JP2001244735A - Oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-frequency oscillation circuit of a differential form with a configuration, where positive feedback is respectively applied between a collector terminal of one transistor(TR) and a base terminal of the other TR and between the collector terminal of the other TR and a base terminal of the one TR in the differential pair TR configuration, that can reduce intermodulation distorting components between harmonics, without losing oscillation performance. SOLUTION: For example, a capacitive element Cx is connected to the output stage of TRs Q1, Q2 and the capacitive element Cx and load resistors R1, R2 configure a low-pass filter LPF. Then, by optimizing a cut-off frequency of the low-pass filter LPF the production of harmonics of the oscillated frequency is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit, and more particularly to a differential high-frequency oscillation circuit used in a local oscillation circuit of a high-frequency electronic tuning tuner used in terrestrial broadcasting / satellite broadcasting and the like. .

[0002]

2. Description of the Related Art Conventionally, as a high-frequency oscillation circuit, a differential high-frequency oscillation circuit in which an oscillator (amplifier) is constituted by a differential pair is known. As shown in FIG. 5, for example, as shown in FIG. 5, one of a pair of transistors Q1 and Q2 forming a differential pair has one transistor Q
1 and the base terminal of the other transistor Q2, and between the base terminal of one transistor Q1 and the collector terminal of the other transistor Q2.
There is a type in which a positive feedback is applied and a tank circuit (LC resonance circuit) 11 is externally connected.

In the case of this high-frequency oscillation circuit,
In principle, no even-order harmonic components are generated. However, actually, transistors Q1 and Q
A harmonic component of each order is generated by a difference in phase and amplitude caused by a difference in pairing of the two, variations in load elements (load resistances) R1 and R2, and differences in load conditions of the differential pair.

It is well known that an oscillation circuit performs a non-linear operation in a steady state.

Therefore, in the above-described conventional high-frequency oscillation circuit, the difference component (intermodulation distortion component) between the harmonic components is superimposed on the oscillation signal, so that the C / N ratio of the oscillation signal is increased.
(Carrier to Noise) ratio and phase noise performance deteriorated.

For example, as shown in FIG. 6, when the second harmonic component is 2f and the third harmonic component is 3f with respect to the oscillation frequency f of a desired oscillation signal, the intermodulation distortion component caused by this is as follows. It can be represented by an equation.

3f−2f = f or 3f + 2f = 5f This equation means that an intermodulation distortion component between harmonic components is superimposed on the oscillation signal. That is, the intermodulation distortion component of the harmonic distortion spectra having the 1 / f noise of the harmonic component or the multiplied noise of the 1 / f noise of the fundamental oscillation signal is regarded as the noise component, and the oscillation frequency f of the oscillation signal is obtained. Is superimposed on the spectrum, and this is a factor that lowers the C / N ratio and phase noise performance of the oscillation signal.

[0008]

As described above, conventionally, when a high-frequency oscillation circuit is constituted by using a differential pair, harmonic components are not generated in principle, but actually, the harmonic components are not generated. Since a harmonic component is generated, an intermodulation distortion component between the harmonic components is superimposed on the oscillation signal, resulting in a problem that the C / N ratio and the phase noise performance of the oscillation signal are reduced.

Therefore, the present invention can reduce the intermodulation distortion component between the harmonic components without impairing the oscillation performance, and can improve the C / N ratio and the phase noise performance of the oscillation signal. It is intended to provide an oscillation circuit.

[0010]

In order to achieve the above object, an oscillation circuit according to the present invention provides a circuit between an output terminal of one transistor and an input terminal of another transistor, and another transistor. And a pair of transistors forming a differential pair, each of which is connected to a resonance circuit portion such that positive feedback is applied between the output terminal of the transistor and the input terminal of one of the transistors. And a load resistor forming a low-pass filter in cooperation with a capacitive element connected between the output terminals of the pair of transistors.

Further, in the oscillation circuit according to the present invention, between the output terminal of one transistor and the input terminal of the other transistor, and between the output terminal of the other transistor and the input terminal of the one transistor. In such a manner that a positive feedback is applied to each of the transistors, a resonance circuit unit is connected, a pair of transistors forming a differential pair, a load resistor respectively connected to an output terminal of each of the transistors, And a capacitor connected between each connection point with the output terminal.

In the oscillation circuit according to the present invention, the resonance circuit is connected so that a positive feedback is applied between the output terminal of at least one transistor and the input terminal of the other transistor. A pair of transistors forming a pair, connected to the output terminal of the at least one transistor to which the resonance circuit portion is connected, and between the output terminal of the one transistor to which the resonance circuit portion is connected and ground. And a load resistor that forms a low-pass filter in cooperation with the connected capacitive element.

