MICROWAVE OSCILLATOR

Abstract: The oscillator uses a three-terminal active element (1), such as a FET with both series feedback (25) and parallel feedback (29). The series feedback comprises an inductive (26) and a capacitive (27) element. The parallel feedback comprises a further capacitive element (28). The starting of the oscillator is thereby improved, while output power is increased and the influence of impedance fluctuations of a load (30) is reduced.

Description: Background of the Invention This invention relates to a microsave oscillator using an active element for oscillation having three terminals. As a conventional microwave oscillator, two types are known, that is, series feedback type oscillation circuit and parallel feedback type oscillation circuit as disclosed in the Japanese Patent Publication No. Sho. 60-47764. Fig. 1 shows an equivalent circuit of series feedback type oscillation circuit with drain grounding in the prior art, in which 1a is a field effect transistor (FET), 2a is a gate terminal, 3a is a drain terminal, and 4a is a source terminal. Reference number 5a denotes a series feedback circuit composed of capacitive or inductive elements 6a, 7a, and these elements 6a, 7a are selected so that one is capacitive and the other inductive, or vice versa. The source terminal 4a is connected to a load 8a, and the other ends of the elements 6a, 7a (load), and 8a are commonly connected. Fig. 2 shows a practical example of this conventional microwave oscillator, and the same parts as in Fig. 1 are identified with same reference numbers. That is, 1a is an FET, 2a is a gate terminal, 3a is a drain terminal, and 4a is a source terminal. Reference number 9a is a microstripline, one end of which is terminated at the gate terminal 2a and the other end at a terminal resistor 10a. Reference number 11a is a dielectric resonator, which is a disposed so as to be coupled with the microstripline 9a. Reference number 12a is a power source terminal, and 13a is a 1/4 wavelength open-ended microstripline having a length of about 1/4 wavelength at the oscillation frequency. Reference number 14a is a self-bias resistor, and 15a is a low pass filter. Reference number 16a is an output terminal. In thus composed conventional microwave oscillator, the reactance caused due to deviation of the line length of the 1/4 wavelength microstripline 13a from the accurate 1/4 wavelength corresponds to the element 6a in Fig. 1, and the resonance circuit composed of the dielectric resonator 11a and microstripline 9a corresponds to the element 7a in Fig. 1, so that the circuit in Fig. 2 is a series feedback oscillation circuit. In Fig. 2, when a direct-current power source is supplied from the power source terminal 12a, the potential at the gate terminal 2a becomes lower than the potential at the source terminal 4a due to the voltage drop by the current flowing in the self-bias resistor 14a. At this time, when the 1/4 wavelength open-ended microstripline 13a is connected to the drain terminal 3a, a negative resistance is generated at the gate terminal 2a, and the reflectivity as seeing the FET 1a side from the gate terminal 2a Γ G becomes |Γ G | > 1. Supposing the reflectivity in the vicinity of the resonance frequency of the dielectric resonator 11a as seeing the microstripline 9a side from the gater terminal 2a to be Γ R , if |Γ R |·|Γ G | ≧ 1 (1) repetitive reflection occurs between the gate terminal 2a and the microtripline 9a, and oscillation is initiated. Its output is obtained from the source terminal. Fig. 3 shows an equivalent circuit of a conventional source-grounded parallel feedback oscillation circuit. The same parts as in Fig. 1 and Fig. 2 are identified with same reference numbers. That is, 1a is an FET, 2a is a gate terminal, 3a is a drain terminal, and 4a is a source terminal. Reference number 17a denotes a parallel feedback circuit composed of capacitive or inductive elements 18a, 19a, and the elements 18a, 19a are selected so that one is capacitive and the other inductive, or vice versa. The element 18a is connected between the gate terminal 2a and source terminal 4a of the FET 1a, the element 19a is connected between the gate terminal 2a and the drain terminal 3a of the FET 1a, and a load admittance element 20a is connected to the drain terminal 3a of the FET 1a. Fig. 4 shows an equivalent circuit of a practical structure of parallel feedback type oscillator, in which 1a is an FET, 2a is a gate terminal, 3a is a drain terminal, and 4a is a source terminal. Reference numbers 21a, 22a are open-ended microstriplines, which are electromagnetically coupled with a dielectric resonator 23a. Reference number 24a is an output terminal connected to the drain terminal. In the circuit shown in Fig. 4, in the vicinity of the resonance frequency