JPH0680979B2 - Voltage-controlled surface acoustic wave oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a voltage-controlled surface acoustic wave oscillator using a surface acoustic wave delay line.

[Conventional technology]

A typical example of this type of voltage control type surface acoustic wave oscillator is shown in FIG. 3, that is, this surface acoustic wave oscillator basically comprises an amplifier 2, a phase shifter 4, and a surface acoustic wave delay line 6. It is configured by connecting in a loop. A directional coupler 8 and a capacitor are used to extract the output.

The phase shifter 4 is for satisfying the oscillation condition. Here, this is a voltage control type including a variable capacitance diode, and the oscillation frequency of the surface acoustic wave oscillator is changed by the control voltage Vt supplied to it. I am allowed to do it.

[Problems to be Solved by the Invention]

However, in such a voltage control type surface acoustic wave oscillator, conventionally, there is a problem that the linear region of the oscillation frequency characteristic with respect to the control voltage Vt (that is, the region where dF / dVt is constant when the oscillation frequency is F) is narrow. there were. More specifically, for example, as shown in FIG. 4, the non-linear portions A and B are present at the lower end and the higher end of the control voltage Vt, respectively.

More specifically, the curve in FIG. 4 is specifically determined by combining the phase characteristic of the surface acoustic wave delay line 6 and the phase characteristic of the phase shifter 4 with respect to the control voltage Vt.

However, since the surface acoustic wave delay line 6 is usually designed so that its phase characteristic becomes a straight line as shown in FIG. 5, for example, the curve of FIG. Has been decided by.

A concrete circuit configuration of the phase shifter 4 is shown in FIG. 6. As described above, the variable capacitance diode 41 is used,
In this variable capacitance diode 41, the control voltage is generally
The capacitance change is large when Vt is low, and the capacitance change is small when the control voltage Vt is high. As a result, the amount of phase shift with respect to the control voltage Vt of the phase shifter 4 becomes as shown in FIG. 7, for example, where the control voltage Vt is low, the slope of the curve becomes steep (A ₁ part) and the control voltage Vt becomes The slope of the curve becomes gentle at high places (B ₁ ). The non-linear portions A and B in the curve of FIG. 4 reflect such non-linear portions A ₁ and B ₁ . 42 and 43 in FIG. 6 are
RFC, 44 and 45 are capacitors for DC cutting.

The above-mentioned non-linearity of the oscillation frequency of the voltage-controlled surface acoustic oscillator causes the oscillator to simultaneously perform FM voice modulation in addition to the function of the original voltage-controlled oscillator (VCO) that changes the carrier frequency itself. (That is, the modulation signal is added to the control voltage Vt) For example, when it is used for a mobile phone, a car phone, etc., it becomes a problem.

This is because when the characteristic of the oscillation frequency with respect to the control voltage Vt is as shown in FIG. 4, the linearity is good in the intermediate portion between A and B, so that the modulation degree is medium when FM modulation is applied here. When FM modulation is applied to the non-linear portion A having the lowest frequency, the modulation degree of that channel becomes deep because the slope of the curve is steep. On the contrary, since the slope of the curve is gentle in the non-linear portion B having a high frequency, the modulation degree in that channel becomes shallow.
This means that this oscillator can be used in a narrow frequency range that does not include the non-linear portions A and B, but cannot be used in a wide frequency range that includes the non-linear portions A and B because the deviation of the modulation degree between channels becomes large. I mean.

Therefore, it is a primary object of the present invention to provide a voltage control type surface acoustic wave oscillator having a wide linear range of oscillation frequency characteristics with respect to a control voltage.

[Means for Solving the Problems]

In order to achieve the above object, the voltage-controlled surface acoustic wave oscillator of the present invention has a phase characteristic of the surface acoustic wave delay line that is non-linear so as to cancel a non-linear portion of the phase characteristic with respect to the control voltage of the phase shifter. It is characterized by having a part.