Further, in the oscillation circuit according to the present invention,
A pair of transistors forming a differential pair, wherein a pair of transistors forming a differential pair are connected so that a positive feedback is applied between an output terminal of at least one transistor and an input terminal of the other transistor; A load resistor connected to the output terminal of the at least one transistor, and a capacitive element connected between the output terminal of the one transistor to which the resonance circuit is connected and the ground. .

According to the oscillation circuit of the present invention, a low-pass filter can be constituted by the load resistance and the capacitance element. This makes it possible to suppress the generation of harmonic components of the oscillation frequency.

[0015]

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

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
10 shows a configuration example of a differential high-frequency oscillation circuit (low harmonic / high C / N oscillation circuit) according to the embodiment.

This high-frequency oscillation circuit includes an IC circuit unit 1 and
An LC resonance circuit (feedback circuit) 2 externally connected to the IC circuit 1.

In the IC circuit section 1, the emitter terminals of a pair of npn transistors Q1 and Q2 forming a differential pair are commonly grounded (connected to a ground potential) via a constant current source I0.

The base terminal (input terminal) of the transistor Q1 is connected to one end of the resistor Ra and the collector terminal (output terminal) of the transistor Q2 via the LC resonance circuit 2. .

The base terminal (input terminal) of the transistor Q2 is connected to one end of the resistor Rb and the collector terminal (output terminal) of the transistor Q1 via the LC resonance circuit section 2. .

The other ends of the resistors Ra and Rb are both grounded via a DC power supply V0.

The collector terminals of the transistors Q1 and Q2 are connected to a power supply (Vcc) (not shown) via the load resistor R1 or the load resistor R2.

The connection point a between the collector terminal of the transistor Q1 and the load resistor R1 to which the base terminal of the transistor Q2 is connected, and the connection point a of the transistor Q2 to which the base terminal of the transistor Q1 is connected. A capacitive element Cx is connected between a connection point b between the collector terminal and the load resistor R2.

That is, a capacitor Cx is connected between the collector terminals of the transistors Q1 and Q2, and the cutoff frequency is determined by the capacitance value (constant) and the output impedance of the load resistors R1 and R2. A low-pass filter (dashed-line frame portion) LPF is configured.

On the other hand, the LC resonance circuit section 2 includes a base terminal of the transistor Q1 and the transistor Q2.
For example, a coil L and a capacitor C for determining the oscillation frequency are connected in parallel between the connection point of the collector terminal of the transistor Q2 and the connection point of the base terminal of the transistor Q2 and the collector terminal of the transistor Q1. L
The C resonance circuit (tank circuit) 11 is provided. In the case of this LC resonance circuit 11, since it can be configured without being grounded, external influence (interference due to disturbance from GND or the like) and external influence (high-frequency GN
D) can be suppressed.

Note that the transistor Q1 is connected between the LC resonance circuit 11 and the base terminal of the transistor Q1.
2 and between the collector terminal of the transistor Q2 and the collector terminal of the transistor Q1, the feedback capacitors Ca, Cb, Cc,
Cd is provided respectively.

FIG. 2 equivalently shows the structure of the above-mentioned capacitive element Cx.

The capacitive element Cx has a configuration in which, for example, two capacitors C0 and C0 are connected in series and has a capacitance value of two (2 × C0). Also,
By preventing the connection point of the capacitive element Cx from being grounded, it is possible to suppress the external influence and the external influence similarly to the case of the LC resonance circuit 11.

The high-frequency oscillation circuit having such a configuration, that is, the transistors Q1 and Q2 serving as oscillators (amplifiers)
Between the collector terminal of one transistor Q1 and the base terminal of the other transistor Q2, and between the collector terminal of the other transistor Q2 and one transistor Q2.
Positive feedback is applied to each of the base terminals, and
In the differential high-frequency oscillation circuit having the configuration in which the LC resonance circuit 11 is connected therebetween, the collector terminal of the transistor Q1 and the base terminal of the transistor Q2 or the base terminal of the transistor Q1 and the collector terminal of the transistor Q2 have the same phase. Oscillation is performed with the relationship
Collector terminal of transistor Q1 and transistor Q
A differential oscillation output can be obtained from the collector terminal 2.

In particular, in the case of the high-frequency oscillation circuit having the above-described configuration, the connection points a and b between the load resistors R1 and R2 and the collector terminals of the transistors Q1 and Q2, which are output stages of the amplifier.
By connecting the capacitive element Cx between them and appropriately selecting the capacitance value according to the output impedance of the actual circuit, the cutoff frequency of the low-pass filter LPF can be easily optimized. As a result, it is possible to suppress the generation of harmonic components of the oscillation frequency.

The capacitance element Cx can be built in the IC circuit 1 or externally provided outside the IC circuit 1.

FIG. 3 shows the spectrum of the oscillation frequency of the differential high-frequency oscillation circuit according to the first embodiment of the present invention in comparison with the conventional one (see FIG. 5). Note that this is an example where the capacitance element Cx is externally provided.

