JP2000315914A - Oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillation circuit that has a characteristic of a filter feedback type, which produces less output higher harmonics and has high stability, and can control its oscillated frequency over a wide range. SOLUTION: A distribution circuit 11 distributes and supplies an output of an amplifier circuit 10 to two band pass filters 13, 14 with different frequency characteristics at a prescribed ratio. An adder circuit 15 sums the outputs of the band pass filters 13, 14. The summed output is fed back to an input of the amplifier circuit 10 and amplified by the amplifier circuit 10. According to the processing above, a part of the output of the amplifier circuit 10 is positively fed back to the input of the amplifier circuit 10, the signal with a prescribed frequency is repetitively amplified resulting in generating an output signal Vout oscillated with the prescribed frequency. In this case, a control circuit 12 varies the prescribed distribution ratio by the distribution circuit 11 to control the oscillated frequency of the output signal Vout.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillating circuit capable of controlling an oscillating frequency, and more particularly to a PLL detector,
It is used for IF detection and the like.

[0002]

2. Description of the Related Art In recent years, in PIF detection of TV, VCO
A system that performs synchronous detection with a signal (voltage controlled oscillator) pulled in by a PLL (phase locked loop) has become mainstream. An oscillation circuit used for PIF detection is required to have a high oscillation frequency of several tens of MHz and a high stability with little frequency jitter. For this reason, an oscillation circuit utilizing resonance by LC as shown in FIG. 7 is generally used.

[0003]

In the above-described oscillation circuit utilizing the resonance by the LC, the inductor element L cannot be integrated, which hinders cost reduction and circuit miniaturization. Further, in the oscillation circuit, although the oscillation frequency can be controlled by making the current amount of the current source variable, the variation width of the oscillation frequency is very narrow.

On the other hand, as shown in FIG.
The oscillation circuit which feeds back the output through the band-pass filter (BPF) 102 has high stability and is easy to use. But,
The oscillation frequency cannot be controlled by a band-pass filter having a fixed center frequency f0. Therefore, if an oscillation circuit using a bicut filter using gm amplifiers 103 and 104 as shown in FIG. 9 can control the center frequency, the oscillation frequency can be controlled. However, gm amplifiers generally have high sensitivity and poor stability because the frequency tends to change in proportion to the control current due to noise.
Sufficient performance cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has an oscillation circuit having a filter feedback type characteristic having low output harmonics and high stability and capable of controlling an oscillation frequency in a wide range. The purpose is to provide.

[0006]

To achieve the above object, an oscillation circuit according to the present invention comprises a plurality of filter circuits having different frequency characteristics from each other, and an addition amplifier for adding and amplifying outputs of the plurality of filter circuits. Means, dividing means for dividing the output of the adding and amplifying means at a desired ratio, and supplying the divided output to the plurality of filter circuits, and control means for setting the ratio in the distributing means. .

Further, in the oscillation circuit according to the present invention, an emitter is connected to first and second transistors constituting a differential amplifier, and a third transistor is connected to the collector of the first transistor. , A fourth transistor,
Fifth and sixth transistors, the emitters of which are connected to each other, the emitters of which are connected to the collectors of the second transistors, and the collectors of the third transistors are connected to the input unit, and the output units are connected to the second transistor. A first filter circuit connected to a base of the transistor, a second filter circuit connected to an input of the collector of the fifth transistor, and an output connected to a base of the first transistor; A first base potential supplied to the bases of a third transistor and a sixth transistor;
And a second base potential supplied to a base of the fifth transistor and a fifth transistor.

According to the oscillation circuit of the present invention, the output of the addition and amplification means is divided once by the distribution means and supplied to a plurality of filter circuits, and is passed through the plurality of filter circuits having different frequency characteristics from each other. Return to input. At this time, the oscillation frequency can be controlled by changing the distribution ratio of the signal supplied to the plurality of filter circuits by the control means.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing a configuration of an oscillation circuit according to a first embodiment of the present invention.

The oscillation circuit includes an amplifier circuit 10 for amplifying an input signal, and a distribution circuit 1 for receiving an output of the amplifier circuit 10 and distributing the signal to a first signal S1 and a second signal S2.
1. a control circuit 12 for controlling a distribution ratio when distributing two signals in a distribution circuit 11; a band-pass filter (BPF) 13 for receiving the first signal and passing through a narrow band around a predetermined center frequency f01 , A band-pass filter (BPF) 1 that receives the second signal and passes a narrow band around a center frequency f02 different from the center frequency f01.
4, an adder circuit 15 that receives the outputs of the two band-pass filters 13 and 14, performs addition processing, and outputs the result to the amplifier circuit 10.

