High frequency oscillator circuit with feedback circuit of fet and short-stub transmission line

In a high frequency oscillator circuit including first and second field effect transistors, the first field effect transistor has a gate connected to a short-stub transmission line and a drain connected to an oscillation output terminal, and the second field effect transistor has a drain connected to a source of the first field effect transistor and a grounded source. The high frequency oscillator circuit oscillates by using a feedback circuit including the short-stub transmission line and the second field effect transistor. A feedback capacitor is further provided which is connected between a gate of the second field effect transistor and the drain of the first field effect transistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high frequency oscillator circuit, a phase-locked loop circuit (referred to as a PLL circuit hereinafter) using the high frequency oscillator circuit, a semiconductor device using the PLL circuit, and a communication apparatus including the semiconductor device. In particular, the present invention relates to a high frequency oscillator circuit for generating a high frequency signal such as a microwave signal, a quasi-millimeter wave signal or a millimeter wave signal, utilizing two field effect transistors with a feedback circuit of a short-stub transmission line and one field effect transistor, and further relates to a PLL circuit using the high frequency oscillator circuit, a semiconductor device using the PLL circuit, and a communication apparatus using the semiconductor device.

2. Description of the Related Art

FIG. 12is a circuit diagram of a high frequency oscillator circuit201according to a first prior art. The high frequency oscillator circuit201is an oscillator circuit using a cross-coupled type multivibrator and, as shown inFIG. 12, is configured to include two field effect transistors51and52, a capacitor C1, inductors L1and L2, and a direct-current voltage source22, and then, achieves an oscillating operation by developing a negative resistance.

FIG. 13is a circuit diagram of a high frequency oscillator circuit202according to a second prior art. The high frequency oscillator circuit202is a gate and source feedback type oscillator circuit, and as shown inFIG. 13, it is configured to include a field effect transistor1, two transmission lines11and12(which are generally microstrip lines or coplanar lines on a semiconductor substrate or a dielectric substrate) constituting short-stub feedback circuits, respectively, a high frequency blocking inductor Lc1, and two direct-current voltage sources21and22, and then, achieves an oscillating operation by developing a negative resistance. The high frequency oscillator circuit202performs the oscillating operation in the case where an input impedance Zin of the field effect transistor1when seen from an output terminal To connected to a drain of the field effect transistor1satisfies the following expressions (1) and (2):
Re(Zin)+RL<0  (1), and
Im(Zin)=0  (2),

where Re(•) denotes a real number part of an argument and Im(•) denotes an imaginary part of the argument, and these will apply hereinafter. In addition, RLdenotes a load resistance value.

FIG. 14is a graph showing simulation results of the high frequency oscillator circuit201shown inFIG. 12and showing a normalized oscillation frequency relative to a Q-value of the inductor. A reference oscillation frequency for normalization is 50 GHz. As apparent fromFIG. 14, the high frequency oscillator circuit201is disadvantageously required to include the inductor having a relatively high Q-value.

Furthermore, the high frequency oscillator circuit202shown inFIG. 13has the following problems. A line length of each of the transmission lines11and12connected to the gate and source of the field effect transistor1, respectively, is relatively large (e.g., about 1.5 millimeters (mm) in a 30-GHz oscillator circuit using microstrip lines having a width of 14 micrometers (μm)). An area of the high frequency oscillator circuit202is made large, a loss of each of the short-stub feedback circuits increases, and a Q-value of the circuit decreases.

Moreover, the Japanese patent laid-open publication No. JP-7-221545-A discloses a cascade-coupled type voltage-controlled oscillator capable of pulling out sufficiently high negative resistance characteristic from the circuit and having strong oscillation power. The voltage-controlled oscillator is a cascade-connected voltage-controlled oscillator in which a direct-current flowing from a power source is applied first to a transistor of an oscillation amplifier unit and then to a transistor of a buffer amplifier. Furthermore, a resistance that decides the direct-current of the voltage-controlled oscillator is connected to the transistor of the buffer amplifier outside of a feedback loop of the oscillation amplifier unit. Due to this, the resistance that decides the direct-current of the voltage-controlled oscillator does not act as a loss resistance of the feedback loop of the oscillation amplifier unit. Therefore, sufficiently high negative resistance characteristic can be pulled out from the voltage-controlled oscillator, and this leads to that the cascade-connected voltage-controlled oscillator can output strong oscillation power. The voltage-controlled oscillator is configured so that not the feedback circuit but the transistor of the oscillation amplifier unit is connected to a source of the transistor of the oscillation amplifier and in which an oscillation signal is outputted from a drain of the transistor of the oscillation amplifier unit.