As is apparent from this figure, a low-pass filter LPF is connected by connecting a capacitive element Cx to the output stage of the amplifier.
It has been confirmed that, in the case where is configured, generation of harmonic components of the oscillation frequency can be suppressed as compared with the related art.

As described above, in the first embodiment of the present invention, in the oscillation signal output stage of the high-frequency oscillation circuit, a low-pass filter is constituted by the load resistor and the capacitor.

That is, in the differential type high-frequency oscillation circuit, a capacitive element is connected to the output stage of the amplifier, and a low-pass filter whose cutoff frequency is determined by the capacitive element and the output impedance of the load resistor is configured. ing. Thereby, by optimizing the cutoff frequency of the low-pass filter, it is possible to suppress the generation of harmonic components of the oscillation frequency. Therefore, it is possible to reduce the intermodulation distortion component between the harmonic components without deteriorating the oscillation performance, thereby improving the C / N ratio and the phase noise performance of the oscillation signal.

In particular, when used in a local oscillation circuit of a high-frequency electronic tuning tuner used in terrestrial broadcasting / satellite broadcasting, the bit error rate of data can be remarkably improved when receiving a digital modulation signal. .

In addition, since the LC resonance circuit and the capacitive element can be configured without being grounded, external influence and external influence can be suppressed.

In the first embodiment, a pair of transistors Q1, Q2 forming a differential pair
Between the collector terminal of one transistor Q1 and the base terminal of the other transistor Q2, and the base terminal of one transistor Q1 and the other transistor Q2
The differential type high-frequency oscillation circuit of the type in which positive feedback is applied to each of the collector terminals is described above, but the present invention is not limited to this. For example, a type in which positive feedback is applied between at least the collector terminal of one transistor Q1 and the base terminal of the other transistor Q2 of a pair of transistors Q1 and Q2 forming a differential pair,
The present invention can be similarly applied to a differential high-frequency oscillation circuit.

(Second Embodiment) FIG. 4 shows a second embodiment of the present invention.
10 shows a configuration example of a differential high-frequency oscillation circuit (low harmonic / high C / N oscillation circuit) according to the embodiment. FIG. 1A is a circuit configuration diagram of a conventional high-frequency oscillation circuit, and FIG. 2B is a circuit configuration diagram of a high-frequency oscillation circuit according to the second embodiment.

This high-frequency oscillation circuit includes an IC circuit 1 '
And an LC externally connected to the IC circuit 1 '.
And a resonance circuit section (feedback circuit) 2 '.

In the IC circuit section 1 ', the emitter terminals of a pair of npn transistors Q1 and Q2 forming a differential pair are commonly grounded (connected to a ground potential) via a constant current source I0.

The base terminal (input terminal) of the transistor Q1 is connected to one end of the resistor Ra.

The base terminal (input terminal) of the transistor Q2 is connected to one end of the resistor Rb and the collector terminal (output terminal) of the transistor Q1 via the LC resonance circuit 2 '. I have.

The other ends of the resistors Ra and Rb are both grounded via a DC power supply V0.

The collector terminals of the transistors Q1 and Q2 are connected to a power supply (Vcc) (not shown) via the load resistor R1 or the load resistor R2.

On the other hand, the LC resonance circuit section 2 'is provided between the connection point between the base terminal of the transistor Q2 and the collector terminal of the transistor Q1 and ground (earth potential) to determine the oscillation frequency. An LC resonance circuit (tank circuit) 11 formed by connecting a coil L and a capacitor C in parallel is provided.

Feedback capacitors Ca and Cb are provided between the LC resonance circuit 11 and the collector terminal of the transistor Q1 and between the LC resonance circuit 11 and the base terminal of the transistor Q2, respectively.

Further, the connection point (the output stage of the amplifier) between the collector terminal of the transistor Q1 and the load resistor R1 to which the base terminal of the transistor Q2 is connected,
For example, it is grounded via a capacitance element Cx 'having the capacitance value of one capacitor C0.

That is, positive feedback is applied between the collector terminal of one transistor Q1 and the base terminal of the other transistor Q2 of the transistors Q1 and Q2 serving as oscillators (amplifiers), and the LC resonance circuit 11 is connected between them. In the differential high-frequency oscillation circuit having a configuration in which the transistors are connected, the collector terminal of the transistor Q1 and the ground (earth potential)
A low-pass filter (broken-line frame portion in the figure) LPF 'whose cutoff frequency is determined by the capacitance value (constant) and the output impedance of the load resistor R1 is connected between the capacitor Cx' and the capacitor Cx '. ing.