The operation of the oscillating circuit thus configured is as follows. First, when the first input signal is input to the amplifier circuit 10, it is amplified and input to the distribution circuit 11.
The first input signal is a noise signal or the like generated in the circuit when the power is turned on. The signal input to the distribution circuit 11 is distributed to two signals, a first signal S1 and a second signal S2. At this time, the first signal S1 and the second signal S2
Is set by the control signal CL output from the control circuit 12 to the distribution circuit 11.

Further, the first signal S1 is input to a band pass filter (BPF) 13, and the second signal S2 is input to a band pass filter (BPF) 14. At this time, the bandpass filters 13 and 14 have different center frequencies f01 and f02, respectively. For this reason, the first signal S1 is input to the addition circuit 15 after the frequency components separated from the center frequency f01 are removed. Similarly, the second signal S
2 is input to the adding circuit 15 after removing the frequency components away from the center frequency f02. The first signal S1 and the second signal S2 input to the addition circuit 15 are added and then input to the amplification circuit 10 again.

FIG. 2A is a diagram showing the relationship between the frequency of the signal output from the adding circuit 15 and the output level, and FIG. 2B is a diagram showing the relationship between the frequency and the phase of the signal. is there. For example, the first signal S1 and the second signal
When the distribution ratio of the signal S2 is distributed with S1: S2 = 1: 0, the signal output from the adder circuit 15 is as shown in FIG.
The signals are as shown by A in (a) and (b). Also,
The distribution ratio of the first signal S1 and the second signal S2 is S1: S2
In the case where the distribution is performed at = 0: 1, the signal output from the adder circuit 15 is a signal indicated by B in FIGS. 2 (a) and 2 (b). When the distribution ratio is S1: S2 = 0.5: 0.5, the signal output from the adder circuit 15 is the same as the signal indicated by C in FIGS. 2 (a) and 2 (b). Become.

By such processing, a part of the output of the amplifier circuit 10 is positively fed back to the input side of the amplifier circuit 10, and the amplification of the signal of the predetermined frequency is repeated. And
The signal of the predetermined frequency saturates at a certain value to maintain the oscillation state, and is output to the outside as an output signal Vout having the predetermined oscillation frequency.

Here, from the control circuit 12 to the distribution circuit 11
The frequency of the signal after adding the first signal and the second signal is changed according to the distribution ratio set by the control signal CL output to the control signal CL. This frequency can be changed between the center frequency f01 and the center frequency f02. As described above, since the signal input to the amplifier circuit 10 can be changed between the center frequency f01 and the center frequency f02, the oscillation frequency can be controlled in a wide range.

The band pass filters 13 and 14 include:
As shown in FIG. 3, a simple circuit combining a first-order high-pass filter (HPF) and a low-pass filter (LPF) composed of a CR can be used. This circuit includes a high-pass filter (H) including a capacitor C1 and a resistor R1.
PF) and a low-pass filter (LPF) composed of a resistor R2 and a capacitor C2. VB in the figure is a bias voltage.

As the bandpass filters 13 and 14, an active filter, for example, a secondary bandpass filter composed of an operational amplifier A1, capacitors C3 and C4, and resistors R3 and R4 as shown in FIG. 4 can be used. .

When the filters shown in FIGS. 3 and 4 are used as the band-pass filters 13 and 14, integration on a semiconductor substrate becomes possible. Thereby, cost reduction and miniaturization can be promoted. Furthermore, when the filter shown in FIG. 4 is used, a high selectivity Q can be obtained. This makes it possible to enhance the selection characteristics of the oscillation frequency and reduce harmonics.

The control circuit 12 includes, for example, FIG.
The circuit shown in FIG. This circuit includes transistors Q1 to Q4 and current sources I1 to I3. The ratio of the output currents I01 and I02 of the control-side amplifier is controlled by changing the ratio of the currents flowing from the current sources I1 and I2. That is, the ratio of the output currents I01 and I02 is
It can be distributed to the ratio of the currents flowing from the current sources I1 and I2. As a result, the first signal S1, distributed by the distribution circuit 11,
The distribution ratio of the second signal S2 can be changed.

