JP2001102863A - Voltage controlled oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage controlled oscillator(VCO) capable of simplifying a circuit configuration and stabilizing an oscillation output. SOLUTION: Concerning the VCO provided with a first oscillating step 1, a second oscillating step 2 for performing the oscillating operation of a frequency band lower than that of the first oscillating step 1 and buffer amplifier step 3 connected to the oscillating steps L and 2 while having a buffer transistor 31 to which a bias current is supplied from a bias terminal, the buffer step 3 is composed of strip lines 33 and 34 arranged between the said bias terminal 32 and the buffer transistor 31 and a switching element 35 for making a gap between the strip lines 33 and 34 into ground potential through a first capacitor 36 when operating the oscillating step 1.

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 used in a mobile communication system such as a car phone or a portable phone.

[0002]

2. Description of the Related Art Conventionally, in a voltage controlled oscillator that outputs two relatively distant frequency bands (for example, 1.5 to 2 times), in order to obtain an output without deterioration of output power, it is necessary to use each band. And two buffer stages matched to each other. That is, the voltage-controlled oscillator has two systems of voltage control circuits each including one oscillation stage and one buffer stage connected in series, corresponding to two frequencies.

In such a configuration, since two buffer stages are included, the shape of the voltage-controlled oscillator becomes large, and the power consumption increases.

In order to solve such a problem, a voltage controlled oscillator in which two buffer stages share one buffer stage is disclosed in, for example, JP-A-9-294018,
No. 0-126152.

FIG. 2 is a circuit diagram of a conventional voltage controlled oscillator. The voltage controlled oscillator performs an oscillation operation in a high frequency band, an oscillating stage 6 oscillating in a lower frequency band compared to the oscillating stage 5, and amplifies the outputs of the oscillating stages 5, 6 in common. And a buffer stage 7.

The oscillating stage 5 mainly comprises a resonance means 51, a varicap diode 52, and an oscillating stage transistor 53. It has a control voltage terminal 8 to which a voltage applied to the varicap diode 52 is supplied, and a base bias terminal 54 for controlling the operation of the oscillation stage 5 at the base of the oscillation stage transistor 53. ing.

The oscillating stage 6 is mainly composed of a resonance means 61, a varicap diode 62, and an oscillating stage transistor 63 substantially like the oscillating stage 5. The varicap diode 62 has a control voltage terminal 8 shared with the oscillation stage 5, and the base of the oscillation stage transistor 53 has a base bias terminal 64 for controlling the operation of the oscillation stage 6. are doing.

The selection of the two oscillation stages 5 and 6 is as follows.
This is enabled by supplying a voltage for operating the oscillation stage transistor 53 or 63 from the base bias terminal 54 or 64, which enables discrete oscillation between a high frequency band and a low frequency band. Within the oscillation frequency band, the frequency from the control voltage terminal 8 enables more continuous frequency control.

The resonance means 51, 52 can be exemplified by coaxial resonators, strip line resonators, etc., and are each set to have a predetermined resonance frequency according to the oscillation frequency band.

The outputs of the oscillation stages 5 and 6 are supplied to a common buffer stage 7. The buffer stage 7 mainly includes a buffer transistor 71, and a trap circuit disposed between the bias terminal 72 and the buffer transistor 71.

The collector of the buffer transistor 71 is
It is led to an output terminal 78 via a capacitor 77. The trap circuit is composed of two strip lines 7.
3, 75, and two capacitors 74, 76. This capacitor 74 connects the bias terminal side of the strip line 73 to ground. Further, the capacitor 76 grounds the bias terminal side of the strip line 75.

The capacitance of the capacitor 74 is set to a value that causes a low impedance in a high oscillation frequency band, and the line length of the strip line 73 is a length corresponding to １ ／ of the wavelength in the high oscillation frequency band. The capacity of the capacitor 76 is set to a value that results in low impedance in a low oscillation frequency band. The length of the strip line 75 is
The impedance when the trap circuit is viewed from the collector of the buffer transistor 71 is set to a large value in a low oscillation frequency band.

For example, when the base bias terminal 54 is on, control in a high-frequency oscillation frequency band is performed by a voltage applied to the control voltage terminal 8. The oscillation output of the oscillation stage 5 is amplified by the buffer stage 7 and output from the output terminal 78.

