colpitts oscillator, whose two outputs have a phase difference of 
180.degree. with each other, and a combining circuit 105 including 
transmission lines having the same electrical lengths for cancelling 
fundamental harmonic components and odd-order harmonic components and 
doubling only even-order harmonic components. 
However, there is a problem that the size of the resonator 103 cannot be 
reduced because an area used for the resonator 103 is large to obtain a 
desired resonance frequency. This is because in the prior art resonator 
103, the length of the resonator 103 is a half-wave which is large. 
Moreover, if the oscillator mentioned above is used in a phase-locked loop 
circuit to form a frequency synthesizer, a divider for dividing the output 
frequency directly is necessary. However, there is a problem the higher 
the frequency of the divider capable of high speed operation the more 
increases the power consumption. 
SUMMARY OF THE INVENTION 
The present invention has been developed in order to remove the 
above-described drawbacks inherent to the conventional push-push 
oscillator. 
According to the present invention there is provided a push-push oscillator 
comprising: a resonator having transmission line and a capacitance 
connected to the transmission line in parallel; an oscillating circuit 
responsive to the resonator for oscillating and for producing first and 
second outputs having an antiphase relation therebetween; an in-phase 
combining circuit for summing the first and second outputs of the 
oscillating circuit to produce a summed signal; and an antiphase combining 
circuit responsive to two components from the resonator having an 
antiphase relation for producing a differential signal in accordance with 
the difference between the two components. 
The transmission line may be made of a dielectric material and is so curved 
to form an open loop whose both ends are connected to a capacitance. The 
resonator may further comprise two second transmission lines, each 
provided to each end of the transmission line, these two second 
transmission lines facing each other with a given distance therebetween, 
the distance and length of the second transmission lines being determined 
such that necessary capacitance is provided. Impedance of each portion of 
the resonator is changed stepwise to miniaturize the resonator. The 
antiphase combining circuit is formed as follows: 
The transmission line of the resonator has a straight line portion 
including a virtual ground point of the transmission line and the 
antiphase combining circuit comprises a second strip line arranged in 
parallel to the straight line, the second strip line being arranged such 
that the virtual ground divides the second strip line into two portions 
having electrical lengths which is equal to each other. 
According to the present invention there is also provided a push-push 
oscillator comprising: a resonator having transmission line and a 
capacitance connected to the transmission line in parallel; an oscillating 
circuit responsive to the resonator for oscillating and for producing 
first and second outputs having an antiphase relation therebetween; and 
antiphase combining circuit responsive to first and second outputs for 
producing a differential signal in accordance with difference between the 
first and second outputs; and an in-phase combining circuit responsive to 
two components from the resonator having an antiphase relation for summing 
the two components. The antiphase combining circuit comprises a balance to 
unbalance converting circuit.

DETAILED DESCRIPTION OF THE INVENTION 
Hereinbelow will be described a first embodiment of this invention of a 
push-push oscillator with reference to FIG. 1. 
FIG. 1 is a block diagram of a push-push oscillator of the first embodiment 
comprising: a resonator 6, an oscillating portion 4, an antiphase 
combining circuit 7 for combining resonator's outputs having antiphase 
relation, and an in-phase combining circuit 58 combining oscillating 
portion's outputs having in-phase relation. 
FIGS. 2-5 show various configurations of the resonator 6. FIG. 6 shows a 
configuration of an antiphase combining circuit 7. FIGS. 7 and 8 show 
examples of configurations of the in-phase combining circuit 58. 
The length of a resonator can be reduced by providing a gap in an annular 
transmission line (strip line or micro strip line) and a capacitor 
connected to both ends of the transmission line. The transmission line 
comprises a strip line. The term "strip line" includes a microstrip line 
and balanced strip line in addition to a strip line throughout the 
specification and the claims. 
FIG. 2 shows an example of a resonator 6 used in the first and second 
embodiments of this invention. In FIG. 2, a first resonator 6a comprises 
an annular transmission line 8 having a gap to which a lumped element 
capacitance, or capacitor 9 is connected. That is, the transmission line 8 
is formed a substantially complete loop having a gap whose both ends are 
connected to a capacitor 9. 
FIG. 3 shows a second resonator 6b used in the first and second embodiments 
of this invention comprising an annular dielectric 10 having a gap to 
which a lumped element capacitance 11 is connected. In other words, an 
open loop whose both ends are connected to a capacitance 11. 
