JP2009296386A - Low-noise voltage-controlled oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-noise voltage-controlled oscillation circuit capable of preventing the deterioration of phase noise without decreasing an output level without being influenced by power source noise. <P>SOLUTION: In the low-noise voltage-controlled oscillation circuit, an amplifying transistor Tr2 of a buffer stage 1 and an oscillating transistor Tr1 of an oscillating stage 2 are connected in cascade, a power source voltage Vcc is applied on a collector of the Tr2 via a coil L1 while an output terminal Fout is drawn out of the collector, a voltage generated by dividing the power source voltage by a resistor R1 and a resistor R2 is applied on a base of the Tr2 while one end of a capacitor C1 is connected to the base and other end is grounded, an emitter of the Tr2 is connected to a collector of the Tr1, an output signal from a resonance circuit 2a is input to a base of the Tr1 while a voltage generated by dividing a voltage of the emitter of the Tr2 with a resistor R3 and a resistor R4 is applied on the base, and an emitter of the Tr1 is grounded via a resistor R5 and a coil L2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a voltage controlled oscillation circuit, and more particularly to a low noise voltage controlled oscillation circuit capable of removing power supply noise and preventing a decrease in power supply voltage.

[Conventional voltage controlled oscillation circuit: Fig. 3]
A conventional voltage controlled oscillation circuit will be described with reference to FIG. FIG. 3 is a configuration diagram of a conventional voltage controlled oscillation circuit.
As shown in FIG. 3, a conventional general voltage controlled oscillator (VCO) has a two-stage configuration of an oscillation stage 2 including a resonance circuit 2 a and a buffer stage 1. Is input to the buffer stage 1, and is amplified by the amplifying transistor Tr2 and output to the output terminal Fout.

In FIG. 3, R represents a resistor, C represents a capacitor, and L represents a coil.
The bases of the oscillation transistor Tr1 of the oscillation stage 2 and the amplification transistor Tr2 of the buffer stage 1 are divided and input from the power supply voltage Vcc, and the collector is connected to the power supply voltage Vcc via a resistor, a coil, and the like. ing.

  The output frequency is determined by the control voltage Vt input to the resonance circuit 2a and the capacitors C2 and C3. Therefore, if the capacitors C2 and C3 are fixed, they are determined only by the control voltage Vt.

[Deterioration of phase noise: Fig. 4]
Next, phase noise deterioration due to power supply noise in a conventional voltage controlled oscillation circuit will be described with reference to FIG. FIG. 4 is a diagram showing deterioration of phase noise due to power supply noise.
As shown in FIG. 4, in the conventional voltage controlled oscillation circuit, the power supply voltage Vcc supplied to the collector of the oscillation transistor Tr1 in the oscillation stage 2 is directly connected to the external power supply, so that the external power supply noise As a result, the phase noise is degraded.

FIG. 4 shows characteristics of phase noise (dBc / Hz) with and without the influence of power supply noise on the offset frequency [offset frequency] (Hz).
When there is an influence of power supply noise, the phase noise is larger than when there is no influence.

[Configuration example of synthesizer: Fig. 5]
Here, a synthesizer using a conventional voltage controlled oscillation circuit will be described with reference to FIG. FIG. 5 is a configuration diagram of a conventional synthesizer.
As shown in FIG. 5, the conventional synthesizer includes a PLL (Phase Locked Loop) circuit (PLL_IC) 20, a loop filter 30, a VCO 10, and a frequency divider (1 / N) 40.

In the conventional synthesizer, the reference signal (REF) and the frequency-divided signal from the frequency divider 40 are input to the PLL circuit 20, phase-detected, and output as a control voltage of the VCO 10 through the loop filter 30.
The VCO 10 outputs a transmission frequency synchronized with the reference signal by the control voltage input from the loop filter 30 and also outputs it as a feedback to the frequency divider 40.

[VCO with Lip Filter Circuit: FIG. 6]
When a synthesizer is configured using a conventional voltage controlled oscillation circuit, a ripple filter circuit or the like may be inserted into the power supply voltage Vcc supplied to the VCO 10 to remove noise in order to reduce the influence of external noise. Conceivable.