Usually, in an oscillation circuit based on feedback using a bandpass filter, the bandpass filter has a resonance frequency f0.
Since the output gain is maximum and the phase becomes 0 degree, by oscillating at almost f0 by setting the feedback gain to 1,
Low harmonics and high stability.

In this embodiment, as described above, by changing the distribution ratio of the currents input to the band-pass filters 13 and 14 having the resonance frequencies (center frequencies) of f01 and f02, respectively, these currents are changed. Of the center frequencies f01 and f02 shown in FIG.
To change between. That is, the bandpass filter 1
By changing the distribution ratio of the currents output to 3 and 14, the same characteristics as changing the center frequency f0 of the bandpass filter can be obtained. By using this to control the center frequency f0 of the bandpass filter, the oscillation frequency of the oscillation circuit of this embodiment can be changed.

The bandpass filter is constituted by CR as shown in FIG. 3, so that an external L is unnecessary and integration is possible. Also, by increasing Q using a fixed active filter as shown in FIG. 4, it is possible to enhance the frequency selection characteristics and reduce harmonics. Further, by narrowing the interval between the center frequency f01 and the center frequency f02, the sensitivity to fluctuations in the control voltage and the like can be reduced, and stable oscillation with high purity can be achieved.

As described above, according to the first embodiment, it is possible to change the oscillation frequency while maintaining the characteristics of a band-pass filter feedback type having a low output harmonic and a high stability.

[Second Embodiment] FIG. 6 is a diagram showing a configuration of an oscillation circuit according to a second embodiment of the present invention.

The oscillating circuit includes the adding circuit 15, the amplifying circuit 10, and the distribution circuit 11 in the first embodiment.
Is realized by a circuit configuration as shown in FIG. Other configurations are the same as those of the first embodiment.

This oscillation circuit is configured as follows. As shown in FIG. 6, a resistor R11 is arranged between the emitters of the transistors Q11 and Q12, and a current source I11 is arranged between the emitter of the transistor Q11 and GND (ground potential point). Further, a current source I is connected between the emitter of the transistor Q12 and GND.
12 are arranged. Thus, a differential amplifier is configured.

The collector of the transistor Q11 is connected to the emitters of the transistors Q13 and Q14, and the collector of the transistor Q12 is connected to the transistor Q1.
5, the emitter of Q16 is connected. The bases of the transistors Q13 and Q16 are connected to each other, and this connection point is connected to the first terminal of the control circuit 12. The bases of the transistors Q14 and Q15 are connected to each other, and this connection point is connected to the second terminal of the control circuit 12.

The collector of the transistor Q13 is connected to the input of the bandpass filter 13, and the collector of the transistor Q15 is connected to the input of the bandpass filter 14. And the band-pass filter 13
Is connected to the base of a transistor Q12, and the output of the bandpass filter 14 is connected to a transistor Q1.
1 base.

The oscillating circuit thus configured operates as follows.

First, the control circuit 12 changes the base potentials of the transistors Q13 and Q16 and the base potentials of the transistors Q14 and Q15. Thus, the output is distributed to the collectors of the transistors Q13 and Q16 and the collectors of the transistors Q14 and Q15, and the output ratio is set.

Thus, the output of the collector of the transistor Q13 is fed back to the base of the transistor Q12 through the band-pass filter 13. Also, the transistor Q15
Is returned to the base of the transistor Q11 through the band-pass filter 14. The differential amplifier composed of the transistors Q11 and Q12 adds and amplifies the output of the input collector, and outputs the amplified output to the emitters of the transistors Q13 and Q14 and the emitters of the transistors Q15 and Q16, which function as distribution circuits. The current input to these emitters is
To Q16, and output to the bandpass filters 13 and 14 again.

By such processing, a part of the output of the differential amplifier is positively fed back to the input side of the differential amplifier, and the amplification of the signal of the predetermined frequency is repeated. Then, the signal of the predetermined frequency saturates at a certain value to maintain the oscillation state, and the output signal Vou having the predetermined oscillation frequency
Output to the outside as t.