The Japanese patent laid-open publication No. JP-8-107309-A discloses a voltage-controlled oscillator circuit capable of dealing with low frequency noise output from a power source circuit of the voltage-controlled oscillator circuit without any connection of a ripple filter or the like to an outside circuit of the voltage-controlled oscillator circuit. The voltage-controlled oscillator circuit is characterized in that a capacitor that grounds a base of an amplification transistor of a buffer amplifier circuit unit in a low frequency alternating current manner, the buffer amplifier circuit is allowed to be regarded as a ripple filter for the low frequency noise added to the buffer amplifier circuit unit from the power source circuit and is allowed to perform ordinary amplification operation for a signal applied from an oscillator circuit unit. The voltage-controlled oscillator circuit is configured so that not a feedback circuit but a transistor of the oscillator circuit unit is connected to a source of the amplification transistor of the buffer amplifier unit.

The Japanese patent laid-open publication No. JP-10-209752-A discloses an oscillator circuit constituted as a microwave integrated circuit so as to be able to obtain optimum oscillation states with selected frequencies even if a resonance frequency of a resonance circuit is selected over a wide frequency range. In the oscillator circuit constituted as a microwave integrated circuit, an external terminal is arranged at a gate of an oscillation field effect transistor, and a resonance circuit is connected to the external terminal. Further, a series-connected circuit in which a first feedback capacitance and a first switch field effect transistor are connected in series and a series-connected circuit in which a second feedback capacitance and a second switch field effect transistor are connected in series are arranged in parallel between a source of the oscillation field effect transistor and a ground. By turning on or off the two switch field effect transistors at a gate-controlled voltage, it is possible to change a feedback capacitance value to, for example, three types of values and to obtain oscillation states optimum for three types of resonance frequencies. The oscillator circuit constituted as a microwave integrated circuit is configured so that a frequency selection switch field effect transistor is connected to the source of the oscillation field effect transistor.

Each of the oscillator circuits disclosed in the Japanese patent laid-open publications Nos. JP-7-221545-A, JP-8-107309-A, and JP-10-209752-A has the following problems. It is difficult to make an area of the oscillator circuit smaller, and it is difficult for the oscillator circuit to oscillate with a higher oscillation frequency.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a high frequency oscillator circuit, a PLL circuit using the high frequency oscillator circuit, a semiconductor device using the PLL circuit, and a communication apparatus using the semiconductor device, which are capable of solving the above-stated problems, without any inductor having a higher Q-value, and are made smaller in size and oscillating with a higher oscillation frequency as compared with the prior arts.

According to a first non-limiting aspect of the present invention, there is provided a high frequency oscillator circuit including first and second field effect transistors. The first field effect transistor has a gate connected to a short-stub transmission line and a drain connected to an oscillation output terminal, and the second field effect transistor has a drain connected to a source of the first field effect transistor and a grounded source. The high frequency oscillator circuit oscillates by using a feedback circuit including the short-stub transmission line and the second field effect transistor.

In addition, the above-mentioned high frequency oscillator circuit preferably further includes a feedback capacitor connected between a gate of the second field effect transistor and the drain of the first field effect transistor.

Further, the above-mentioned high frequency oscillator circuit preferably further includes a variable reactance element connected to a gate of the second field effect transistor, where an oscillation frequency of the high frequency oscillator circuit is changed by adjusting a reactance value of the variable reactance element.

According to a second non-limiting aspect of the present invention, there is provided a PLL circuit including the voltage-controlled oscillator circuit.

According to a third non-limiting aspect of the present invention, there is provided a semiconductor device including the PLL circuit.

According to a fourth non-limiting aspect of the present invention, there is provided a communication apparatus including the semiconductor device.

According to a non-limiting embodiment of the high frequency oscillator circuit, it is not necessary to provide any inductor having-a large Q-value, and the high frequency oscillator circuit can be made so as to be smaller in size and to oscillate with a higher oscillation frequency than those of the prior arts. In addition, by constituting the PLL circuit using the high frequency oscillator circuit or the communication apparatus using the PLL circuit, it is advantageously possible to generate a local oscillation signal in a band of, for example, several tens of gigahertz, to realize high-speed transmission of large-capacity information, and to satisfy requirements of downsizing and the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described hereinafter with reference to the drawings. In the preferred embodiments, the same components are denoted by the same reference symbols.

