JPH09294020A - Voltage-controlled oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the factors of malfunctions and abnormal oscillations by preparing an HPF and an LPF having the frequency cut-off characteristic where the attenuation response characteristics are overlapping with each other together with one of HPF and LPF serving as a variable filter. SOLUTION: The input of an LPF 2 is connected to the output of a differential amplifier 1, and the input and the output of a variable HPF 3 are connected to the output of the LPF 2 and the positive phase input of the amplifier 1 respectively. The output of the amplifier 1 is positively fed back to the positive phase input of the amplifier 1 via the LPH 2 and the HPF 3. Then the bias voltage of a low voltage source 5 is supplied to the opposite phase input side of the amplifier 1, and the frequency characteristic of the HPF 3 is controlled by the control voltage VH. Both LPF 2 and HPF 3 control the positive feedback value set to the amplifier 1 based on the frequency and performs the control of oscillation frequency fo. In other words, the frequency fo is controlled by the control of the characteristic of the LPF 3. Furthermore, the range of oscillation frequency is limited by the LPF 2 of a higher order and the sharp cut-off characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage controlled oscillator circuit, and more particularly to a voltage controlled oscillator circuit (hereinafter VCO) used in a PLL (phase locked loop).

[0002]

2. Description of the Related Art A VCO system is a PLL (Phase).
Locked Loop) is essential for operation,
At present, how to operate stably and how to simplify can be a problem.

FIG. 1 is a block diagram showing a conventional first VCO.
5, the first conventional VCO has a differential amplifier 1 whose output is positively fed back and outputs an output signal O, a capacitor C10 connected between the output of the differential amplifier 1 and the ground, and a capacitor C.
10, a variable reactance circuit 101 connected between the output of the differential amplifier 1 and ground, which is controlled in response to the supply of the control voltage VX, an anti-phase input of the differential amplifier 1 and ground. And a constant voltage source 5 for bias connected between them.

Now, assuming that the capacitance value of the capacitance C10 is C, the inductance value of the inductance L10 is L, and the equivalent capacitance value of the variable reactance circuit 101 is Cx, the VCO
Oscillates at the oscillation frequency fo of the equation (1).

Fo = 1 / 2π {L (C + Cx)} ^1/2 (1) The oscillation frequency fo corresponds to the equivalent capacitance value Cx of the variable reactance circuit 101 by the control voltage VX. It can be controlled and varied.

The output impedance Z1 is given by the equation (2).

Z1 = jωL / {(1-ω ² L (C + Cx)} ………………………… (2) From equations (1) and (2), the output impedance is large when the oscillation frequency is high. I see.

Referring to FIG. 16, which shows a block diagram of the conventional second VCO in common with reference numerals / numerals common to those of FIG. 15, the second conventional VCO is shown.
Is a differential amplifier 1 common to the first VCO, a variable reactance circuit 101, a constant voltage source 5, and a capacitance C1.
An oscillator 102 connected between the output of the differential amplifier 1 and the ground is provided instead of 0 and L10.

FIG. 15 showing an equivalent circuit of the oscillator 102.
Referring to (B), this oscillator 102 has a resistor R20.
This is equivalent to the parallel connection of the series component of 1, the inductance L201, and the capacitance C201 and the capacitance C202. Now here,
The value of the resistor R201 is R, the value of the inductance L201 is L, the value of the capacitor C201 is C1, and the value of the capacitor C202 is C.
0, and the equivalent capacitance value of the variable reactance circuit 101 is Cx, the VCO oscillates at the oscillation frequency fo of the equation (3). fo = 1 / 2π {L (C0 + Cx) C1 / (C0 + C1 + Cx)} ^1/2 (3) Like the first VCO, the oscillation frequency fo controls the equivalent capacitance value Cx of the variable reactance circuit 101 by the control voltage VX. Can be changed.

By using the oscillator 102, the external parts are simplified as compared with the first conventional VCO.