of the dielectric resonator 23a, a positive feedback is applied from the drain terminal 3a to the gate terminal 2a by way of the microctriplines 21a, 22a, and dielectric resonator 23a. Supposing the gain of this feedback route to be G R (|G R | < 1), and the gain between the gate terminal 2a and source terminal 3a of the FET 1a to be G F , if |G R | · |G F | ≧ 1 (2) the circuit in Fig. 4 starts oscillation in the vicinity of the resonance frequency of the dielectric resonator 23a, and its output is obtained from the output terminal 24a. In the constitution as shown in Fig. 1, however, if the gain of the FET 1a is low or the gate-source capacity in the FET 1a is large, the absolute value of reflectivity |Γ G | as seeing the FET 1a side from the gate terminal 2a is low, and the start of oscillation is not secure. Yet, in the drain-grounded oscillator as shown in Fig. 2, if the FET 1a is a chip or the entire circuit is composed in a monolithic integrated circuit, the floating capacity which exists in the package FET does not exist, and the FET characteristic changes, and the negative resistance generated at the gate terminal decreases, and the stability of oscillation is lowered. Or, in the construction of Fig. 3, if the absolute gain |G F | of the FET 1a is low, or when the absolute gain |GR| of the feedback route feeding back to the gate terminal 2a from the drain terminal 3a through the microstriplines 21a, 22a and dielectric resonator 23a is low, oscillation is not started or the output is lowered. Summary of the Invention In the light of the above-discussed points, hence, it is a primary object of this invention to present a microwave oscillator which oscillates stably if the gain of the active element for oscillation is somewhat low or if the internal capacity is large. To achieve the above object this invention presents a microwave oscillator which comprises a three-terminal active elements having first, second and third terminals, a first inductive element of which one end is grounded at high frequency and the other end is connected to the first terminal, a resonance circuit connected to the second terminal, and a first capacitive element of which one end is connected to the first terminal and the other end is connected to the third terminal, wherein an output can be taken out from the third terminal. While the novel features of the invention are set forth in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings. Brief Description of the Drawings Fig. 1 is an equivalent circuit diagram of a conventional microwave oscillator; Fig. 2 is a circuit structural drawing of a conventional microwave oscillator; Fig. 3 is an equivalent circuit diagram of a conventional microwave oscillator; Fig. 4 is a circuit structural drawing of a conventional microwave oscillator; Fig. 5 is an equivalent circuit diagram of a microwave oscillator in a first embodiment of this invention; Fig. 6 is a circuit structural drawing of a microwave oscillator in the first embodiment of this invention; Fig. 7 is a characteristic diagram showing the effects of the first embodiment of this invention; Fig. 8 is a circuit structural drawing of a microwave oscillator in a second embodiment of this invention; Fig. 9 is a characteristic diagram showing the effects of the second embodiment of this invention; Fig. 10 is a circuit structural drawing of a microwave oscillator in a third embodiment of this invention; Fig. 11 is a characteristic diagram showing the effects of the third embodiment of this invention; Fig. 12 is a circuit structural drawing of a microwave oscillator in a fourth embodiment of this invention; Fig. 13 is a characteristic diagram showing the effects of the fourth embodiment of this invention; Fig. 14 is a circuit structural drawing of a microwave oscillator in a fifth embodiment of this invention; Fig. 15 is a characteristic diagram showing the effects of the fifth embodiment of this invention; Fig. 16 is a circuit structural drawing of a microwave oscillator in a sixth embodiment of this invention; Fig. 17 is a characteristic diagram showing the effects of the sixth embodiment of this invention; Fig. 18 is a pattern diagram of an MMIC (monolithic microwave integrated circuit) chip of a microwave oscillator in a seventh embodiment of this invention; Fig. 19 is an equivalent circuit diagram of the MMIC chip of the microwave oscillator in the embodiment in Fig. 18; Fig. 20 is a structural drawing of a microwave oscillator using the MMIC of Fig. 18; Fig. 21 is a pattern diagram of an MMIC chip of a microwave oscillator in an eighth embodiment of this invention; Fig. 22 is a pattern diagram of an MMIC chip of a microwave oscillator in a ninth embodiment of this invention; and Fig. 23 is an equivalent circuit diagram of the MMIC chip of the