[Action]

The oscillation frequency characteristic of the voltage controlled surface acoustic wave oscillator with respect to the control voltage is determined by combining the phase characteristic of the surface acoustic wave delay line and the phase characteristic of the phase shifter with respect to the control voltage, as described above. Therefore, if the phase characteristics of the surface acoustic wave delay line are set as described above, the non-linear portions are offset from each other, so that the linear region of the oscillation frequency characteristic with respect to the control voltage of the voltage controlled surface acoustic wave oscillator is wide. Become.

〔Example〕

The voltage control type surface acoustic wave oscillator according to this embodiment also has a circuit configuration as shown in FIG. 3, and therefore, the description will be made with reference to it. In the following, differences from the conventional example will be mainly described. .

Generally, in the surface acoustic wave delay line 6, its amplitude characteristic and phase characteristic can be designed independently of each other, as is well known.

Therefore, when the characteristic of the phase shifter 4 has the non-linear portions A ₁ and B ₂ as shown in FIG. 7, for example, the phase characteristic of the elastic surface delay line 6 is as shown in FIG. 1, for example. to the non-linear portion a ₁ and B ₁ as the cancel each such non-linear portion a ₂
And when the one having a B _2, the control voltage of the oscillator
Since the oscillation frequency characteristic with respect to Vt is determined by the combination of the phase characteristic of the surface acoustic wave delay line 6 and the phase characteristic of the phase shifter 4 as described above, the non-linear portions are canceled by each other. As shown in, the linear area becomes wide. In this embodiment, the surface acoustic wave delay line 6 having such characteristics is designed and used.

It should be noted that if the IDT that constitutes the surface acoustic wave delay line 6 is point-symmetric with respect to the center (when weighted), or if it is in the normal form.
In the case of IDT (which is naturally line symmetric), the phase characteristic of the surface acoustic wave delay line 6 becomes a straight line as shown in FIG. Therefore, in order to give the phase characteristics of the surface acoustic wave delay line 6 the above-mentioned non-linear portions A ₂ and B ₂ , specifically, for example, the weighting for the IDT may be slightly shifted from the point symmetry.

〔The invention's effect〕

As described above, according to the present invention, the phase characteristic of the surface acoustic delay line has the non-linear portion that cancels the non-linear portion of the phase characteristic with respect to the control voltage of the phase shifter. The linear region of the oscillation frequency characteristic with respect to the control voltage of the surface acoustic wave oscillator becomes wider.

As a result, for example, when the oscillator is used, the deviation of the modulation degree between channels is reduced in an FM mobile radio such as a car telephone, and a good quality radio wave can be emitted.

Further, it is said that the voltage control type surface acoustic wave oscillator generally has a narrow frequency variable bandwidth. However, according to the oscillator of the present invention, it is possible to add a part which cannot be used conventionally to the variable band. The variable bandwidth can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of amplitude and phase characteristics of a surface acoustic wave delay line in a voltage control type surface acoustic wave oscillator according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of oscillation frequency characteristics of the same voltage control type surface acoustic wave oscillator with respect to a control voltage. FIG. 3 is a block diagram showing an example of the voltage control type surface acoustic wave oscillator. FIG. 4 is a diagram showing an example of oscillation frequency characteristics with respect to a control voltage of a conventional voltage control type surface acoustic wave oscillator. FIG. 5 is a diagram showing an example of amplitude and phase characteristics of a surface acoustic wave delay line in a conventional voltage control type surface acoustic wave oscillator. FIG. 6 is a circuit diagram showing a specific configuration example of the phase shifter in FIG.
FIG. 7 is a diagram showing an example of the amount of phase shift with respect to the control voltage of the phase shifter of FIG. 2 ... Amplifier, 4 ... Phase shifter, 41 ... Variable capacitance diode, 6 ... Surface acoustic wave delay line.

Claims (1)

[Claims] 1. A voltage control type surface acoustic wave oscillator configured by connecting at least an amplifier, a voltage control type phase shifter including a variable capacitance diode, and a surface acoustic wave delay line in a loop shape. A voltage controlled surface acoustic wave oscillator, wherein the phase characteristic of the surface wave delay line has a non-linear portion that cancels out the non-linear portion of the phase characteristic with respect to the control voltage of the phase shifter.