The trap circuit of the buffer stage 7 is provided to ensure that the impedance when the collector bias terminal 72 is viewed from the buffer stage transistor 71 is sufficiently larger than the impedance when the output terminal 78 is viewed. In a high oscillation frequency band in which the oscillation stage 5 operates, the impedance of the trap circuit is determined by the length of the strip line 73 and the capacitance of the capacitor 74. Conversely, the impedance in the low oscillation frequency band (the base bias terminal 64 is turned on and the oscillation stage 6 operates) is determined by adjusting the length of the strip line 75 and the capacitance of the capacitor 76.

In this case, the output signal is not affected by the collector bias terminal 72 in both of the two oscillation frequency bands. In the low oscillation frequency band, the capacitor 74 does not have a low impedance, but has a function of extending the line length of the strip line, so that the sum of the lengths of the strip line 75 and the strip line 73 is 1/1/1 of the wavelength of the low oscillation frequency. It can be set to a value shorter than 4.

Thus, when the trapping circuit is viewed from the buffer transistor 71, the impedance becomes high at a high frequency when the oscillation stage 5 is operating, and becomes high at a low frequency when the oscillation stage 6 is operating. Thus, deterioration of the output power is prevented.

[0017]

However, as the use of the above-mentioned voltage controlled oscillator, the relationship between the oscillation frequency band of the oscillation stage 5 and the oscillation frequency band of the oscillation stage 6 is often about twice. For example, in a mobile communication telephone, there are a GSM communication system (900 MHz band) and a DCS communication system (1.8 GHz band).

In the above-described voltage-controlled oscillator, when the oscillation stage 6 that oscillates in a low frequency band is operated, for example, the trap circuit operates effectively for an output in the 900 MHz band. The signal of the double harmonic component generated by the above operation cannot be sufficiently suppressed by the above trap circuit, and the output of the unnecessary double harmonic component is derived from the output terminal 78. Will be done.

Therefore, practically, the output terminal 78 is connected to two terminals.
As shown in FIG. 3 of Japanese Patent Application Laid-Open No. H10-126152, it was necessary to sort by a low-pass filter or a high-pass filter. That is, in order to obtain a stable oscillation output, a filter component (filter circuit) is further required, and the circuit becomes large.

The present invention has been devised in view of the above-described problems, and has as its object to simplify the circuit configuration and perform an oscillation stage for oscillating in a high frequency band and oscillating in a low frequency band. It is an object of the present invention to provide a voltage-controlled oscillator that can use a shared buffer stage as an oscillation stage, has a simplified circuit configuration, and can output a stable oscillation output.

Further, it is an object of the present invention to provide a voltage controlled oscillator having a small reflection loss when these oscillation outputs are led to an output terminal.

[0022]

According to the present invention, a first oscillating stage for oscillating in a predetermined frequency band and a second oscillating operation for oscillating in a frequency band lower than the frequency band of the first oscillating stage are provided. An oscillation stage, a voltage controlled oscillator comprising a buffer amplifier stage having a buffer transistor connected to each of the oscillation stages and supplied with a bais current from a bais terminal, wherein the buffer stage comprises a bias terminal and the buffer transistor And a switching element for setting the middle of the strip line to a ground potential via a first capacitor during the operation of the first oscillation stage. is there.

Preferably, the buffer stage has an impedance matching circuit composed of a second capacitor disposed between the buffer transistor and an output terminal, and the strip line. It is a voltage controlled oscillator.

[0024]

According to the present invention, the impedance control between the buffer transistor and the bias terminal in the buffer stage is forcibly controlled by a switching diode synchronized with the operation of the first oscillation stage.

In the oscillation in the high frequency band, the strip line is specified by the strip line on the side close to the buffer transistor and the capacitor connected to the switching diode, and the parallel resonance circuit including the strip line specifies the strip line. The impedance is set to a high value. As a result, an oscillation output in a high frequency band is stably supplied to the output terminal.

In oscillation in a low frequency band, one end of the strip line near the buffer transistor is not grounded, and two
It operates as one strip line, one end of the strip line near the bias terminal is grounded via a capacitor, and the impedance in a low frequency band is made high by a parallel resonance circuit including this strip line. As a result, an oscillation output in a low frequency band is supplied stably.

At the same time, even for a signal having a harmonic component twice as high as that of the low frequency band, the signal is not supplied to the output terminal because the two strip lines are not grounded. .

Moreover, in the present invention, a high-pass type matching circuit is constituted by the second capacitor and the operating strip line. With this matching circuit, the impedance when the transistor is viewed from the output terminal side can be converted to an external load impedance, for example, 50Ω.

Therefore, the matching with the external circuit connected to the output terminal is improved, and the reflection loss at this connection portion can be reduced.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a voltage controlled oscillator according to the present invention will be described with reference to the drawings. FIG. 1 shows a circuit diagram of the voltage controlled oscillator of the present invention. In the drawings, the same parts as those in the related art will be described with the same reference numerals.