The output impedance Z2 is given by equation (4). ^{Z2 = (1-ω 2 C1L} + jωRC1) / {- ω 2 C1 (CO + Cx) R + jω (R + C1) ω 2 CC1 (CO + Cx) L} .................................... (4) (3) wherein From equation (4), it can be seen that the output impedance increases when the oscillation frequency is high.

In addition, the output impedance | Z2 | of the conventional second VCO which is most often used in recent years (C
The rate of change with respect to O + Cx) is calculated as (Co +
If Cx) is Cv, the rate of change d | Z | (CV) / d
(CV) is expressed by the following equation (5). d | Z | (CV) / d (CV) = {LC1 (2Cv + C1) (R ² Cv ² + R ² C1Cv + 2LC1)} / {2RCv ² (Cv + C1) (LR ² C1Cv ² + L R ² C1 ² Cv + L ² C1 ² ) } ^1/2 ………………………………………… (5) From this, there is a pole at Cv = -C1 / 2 and a discontinuity at Cv = 0, -C1. Since Cv is considered to be 0 or more, C
Discontinuity that occurs when v = 0, that is, Cv = Co + Cx
= 0, there is a possibility of abnormal oscillation. Therefore, in the negative capacitance region of the variable reactance circuit, it is not possible to control the value above the value CO of the parallel capacitance C202 of the oscillator 102. That is, the variable range is limited by the oscillator 102, and there is a problem that the capture range can be secured only about ± several%.

[0013]

The above-mentioned first and second conventional voltage controlled oscillator circuits always require a coil (inductance L) and an oscillator for setting the oscillation frequency,
Since it is difficult to incorporate the LSI in consideration of the LSI, it has a drawback that the number of external elements is increased and the size of the substrate is hindered.

When the oscillating frequency becomes high, the output increases with the increase of the output impedance, and the variable range in the high range is avoided in order to avoid the inoperability due to the saturation of the circuit caused by the input / output dynamic range excess of the differential amplifier or the like. However, there are drawbacks such as the limitation of the above, or a special circuit configuration corresponding to the oscillation frequency range. An object of the present invention is to solve the above-mentioned drawbacks and to eliminate the need for an external element to facilitate LSI implementation, and to prevent malfunctions due to excess of the dynamic range due to an increase in oscillation frequency, abnormal oscillation, control oscillation range restrictions, or circuit configuration. An object is to provide a voltage controlled oscillator circuit that solves the problem of complication.

[0015]

SUMMARY OF THE INVENTION A voltage controlled oscillator circuit of the present invention includes an amplifier circuit having a positive feedback path for an output signal and outputting the output signal as an oscillation signal, and a control voltage supplied to the positive feedback path. In a voltage controlled oscillator circuit including a frequency control means for responding to change the reactance and controlling the frequency characteristic of the positive feedback path, the frequency control means comprises:
A high-pass filter that is a variable filter that has predetermined cut-off frequency characteristics such that attenuation response characteristics overlap in a predetermined frequency range, and one of which has a variable cut-off frequency characteristic in response to the supply of the control voltage; And a low pass filter.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the first embodiment of the present invention will be described with reference to FIG. If you refer to
The voltage controlled oscillator circuit according to the present embodiment shown in this figure has a low-pass filter (hereinafter referred to as an LPF) in which an input is connected to the output of the differential amplifier 1 in addition to the differential amplifier 1 and the constant voltage source 5 which are common to the conventional one. 2) and a variable high-pass filter (hereinafter referred to as HPF) 3 having an input connected to the output of the LPF 2 and an output connected to the positive phase input of the differential amplifier 1.

The output of the differential amplifier 1 is the LPF 2 and the variable HP.
A positive feedback side is fed to the positive phase input of the differential amplifier 1 via F3, the bias voltage of the constant voltage source 5 is supplied to the negative phase input side of the differential amplifier 1, and the variable HPF has a frequency characteristic by the control voltage VH. Is controlled.