Here, a configuration provided with a ripple filter circuit will be described with reference to FIG. FIG. 6 is a configuration diagram in which a ripple filter circuit is provided.
As shown in FIG. 6, the ripple filter circuit 50 connected to the VCO 10 has a power supply voltage Vcc connected to the VCO 10 via a transistor Tr, and is connected between a resistor R and a capacitor C connected in series to the base of the transistor Tr. The voltage extracted from the power supply voltage Vcc is applied to remove noise from the power supply voltage Vcc.

[Characteristics with ripple filter circuit: Fig. 7]
Here, the characteristics of the output power level [output power] (dBm) with respect to the control voltage (V) with and without the ripple filter circuit are shown in FIG. FIG. 7 is a diagram showing characteristics with a ripple filter circuit.
As shown in FIG. 7, when a ripple filter circuit is inserted outside, the power supply voltage applied to the VCO 10 is reduced by Vce (voltage between the collector and the emitter) of the transistor Tr. As compared with the above, the output level of the VCO 10 output is lowered.

As related prior art, there are JP-A-08-107309 (Patent Document 1) and JP-A-2004-064598 (Patent Document 2).
In Patent Document 2, an amplifying transistor Tr2 and an oscillating transistor Tr1 are connected in series to a power supply voltage Vcc, and an output from a resonance circuit is input to the base of the oscillating transistor Tr1, and oscillated from a collector of the amplifying transistor Tr2. A configuration for outputting a frequency is shown.

  In Patent Document 1, a capacitor C10 for grounding the base of the amplifying transistor Tr2 of the buffer circuit unit 1 in a low-frequency alternating manner is provided, and a ripple filter is provided for low-frequency noise applied to the buffer circuit unit 1 from the power supply terminal B. A voltage-controlled oscillation circuit is shown in which a normal amplification operation is performed on a signal applied from the oscillation circuit unit 2 so that the signal can be considered.

[Configuration of Voltage Controlled Oscillator Circuit of Patent Document 1: FIG. 8]
Here, the voltage controlled oscillation circuit of Patent Document 1 will be described with reference to FIG. FIG. 8 is a configuration diagram of the voltage controlled oscillation circuit of Patent Document 1. In FIG.
As shown in FIG. 8, the voltage-controlled oscillation circuit of Patent Document 1 has a configuration in which a resistor R3 and a capacitor C10 connected in series to a power supply terminal B are provided at the base of a buffer (amplification) transistor Tr2. Therefore, when viewed from the oscillation transistor Tr1, this portion can be regarded as a ripple filter.
However, a voltage divided by resistors R1, R2, and R3 connected in series to the power supply terminal is applied to the base of the oscillation transistor Tr1.

Japanese Patent Laid-Open No. 08-107309 JP 2004-064598 A

  However, the general conventional voltage controlled oscillation circuit has a problem that the phase noise deteriorates due to the influence of external power supply noise.

  As a countermeasure, when a ripple filter circuit or the like is inserted between the power supply and the voltage controlled oscillation circuit, the output level of the voltage controlled oscillation circuit is lower than when no ripple filter circuit or the like is inserted. There was a problem that it decreased.

  In Patent Document 1, although it is an attempt to provide the buffer transistor Tr2 with the function of a ripple filter, a configuration in which a power supply voltage is directly applied to the base of the oscillation transistor Tr1 via resistors R3 and R2. Therefore, the base of the oscillation transistor Tr1 is affected by power supply noise, and there is a problem that countermeasures against phase noise are not sufficient.

  The present invention has been made in view of the above circumstances, and provides a low noise voltage controlled oscillation circuit that can prevent deterioration of phase noise without lowering the output level and without being affected by power supply noise. Objective.