microwave oscillator in the embodiment in Fig. 22. Detailed Description of the Invention Referring now to the drawings, some of the embodiments of this invention are described in details below. Fig. 5 shows a high frequency equivalent circuit diagram of a microwave oscillator in one of the embodiments of this invention. In Fig. 5, reference number 1 denotes an FET, 2 is a gate terminal, 3 is a drain terminal, and 4 is a source terminal. Reference number 25 denotes series feedback circuit, which is composed of an inductive element 26 and a capacitive element 27. Reference number 28 is another capacitive element, of which one end is connected to the source terminal 4 and the other end to the drain terminal 3, thereby making up a parallel feedback circuit 29. The source terminal 4 is connected to a load impedance element 30, and the other ends of the elements 26, 27, 30 are commonly connected. As evident by comparing Fig. 5 with Fig. 1 and Fig. 3, this is neither the conventional series feedback type oscillation circuit nor the parallel feedback type oscillation circuit, but it is a series-parallel both feedback compatible type oscillation circuit. Fig. 6 shows an example of practical structure of the microwave oscillator of the first embodiment, in which 30 is a load, and 31 is an FET having the following S-parameter at 10.75 GHz. S-parameter of chip FET S₁₁ S₂₁ S₁₂ S₂₂ MAG 0.71 1.58 0.09 0.495 ANG -132 78 45 -34 f₀ = 10.75 GHz Reference number 32 is a gate terminal, 33 is a drain terminal, and 34 is a source terminal. Reference number 35 is an inductor, which corresponds to the element 26 in Fig. 5, with one end connected at high frequency by way of a bypass capacitor 36, and the other end connected to the drain terminal 33. Reference number 37 is a capacitor, of which one end is connected to the source terminal 34 and the other end to the drain terminal 33. Reference number 38 is a microstripline, of which one end is terminated at a terminal resistor 39, and the other end is connected to the gate terminal 32. Reference number 40 is a dielectric resonator which is disposed so as to be electromagnetically coupled with the microstripline 38. A resonance circuit is composed of the microstripline 38, terminal resistor 39, and dielectric resonator 40, and the impedance in the vicinity of the resonance frequency of this resonance circuit corresponds to the impedance of the element 27 in Fig. 5. Reference number 42 is a self-bias resistor, and 43 is a 1/4 wavelength microstripline having a length of 1/4 of the wavelength at oscillation frequency. Reference number 44 is a bias terminal, and 45 is an output terminal. The operation of thus composed microwave oscillator in the embodiment in Fig. 6 is as follows. The 1/4 wavelength microstripline 43, which is grounded at one end, is open at the oscillation frequency at the other end, and passes only direct-current bias current, thereby preventing the output signal from being consumed in the self-bias resistor 42. The inductor 35 and capacitor 37, having their inductance and capacitance set properly, act to increase the absolute value of the reflectivity |P G | seen from the gate terminal 32 of the FET 31 to the FET 31 side. Supposing the absolute value of the reflectivity in the vicinity of the resonance frequency of the dielectric resonator 40 in the resonance circuit 41 to be |Γ|, if |Γ r | · |Γ G | ≧ 1 (3) they only the signal in the vicinity of the resonance frequency of the dielectric resonator 40 is repetitively reflected between the gate terminal 32 and resonance circuit 41, and oscillation is started. Fig. 7(a) shows the relation between the reflectivity |Γ G | at the oscillation frequency 10.75 GHz as seen from the gate terminal 32 to the FET 31 side and the inductance L of the inductor 35, as calculated on a certain chip FET in terms of capacitance C of the capacitor 37. Fig. 7(b) shows the characteristics at 1, 2, 3, 4, 5 in Fig. 7(a). In the case of Fig. 7(a), when the drain terminal 33 is grounded by way of the inductor 2 of 0.8 nH to set the capacitance C₁ of the capacitor 37 to 0.2 pF (at this time, the relation of is established), rather than when it is directly grounded at high frequency (equivalent to L=0), the absolute value of the reflectivity |Γ G | as seen from the gate terminal 32 to the FET side can be set higher, so that the oscillation condition in formula (3) may be satisfied even if the reflectivity |P R | of the resonance circuit is low. Therefore, it is possible to obtain a microwave oscillator which can start oscillation securely even if |P R | is low. Meanwhile, the oscillation signal generated between the dielectric resonator 40 and the gate terminal 30 is amplified by the gain shown in Fig. 7(b), and is taken out from the output terminal. During oscillation, the