With such a configuration, the first
Almost as in the case of the embodiment, the low-pass filter LP
By optimizing the cutoff frequency of F ′, it is possible to suppress the generation of harmonic components of the oscillation frequency. Therefore, it is possible to reduce the intermodulation distortion component between the harmonic components without deteriorating the oscillation performance, thereby improving the C / N ratio and the phase noise performance of the oscillation signal.

In each of the first and second embodiments, an LC resonance circuit in which a coil and a capacitor are connected in parallel has been described as an example of the tank circuit connected to the amplifier. However, the present invention is not limited to this. For example, a configuration in which a coil and a capacitor are connected in series, or a configuration having frequency selectivity using a variable capacitance element such as a varicap may be used.

Further, a tank circuit and a feedback capacitor connected to an amplifier together with the tank circuit to constitute a resonance circuit section may be built in the IC circuit, and various other modifications may be made without departing from the scope of the present invention. Of course, it can be implemented.

[0053]

As described above, according to the present invention, the intermodulation distortion component between the harmonic components can be reduced without deteriorating the oscillation performance, and the C / N of the oscillation signal can be reduced.
An oscillation circuit capable of improving the ratio and the phase noise performance can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram schematically showing a differential high-frequency oscillation circuit according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram equivalently showing a capacitive element in a high-frequency oscillation circuit.

FIG. 3 is a schematic diagram showing the spectrum of the oscillation frequency of the high-frequency oscillation circuit in comparison with a conventional example.

FIG. 4 is a circuit configuration diagram schematically showing a differential high-frequency oscillation circuit according to a second embodiment of the present invention in comparison with a conventional high-frequency oscillation circuit.

FIG. 5 is shown to explain the prior art and its problems;
FIG. 3 is a circuit configuration diagram of a differential high-frequency oscillation circuit.

FIG. 6 is a schematic diagram showing the spectrum of the oscillation frequency of the conventional high-frequency oscillation circuit.

[Explanation of symbols]

 1, 1 '... IC circuit section 2, 2' ... LC resonance circuit section 11 ... LC resonance circuit Q1, Q2 ... npn transistor I0 ... constant current source V0 ... DC power supply Ra, Rb ... resistance R1, R2 ... load resistance Cx, Cx ': Capacitance element C0: Capacitor C: Capacitor Ca, Cb, Cc, Cd: Feedback capacitor L: Coil LPF, LPF': Low-pass filter

Continued on the front page (72) Inventor Yasuhiro Kanno 3-3-9, Shimbashi, Minato-ku, Tokyo F-term in Toshiba Abu E Co., Ltd. 5J081 AA02 BB03 BB06 BB07 CC03 CC30 DD03 DD11 EE02 EE03 FF02 FF09 FF21 LL01 MM01 MM04

Claims (8)

[Claims] A resonance circuit is provided so that positive feedback is applied between the output terminal of one transistor and the input terminal of the other transistor, and between the output terminal of the other transistor and the input terminal of the one transistor. A pair of transistors forming a differential pair to which a circuit unit is connected; and a low-pass filter connected to an output terminal of each of the transistors and cooperating with a capacitive element connected between the output terminals of the pair of transistors. An oscillation circuit comprising: a load resistor constituting the oscillation circuit. 2. A resonance circuit is provided so that positive feedback is applied between the output terminal of one transistor and the input terminal of the other transistor and between the output terminal of the other transistor and the input terminal of the one transistor. A pair of transistors forming a differential pair to which a circuit unit is connected; a load resistor connected to an output terminal of each of the transistors; and a connection between each connection point of the load resistor and the output terminal of the transistor. An oscillation circuit comprising: a capacitive element; 3. The oscillation circuit according to claim 1, wherein the capacitance element is not connected to a ground. 4. A pair of transistors forming a differential pair, the resonance circuit unit being connected so that positive feedback is applied between an output terminal of at least one transistor and an input terminal of the other transistor; The resonance circuit is connected to the output terminal of the at least one transistor to which the resonance circuit is connected, and cooperates with a capacitor connected between the output terminal of the one transistor to which the resonance circuit is connected and the ground. An oscillation circuit comprising a load resistor constituting a low-pass filter. 5. A pair of transistors forming a differential pair, the resonance circuit unit being connected such that positive feedback is applied between an output terminal of at least one transistor and an input terminal of the other transistor; A load resistor connected to an output terminal of the at least one transistor to which the resonance circuit is connected; and a capacitor connected between the output terminal of the one transistor to which the resonance circuit is connected and the ground. An oscillation circuit, comprising: 6. The transistor according to claim 1, wherein said transistor is an npn transistor, said output terminal is a collector terminal of said npn transistor, and said input terminal is a base terminal of said npn transistor.
The oscillation circuit according to 1. 7. The oscillation circuit according to claim 1, wherein the capacitance element is built in an IC circuit. 8. The oscillation circuit according to claim 1, wherein the capacitance element is externally provided outside an IC circuit.