Next, the operation of the present embodiment will be described with reference to FIG. 1 (A) and FIG. 2 (A) showing operating characteristics in a graph. The LPF2 and the variable HPF3 are differentially operated depending on the frequency. The amount of positive feedback to the amplifier 1 is controlled to control the oscillation frequency fo.

Referring to FIG. 2A, when the cutoff characteristics of the variable HPF 3 are set to H1, H2, and H3, the positive feedback amount is the frequency at which the positive feedback amount to the differential amplifier 1 becomes maximum, that is, maximum feedback. The frequencies are f1 and f, respectively
2, f3, and this VCO is f1, f2, f3
Oscillates at. That is, the oscillation frequency fo can be controlled by controlling the variable HPF characteristic.

Referring to FIG. 2B, which shows a graph of the operating characteristics when the LPF2 is of a higher order, that is, when the cutoff characteristics are sharpened, referring to FIG. 2B, the cutoff characteristics of the variable HPF3 are H1, H2 and H3 as in FIG. 2A. When each is set to, the maximum feedback frequencies f1A, f2A, and f3A have a smaller frequency width than (A). In other words, the oscillation frequency range can be limited by setting the LPF 2 to a higher order and sharpening the cutoff characteristic, and abnormal oscillation or the like at the time of power supply rising or the like when the circuit is unstable can be prevented.

Referring to FIG. 1B, which is a circuit diagram showing the configuration of the first concrete circuit of the present embodiment, the VCO L
PF2 is a resistor R whose one end is connected to the output of the differential amplifier 1.
21 and a capacitor C21 connected between the other end of the resistor R21 and the ground.

The variable HPF 3 has a capacitor C31 having one end connected to the other end of the resistor R21 and the other end connected to the positive phase input of the differential amplifier 1, and a resistor R31 having one end connected to the power supply VCC.
A PNP transistor Q31 having an emitter connected to the power supply VCC; a PNP transistor Q32 having an emitter connected to the other end of the resistor R31 and a base and a collector connected to the base of the transistor Q31 to form a current mirror circuit with Q31; N is connected to the collector of the transistor Q32, the emitter of which is connected to the other end of the resistor R32 whose one end is grounded, and the base of which is supplied with the control voltage VH.
A PN transistor Q33 and an NPN transistor Q3 having a collector connected to the other end of the capacitor C31, a base connected to the collector of the transistor Q31 and an emitter connected to ground.
4 is provided.

To explain the operation, the transistor Q
33 controls the collector current, that is, the collector current of the transistor Q32 constituting the input side of the current mirror circuit, in response to the control voltage VH supplied to the base. The collector current of the transistor Q32 is supplied as the collector current of the transistor Q31 on the output side of the current mirror circuit, that is, the base current of the transistor Q34.
The collector-emitter resistance (hereinafter collector resistance) Z34 of the transistor Q34 is controlled. As a result, the frequency cutoff characteristic of the HPF including the collector resistance Z34 and the capacitance C31 is controlled. The collector resistance Z34 is expressed by the following equation. Z34 = α / (R31 · VH) …………………………………… (6) where α is the proportional constant, R31 is the resistance value of the resistor R31 (hereinafter, for other elements, VH is the voltage of the control voltage VH.

The cutoff frequency fsh of the variable HPF 3 is given by the following equation. fsh = 1 / (2πZ34C31) …………………………………… (7) If this circuit is implemented as an LSI, if resistors R21 and R31 are the same type of resistor, the manufacturing resistance will increase. It is possible to cancel the variation of.

FIG. 1 shows a second specific circuit example of this embodiment.
Referring to FIG. 3 in which components common to those are attached with common characters and similarly shown in the circuit diagram, the difference from the first specific circuit example described above is that the variable HPF 3A includes a transistor Q34 for varying the output resistance. Of the differential amplifier 31 which is totally fed back, and the output side transistor Q31 of the first current mirror circuit.
Is provided with a second current mirror circuit including transistors Q35 and Q36 for controlling the gain of the differential amplifier 31 in response to the supply of the collector current of the above.