FET works on a large signal. Accordingly, the output power of the FET is saturated, and the signal is not amplified exactly according to the gain in Fig. 7(b), but the oscillation output is higher when the gain is higher. Hence the oscillation output is higher when capacitance C₁ = 0.2 pF, rather than when C₁ = 0 pF as in the prior art. Incidentally, the maximum VSWR of the load becoming |ΓG| > 1 in all phases is largest when C₁ = 0.2 to 0.3 pF, and the oscillation is maintained if the impedance of the load 30 changes significantly. What is more, by setting the capacitor 37 at a proper capacitance, the inductance of the inductor 35 may be reduced, and the size of the oscillator may be hence reduced. Thus, according to this embodiment, in the microwave oscillator, by grounding the drain terminal 33 of the FET 31 by way of the inductor 35 having a proper value, and connecting the drain terminal 33 and source terminal 34 of the FET 31 with the capacitor 37 having a proper value, it is possible to obtain a microwave oscillator which starts oscillation securely, and is high in the oscillation output power and resistant to the impedance fluctuations of the load 30. Still more, since the inductance of the inductor 35 can be decreased, it is suited to reduction of size and IC designing. Fig. 8 shows a microwave oscillator is a second embodiment of this invention. The parts same as those in Fig. 6 are identified with same reference numbers. The configuration is similar to Fig. 6, except that a capacitor 46 is inserted in series between a source terminal 34 and an output terminal 46. The operation of thus composed micorwave oscillator embodied in Fig. 8 is explained below. In Fig. 8, the operation is exactly the same as in Fig. 6, except for the operation of the capacitor 46. That is, the capacitor 46 acts to increase the absolute value of reflectivity |ΓG| as seen from the gate terminal 32 of the FET 31 to the FET 31 side at the oscillation frequency, more than in the case of the micorwave oscillator shown in Fig. 6. Fig. 9 shows the relation among the capacitance C₂ of the capacitor 46, the absolute reflectivity |ΓG| as seen from the gate terminal 32 to the FET side at oscillation frequency of 10.75 GHz, the gain between the gate terminal 32 and output terminal 45, and the maximum VSWR of the load 30 to establish the relation of |Γ G | > 1, in the FET 31 having the same characteristics as in Fig. 6, setting the inducrance L of the inductor 35 at 0.8 nH, and the capacitance C₁ of the capacitor 37 at 0.2 pH, in which when the capacitance C₂ of the capacitor 46 is 0.2 pF, all of the absolute reflectivity |ΓG| as seen from the gate terminal 32 to the FET 31 side, the gain between gate terminal 32 and output terminal 45, and the maximum VSWR of the load 30 to set the relation of |Γ G | > 1 are greater than in Fig. 6. It is therefore possible to obtain a microwave oscillator having a higher performance. Moreover, since the output terminal 45 and source terminal 34 are isolated in terms of DC by the capacitor 46, it is not necessary to newly insert a DC shut-off capacitor into the output side. Thus, according to the embodiment in Fig. 8, by inserting the capacitor 46 near the chip FET 31 in the microwave oscillator in Fig. 6 and between the source terminal 34 and output terminal 45, it is possible to obtain a microwave oscillator which starts oscillation more securely, and is larger in output power, and is capable of maintaining oscillation if the impedance of the load 30 fluctuates extremely largely. Fig. 10 shows a microwave oscillator in a third embodiment of this invention. The parts same as those in Figs. 6, 8 are identified with same reference numbers. The configuration in Fig. 10 is similar to that in Fig. 8, except that a capacitor 47 is inserted between the output terminal 45 and the ground. The operation of thus composed microwave oscillator embodied in Fig. 10 is described below. Fig. 11 is a Smith chart plotting of the impedance seen from the source terminal 34 to the load 30 side, supposing the impedance of the load 30 to be 50 Ω, in the embodiment shown in Fig. 10. The impedance seen from the source terminal 43 to the load side (except for capacitor 37) connected to the capacitors 46, 47 and terminal 45 can be realized at all points in the shaded area 48 in Fig. 11 by varying the capacitance of the capacitors 46, 47. It is hence easy to adjust the load impedance of the FET 31 to an optimum load impedance for large signal operation during oscillation. By optimizing the load impedance, it is possible to obtain a microwave oscillator having a large output power, or a microwave oscillator having a higher stability, not stopping oscillation if the load impedance changes significantly. Thus, in the embodiment in Fig. 10, by properly setting