JPH08107309A - Voltage controlled oscillator circuit - Google Patents

Abstract

PURPOSE: To allow the circuit to cope with low frequency noises of a built-in power supply circuit output without the need for connection of a ripple filter or the like at the outside by providing a capacitor to the base of an amplifier transistor(TR) to connect the base to ground in terms of low frequency AC. CONSTITUTION: A capacitor C10 is connected to the base of a Tr2 of a buffer amplifier circuit section 1 to connect the base to ground in terms of low frequency AC. An impedance of a coil L1 is selected to be sufficiently large with respect to an oscillated frequency of a VCO 100 and to be sufficiently smaller with respect to a ripple frequency of a power supply voltage to a power terminal B. Thus, a buffer amplifier section 2 acts like a ripple filter with respect to a low frequency noise from the power terminal B and acts like a conventional amplifier with respect to a signal fed from an oscillation circuit section 2. When the VCO 100 is designed as a module, which is used for a component of a synthesizer circuit for a radio telephone set or the like, no additional ripple filter is required outside the circuit and the power supply Vcc is connected directly to the VCO 100.

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 suitable for use in a synthesizer circuit such as a radio telephone device.

[0002]

2. Description of the Related Art Conventionally, a voltage controlled oscillator circuit (hereinafter referred to as VCO) used in a synthesizer circuit of a radio telephone device or the like is constructed as shown in FIG.

That is, the VCO 10 shown in FIG. 3 comprises a buffer amplifier circuit section 1 and an oscillating circuit section 2, and the oscillating circuit section 2 has its resonance frequency changed by a control voltage inputted from a control voltage terminal Vcon. Resonance circuit U1 composed of a coil, a capacitor, and the like, and this resonance circuit U
Including a transistor Tr1 that oscillates at a resonance frequency of 1.
The buffer amplifier circuit unit 1 includes a transistor Tr2 that amplifies the output of the oscillation circuit unit 2, and the emitter of the transistor Tr1 of the oscillation circuit unit 2 has a coupling capacitor C at the base of the transistor Tr2 of the buffer amplifier circuit unit 1.
Transistor Tr of the oscillation circuit section 2 connected through
The collector of 1 is cascode-connected to the emitter of the transistor Tr2 of the buffer amplifier circuit section 1 via the coil L3, and the collector of the transistor Tr2 of the buffer amplifier circuit section 1 is connected to the output terminal Pout via the capacitor C8.
Is configured to obtain an output signal from

A power supply voltage is supplied to the power supply terminal B, and the power supply voltage is divided by the resistors R1, R2 and R3,
A base bias is supplied to the transistor Tr1 of the oscillator circuit section 2 and the transistor Tr2 of the buffer amplifier circuit section 1.

R1 to R4 are resistors, C1 to C10 are capacitors, and L1 to L3 are coils.

In such a configuration, the resonance circuit U1 of the oscillation circuit section 2 resonates together with the capacitors C2 and C3, and the resonance frequency changes depending on the control voltage applied to the control voltage terminal Vcon.

The output of the resonance circuit U1 is the capacitor C
It is input to the base of the transistor Tr1 via 1 and this transistor Tr1 cancels the loss of the resonance circuit U1 by its load resistance and continues oscillation.

By the way, if a load is directly connected to the emitter of the transistor Tr1, it is equivalent to that a load is connected in parallel with the capacitor C3, and the oscillation frequency of the circuit changes, so that the output of the emitter of the transistor Tr1 is coupled. In addition to the base of the transistor Tr2 of the buffer amplifier circuit unit 1 via the capacitor C4, the collector output of this transistor Tr2 is led to the output terminal Pout via the capacitor C8, and the oscillation output is obtained from this output terminal Pout.

Here, the power supply voltage supplied from the power supply terminal B is divided by the resistors R1, R2 and R3 to supply the base bias to the transistors Tr1 and Tr2 and the collector currents of the transistors Tr1 and Tr2. Determine, capacitors C5-C
7 and C9 function as pass capacitors, and coil L
2 to L3 function as matching coils.

By the way, when the VCO 10 shown in FIG. 3 is modularized and a synthesizer circuit such as a radiotelephone device is formed as an independent unit, it is generated due to noise inside the device or noise such as a power source to which the device is connected. In order to prevent this VCO 10 from being affected by low frequency noise (hereinafter referred to as power supply ripple) of the output of the power supply circuit in the device,
Conventionally, as shown in FIG. 4, the power supply terminal B of this VCO 10
The ripple filter 20 was connected to.

Here, the ripple filter 20 shown in FIG.
Is provided with a transistor Tr, a resistor R, and a capacitor C, and a voltage of Vcc (v) is applied to the Vcc terminal of this ripple filter 20 from the power supply circuit of the device.