First Preferred Embodiment

FIG. 1is a circuit diagram of a high frequency oscillator circuit101according to a first preferred embodiment of the present invention. The high frequency oscillator circuit101according to the first preferred embodiment is characterized, as compared with the high frequency oscillator circuit202ofFIG. 13, in that a field effect transistor2operating as a feedback circuit is connected to a source of an oscillation field effect transistor2in place of the transmission line12ofFIG. 13.

Referring toFIG. 1, a gate of the oscillation field effect transistor1is grounded via a short-stub transmission line (or short-circuit stub transmission line)11having a characteristic impedance Zo and a delay time τg and a variable direct-current voltage source21for applying a gate bias voltage Vg1, and further, a drain of the oscillation field effect transistor1is grounded via a high frequency blocking inductor Lc1and a direct-current voltage source22for applying a direct-current voltage Vd. A source of the oscillation field effect transistor1is connected to a drain of the field effect transistor2acting as a feedback circuit and having a grounded source, and a gate of the field effect transistor2is grounded via an inductor Lc2and a variable direct-current voltage source23for applying a gate bias voltage Vg2. In addition, an oscillation signal output from the drain of the oscillation field effect transistor1is grounded via an output terminal To, a load resistance RL, and a coupling capacitor Cc.

The high frequency oscillator circuit101configured as stated above exhibits the following characteristic functions and advantageous effects as will be described later in detail with reference to simulation results shown inFIGS. 5 to 10.

(1) The high frequency oscillator circuit101can oscillate with a higher oscillation frequency and can be made smaller in area as compared with the prior arts since it is advantageously possible to reduce a line length by replacing the source-side transmission line12by the field effect transistor2.

(2) A change in the oscillation frequency according to a change in an inductance of the inductor Lc2can be suppressed quite small, and the deviation in the oscillation frequency can be reduced even if a process irregularity is present. In other words, inductance dependency of the circuit101(sensitivity to change in inductance) can be reduced and the margin between the actual value and the design value can be made larger, and this leads to easily designing of the circuit101.

Second Preferred Embodiment

FIG. 2is a circuit diagram of a high frequency oscillator circuit102according to a second preferred embodiment of the present invention. As shown inFIG. 2, the high frequency oscillator circuit102according to the second preferred embodiment is characterized, as compared with the high frequency circuit101ofFIG. 1, in that a capacitor Cf for feeding back an oscillation output signal to a field effect transistor2is inserted between the gate of the field effect transistor2and the drain of the field effect transistor1. In this case, the feedback capacitor Cf and the inductor Lc2constitute a high-pass filter circuit.

The high frequency oscillator circuit102configured as stated above can exhibit the same functions and advantageous effects as those of the high frequency oscillator circuit101as will be described later in detail with reference to the simulation results shown inFIGS. 5 to 10. In addition, the high frequency oscillator circuit102can perform an oscillating operation with a higher oscillation frequency than that of the high frequency oscillator circuit101, further reduce the change in the oscillation frequency according to the change in the inductance of the inductor Lc2, i.e. the sensitivity can be further reduced. Besides, even if the process irregularity is present, it is possible to further reduce the deviation in the oscillation frequency.

Third Preferred Embodiment

FIG. 3is a circuit diagram of a voltage controlled type high frequency oscillator circuit103according to a third preferred embodiment of the present invention. As shown inFIG. 3, the voltage controlled type high frequency oscillator circuit103according to the third preferred embodiment is characterized, as compared with the high frequency circuit102ofFIG. 2, in that a varactor diode D1is inserted between a gate of a field effect transistor2and a direct-current voltage source21. In this case, one end of a transmission line11is connected to a gate of a field effect transistor1, the other end of the transmission line11is connected to a cathode of the varactor diode D1, and an anode of the varactor diode D1is grounded. In addition, the cathode of the varactor diode D1is connected to the variable direct-current voltage source21via a high frequency blocking inductor Lc3. The variable direct-current voltage source21applies a direct-current bias voltage Vg1to the inductor Lc3, the varactor diode D1, and the field effect transistor1. By changing the direct-current bias voltage Vg1applied from the variable direct-current voltage source21, a capacitance value of the varactor diode D1is changed. It is thereby possible to change an electric length of a feedback circuit connected to the gate of the field effect transistor1and to change an oscillation frequency of the high frequency oscillator circuit103.

The voltage controlled type high frequency oscillator circuit103configured as stated above can exhibit the same functions and advantageous effects as those of the high frequency oscillator circuits101and102. In addition, the oscillation frequency of the high frequency oscillator circuit103can be easily changed by adjusting or changing the direct-current bias voltage Vg1.