Output impedance Z3 of the differential amplifier 31
1 is represented by the following equation. Z31 = β / R31 · VH ………………………………………… (8) where β is a proportional constant.

The cutoff frequency fsha of the variable HPF 3A is given by the following equation. fsha = 1 / (2πZ31C31) …………………………………………………………………………………………………………………………………………………………………… (9) Referring to FIG. 4, which is also shown in a circuit diagram, the difference from the above-described first specific circuit example is that the variable HPF 3B of this circuit turns on / off the transistor Q34 corresponding to the voltage of the power supply VCC. That is, the comparison circuit 32 for control is provided.

The voltage comparison circuit 32 has resistors R33 to R35 each having one end connected to the power supply VCC, a PNP transistor Q37 having an emitter connected to the resistor R34, a base connected to the other end of the resistor R33, and a collector connected to ground.
Diodes D31 to D33, which are connected in series and whose cathode is grounded at a common connection point between the other end of the resistor R33 and the transistor Q37, the emitter is the emitter of the transistor Q37, the base is the other end of the resistor R35, and the collector is the transistor Q31. , And a resistor R36 whose one end is connected to the other end of the resistor R35 and whose other end is connected to the ground.

The comparison circuit 32 operates under the condition of the following expression of the power supply voltage VCC. 3VBE (R35 + R36) / R46 <VCC ... (10) However, VBE represents the forward voltage of the diodes D31 to D33.

As can be seen from the equation (10), the transistor Q34 is forcibly operated until VCC becomes larger than the voltage value determined by the diodes D31 to D33 and the resistors R35 and R36, and the collector resistor Z34 of the transistor Q34 is operated.
Is held at the lowest value, the positive feedback amount of the differential amplifier 1 is held at the lowest. As a result, abnormal oscillation that occurs when the power is turned on is prevented, and control is performed so that the oscillation operation is performed at or above VCC at which stable operation is performed.

Next, a second embodiment of the present invention will be described with reference to FIG.
Constituent elements common to (A) are designated by common characters and are similarly represented by blocks. With reference to FIG. 5A, the difference between this embodiment shown in this figure and the first embodiment described above is shown. The point is L
Instead of the PF2, a variable LPF7 whose frequency characteristic is controlled in response to the supply of the control voltage VL is provided, and instead of the variable HPF3, a fixed HPF8 is provided.

Next, the operation of the present embodiment will be described with reference to FIG. 5A and FIG. 6A showing the operating characteristics in the form of a graph. In the same way as in the first embodiment, the variable LPF will be described.
7 and the HPF 8 control the amount of positive feedback to the differential amplifier 1 depending on the frequency to control the oscillation frequency fo.

Referring to FIG. 6A, when the cutoff characteristics of the variable LPF 7 are set to L1, L2, and L3, the positive feedback amount is the frequency at which the positive feedback amount for the differential amplifier 1 becomes maximum, that is, the maximum feedback amount. The frequencies are f1 and f, respectively
2, f3, and this VCO is f1, f2, f3
The oscillation frequency fo can be controlled by controlling the variable LPF characteristic.

Referring to FIG. 6 (B), which is a graph showing the operating characteristics when the HPF 8 is of a higher order, that is, when the cutoff characteristics are sharpened, referring to FIG. 6B, the cutoff frequency variation in the same range of the variable LPF 7 is the same as in the first embodiment. It is possible to limit the oscillation frequency range with respect to the range, and prevent abnormal oscillation and the like when the circuit is unstable, such as when the power is turned on.

