JPS6285505A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To increase the variable width of frequency by inserting a parallel circuit of a variable capacity diode and an inductance in series of a piezoelectric resonator. CONSTITUTION:A parallel circuit is formed by connecting a variable capacity diode Cj in series to a piezoelectric resonator 1 together with an inductance Ls connected in parallel to the diode Cj. Thus the adverse bias voltage impressed to the diode Cj is varied to secure the function of a voltage controlled oscillator. Here a constant is set so that the parallel resonance frequency of the diode Cj and an inductance L3 is higher than the anti-resonance frequency of the resonator 1. Then the function of an inductance L is secured in a using frequency band. Thus the variable width of frequency is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a voltage controlled oscillator configured using a piezoelectric resonator as an oscillator.

[Technical background of the invention and its problems]

Resonators that utilize piezoelectricity include crystal oscillators, surface acoustic wave resonators, and piezoelectric book resonators, but these piezoelectric resonators can all be expressed as electrical equivalent circuits as shown in Figure 5. can be shown.

In Figure 5, CO is the sum of the capacitance between the electrodes and the stray capacitance between the terminals, and the series resonant circuit consisting of the inductance h, capacitance C1, and resistance range represents the resonance phenomenon of the resonator. .

FIG. 6 shows a Colpitts-type voltage controlled oscillator, which is most commonly used in the past, and is constructed using such a resonator as an oscillator. In Fig. 6, 1 is a resonator, 2 is a circuit including an oscillation transistor on the right side of the broken line, %CJ is a variable capacitance diode, 01 to C4 are capacitances, and 8 to
R4 each represents a resistance.

If this oscillator is divided into the resonator 1 side and the other circuit 2, it can be expressed as a two-terminal equivalent circuit as shown in FIG. In the Colpitts oscillator, in order to satisfy the oscillation conditions, the resonator 1 is used at a frequency between resonance and anti-resonance, and is effectively operated as an inductive reactance, that is, an inductance L.

In this case, the circuit operates as a capacitor, and the actance on the circuit 2 side can be expressed by the capacitance (load capacitance) CL, and the oscillation frequency is approximately the inductance L,
This is the series resonance frequency of the variable capacitance diode Oj and the load capacitance tOL.

Therefore, a variable capacitance diode O connected in series to resonator 1
By changing the reverse bias voltage (control voltage) Va applied to j, its capacitance changes in proportion to the control voltage VR, and the oscillation frequency fO can be varied according to equation (11).

However, r is the capacitance ratio C! of resonator 1! o/Ct, ΔC
is the amount of change in capacitance of variable capacitance diode Cj.

Here, in order to change the oscillation frequency f0 over a wide frequency band, it is necessary to use a resonator with a wide resonance-anti-resonance frequency range, that is, a resonator 1 with a small capacitance ratio r, and a variable capacitance diode Oj with a large capacitance change. It won't happen.

However, since the variable capacitance diode Oj and the load capacitance CL are inserted in series with the resonator 1, the resonant frequency increases and the apparent capacitance ratio of the resonator 1 increases. The resonator 1 is inserted in series with the resonator 1, and the resonant frequency is lowered by or more than the increase in the resonant frequency due to the series capacitance, and the inductive region of the resonator 1 is widened. FIG. 9 shows its equivalent circuit.

However, even with such K, it is difficult to obtain a sufficiently wide band variable because the capacitance change of the variable capacitance diode Cj is small.

[Purpose of the invention]

This invention was made to eliminate the above-mentioned drawbacks.
The present invention aims to provide a voltage controlled oscillator that can widen the variable frequency range without deteriorating the capacitance ratio of the resonator.

[Summary of the invention]

The present invention is characterized in that, in a voltage controlled oscillator using a piezoelectric resonator as an oscillator, a parallel circuit of a variable capacitance diode and an inductance is inserted and connected in series with the piezoelectric resonator.

〔Effect of the invention〕

According to this invention, if a variable capacitance diode and an inductance are connected in parallel and the resonant frequency ω0 is set higher than the operating frequency as shown in FIG. This introduces inductance, which often narrows the region that operates as the inductance of the resonator like in conventional series-connected circuits, and because changes in the capacitance of the variable capacitance diode are converted to changes in inductance, it is necessary to create a wide-band variable oscillator. can be obtained easily.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a case in which the present invention is applied to a 400 MHz band voltage controlled oscillator and configured as a Colpitts type.

In FIG. 1, reference numeral 1 denotes a resonator, specifically a one-pair type pseudo surface acoustic wave resonator using a 36° rotated Y plate of lithium tantalate (Li Tag) as a piezoelectric substrate. 2 is the oscillation transistor Tr on the right side of the broken line
In this circuit, C1 to C4 are capacitances, respectively.
8 to R4 are resistors, respectively.

A variable capacitance diode Oj is connected in series with the resonator 1,
An inductance Ls is connected in parallel with this diode Oj to form a parallel circuit.

As shown in the equivalent circuit of FIG. 2, circuit 2 has a negative resistance -R
It can be expressed as a series circuit with a load capacity of -3110L. Therefore, by connecting the resonator 1 and the variable capacitance diode Oj, a Myo-Colpitts type oscillation circuit can be configured, and by varying the reverse bias voltage (control voltage) Vcon applied to the variable capacitance diode Cj, it becomes a voltage controlled oscillator. .

In the parallel circuit of the variable capacitance diode Oj and the inductance Ls, a constant is set so that its parallel resonance frequency is higher than the anti-resonance frequency of the resonator 1, and the circuit is operated as an inductance L in the frequency band used.

That is, the inductance L is changed by changing the variable capacitance diode Cj.

FIG. 4 shows the change in oscillation frequency when the control voltage Vcon is varied in the range of 0 to 6T.

The constants of each element are Ls=15nH, 0j=5.9P F=
1.8PF.

0L=xOFF', curve A is for the conventional voltage controlled oscillator shown in FIGS. 8 and 9, and curve 114B is for the voltage controlled oscillator according to the present invention.

It is clear from FIG. 9 that a large control sensitivity can be obtained in the voltage controlled oscillator according to the present invention. Note that the present invention is not limited to the above embodiments, and can be implemented with various modifications without changing the gist. be able to.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of an embodiment of the present invention, Fig. 2 is an electrical equivalent circuit diagram of the same embodiment in two-terminal representation, and Fig. 3 is a diagram of the conventional voltage controlled oscillator and the voltage according to the present invention. Figure 40 shows the actance curve in comparison with (6) in the case of a controlled oscillator.
%), Figure 5 is an electrical equivalent circuit diagram of a piezoelectric resonator, Figure 6 is a circuit diagram of a conventional Colpitts voltage controlled oscillator, and Figure 7 is an electrical equivalent of the oscillator in Figure 6. Circuit diagram, Figure 8 is a circuit configuration diagram of a conventional Colpitts type voltage controlled oscillator in which an inductance is connected in series with a piezoelectric resonator, Figure 9
The figure is an electrical equivalent circuit diagram of the oscillator of FIG. 8.

Claims (2)

[Claims] (1) A voltage controlled oscillator using a piezoelectric resonator as an oscillator, characterized in that a parallel circuit of a variable capacitance diode and an inductance is inserted and connected in series with the piezoelectric resonator. (2) The voltage controlled oscillator according to claim 1, wherein the parallel circuit of the variable capacitance diode and the inductance is inductive in the operating frequency range.