In such an oscillation circuit, since no extra amplifier or resistor is inserted in the middle of the circuit, the frequency limit is small, the characteristics of the band-pass filter become oscillation characteristics as they are, and stable oscillation up to high frequencies is possible. FIG.
The addition circuit, amplification circuit, and distribution circuit shown in (1) can be configured by extremely simple circuits. Also in the second embodiment, the circuits shown in FIGS. 3 and 4 can be used for the band-pass filters 13 and 14, and the circuit shown in FIG. 5 can be used for the control circuit 12.

As described above, according to the second embodiment, it is possible to change the oscillation frequency while maintaining the characteristics of a band-pass filter feedback type having a small output harmonic and a high stability.

In the first and second embodiments, two outputs of the distribution circuit and two band-pass filters are provided.
More than one may be provided.
By distributing the current, the oscillation frequency can be changed over a wider range while maintaining a higher Q.

As shown in FIG. 1, the adder circuit is provided before the amplifier circuit. However, it is also possible to provide an amplifier circuit after each bandpass filter and provide an adder circuit after these amplifier circuits. Is the same. Since there are a plurality of outputs, the signal path can be easily differentiated, and the circuit is suitable for high frequencies.

[0038]

As described above, according to the present invention, there is provided an oscillating circuit which has a filter feedback type characteristic with low output harmonics and high stability and which can control the oscillating frequency in a wide range. It is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an oscillation circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a frequency characteristic of a signal output from an adding circuit in the oscillation circuit.

FIG. 3 is a circuit diagram showing a configuration example of a bandpass filter in the oscillation circuit.

FIG. 4 is a circuit diagram showing another configuration example of the band pass filter in the oscillation circuit.

FIG. 5 is a circuit diagram showing a configuration example of a control circuit in the oscillation circuit.

FIG. 6 is a diagram illustrating a configuration of an oscillation circuit according to a second embodiment of the present invention.

FIG. 7 is an example of a conventional LC oscillation circuit.

FIG. 8 is an example of a conventional feedback oscillation circuit.

FIG. 9 is an example of an oscillation circuit using a conventional bicut filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Amplification circuit 11 ... Distribution circuit 12 ... Control circuit 13 ... Band pass filter (BPF) 14 ... Band pass filter (BPF) 15 ... Addition circuit A1 ... Op amp C1-C4 ... Capacitor I1-I3 ... Current source I11, I12 ... Current sources R1 to R4 ... resistors R11 ... resistors Q1 to Q4 ... transistors Q11 to Q16 ... transistors

Claims (8)

[Claims] A plurality of filter circuits having different frequency characteristics from each other; an adding and amplifying means for adding and amplifying outputs of the plurality of filter circuits; and an output of the adding and amplifying means being divided at a desired ratio. An oscillator circuit, comprising: a distribution unit that supplies the filter circuit of (1), and a control unit that sets the ratio in the distribution unit. 2. The oscillation device according to claim 1, wherein said adding / amplifying means includes an adding means for adding outputs of said plurality of filter circuits, and an amplifying means for amplifying outputs of said adding means. circuit. 3. The adding and amplifying means comprises a plurality of amplifying means for amplifying outputs of the plurality of filter circuits, and an adding means for adding outputs of the plurality of amplifying means. The oscillation circuit according to 1. 4. A first and a second transistor forming a differential amplifier, both having an emitter connected thereto, and a third and a fourth transistor having the emitter connected to a collector of the first transistor. Fifth and sixth transistors having an emitter connected, the emitter being connected to the collector of the second transistor, and the collector of the third transistor being connected to an input portion, and having the output portion being connected to the second transistor. A first filter circuit connected to the base of the first transistor; a second filter circuit connected to the input of the collector of the fifth transistor; and the output of the fifth transistor connected to the base of the first transistor; The first base potential supplied to the bases of the third transistor and the sixth transistor, and the base potential of the fourth transistor and the fifth transistor. An oscillation circuit for a control means for controlling the second base potential supplied, characterized by comprising a. 5. The oscillation circuit according to claim 1, wherein the filter circuit is a band-pass filter having different center frequencies. 6. The oscillation circuit according to claim 5, wherein the band-pass filter is a circuit combining a high-pass filter and a low-pass filter. 7. The oscillation circuit according to claim 5, wherein the band pass filter is an active filter. 8. The oscillation circuit according to claim 1, wherein said adding and amplifying means comprises a differential amplifier.