Referring to FIG. 5B, which is a circuit diagram showing the configuration of the first specific circuit of the present embodiment, the variable LPF 7 of this VCO is an NPN type whose collector is connected to the output of the differential amplifier 1. A transistor Q71, a capacitor C81 having one end connected to the emitter of the transistor Q71 and the other end connected to the ground, and a resistor R71 having one end connected to the power supply VCC,
A PNP transistor Q72 having an emitter connected to the power supply VCC, an emitter connected to the other end of the resistor R71, a base and a collector connected to the base of the transistor Q72, respectively.
71, a PNP transistor Q73 forming a current mirror circuit, and an NPN whose collector is connected to the collector of the transistor Q73 and the other end of a resistor R72 whose emitter is grounded at one end, and whose base is supplied with the control voltage VL.
Type transistor Q74.

The HPF 8 has a capacitor C81 having one end connected to the emitter of the transistor Q71 and the other end connected to the positive phase input of the differential amplifier 1, and a resistor R81 connected between the other end of the capacitor C81 and the ground. .

To explain the operation, the transistor Q
74 controls the collector current, that is, the collector current of the input side transistor Q73 of the current mirror circuit in response to the control voltage VL supplied to the base. The collector current of the transistor Q73 is supplied as the collector current of the output side transistor Q72 of the current mirror circuit, that is, the base current of the transistor Q71, and controls the collector-emitter resistance (hereinafter collector resistance) Z71 of the transistor Q71. As a result, the collector resistance Z71
The frequency cutoff characteristic of the LPF including the capacitor C71 and the capacitor C71 is controlled. The collector resistance Z71 is expressed by the following equation.

Z71 = γ / (R71 · VL) …………………………………… (11) where γ is a proportional constant.

The cutoff frequency fsl of the variable LPF 7 is given by the following equation. fsl = 1 / 2πZ71C71 ………………………………………… (12) When this circuit is implemented as an LSI, the resistors R71 and R81 are of the same type as in the first embodiment. If a resistor is used, it is possible to cancel variations in resistance due to manufacturing.

FIG. 5 shows a second concrete circuit example of the present embodiment.
Referring to FIG. 7 in which components common to those are denoted by common characters in the same manner as in the circuit diagram, the difference from the first specific circuit example is that the variable LPF circuit 7A is the same as that of the first embodiment. The third
The comparison circuit 32 for preventing abnormal oscillation at power-on similar to the specific circuit example of is provided.

FIG. 5 shows a third specific circuit example of this embodiment.
Referring to FIG. 8 in which components common to and are similarly attached with common characters are shown in a circuit diagram, the difference from the above-described first specific circuit example is that the variable LPF 7B has a differential amplifier 1 at one end. Of the resistor R73 whose other end is connected to one end of the capacitor 81, respectively.
A capacitor C72 having one end connected to the other end of the resistor R73 and the other end connected to the ground, and a multiplication circuit 71 that outputs a current IV in response to a voltage difference between the control voltage VL and the constant voltage source V71.
And a current mirror circuit 72 including transistors Q81 and Q82 for supplying the current IL to the other end of the resistor R73 in response to the supply of the current IV, and the transistor Q8.
3, Q84 and transistors Q85, Q86, and current mirror circuits 73, 74 for supplying the required current of the multiplication circuit 71.

The multiplication circuit 71 includes transistors Q75 to Q8.
0, constant voltage sources V71, V72, constant current sources I71, I72
The capacitor C73 and the capacitor C73 form a known double-balanced multiplication circuit.

The operation will be described with reference to FIG.
When the multiplication circuit 71 outputs a current IV that changes in response to the voltage difference between the control voltage VL and the voltage source V71, the current mirror circuit 72 causes a corresponding output current IL to flow, and this current I
A voltage VCL corresponding to L is generated, and the capacitance component CL seen from the collectors of the output side transistors Q82 and Q85 of the current mirror circuits 72 and 74 corresponding to this voltage VCL.
Changes. The combined capacitance (CL + C72) of the variable capacitance CL and the capacitance C72 and the resistor R73 form an LPF.