the inductance and capacitance of the inductor 35, and capacitors 37, 46, 47, it is possible to obtain a microwave oscillator which starts oscillation securely and has a large output power, or a micorwave oscillator which is highly stable, not stopping oscillation if the load impedance fluctuates largely. Fig. 12 shows a microwave oscillator in a fourth embodiment of this invention. The parts same as those in Figs. 6, 8, 10 are identified with same reference numbers. That is, 31 is a chip FET, 32 is a gate terminal, 33 is a drain terminal, and 34 is a source terminal. Reference number 37 is a capacitor of which one end is connected to the drain terminal 33, and the other end to the source terminal 34. Reference number 38 is a microstripline of which one end is connected to the gate terminal 32, and the other end is terminated at a terminal resistor 39. Reference number 40 is a dielectric resonator 40 which is so disposed as to be electromagnetically coupled with the microstripline 38. Reference number 41 is a resonance circuit composed of microstripline 38, terminal resistor 39, and dielectric resonator 40. Reference number 36 is a bypass capacitor, 42 is a self-bias resistor, 43 is a 1/4 wavelength microstripline having a length of 1/4 of wavelength at oscillation frequency with one end ground, and 44 is a power source terminal. Moreover, 45 is an output terminal, 49 is a capacitor, 49 is a capacitive open-ended microstripline with a characteristic impedance of Z₀₁, length of ℓ₁, 50 is a microstripline with a characteristic impedance of Z₀₂, length of ℓ₂, and 51 is a microstripline with a characteristic impedance of Z₀₃, length of ℓ₃. The operation of thus composed microwave oscillator embodied in Fig. 12 is described below. The 1/4 wavelength microstripline 43, which is grounded at one end, is open at the oscillation frequency at the other end, and passes only DC bias current, and prevents the output signal from being consumed at the self-bias resistor 42. The microstripline 51 comes to have an inductance equivalent to that of the inductor 35 in Figs. 6, 8, 10, by properly setting its characteristic impedance Z₀₃ and length ℓ₃. The capacitors 37, 46 work to further increase the absolute value of the reflectivity seen from the gate terminal 32 to the FET 31 side, same as in the embodiment in Figs. 6, 8. Moreover, the capacitive open-ended microstripline 49 equivalently acts as a capacitor by setting its length shorter than 1/4 of the wavelength at the oscillation frequency. Furthermore, by properly setting the characteristic impedance Z₀₁, Z₀₂, and lengths ℓ₁,ℓ₂ of the microstriplines 49, 50, the impedance seen from the source terminal 34 of the FET 31 to the load side can be set in a wider range than in the embodiment in Fig. 10. Fig. 13 is a Smith chart plotting of the impedance seen from the source terminal 34 of the FET 31 to the load side (excluding the capacitor 37), in the microwave oscillator in Fig. 12. The impedance seen from the source terminal 34 to the load side can realize all points in the shaded area 52 in Fig. 13, by varying the capacitance of the capacitor 46, characteristic impedance Z₀₁ length ℓ₁ of the microstripline 49, and characteristic impedance Z₀₂, lenght ℓ₂ of the microstripline 50. This area 52 is wider than the range 48 in Fig. 11 obviously. Therefore, in the embodiment in Fig. 12, since the setting range of the load impedance is wider than in the embodiment in Fig. 10, it is possible to obtain, more easily than in the embodiment in Fig. 10, a microwave oscillator which is higher in performance, larger in output power, and more resistant to load impedance fluctuations. Thus, in the embodiment in Fig. 12, by properly setting the element values of capacitors 37, 46, and dimensions of the microstriplines 49, 50, 51, it is easy to obtain a microwave oscillator having a higher performance than in the embodiments in Figs. 6, 8, 10. Fig. 14 shows a fifth embodiment of microwave oscillator of this invention. The parts same as those in Figs. 6, 8, 10, 12 are identified with same reference numbers. The configuration is similar to Fig. 6, except that a capacitor 53 is inserted between a source terminal 34 and the ground. The operation of thus composed microwave oscillator embodied in Fig. 14 is described below. In Fig. 14, the operation is exactly same as in Fig. 6, except for the operation of the capacitor 53. The capacitor 53 acts to increase the absolute reflectivity |Γ G | seen from the gate terminal 32 of the FET 31 to the FET 31 side at oscillation frequency, and the gain between the gate terminal 32 and output terminal 45, more than in the case of Fig. 6. Fig. 15 shows the relationship among the capacitance C₂ of the capacitor 53, the absolute reflectivity |Γ G | seen from the gate terminal 32 to the