In the present preferred embodiment, the varactor diode D1is used, however, the present invention is not limited to this. A variable reactance element that can change a reactance value can be used in place of the varactor diode D1. In addition, the high frequency oscillator circuit103may dispense with the feedback capacitor Cf.

Fourth Preferred Embodiment

FIG. 4is a circuit diagram of a PLL circuit70including the high frequency oscillator circuit103according to a fourth preferred embodiment of the present invention.

Referring toFIG. 4, a reference oscillation signal generated by a reference oscillator31and having a reference oscillation frequency is inputted to a phase comparator32whereas a high frequency oscillation signal from a voltage-controlled oscillator circuit103is inputted to the phase comparator32via a 1/N frequency divider34dividing an input signal by a frequency division ratio N. The phase comparator32outputs a signal indicating a result of phase comparison between the input two signals to the voltage-controlled oscillator circuit (VOC)103via a low-pass filter (LPF)33. The VOC circuit103outputs a high frequency oscillation signal to a load resistance RL via an output terminal To and a coupling capacitor Cc, and also outputs the same signal to the 1/N frequency divider34. The direct-current bias voltage Vg2shown inFIG. 3corresponds to an output voltage from the LPF33.

The PLL circuit70as configured as stated above can oscillate and output a high frequency oscillation signal synchronously with the reference oscillation signal generated by the reference oscillator31having higher oscillation frequency accuracy and having a frequency of N times as high as the reference oscillation frequency as well known.

FIG. 15is a block diagram of a wireless data communication transceiver including the PLL circuit70ofFIG. 4.

Referring toFIG. 15, the wireless data communication transceiver includes an antenna71, a circulator72, a low-noise amplifier73, a mixer74, a band-pass filter75, a demodulator76, a signal processing circuit80, a modulator77, a mixer78, a band-pass filter79, a power amplifier81, and the PLL circuit70ofFIG. 4, which is used as a local oscillator for generating local oscillation signals for transmission and receiving and outputting the same local oscillation signals to the mixers74and78. The PLL circuit70, the mixer74and the low-noise amplifier73can be constituted by a RF LSI (Radio Frequency Large Scaled Integrated circuit)70of a semiconductor device.

Referring toFIG. 15, the signal processing circuit80receives a data signal, performs a predetermined transmission signal processing on the received data signal, and output a resulting baseband signal including the data signal to a modulator77, which modulates a carrier signal according to the inputted baseband signal and outputs a modulated signal to a mixer78. The mixer78mixes the modulated signal with the local oscillation signal from the PLL circuit70to generate a mixed signal to the power amplifier81through the band-pass filter79for passing therethrough a wireless transmission signal, which is outputted to the antenna71through the circulator72to radiate the wireless transmission signal from the antenna71.

On the other hand, a wireless received signal is received by the antenna71, and is inputted to the mixer74through the circulator72and the low-noise amplifier73. The mixer74mixes the wireless received signal with the local oscillation signal from the PLL circuit70, and outputs a mixed signal through a band-pass filter75to the demodulator76, which demodulates a filtered mixed signal to generate and output a demodulated baseband signal to the signal processing circuit80. The signal processing circuit80receives the same baseband signal, performs a predetermined receiving signal processing on the baseband signal, and output a resulting data signal.

The simulations of CMOS integrated circuits including the high frequency oscillator circuits101,102,201and202according to the first preferred embodiment, the second preferred embodiment, the first prior art, and the second prior art, respectively and formed by 0.18 μm process, and simulation results will next be described.

FIG. 5is a graph showing simulation results of the high frequency oscillation circuit201shown inFIG. 12according to the first prior art and showing a normalized oscillation frequency relative to the inductance of the inductors L1and L2(L1=L2).FIG. 6is a graph showing simulation results of the high frequency oscillation circuit202shown inFIG. 13according to the second prior art and showing a normalized oscillation frequency relative to the delay time τs of the source-side transmission line12.FIG. 7is a graph showing simulation results of the high frequency oscillation circuit101shown inFIG. 1according to the first preferred embodiment and showing a normalized oscillation frequency relative to the inductance of the inductor Lc2.FIG. 8is a graph showing simulation results of the high frequency oscillation circuit102shown inFIG. 2according to the second preferred embodiment and showing a normalized oscillation frequency relative to the inductance of the inductor Lc2. In the simulations ofFIGS. 5 to 8, the reference oscillation frequency for normalization is 50 GHz.