The control voltage VL is the voltage V7 of the constant voltage source V71.
When it is lower than 1, each of the voltage VCL and the current IL is VCL.
1 and IL1, the impedance ZCL1 seen from the collectors of the transistors Q82 and Q85 is expressed by the following equation. ZCL1 = VCL1 / 2IL1 = VCL1 / 2gm VCL1 = 1 / 2gm = 2jωC73 …………………………………………………… (13) However, gm consists of transistors Q79 and Q80. It is the transconductance of the differential circuit.

Next, when the control voltage VL is higher than the voltage V71 of the constant voltage source V71, assuming that the voltage VCL and the current IL are VCL2 and IL2, the transistors Q82 and Q8 are set.
The impedance ZCL2 seen from the collector of No. 5 is expressed by the following equation. ZCL2 = VCL2 / 2IL2 = -VCL2 / 2gm VCL2 = -1 / 2gm = -2jωC73 ……………………………………………… (14) Due to the above, the control voltage VL is variable. By this, the capacitance component ZCL viewed from the collectors of the transistors Q79 and Q80 can be controlled from -2C73 to 2C73, and the variable range of the cutoff frequency fsl of the variable LPF 7B is expressed by the following equation. −1 / 4πR73C73 ≦ fs1 ≦ 1 / 4πR73C73 (15) Next, the same components as those of the third embodiment of the present invention in FIG. Referring to FIG. 9 shown by a block in FIG. 9, the difference between the present embodiment shown in this figure and the above-mentioned first embodiment is that, instead of the differential amplifier 1, the positive feedback is directly fed from the output to the positive phase input. Differential amplifier 11 and L
Instead of each of the PF2 and the variable HPF3, an LPF12 and a variable H connected as a load between the output of the differential amplifier 11 and the ground.
Each of the PFs 13 is provided.

Similar to the first embodiment, this embodiment also has the LPF 12 loaded with the positive feedback amount of the differential amplifier 11,
Since it depends on the frequency characteristics of the variable HPF 13, the variable HP
The oscillation frequency can be controlled by controlling F13.

Next, a fourth embodiment of the present invention will be described with reference to FIG.
Referring to FIG. 10, in which components common to (A) have common characters and are similarly represented by blocks, the difference between the present embodiment shown in this drawing and the second embodiment described above is as follows. Instead of the differential amplifier 1, a differential amplifier 11 directly positively fed back from an output to a positive phase input, and instead of each of the variable LPF 7 and HPF 8, a variable LPF 17 and a HPF 18 connected as a load between the output of the differential amplifier 11 and the ground. It is to have each of.

Similar to the second embodiment, this embodiment also has a variable LPF 1 loaded with the positive feedback amount of the differential amplifier 11.
7. Since it depends on the frequency characteristics of HPF 18, variable LP
The oscillation frequency can be controlled by controlling F17.

Next, a fifth embodiment of the present invention will be described with reference to FIG.
Referring to FIG. 11 in which components common to (A) have common characters and are similarly represented by blocks, the difference between this embodiment shown in this drawing and the first embodiment described above is as follows. LPF
A high cut filter 20 including an HPF 21 and a subtractor 22 each of which has an input connected to the output of the differential amplifier 1 instead of 2, and a variable low cut filter 40 including a variable LPF 41 and a subtractor 42 instead of the variable HPF 3. Equipped with.

The high cut filter 20 is the differential amplifier 1
Of the differential amplifier 1 and the subtracter 22 having one input connected to the output of the differential amplifier 1 and the other input connected to the output of the HPF 21, respectively.

The variable low-cut filter 40 is controlled by the control voltage VL and has a variable LPF 41 whose input is connected to the output of the subtractor 22, and one input which is connected to the output of the subtractor 22 and the other input which is connected to the output of the variable LPF 41. And the subtractor 42.