FET 31 side at oscillation frequency of 10.75 GHz, the gain between gate terminal 32 and output terminal 45, and the maximum VSWR value of the load to keep the relation of |Γ G | > 1, concerning a certain chip FET, supposing the inductance of the inductor 35 to be 0.8 nH and the capacitance C₁ of the capacitor 37 to be 0.2 pF. It is apparent from Fig. 15 that, when the capacitance C₂ of the capacitor 53 is 0.15 pF, the absolute reflectivity |Γ G | seen from the gate terminal 32 to the FET 31 side becomes the maximum, whereas the gain between the gate terminal 32 and the output terminal 45 also reaches the maximum. Hence, in the embodiment in Fig. 15, it is possible to compose a microwave oscillator which starts oscillation more securely, and maintains the oscillation if the impedance of the load 30 varies significantly, as compared with the embodiment in Fig. 6 without the capacitor 53. Thus, according to the embodiment in Fig. 14, by connecting the capacitor 53 having a proper capacitance to the microwave oscillator in Fig. 6 near the chip FET 31 with the end grounded to the source terminal 34, it is possible to obtain a microwave oscillator which starts oscillation more securely. Fig. 16 shows a sixth embodiment of this invention, showing a circuit structural drawing of a microwave oscillator. The parts same as those in Figs. 6, 8, 10, 12, 14 are identified with same reference numbers. The configuration is similar to that of Fig. 14, except that one end of a capacitor 54 is connected to the non-grounded terminal of the capacitor 53 while the output is obtained from the other end. The operation of thus composed microwave oscillator embodied in Fig. 16 is described below. In the embodiment in Fig. 16, the load impedance of the microwave oscillator can be set in a wide range by means of capacitors 53, 54. Fig. 17 is a Smith chart plotting of the impedance seen from the source terminal 34 to the load side (except for the capacitor 37), in the embodiment in Fig. 16. The impedance seen from the source terminal 34 to the load side can realize all points in the shaded area 55 in Fig. 17 by varying the values of the capacitors 53, 54. Accordingly, it is possible to adjust the load impedance of the FET 31 easily to the optimum load impedance for large signal operation during oscillation. By optimizing the load impedance, it is possible to obtain a microwave oscillator having a large output power, or a microwave oscillator of a higher stability, not stopping oscillation if the load impedance fluctuates largely. What is more, it is not necessary to install newly a DC shut-off circuit because the output terminal 45 and source terminal 34 can be isolated in terms of DC by the capacitor 54. Thus, in the embodiment in Fig. 16, by properly setting the element values of the inductor 36 and capacitors 37, 53, 54, a highly stable microwave oscillator may be obtained. Figs. 18, 19, 20 refer to a seventh embodiment of this invention. Specifically, Fig. 18 is a pattern diagram of an MMIC (monolithic microwave integrated circuit) chip Fig. 19 is an equivalent circuit diagram of the MMIC chip, and Fig. 20 is a structural drawing of a microwave oscillator using this MMIC chip. The parts same as those in Figs. 6, 8, 10, 12, 14, 16 are identified with same reference numbers. Incidentally, the microstripline 51 in Fig. 18 corresponds to the inductor 35 in Fig. 19. As it may be easily understood by comparing Figs. 19, 20 with Fig. 10, the circuit configuration in this embodiment is similar to that of the foregoing embodiment, except for three different points: that is, a high resistor 63 of 5 kΩ is present between a gate terminal 32 and a drain terminal 33, a capacitor 61 having a low impedance at oscillation frequency is present, and a terminal resistor 39 is grounded at high frequency by 1/4 wavelength microstripline 65. Capacitors 36, 37, 46, 47, 61 are MIM capacitors. Since the resistor 63 has a high resistance, it does not affect the high frequency signal. Since the capacitor 61 has an extremely low impedance at the oscillation frequency, the output terminal 62 and the gate terminal 32 may be regarded to have a short circuit at the oscillation frequency. Accordingly, the embodiment in Fig. 19 presents an oscillator, same as in the embodiment in Fig. 10, that can start oscillation securely, and is high in output power, and can maintain oscillation if the impedance of the load fluctuates largely. In terms of DC, the gate terminal 32 is grounded by way of high resistor 63 and 1/4 wavelength microstripline 43, and the resonance circuit connection terminal 62 and the gate terminal 32 are isolated. It is hence not necessary to ground the gate terminal in terms of DC within the resonance circuit 67 disposed on a microwave board 66, and the configuration of the