  The present invention for solving the problems of the conventional example described above is a voltage controlled oscillation circuit having an oscillation stage that outputs an oscillation frequency and a buffer stage that amplifies the output from the oscillation stage. A resonance circuit whose resonance frequency is adjusted by a control voltage and an oscillation transistor that oscillates according to an output signal from the resonance circuit are provided, and the buffer stage amplifies the signal according to the oscillation operation of the oscillation transistor. An amplifying transistor is provided, and the amplifying transistor and the oscillating transistor are cascade-connected. A power supply voltage is applied to the collector of the amplifying transistor via the first coil, and an output terminal is derived, thereby amplifying the transistor. A voltage obtained by dividing the power supply voltage by the first resistor and the second resistor is applied to the base of the transistor, and one end of the first capacitor is connected. The other end is grounded, the emitter of the amplifying transistor is connected to the collector of the oscillation transistor, the output signal from the resonance circuit is input to the base of the oscillation transistor, and the third resistor and the A voltage obtained by dividing the emitter voltage of the amplifying transistor by a resistor of 4 is applied, and the emitter of the oscillation transistor is grounded via a fifth resistor and a second coil.

  According to the present invention, in the low noise voltage controlled oscillation circuit, the base of the oscillation transistor is connected to one end of the second capacitor and the third capacitor connected in series, the other end is grounded, A point between the third capacitor is connected to the emitter of the oscillation transistor, one end of the fourth capacitor is connected to the emitter, the other end is connected to the base of the amplification transistor, and the collector of the oscillation transistor is connected. Is grounded via a fifth capacitor, a sixth capacitor is connected in series between the collector and output terminal of the amplifying transistor, and the emitter of the amplifying transistor is connected via the seventh capacitor. It is characterized by being grounded.

  The present invention is characterized in that, in the low noise voltage controlled oscillation circuit, a dielectric ceramic resonator is used for the resonance circuit.

  According to the present invention, the amplifying transistor and the oscillating transistor are cascade-connected, and the power supply voltage is applied to the collector of the amplifying transistor via the first coil, and the output terminal is derived, A voltage obtained by dividing the power supply voltage by the first resistor and the second resistor is applied to the base of the transistor, one end of the first capacitor is connected, the other end is grounded, and the collector of the oscillation transistor is connected. Is connected to the emitter of the amplifying transistor, the output signal from the resonance circuit is input to the base of the oscillating transistor, and the voltage of the emitter of the amplifying transistor is set by the third resistor and the fourth resistor. The divided voltage is applied, and the emitter of the oscillation transistor is a low noise voltage controlled oscillation circuit that is grounded via the fifth resistor and the second coil. Because, without lowering the output level from the output terminal, without being affected by power supply noise, there is an effect of preventing the deterioration of the phase noise.

Embodiments of the present invention will be described with reference to the drawings.
[Outline of the embodiment]
The low noise voltage controlled oscillation circuit according to the embodiment of the present invention includes an oscillation stage that outputs an oscillation frequency, and a buffer stage that amplifies the output from the oscillation stage, and an amplification transistor Tr2 in the buffer stage and the oscillation stage The oscillation transistor Tr1 is cascade-connected, and the power supply voltage Vcc is applied to the collector of the amplifying transistor Tr2 via the first coil L1, and the output terminal Fout is derived. The base of the amplifying transistor Tr2 A voltage obtained by dividing the power supply voltage by the first resistor R1 and the second resistor R2 is applied to the first capacitor C1, one end of the first capacitor C1 is connected, the other end is grounded, and the oscillation transistor Tr1 is connected. The collector is connected to the emitter of the amplifying transistor Tr2. The output signal from the resonance circuit is input to the base of the oscillating transistor Tr1, and the third resistor R3 and the fourth resistor A voltage obtained by dividing the voltage of the emitter of the amplifying transistor Tr2 by the resistor R4 is applied, and the emitter of the oscillating transistor Tr1 is grounded via the fifth resistor R5 and the second coil L2. Therefore, it is possible to prevent deterioration of phase noise without lowering the output level from the output terminal, without being affected by power supply noise.

  In the low noise voltage controlled oscillation circuit according to the embodiment of the present invention, one end of the second capacitor C2 and the third capacitor C3 connected in series is connected to the base of the oscillation transistor Tr1, and the other end is connected. A point between the second capacitor C2 and the third capacitor C3 is grounded and connected to the emitter of the oscillation transistor Tr1, and one end of the fourth capacitor C4 is connected to the emitter, and the other end is for amplification. Connected to the base of the transistor Tr2, grounded to the collector of the oscillating transistor Tr1 through a fifth capacitor C5, and a sixth capacitor C6 connected in series between the collector of the amplifying transistor Tr2 and the output terminal. The emitter of the amplifying transistor Tr2 is grounded via the seventh capacitor C7.