FIG. 4 shows a third resonator 6c used in the first and second embodiment 
of this invention, comprising an essentially annular transmission line 12 
having coupled transmission lines 12a and 12b. 
Assuming that an impedance of the annular transmission line 12 is Zs.sub.1, 
an even mode impedance of the coupled transmission lines 12a and 12b is 
Zpe.sub.1, and an odd mode impedance is Zpo.sub.1, each dimension of the 
third resonator 6c is determined in accordance with Zs.sub.1.sup.2 
=Zpe.sub.1 .multidot.Zpo.sub.1. 
FIG. 5 shows a fourth resonator 6d used in the first and second embodiments 
of this invention, comprising coupled lines 13a and 13b and U-shaped 
transmission line 13 whose impedance is changed stepwise from the coupled 
lines 13a and 13b. It is assumed that the impedance of the U-shaped 
transmission line 13 is Zs.sub.2, an even mode impedance of the coupled 
transmission lines 13a and 13b is Zpe.sub.2, and an odd mode impedance is 
Zpo.sub.2. The length of the fourth resonator 6d can be further decreased, 
compared with the third resonator shown in FIG. 4 by determining each 
dimensions of the resonator 6d in accordance with Zs.sub.2.sup.2 
&gt;Zpe.sub.2 .multidot.Zpo.sub.2. 
According to the above-mentioned structure, a miniaturized resonator 6 
whose output signals at both ends have a phase difference of 180.degree. 
at the resonance frequency is formed. 
Coupling between the resonator 6 and the oscillator 4a or 4b is effected by 
capacitive coupling at an end of the U-shaped resonator or by 
electro-magnetic coupling at a corner of the U-shaped resonator. Phase 
relation at a pair of outputs of the resonator is dependent on the 
location of the coupling. Therefore, suitable coupling portions are 
selected. Outputs of the resonator 6 to the oscillators 4a and 4b have 
antiphase relation therebetween. 
The oscillating portion 4 has two well-known oscillators 4a and 4b, such as 
a Colpitts oscillator, which have the same circuit structure with each 
other and are arranged symmetrically. Therefore, outputs of those 
oscillators 4a and 4b have 180.degree. phase difference therebetween. 
Two outputs from the oscillating portion 4 have a phase difference of 
180.degree. therebetween. Therefore, if in-phase combining is effected to 
the outputs of the oscillating portion 4, the fundamental wave components 
cancel each other and second harmonics wave components are doubled. On the 
other hand if antiphase combining is effected to the outputs of the 
oscillating portion 4, the second harmonic wave components cancel each 
other and fundamental components are doubled. In this embodiment, the 
outputs of the oscillating portion 4 are in-phase combined, so that the 
second harmonic wave component is obtained from the in-phase combining 
circuit. 
FIG. 6 shows a configuration of the antiphase combining circuit 7 of the 
first embodiment. This antiphase combining circuit 7 comprises a U-shaped 
transmission line whose both ends are capacitively coupled and a second 
transmission line 65 arranged parallel to the bottom portion 21 of the 
U-shaped transmission line. The transmission line 19 acts as a resonator 
also. The middle point of the bottom portion 21 is a virtual ground. The 
transmission line 65 being formed such that the virtual ground divides the 
second strip line 65 into two portions having electrical lengths which are 
equal to each other. One end of the second transmission line 65 is 
grounded. Its output is obtained at the other end of the second 
transmission line 65. 
FIG. 7 shows a configuration of an example of an in-phase combining circuit 
66 used in the first and second embodiments of this invention. The 
in-phase combining circuit 66 comprises transmission lines 66a and 66b 
having the same electrical length .theta.1 and the same impedance Z1. The 
strip line 66c is for impedance matching to the following stage. 
FIG. 8 shows a schematic drawing of an example of an in-phase combining 
circuit 67 of the first embodiment. The outputs of the oscillating portion 
4 are directly connected through capacitors 67a and 67b. That is, the 
outputs of the oscillating portion 4 are connected to one end of 
respective capacitors 67a and 67b having the same small capacitance The 
other ends of the capacitors 67a and 67b are connected to each other and 
the output is obtained therefrom. Isolation between both oscillation 
portions 4a and 4b can be maintained because the capacitance is 
considerably small. 