By the way, in this structure, the base-emitter voltage V of the transistor Tr of the ripple filter 20 is increased.
BE 0.7v, collector-emitter voltage VCE almost 0
Then, the power supply terminal B of the VCO 10 has Vcc-0.
A voltage of 7 (v) will be applied.

That is, when the ripple filter 20 as shown in FIG. 4 is used, the power supply voltage of the VCO 10 has a voltage drop of 0.7 (v) with respect to the power supply voltage of the device.

However, this voltage drop is not a problem when the power supply voltage of the device is sufficiently higher than the power supply voltage of the VCO 10.

However, in recent years, as seen in wireless telephone devices, the power supply voltage of the VCO 10 must be lowered due to the lowering of the power supply voltage accompanying the portability and downsizing of the device, and the VCO 10 is lowered here. When operating with voltage, it is difficult to maintain the performance of C / N, S / N, etc. as set values, and this 0.7 (v) voltage drop cannot be ignored.

Further, providing the ripple filter 20 as shown in FIG. 4 on the outside has a problem that cost, space, etc. increase.

[0017]

As described above, in the conventional voltage controlled oscillator, it is necessary to connect a ripple filter or the like to the outside. Therefore, due to the voltage drop due to the external ripple filter or the like, C / N, S or S. There is a problem that it is difficult to maintain the performance such as / N and the like as set values, and the cost and space are increased by providing an external ripple filter or the like.

Therefore, it is an object of the present invention to provide a voltage controlled oscillator circuit which does not require an external ripple filter or the like to be connected and which can cope with low frequency noise of the power supply circuit output in the apparatus.

[0019]

To achieve the above object, the present invention provides an oscillation circuit section including a resonance circuit whose resonance frequency is changed by a control voltage and an oscillation transistor which oscillates at the resonance frequency of the resonance circuit. A buffer amplifier circuit section including an amplification transistor for amplifying an output of the oscillation circuit section, the emitter of the oscillation transistor is connected to the base of the amplification transistor, and the collector of the oscillation transistor is the amplification transistor. In the voltage-controlled oscillator circuit cascode-connected to the emitter of, the capacitor for grounding the base of the amplifying transistor in a low-frequency alternating current is provided.

[0020]

According to the present invention, the base of the amplifying transistor of the buffer amplifier circuit section is provided with a capacitor for grounding in a low frequency AC manner, and the low frequency noise added from the power supply terminal to the buffer amplifier circuit section can be regarded as a ripple filter. The signal applied from the oscillation circuit section is made to perform a normal amplification operation. Therefore, it is not necessary to newly provide a ripple filter or the like outside.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a voltage controlled oscillator circuit (VCO) according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled oscillator circuit (VCO) according to the present invention. In addition,
In FIG. 1, the same reference numerals as those used in FIG. 3 are given to the components corresponding to the conventional VCO shown in FIG. 3 for convenience of description.

In FIG. 1, a voltage controlled oscillator circuit (VCO) 100 of this embodiment is composed of a buffer amplifier circuit section 1 and an oscillation circuit section 2 as in the VCO 10 shown in FIG. The circuit unit 2 has a control voltage terminal Vco.
A resonance circuit U1 including a coil and a capacitor whose resonance frequency changes according to a control voltage input from n, and a transistor T oscillating at the resonance frequency of the resonance circuit U1.
r1 and the buffer amplifier circuit unit 1 includes the oscillator circuit unit 2
Of the transistor Tr1 of the oscillation circuit unit 2 is connected to the base of the transistor Tr2 of the buffer amplifier circuit unit 1 via the coupling capacitor C4, and the collector of the transistor Tr1 of the oscillation circuit unit 2 is included. Is cascode-connected to the emitter of the transistor Tr2 of the buffer amplifier circuit unit 1 via the coil L3, and is configured to obtain an output signal from the output terminal Pout from the collector of the transistor Tr2 of the buffer amplifier circuit unit 1 via the capacitor C8. There is.

A power supply voltage is supplied to the power supply terminal B, and this power supply voltage is divided by the resistors R1, R2 and R3,
A base bias is supplied to the transistor Tr1 of the oscillator circuit section 2 and the transistor Tr2 of the buffer amplifier circuit section 1.

R1 to R4 are resistors, C1 to C10 are capacitors, and L1 to L3 are coils.

By the way, the VCO of this embodiment shown in FIG.
In 100, the base of the transistor Tr2 of the buffer amplifier circuit unit 1 is connected to a capacitor C10 that grounds the low frequency AC.

In such a structure, the VCO shown in FIG.
Similar to the conventional VCO 10 shown in FIG. 3, the resonance circuit U1 of the oscillator circuit 100 resonates with the capacitors C2 and C3, and the resonance frequency changes depending on the control voltage applied to the control voltage terminal Vcon.