The voltage controlled oscillator uses an oscillation stage 1 for oscillating in a high frequency band, an oscillation stage 2 for oscillating in a lower frequency band than the oscillation stage 1, and an output of the oscillation stages 1 and 2 in common. And a buffer stage 3 for performing amplification.

The oscillating stage 1 is mainly composed of a strip line 11 as a resonance means, a varicap diode 12, and an oscillating stage transistor 13. Further, it has a control voltage terminal 41 to which a voltage applied to the varicap diode 12 is supplied. The base of the oscillation stage transistor 13 has a base bias terminal 14 for controlling the operation of the oscillation stage 1.

The oscillating stage 2 is, like the oscillating stage 1, substantially composed of a strip line 21, a varicap diode 22, and an oscillating stage transistor 23 as resonance means. And the varicap diode 22
Has a control voltage terminal 41 shared with the oscillation stage 2. The base of the oscillation stage transistor 23 has a base bias terminal 24 for controlling the operation of the oscillation stage 2.

The operation of the oscillation stage 1 is based on the base bias terminal 1
4 supplies a predetermined voltage to the oscillation stage transistor 13.
Thus, the oscillation condition of the resonance circuit including the strip line 11 is adjusted, and the oscillation output in a high frequency band is supplied to the buffer stage 3. Further, in this high oscillation frequency band, the capacitance of the varicap diode 12 can be varied by the control voltage from the control voltage terminal 41, so that the oscillation frequency can be continuously controlled.

The operation of the oscillation stage 2 is based on the base bias terminal 2
4 supplies a predetermined voltage to the oscillation stage transistor 23.
Thus, the oscillation condition of the resonance circuit including the strip line 21 is adjusted, and the oscillation output in the high frequency band is supplied to the buffer stage 3. Further, in this low oscillation frequency band, the capacitance of the varicap diode 22 can be varied by the control voltage from the control voltage terminal 41, so that the oscillation frequency can be continuously controlled.

The outputs of the oscillation stages 1 and 2 are supplied to a common buffer stage 3. The buffer stage 3 includes a buffer transistor 31, two strip lines 33 and 34 disposed between the bias terminal 32 and the buffer transistor 31, and strip lines 33 and 34.
And a plurality of capacitors 36 to 39 for controlling the operation of.

Further, the collector of the buffer transistor 31 is led to an output terminal 78 via a second capacitor 38. The end of the second capacitor 38 on the buffer transistor 31 side is connected to the ground potential via the third capacitor 39.

At a connection point X between the two strip lines 33 and 34, a first capacitor 36 is disposed.
5 is grounded.

The end of the strip line 34 on the bias terminal 32 side is grounded via a capacitor 37.

In particular, in the present invention, the end of the strip line 33 on the bias terminal 32 side is connected to the first capacitor 3.
As a means for forcibly grounding via the oscillator 6, the voltage of the base bias terminal 14 for controlling the operation of the oscillation stage 1
It has a switching diode 35 that performs an ON-OFF operation.

For example, in order to oscillate at a high frequency,
When a predetermined voltage is supplied to the base bias terminal 14, a high-frequency oscillation output is supplied to the buffer stage 3 from the oscillation stage 1. At the same time, a predetermined voltage is applied to the base bias terminal 14 as a bias for the switching diode 35 of the buffer stage 3, so that the switching diode 3
5 turns on. Thereby, strip line 3
3 is connected to the first capacitor 3.
6 will be grounded. That is, a parallel resonance circuit is formed by the strip line 33 and the third capacitor 39, the impedance is infinite at a preset resonance frequency (high oscillation frequency band) of the parallel resonance circuit, and the output is the buffer transistor 31. From the collector to the output terminal 40 in a stable manner.

When a predetermined voltage is supplied to the base bias terminal 24 to oscillate at a low frequency, an oscillation output at a low oscillation frequency is supplied to the buffer stage 3 from the oscillation stage 2. In this case, since the switching diode 35 of the buffer stage 3 is turned off, the first capacitor 36 is ignored in terms of high frequency.

Therefore, the strip lines 33 and 34 are
One end is grounded via the capacitor 37. That is, a parallel resonance circuit is formed by the strip lines 33 and 34 and the third capacitor 39, the impedance is infinite at a preset resonance frequency (low oscillation frequency band) of the parallel resonance circuit, and the output is a buffer transistor. A stable output from the collector 31 to the output terminal 40 is provided.