Next, the operation of the present embodiment will be described with reference to FIG. 11 and FIG. 12 showing operating characteristics in a graph. The high cut filter 20 and the variable low cut filter 40 are connected to the differential amplifier 1 depending on the frequency. The amount of positive feedback is controlled to control the oscillation frequency fo. Referring to FIG. 12, the variable low-cut filter 40 has a low-cut characteristic L
When C1, LC2, and LC3 are set, the maximum feedback frequency, that is, the oscillation frequency fo is f1, f2, and
It becomes f3. That is, the oscillation frequency fo can be controlled by controlling the variable low-cut characteristic.

Next, FIG. 11 shows a sixth embodiment of the present invention.
13 in which components common to those are denoted by common characters and similarly shown in blocks, the difference between the fifth embodiment shown in this figure and the fifth embodiment described above is that the high-cut filter 20 Is provided with a variable high-cut filter 25 having a variable HPF 23, and a low-cut filter 45 having an LPF 43 instead of the variable low-cut filter 40.

Next, the operation of the present embodiment will be described with reference to FIG. 13 and FIG. 14 showing the operating characteristics in the form of a graph. The high-cut characteristics HC1 of the variable high-cut filter 25 in place of the low-cut characteristics of the fifth embodiment will be described below. HC
Oscillation frequency fo by setting 2 and HC3 respectively
Can be controlled to f1, f2, and f3, respectively.

[0055]

As described above, the voltage controlled oscillator circuit of the present invention has a cut-off frequency characteristic in which attenuation response characteristics overlap in a predetermined frequency range, and one of them has a variable filter variable with the control voltage. Since the HPF and the LPF as described above are provided, the maximum level of the positive feedback amount can be easily estimated and set by the respective characteristics of the HPF and the LPF, so that the limit oscillation level and the oscillation frequency range can be easily set. It becomes possible to limit, and there is an effect that stable oscillation is possible by eliminating the cause of malfunction or abnormal oscillation.

Further, since the resistor, the capacitor, and the transistor, which can be easily formed on the semiconductor substrate, can be used for the configuration, the external elements which have been conventionally required can be eliminated and the LS can be easily performed.
It is possible to reduce the cost and the mounting area in addition to the I-type.

[Brief description of drawings]

FIG. 1 is a block diagram and a circuit diagram showing a first embodiment of a voltage controlled oscillator circuit of the present invention.

FIG. 2 is a characteristic diagram showing an example of operating characteristics in the voltage controlled oscillator circuit according to the present embodiment.

FIG. 3 is a circuit diagram showing a second specific example of the present embodiment.

FIG. 4 is a circuit diagram showing a third specific example of the present embodiment.

FIG. 5 is a block diagram and a circuit diagram showing a second embodiment of the voltage controlled oscillator circuit of the present invention.

FIG. 6 is a characteristic diagram showing an example of operating characteristics in the voltage controlled oscillator circuit according to the present embodiment.

FIG. 7 is a circuit diagram showing a second specific example of the present embodiment.

FIG. 8 is a circuit diagram showing a third specific example of the present embodiment.

FIG. 9 is a block diagram showing a third embodiment of the voltage controlled oscillator circuit of the present invention.

FIG. 10 is a block diagram showing a fourth embodiment of the voltage controlled oscillator circuit of the present invention.

FIG. 11 is a block diagram showing a fifth embodiment of the voltage controlled oscillator circuit of the present invention.

FIG. 12 is a characteristic diagram showing an example of operating characteristics in the voltage controlled oscillator circuit according to the present embodiment.

FIG. 13 is a block diagram showing a sixth embodiment of the voltage controlled oscillator circuit of the present invention.

FIG. 14 is a characteristic diagram showing an example of operating characteristics in the voltage controlled oscillator circuit according to the present embodiment.

FIG. 15 is a block diagram showing an example of a first conventional voltage controlled oscillator circuit.

FIG. 16 is a block diagram showing an example of a second conventional voltage controlled oscillator circuit.