[Configuration of Low Noise Voltage Control Oscillator Circuit: Fig. 1]
A low noise voltage controlled oscillation circuit according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of a low noise voltage controlled oscillation circuit according to an embodiment of the present invention.
The low noise voltage controlled oscillator circuit (this circuit) according to the embodiment of the present invention basically includes a buffer stage 1 and an oscillation stage 2 as shown in FIG.

Each part of the circuit will be specifically described.
[Oscillation stage 2]
The oscillation stage 2 in this circuit basically includes a resonance circuit 2a that receives a control voltage Vt and outputs an oscillation frequency corresponding to the control voltage Vt, and an oscillation transistor Tr1.

  The oscillation transistor Tr1 inputs the output from the resonance circuit 2a to the base (B), and the collector (C) is connected to the emitter (E) of the amplification transistor Tr2 in the buffer stage 1, and the emitter (E) is a resistance. It is grounded via R5 and coil L2.

  Further, the base of the oscillation transistor Tr1 is applied by dividing the voltage of the emitter of the amplification transistor Tr2 by the resistor R3 and the resistor R4, and one of the capacitors C2 and C3 connected in series (C2 side) is applied to the base. ) Are connected, and the other (C3 side) is grounded.

A point between the capacitors C2 and C3 and a point between the emitter of the oscillation transistor Tr1 and the resistor R5 are connected.
One end of a capacitor C5 is connected to the collector of the oscillation transistor Tr1, and the other end is grounded.

[Buffer stage 1]
The buffer stage 1 in this circuit includes an amplifying transistor Tr2, a power supply voltage Vcc is applied to its collector (C) via a coil L1, its emitter (E) is connected to the collector of the oscillating transistor Tr1, A power supply voltage Vcc is applied to the base (B) via a resistor R1, and a capacitor C1 and a resistor R2 are connected in parallel to the base and grounded.

Also, one end of the capacitor C4 is connected to the base, and the other end is connected to a line connecting the point between the capacitors C2 and C3 of the oscillation stage 2 and the point between the emitter of the oscillation transistor Tr1 and the resistor R5. ing.
Furthermore, one end of a capacitor C7 is connected to the emitter of the amplifying transistor Tr2, and the other end is grounded.

  An output terminal Fout is derived from between the coil L1 and the collector of the amplifying transistor Tr2 via the capacitor C6, and an output signal is obtained.

[Features of this circuit]
When viewed from the oscillation stage 2, the emitter of the amplification transistor Tr 2 in the buffer stage 1 and the collector of the oscillation transistor Tr 1 in the oscillation stage 1 are cascade-connected, and the capacitor C 1 is connected to the base of the amplification transistor Tr 2. The buffer stage 1 is configured to be a ripple filter circuit against noise applied from the power supply terminal.

In particular, in this circuit, compared with Patent Document 1, the power supply voltage Vcc is not applied to the base of the oscillation transistor Tr1, and the voltage of the ripple filter composed of the resistor R1, the capacitor C1, and the amplification transistor Tr2 is the oscillation transistor. Since the voltage of the emitter of Tr1 is divided by the resistor 3 and the resistor R4 to become the bias voltage of the base of the oscillation transistor Tr1, the effect on the power supply noise can be reduced and reduced.
Since it is configured to be applied, there is an effect that the influence on the power supply noise can be reduced as much as possible.

  Further, since the emitter (output side) of the oscillation transistor Tr1 of the oscillation stage 1 is connected to the base of the amplification transistor Tr2 via the capacitor C4, the amplification transistor Tr2 performs a normal transistor amplification operation. It has become.

[Configuration of resonant circuit: Fig. 2]
Next, the configuration of the resonance circuit 2a in this circuit will be described with reference to FIG. FIG. 2 is a configuration diagram of the resonance circuit.
In the resonant circuit of this circuit, as shown in FIG. 2, the anode of the diode D11 is grounded, the cathode of the diode D11 is connected to the cathode of the diode D12, the anode of the diode D12 is connected to the anode of the diode D13, Is connected to the cathode of the diode D14, the anode of the diode D14 is grounded via the coil L14, the input terminal is branched, and one is connected between the cathode of the diode D11 and the cathode of the diode D12 via the coil L11. The other input terminal is connected between the cathode of the diode D13 and the cathode of the diode D14 via the coil L12, and the point between the anode of the diode D14 and the coil L14 is the output terminal via the capacitor C11, the resonator, and the capacitor C12. Connected to.