In particular, the two strip lines 33, 34
Although the connection point X is connected to the first capacitor 36, it can be ignored since the switching diode 35 is in the OFF state, and the strip lines 33 and 34 can be regarded as a series of strip lines.

From this, even when, for example, a double harmonic component occurs at the time of oscillation in a low frequency band, a parallel resonance circuit is not constituted only by the strip line 33.
No harmonic component is derived from the output terminal 40 at all.

Therefore, even if the high frequency band is set to be about twice the low frequency band as in the case of the GSM system or the DCS system, for example, as in the case of the GSM system or the DCS system, the voltage controlled oscillator of the present invention will In addition, the harmonic components in the low frequency band are not suppressed and are not derived from the output terminal at all, and only the output in the predetermined frequency band can be stably derived to the output terminal.

Further, in the present invention, a second capacitor 38 is arranged between the collector of the buffer transistor 31 and the output terminal 40, and further, a connection between the collector of the buffer transistor 31 and the second capacitor 38 is provided. A third capacitor 39 is arranged between the point Z and the ground potential.

The high-pass type is formed by the capacitance component of the second capacitor 38 and the inductance component of the operating strip line 33 or the inductance components of the strip lines 33 and 34 (including the inductance component of the switching diode 35). This constitutes a matching circuit.

The impedance conversion is performed by the high-pass type matching circuit. In general, the load impedance is 50Ω, and the impedance of the collector of the buffer transistor 31 as viewed from the output terminal 40 is, for example, about several hundreds Ω. Further, a stable output can be derived.

For example, when the oscillation is performed in a high frequency band (the oscillation stage 1 operates), the high-pass type is formed by the inductance component of the strip line 33 and the switching diode 35 in the ON state and the component of the second capacitor 38. A matching circuit is formed, and load impedance matching is performed.

In the case where oscillation occurs in a low frequency band (the oscillation stage 2 operates), the strip lines 33 and 34
And a capacitance component of the second capacitor 38, a high-pass matching circuit is formed, and load impedance matching is performed.

For example, at the time of oscillation in a high frequency band, a parallel resonance circuit is formed by the inductance component of the strip line 33 (including the inductance component of the switching diode) and the third capacitor 39 so as to meet a desired frequency. Thereafter, output matching is performed by the second capacitor 38. Equivalently, a part of the strip line 33 and the capacitor 38 constitute a high-pass matching circuit. Thus, the output impedance derived from the output terminal 40 can be set to 50Ω.

In the above-described embodiment, the description has been given of the voltage controlled oscillator having the two oscillation stages in the relation of the two discrete frequency bands. , Switching diodes, first capacitors, and strip lines may be increased.

[0054]

As described above, according to the present invention, each oscillation stage in a discrete oscillation frequency band can be output from one buffer stage. This simplifies the voltage-controlled oscillation circuit, resulting in a small voltage-controlled oscillator.

When operating in a low frequency band,
Since the harmonic components can be completely suppressed, stable output can be achieved without power degradation.

Furthermore, since the impedance seen from the output terminal to the buffer transistor can be approximated to the load impedance, the reflection loss at the output terminal is small, and the power is not deteriorated and the stable output is possible.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram of a conventional voltage controlled oscillator.

[Explanation of symbols]

 1 1st (high frequency band) oscillation stage 2 2nd (low frequency band) oscillation stage 3 buffer stage 31 buffer transistor 32 bias terminal 33 ... first strip line 34 ... second strip line 35 ... switching diode 36 ... first capacitor 37 ... capacitor 38 ... second capacitor 39 ... third Capacitors

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J081 AA03 AA11 AA19 BB01 CC10 CC42 DD03 DD20 EE03 EE09 EE14 EE18 FF04 FF17 FF19 FF21 FF23 FF25 GG05 GG07 KK02 KK09 KK22 KK23 LL05 MM01

Claims (2)

[Claims] A first oscillation stage for performing an oscillation operation in a predetermined frequency band; a second oscillation stage for performing an oscillation operation in a frequency band lower than a frequency band of the first oscillation stage; and each of the oscillation stages. And a buffer amplifier stage having a buffer transistor to which a bais current is supplied from a bais terminal, wherein the buffer stage comprises a strip disposed between a bias terminal and the buffer transistor. A voltage-controlled oscillator comprising: a line; and a switching element for setting a midpoint of the strip line to a ground potential via a first capacitor when the first oscillation stage operates. 2. The buffer stage according to claim 1, wherein said buffer stage has an impedance matching circuit comprising a second capacitor disposed between said buffer transistor and an output terminal, and said strip line. A voltage controlled oscillator as described.