[Explanation of symbols]

1, 11, 32 Differential amplifier 2, 12, 43 LPF 3, 3A, 3B, 13, 23 Variable HPF 40, 45 Variable low-cut filter 5, V71, V72 Constant voltage source 7, 7A, 7B, 17, 41 Variable LPF 8,18,21 HPF C21, C31, C71, C72, C73, C81
Capacity R21, R31 to R36, R71, R72, R81
Resistors Q31 to Q38, Q71 to Q86 Transistors

Claims (16)

[Claims] 1. An amplifier circuit which has a positive feedback path for an output signal and outputs this output signal as an oscillation signal, and a reactance which is changed in response to the supply of a control voltage to the positive feedback path to change the frequency of the positive feedback path. In a voltage controlled oscillator circuit comprising frequency control means for controlling characteristics, the frequency control means has predetermined cutoff frequency characteristics such that attenuation response characteristics overlap in a predetermined frequency range, and either one of the frequency control means has the cutoff frequency characteristic. A voltage-controlled oscillation circuit comprising a high-pass filter and a low-pass filter which are variable filters that change the cutoff frequency characteristics in response to supply of a control voltage. 2. The amplifier circuit is a differential amplifier circuit in which a bias voltage source is connected to a negative phase input terminal and the positive feedback path is connected to a positive phase input terminal. Voltage controlled oscillator circuit. 3. The voltage controlled oscillator circuit according to claim 1, wherein the fixed filter that is not the variable filter of the high-pass filter and the low-pass filter is a high-order filter of at least a second order or more. 4. The voltage controlled oscillator circuit according to claim 1, wherein the high-pass filter and the low-pass filter are connected in series to form the positive feedback path. 5. The variable filter includes a transistor whose conduction resistance changes in response to the supply of the control voltage and a first capacitor having a predetermined capacitance value.
The voltage controlled oscillator circuit described. 6. The voltage control according to claim 1, wherein the variable filter includes an operational amplifier whose output impedance changes in response to the supply of the control voltage, and a first capacitance having a predetermined capacitance value. Oscillator circuit. 7. The variable filter comprises a variable reactance circuit whose output reactance changes in response to a difference between a resistance having a predetermined resistance value and the control voltage and a second reference voltage. 1. The voltage controlled oscillator circuit according to 1. 8. The voltage controlled oscillator circuit according to claim 1, wherein the high-pass filter and the low-pass filter are connected in parallel to an input end of the positive feedback path as a load of the amplifier circuit. 9. The voltage controlled oscillator circuit according to claim 1, wherein the high pass filter is a variable high pass filter which is the variable filter. 10. The voltage controlled oscillator circuit according to claim 1, wherein the low-pass filter is a variable low-pass filter which is the variable filter. 11. The variable high-pass filter comprises: the variable low-pass filter; and a subtractor that takes a difference between an input and an output of the variable low-pass filter and outputs a difference signal. The voltage controlled oscillator circuit described. 12. The voltage controlled oscillator circuit according to claim 1, wherein the high pass filter is a variable high pass filter which is the variable filter. 13. The voltage controlled oscillator circuit according to claim 1, wherein the low pass filter is a variable low pass filter which is the variable filter. 14. The variable low-pass filter comprises: the variable high-pass filter; and a subtractor that takes a difference between an input and an output of the variable high-pass filter and outputs a difference signal. The voltage controlled oscillator circuit described. 15. The variable filter according to claim 5, further comprising a comparison circuit that controls the conduction resistance to a minimum value when the power supply voltage is lower than a predetermined first reference voltage. Voltage controlled oscillator circuit. 16. The variable reactance circuit includes a first differential circuit for comparing the control voltage and a second reference voltage, and an emitter power source for each of the first differential circuit and the second differential circuit. 8. The voltage controlled oscillator circuit according to claim 7, further comprising a double-balanced type multiplying circuit including a second capacitor having a predetermined capacitance value inserted in the.