The output of the resonance circuit U1 is the capacitor C
It is input to the base of the transistor Tr1 via 1 and this transistor Tr1 cancels the loss of the resonance circuit U1 by its load resistance and continues oscillation.

Here, if a load is directly connected to the emitter of the transistor Tr1, it is equivalent to a load being connected in parallel with the capacitor C3, and the oscillation frequency of the circuit changes, so that the output of the emitter of the transistor Tr1 is cupped. In addition to the base of the transistor Tr2 of the buffer amplifier circuit unit 1 via the ring capacitor C4, the collector output of this transistor Tr2 is led to the output terminal Pout via the capacitor C8, and the oscillation output is obtained from this output terminal Pout.

Further, the power supply voltage supplied from the power supply terminal B is divided by the resistors R1, R2 and R3, and the transistor T
The base bias is supplied to r1 and the transistor Tr2, the collector currents of the transistors Tr1 and Tr2 are determined, and capacitors C5 to C7 are used.
And C9 function as pass capacitors, and coil L2
~ L3 functions as a matching coil.

By the way, in the embodiment shown in FIG. 1, in addition to the structure shown in FIG. 3, a capacitor C10 is connected to the base of the transistor Tr2 of the buffer amplifier circuit section 1 via the coil L1.

Here, the coil L1 is the VCO100.
It seems that the resistance is sufficiently large for the oscillation frequency of the power supply terminal B
Is a constant that appears to be a resistor that is sufficiently small with respect to the power supply ripple frequency of the power supply voltage.

With the structure as described above, even if a rippled power source voltage is applied to the power source terminal B, the ripple component is absorbed by the capacitor C10, so that it does not affect other parts.

The output of the oscillation circuit section 2 is the coil L1.
Looks like a sufficiently large resistance, so almost all is output from the output terminal Pout.

As described above, in this embodiment, the capacitor C10 is provided in the buffer amplifier section 2 of the voltage controlled oscillator.
Is added, the low-frequency noise applied to the buffer amplifier section 2 from the power supply terminal B can be regarded as a ripple filter, and the signal applied from the oscillation circuit section 2 is normally amplified. Therefore, when the VCO 100 is modularized to form a synthesizer circuit such as a wireless telephone device as an independent unit, as shown in FIG. 2, it is not necessary to newly provide an external ripple filter or the like, and a direct power source is provided. Vcc to VCO1
00 can be connected.

Therefore, it is possible to obtain a voltage controlled oscillator in which the power supply voltage of the device can be directly used as the power supply voltage without using a ripple filter or the like.

[0037]

As described above, according to the present invention,
A capacitor that grounds the amplifying transistor base of the buffer amplifier circuit in low-frequency AC is provided so that low-frequency noise added to the buffer amplifier circuit from the power supply terminal can be regarded as a ripple filter, and added from the oscillator circuit. Since the signal is configured to perform normal amplification operation, it is not necessary to newly install a ripple filter or the like outside, and it is possible to cope with the low frequency noise of the power supply circuit output in the device, and the cost and space are reduced. It is possible to provide a voltage-controlled oscillation circuit that does not increase.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a voltage controlled oscillator circuit according to the present invention.

FIG. 2 is a configuration diagram of the voltage controlled oscillator shown in FIG. 1 when modularized.

FIG. 3 is a circuit diagram showing a conventional voltage controlled oscillator circuit.

FIG. 4 is a configuration diagram of a case where the conventional voltage controlled oscillator circuit shown in FIG. 3 is modularized.

[Explanation of symbols]

 1 Buffer Amplifier Circuit Section 2 Oscillation Circuit Section 10 Voltage Control Oscillation Signal Circuit (VCO) 20 Ripple Filter 100 Voltage Control Oscillation Signal Circuit (VCO) U1 Resonance Circuit Tr1 Oscillation Transistor Tr2 Amplification Transistors R1 to R4, R Resistors C1 to C10 , C capacitors L1 to L3 coils

Claims (2)

[Claims] 1. A buffer amplifier including a resonance circuit whose resonance frequency changes according to a control voltage, and an oscillation circuit section including an oscillation transistor which oscillates at the resonance frequency of the resonance circuit, and an amplification transistor which amplifies the output of the oscillation circuit section. And a circuit section, wherein the emitter of the oscillation transistor is connected to the base of the amplification transistor, and the collector of the oscillation transistor is cascode-connected to the emitter of the amplification transistor. A voltage controlled oscillator circuit comprising a capacitor for grounding the base of a transistor in a low-frequency alternating current. 2. The voltage controlled oscillator circuit according to claim 1, wherein the voltage controlled oscillator circuit is modularized into an independent unit.