As mentioned above, according to this embodiment, the push-push oscillator 
comprises the resonator 6 having a capacitance for resonance and a 
transmission line connected to the capacitance in parallel, the 
oscillating portion 4 having two oscillators 4a and 4b having the same 
structure arranged symmetrically, the in-phase combining circuit 58 for 
in-phase-combining two outputs of the oscillating portion 4 having 
antiphase relation, and the antiphase combining circuit 7 for 
antiphase-combining two outputs of the resonator 6 having antiphase 
relation. The antiphase combining circuit 7 is coupled to the resonator 6 
and the in-phase combining circuit 58 is connected to the oscillating 
portion 4, so that a length of the resonator is made considerably smaller 
than that of the half-wave resonator. Moreover, if this oscillator 
mentioned above is used in a phase locked loop circuit to form a frequency 
synthesizer, there is provided a second harmonic output in addition to a 
fundamental frequency output, so that the power consumption of the 
frequency synthesizer can be reduced. 
Hereinbelow will be described a second embodiment with reference to 
drawings. 
FIG. 9 is block diagram of the second embodiment of the invention of a 
push-push oscillator. In FIG. 9, the push-push oscillator of the second 
embodiment comprises: a resonator 6, the oscillating portion 4, an 
antiphase combining circuit 47 as differential means for 
antiphase-combining oscillator's outputs having antiphase relation, and an 
in-phase combining circuit 18 in-phase-combining outputs of the resonator 
6 having antiphase relation. The structures of the oscillating portion 4 
and the resonator 6 are the same as those of the first embodiment 
respectively. Thus, a detailed description is omitted. 
FIG. 10 shows a balance-unbalanced converting circuit 47a of the second 
embodiment as a such antiphase combining circuit of the push-push 
oscillator shown in FIG. 9 for combing two inputs such that two in-phase 
components cancel each other and two antiphase components are doubled in 
amplitude. A first antiphase combing circuit 47a comprises a first coil 
69a, whose one end is supplied with a first input INPUT1 and whose another 
end is supplied with a second input INPUT2, and a second coil 69b whose 
one end is grounded and an output appears at another end. 
FIG. 11 shows a rat race circuit 47b as a second antiphase combining 
circuit 47 of the second embodiment of the push-push oscillator shown in 
FIG. 9. The antiphase combining circuit 47b produces a differential signal 
in accordance with difference between input signals INPUT1 and INPUT2. 
FIG. 12 shows a third antiphase combining circuit 47c of the second 
embodiment comprising transmission lines 15a and 15b having a phase 
difference of 180.degree. in electrical length at a resonance frequency of 
the resonator for producing the differential signal between two input 
signals INPUT1 and INPUT2. 
FIG. 13 shows a differential amplifier of the second embodiment as an 
antiphase combining circuit 47d, comprising a pair of transistors 16a and 
16b, a constant current source 16c, and resistors 16d and 16e. The pair of 
transistors 16a and 16b amplify the difference between two inputs INPUT1 
and INPUT2 to produce two outputs in order to effect antiphase-combining. 
FIG. 14A shows a schematic drawing of an example of an in-phase combining 
circuit 18 of the second embodiment of the push-push oscillator. The 
in-phase combining circuit 18 comprises transmission lines 18a and 18b 
having the same electrical length .theta.1 and the same impedance Z1 as 
shown in FIG. 14A. The transmission lines 18a and 18b are connected to two 
output points of the resonator 8 respectively. The two output points are 
provided symmetrically with respect to a virtual ground G of the resonator 
8 at the same electrical length from said virtual ground G. 
When this oscillator mentioned above is used in a phase synchronizing 
circuit to form a frequency synthesizer, there is provided a high 
frequency output and the power consumption can be reduced. 
FIG. 14B shows a schematic drawing of an example of an in-phase combining 
circuit 70 of the second embodiment of the push-push oscillator. Two 
output points 8a and 8b of the resonator 8 are connected through 
capacitors 70a and 70b to an output terminal. That is, two output points 
8a and 8b of the resonator 8 are connected to one end of respective 
capacitors 70a and 70b having the same small capacitance. The other ends 
of the capacitors 70a and 70b are connected to each other and the output 
is obtained therefrom. Isolation between both output points 8a and 8b of 
the resonator 8 can be maintained because the capacitance is considerably 
small. The two output points 8a and 8b are provided symmetrically with 
respect to a virtual ground G of the resonator 8 at the same electrical 
length from said virtual ground G. 
When this oscillator mentioned above is used in a phase locked loop circuit 
to form a frequency synthesizer, there is provided a high frequency output 
and the power consumption can be reduced.