resonance circuit 67 is simplified. Incidentally, during oscillation which becomes large amplitude operation, the potential of the gate terminal 32 periodically becomes positive as compared with the potential of the source terminal 34. It causes to generate a forward gate current, which occasionally damaged the gate. However, since the resistor 63 has a high resistance of 5 kΩ, it is possible to suppress the forward gate current, so that the deterioration of the MMIC can be prevented. A GaAs MMIC corresponding to the embodiment in Fig. 19 was experimentally manufactured. The microstripline 51 was designed at the width of 70 µm and length of 1000 µm. The capacitor 37 had 0.2 pF, the capacitor 46 had 0.21 pF, and the capacitor 47 was composed of open-ended microstripline with characteristic impedance of 50 Ω and length of 800 µm. The capacitor 61 was designed at 3.6 pH, and the resistor 63 at 5 kΩ. Connecting the resonance circuit 67 of 10.75 GHz, it was oscillated at a supply voltage of 5 V. At this time, the output power was 12.4 dBm, and the maximum VSWR of the load to keep the relation of |Γ G | > 1 was > 15. As compared with the MMIC oscillator known so far, the output power was higher by more than 2 dB. Fig. 21 is an eighth embodiment of this invention, showing a pattern diagram of MMIC chip. The parts same as those in Figs. 6, 8, 10, 12, 14, 16, 18 are identified with same reference numbers. The configuration is similar to that of Fig. 18, except that one end of the resistor 63 is connected to a bonding pad 70 for grounding. The oscillator in Fig. 21 operate exactly same as the oscillator in Fig. 18, as an oscillator. In the oscillator in Fig. 18, the gate terminal 32 and source terminal 34 are connected with each other in terms of DC, by way of the 1/4 wavelength microstripline 43 and resistor 63. Therefore, when inspecting the DC characteristic of the FET 31, an electric current also flows into the resistors 42, 63, and the DC characteristic of the FET 31 cannot be inspected. In Fig. 21, the gate terminal 32 and source terminal 34 are not connected with each other in terms of DC in the MMIC chip 71 alone. Accordingly, the DC characteristic of the FET 31 can be inspected easily at the time of production. Figs. 22, 23 refer to a ninth embodiment of this invention, Fig. 22 showing a pattern diagram of MMIC chip, and Fig. 23 its equivalent circuit. The parts same as those in Figs. 6, 8, 10, 12, 14, 16, 18, 20, 21 are identified with same reference numbers. The configuration in Figs. 22, 23 is similar to that in Figs. 18, 21, except that one end of the resistor 63 is connected to the ground side of the bypass capacitor, and that the ground sides of the 1/4 wavelength microstripline 43 and capacitor 47 are mutually connected to form a bonding pad 81 for grounding. The MMIC chip in Fig. 22 functions exactly same as that in Fig. 18 or Fig. 21 as an oscillator. The gate terminal 32 and source terminal 34 of the FET 31 are isolated in terms of DC. Accordingly, same as in the embodiment shown in Fig. 21, the DC characteristic of the FET 31 may be easily inspected at the time of production. Still more, as compared with the configuration in Fig. 21, the bonding pad for grounding may be reduced in two position. Hence, the MMIC may be reduced in size, and the manpower in assembling process may be saved. Meanwhile, in the embodiment in Figs. 6, 8, 10, 12, 14, 16, the chip FET was used, but this is not limitative, and package FET, bipolar transistor, or other active elements for oscillation having three terminals may be used. Besides, the circuit may be designed in MMIC either wholly or partly. In Figs. 6, 8, 10, 12, 14, 16, 20, the resonance circuit 41 using dielectric resonator 40 was used, but other resonator or resonance circuit may be equally used. In Figs. 6, 8, 10, 14, 16, 18, 19, 21, 22, 23, the inductors and capacitors expressed by centralized constants may be also realized by distribution constant circuits such as equivalent stub stripline. In Fig. 12, either one or both of microstriplines 50, 51 may be realized by inductors of concentrated constant elements. Similarly, in Fig. 12, the microstripline 49 may be replaced by capacitive shorted-end stripline or centralized constant element such as MIM (metal-insulator-metal) capacitor. In the drawings from Fig. 5 go Fig. 23, needless to say, the optimum values of the industance and capacitance of inductor 35 and capacitors 37, 46, 47, 53, 54 may be different depending on the characteristic of the FET 31 or oscillation frequency. While specific embodiments of the invention have been illustrated and described herein, it is realized that other modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all modifications and changes as fall within the true spirit and scope of the invention.