In the resonator, one of a capacitor C13 and a coil L15 connected in parallel is connected to a line connecting the capacitors C11 and C12, and the other is grounded.
In FIG. 2, the dotted line portion is a resonator, but this may be constituted by a dielectric ceramic resonator having a high Q (Quality factor).

[Effect of the embodiment]
According to this circuit, the amplifier transistor Tr2 of the buffer stage 1, the resistor R1, and the capacitor C1 are configured to serve as a ripple filter circuit, so that the deterioration of the phase noise can be prevented without being affected by the power supply noise. effective.

  In particular, as compared with Patent Document 1, this circuit is more effective in preventing deterioration of phase noise by adopting a configuration in which the power supply voltage is not directly applied to the base of the oscillation transistor Tr1.

  According to this circuit, since it is not necessary to insert a ripple filter circuit or the like between the power supply and the power supply voltage is not lowered, the output level can be prevented from being lowered.

  The present invention is suitable for a low noise voltage controlled oscillator circuit that can prevent deterioration of phase noise without being affected by power supply noise without lowering the output level.

It is a block diagram of the low noise voltage control oscillation circuit which concerns on embodiment of this invention. It is a block diagram of a resonance circuit. It is a block diagram of the conventional voltage controlled oscillation circuit. It is a figure which shows deterioration of the phase noise by power supply noise. It is a block diagram of the conventional synthesizer. It is the block diagram which provided the ripple filter circuit. It is a figure which shows the characteristic with a ripple filter circuit. 2 is a configuration diagram of a voltage controlled oscillation circuit of Patent Document 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Buffer stage, 2 ... Oscillation stage, 2a ... Resonance circuit, 10 ... VCO (voltage control oscillation circuit), 20 ... PLL circuit, 30 ... Loop filter, 40 ... Frequency divider, Tr1 ... Oscillation transistor, Tr2 ... Amplification Transistor

Claims (3)

A voltage-controlled oscillation circuit having an oscillation stage for outputting an oscillation frequency and a buffer stage for amplifying an output from the oscillation stage;
The oscillation stage includes a resonance circuit whose resonance frequency is adjusted by a control voltage, and an oscillation transistor that performs an oscillation operation according to an output signal from the resonance circuit,
The buffer stage includes an amplifying transistor that amplifies a signal according to the oscillation operation of the oscillating transistor;
Cascade connection of the amplification transistor and the oscillation transistor,
A power supply voltage is applied to the collector of the amplifying transistor via the first coil, and an output terminal is derived,
A voltage obtained by dividing the power supply voltage by the first resistor and the second resistor is applied to the base of the amplifying transistor, one end of the first capacitor is connected, and the other end is grounded.
The collector of the oscillation transistor is connected to the emitter of the amplification transistor,
An output signal from the resonance circuit is input to the base of the oscillation transistor, and a voltage obtained by dividing the voltage of the emitter of the amplification transistor by a third resistor and a fourth resistor is applied,
A low noise voltage controlled oscillation circuit characterized in that the emitter of the oscillation transistor is grounded via a fifth resistor and a second coil. One end of a second capacitor and a third capacitor connected in series is connected to the base of the oscillation transistor, and the other end is grounded.
A point between the second capacitor and the third capacitor is connected to the emitter of the oscillation transistor, one end of the fourth capacitor is connected to the emitter, and the other end is connected to the base of the amplification transistor. Connected,
The collector of the oscillation transistor is grounded via a fifth capacitor,
A sixth capacitor is connected in series between the collector of the amplifying transistor and the output terminal;
2. The low noise voltage controlled oscillator circuit according to claim 1, wherein an emitter of the amplifying transistor is grounded via a seventh capacitor.   3. The low noise voltage controlled oscillation circuit according to claim 1, wherein a dielectric ceramic resonator is used for the resonance circuit.

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