The oscillation frequency of the high frequency oscillator circuit101shown inFIG. 7is almost equal to that of the high frequency oscillator circuit202shown inFIG. 6. However, the oscillation frequency of the high frequency oscillator circuit102shown inFIG. 8is about 1.2 times as high as that of the high frequency oscillator circuit201shown inFIG. 5and about 1.5 times as high as that of the high frequency oscillator circuit202shown inFIG. 6. Therefore, it is seen that the high frequency oscillator circuits101and102according to the first and second preferred embodiments, respectively, can oscillate with a higher frequency. Moreover, the high frequency oscillator circuit102shown inFIG. 8can make the change in the oscillation frequency small according to the change in the inductance of the inductor Lc2. Even if the process irregularity is present, the irregularity in the oscillation frequency can be reduced. In other words, the inductance dependency can be reduced and the margin between the actual value and the design value can be made larger, and this leads to easily designing of the same circuit.

FIG. 11is a circuit diagram for explaining an input impedance Zin of an ordinary RLC series-connected oscillator circuit105which corresponds to an oscillator circuit unit of each of the high frequency oscillator circuits101,102and103according to the first, second and third preferred embodiments and to which a load resistance RL is connected when seen from an output terminal To of the ordinary RLC series-connected oscillator circuit105. The oscillation conditions for this ordinary oscillation circuit105are similar to those represented by the above expressions (1) and (2), and an oscillation frequency of the ordinary oscillation circuit105corresponds to the frequency when the value of a left-hand side of the expression (2) changes from negative to positive.

FIG. 9is a graph showing simulation results of the high frequency circuit101and showing a frequency characteristic of the impedance.FIG. 10is a graph showing simulation results of the high frequency circuit102and showing a frequency characteristic of the impedance. At a point61ofFIG. 9, an imaginary part Im(Zin)=0 but a real number part Re(Zin)+RL>0. Due to this, the above-stated oscillation conditions are not satisfied. That is, if there is no feedback capacitance in the high frequency oscillator circuit101shown inFIG. 9, it is necessary to increase a line length of the gate-side transmission line11so as to satisfy the oscillation conditions. This disadvantageously makes the oscillation frequency lower. In order to solve this problem, the feedback capacitor Cf is inserted in the high frequency oscillator circuit102shown inFIG. 2. Then this leads to that the negative resistance can be intensified and the oscillation frequency can be made higher as obvious fromFIG. 10.

As stated so far, each of the high frequency oscillator circuits101,102and103according to the respective preferred embodiments of the present invention can satisfy the oscillation conditions even if the line length of the gate-side transmission line is smaller than that of the gate-side transmission line satisfying the oscillation conditions in the gate and source feedback oscillator circuit. That is, it is possible to satisfy the oscillation conditions even with a higher frequency. Furthermore, by making the gate-side transmission line11shorter and replacing the source-side transmission line12by the field effect transistor2, it is possible to make the circuit area smaller.

In the high frequency oscillator circuit102shown inFIG. 2, the inductance of the inductor Lc2of the high-pass filter circuit constituted by the feedback capacitor Cf and the inductor Lc2is equal to or smaller than 0.1 nH, and the increase in area is small. In addition, since the change in the oscillation frequency according to the inductance and the capacitance of the high frequency oscillator circuit102is small and the oscillation frequency is decided by the line length of the gate-side transmission line11, the high frequency oscillator circuit102is excellent in design and reproducibility. Besides, by adopting a microstrip line having a grounded bottom-layer wiring as the transmission line11, it is possible to remove the influence of, for example, conductive silicon semiconductor substrate.

Each of the high frequency oscillator circuits101,102and103and the PLL circuit using the high frequency oscillator circuit103configured as stated so far according to the respective preferred embodiments can be formed in a semiconductor device such as a CMOS semiconductor integrated circuit, and the PLL circuit can generate a local oscillation signal in a band of, for example, several tens of gigahertz. A wireless communication apparatus using the PLL circuit can realize high-speed transmission of large-capacity information and can satisfy requirements such as downsizing. The examples of the wireless communication apparatus include a portable telephone, and examples of the semiconductor device used in the wireless communication apparatus include applications such as UWB (Ultra Wide Band) applications and a transceiver LSI for high-speed communication in a 60 GHz band.

As stated so far in detail, the high frequency oscillator circuit according to the present invention can advantageously dispense with an inductor having a higher Q-value, and can advantageously be made small in size and oscillate with an oscillation frequency higher than that of the prior arts. In addition, by constituting the PLL circuit using the high frequency oscillator circuit or the communication apparatus using the PLL circuit, it is advantageously possible to generate a local oscillation signal in a band of, for example, several tens of gigahertz, to realize high speed transmission of large-capacity information, and to satisfy such requirements as downsizing.