Claims: A microwave oscillator comprising: a three-terminal active element having first, second and third terminals; a first inductive element of which one end is grounded at high frequency and the other end is connected to said first terminal for series feedback; a resonance circuit connected to said second terminal; and a first capacitive element of which one end is connected to said first terminal and the other end is connected to said third terminal for parallel feedback, wherein an output is taken out from said third terminal. A microwave oscillator according to claim 1, wherein the inductance L of the first inductive element and the capacitance C of the first capacitive element are selected so that the relation of f ≒ 1/(2π√ L · C ) may be established, where f is the oscillation frequency. A microwave oscillator according to claim 1, wherein an FET is used as the three-terminal active element, in which the first terminal is the drain terminal of the FET; the second terminal is the gate terminal of the FET; and the third terminal is the source terminal of the FET. A microwave oscillator according to claim 3, further comprising: an output terminal; and a second capacitive element of which one end is connected to the source terminal and other end is connected to the output terminal. A microwave oscillator according to claim 4, moreover comprising a third capacitive element of which one end is grounded and other end is connected to the output terminal. A microwave oscillator according to claim 3, further comprising: an output terminal; a series circuit of a second capacitive element and a second inductive element of which one end is connected to the source terminal and other end is connected to the output terminal; and a third capacitive element of which one end is grounded and other end is connected to the output terminal. A microwave oscillator according to claim 3, also comprising a fourth capacitive element of which one end is grounded and other end is connected to the source terminal of the FET, wherein an output is taken out from the source terminal. A microwave oscillator according to claim 7, further comprising: an output terminal; and a fifth capacitive element of which one end is connected to the source terminal and other end is connected to the output terminal. A microwave oscillator according to claim 3, further comprising: a 1/4 wavelength microstripline of which one end is grounded, having a line length of about 1/4 of wavelength of oscillation signal; a low resistance element of which one end is connected to the source terminal and other end is connected to the other end of said 1/4 wavelength microstripline; and a high resistance element of which one end is connected to the other end of said 1/4 wavelength microstripline and other end is connected to the gate terminal. A microwave oscillator according to claim 3, further comprising: a 1/4 wavelength microstripline of which one end is grounded, having a line length of about 1/4 of wavelength of oscillation signal; a low resistance element of which one end is connected to the source terminal and other end is connected to the other end of the 1/4 wavelength microstripline; and a high resistance element of which one end is grounded and other end is connected to the gate terminal. A microwave oscillator according to claim 3, forming circuit elements at least other than resonance circuit in monolithic integrated circuit on a semiconductor substrate, further comprising: a 1/4 wavelength microstripline of which one end is grounded, having a line length of about 1/4 of wavelength of oscillation signal; a low resistance element of which one end is connected to the source terminal and other end is connected to the other end of the 1/4 wavelength microstripline; and a high resistance element disposed on said semiconductor substrate of which one end is connected to the grounding side electrode of bypass capacitor and other end is connected to the gate terminal. A microwave oscillator according to claim 9, wherein a DC block circuit is disposed between the gate terminal of FET and resonance circuit, and this DC block circuit is mounted on the semiconductor substrate. A microwave oscillator according to claim 1, wherein a bipolar transistor is used as the three-terminal active element, using: the first terminal as the collector terminal of the bipolar transistor; the second terminal as the base terminal of the bipolar transistor; and the third terminal as the emitter terminal of the bipolar transistor.

Inventors: MEKATA, TSUYOSHI, SAKA, KIROSHI, TANAKA, TOSHIHIDE
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1988
Main classification: H03B5
IPC codes: H03B7, H03B5