JPS61253904A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To stabilize the frequency characteristic of a phase leveling loop (PLL) circuit by providing the electrostatic capacity of a diode having variable capacity with a value coincident with the load capacity/oscillating frequency characteristics of a voltage controlled type oscillator. CONSTITUTION:In the voltage controlled oscillator (VCO) 4, the capacitance of the variable capacity diode 42 is changed by a control voltage Vc and the oscillating frequency of a piezoelectric vibrator 43 is also changed is response to said change to obtain output frequency fVCO. The characteristics of the diode 42 are made coincide with the load capacity/oscillating frequency characteristics of the VCO 4 so that the output frequency fVCO having high linearity corresponding to the change of the control voltage Vc is obtained. In addition, the piezoelectric vibrator 43 reduces the changing range of the frequency fVCO as compared with the change of the voltage Vc. Consequently, influences due to the change of voltage, noise, etc. can be reduced and the PLL circuit can execute stable operation as a whole.

Description

Detailed Description of the Invention (Summary) This is a voltage controlled oscillator particularly suitable for use in a VHFHF phase phase-locked loop frequency oscillator, which has a variable capacitance diode and a piezoelectric vibrator, and has an oscillation frequency that is nearly constant. The capacitance of the variable capacitance diode has a value that matches the load capacitance-oscillation frequency characteristic of the voltage controlled oscillator.

[Industrial application field]

The present invention relates to a frequency oscillator, and particularly to a voltage controlled oscillator (VCO) in a VHF band multi-channel oscillator using a phase-locked loop (CF'LL).

[Prior art and problems to be solved by the invention]

A vCO is used in a PLL circuit, etc., and conventional vCOs include an LC oscillation VCO and a transistor transistor logic (TTL) circuit vCO.

LC oscillation vCO has problems in that the inductance L changes depending on temperature and power supply voltage fluctuations, the oscillation frequency also changes, and the noise level is also high. Such LC oscillation vCO
When the inductance L is incorporated into a PLL circuit, the above fluctuation in the inductance L tends to be compensated to some extent, but it is not sufficiently compensated.

The TTL circuit vCO also has the problem that the characteristics of the transistor change due to temperature fluctuations, causing the oscillation frequency to fluctuate as described above. Furthermore, since it has an unstable multi-by-break configuration, there is a problem that the linearity of the oscillation frequency with respect to the input voltage is insufficient.

Furthermore, a PLL synthesizer with a conventional configuration uses a low power Schottky (LS-) TTL.

Normal (N) - Because the operating frequency of TTL, 0MO3, etc. is not high enough, it is not possible to directly divide signals in the frequency band of approximately 30MHz to 300MHz, the so-called VHF band, with a programmable frequency divider, and the VHF band PLL of
It is difficult to realize a frequency oscillation circuit.

[Means for solving problems]

FIG. 1 shows a block diagram of the principle of the present invention, and FIG. 1(a)
is a block diagram of a PLL frequency oscillation circuit having a VCO according to the present invention, and FIG. 1(b) shows the circuit of the VCO.

In FIG. 1, the PLL frequency oscillation circuit includes a frequency divider 1 that divides an input frequency II by 1/M, the divided input frequency j1, and an output frequency division frequency t' of a programmable frequency divider 5, which will be described later. A phase comparator 2 that inputs the VCO and VCO, compares their phases, and outputs a signal according to the phase difference; a low-pass filter 3 that filters the output of the phase comparator 2 and outputs a control voltage for the subsequent VCO 4; and the low-pass filter A control voltage VC from 3 is input, and a frequency t VC is determined according to the control voltage.

It has a VCO 4 that outputs a frequency f of the VCO 4, and a programmable frequency divider 5 that divides the frequency of the VCO by 1/N. Further, the PLL frequency oscillation circuit is provided at the subsequent stage of the VCO4, and has an output frequency fVc of the VCO4.

It has a multiplier 6 that outputs the magnification and multiplies it.

The VCO 4 is an oscillation circuit having a variable capacitance diode 42 and a piezoelectric vibrator 43. VCO 4 also has an input resistor 41 and an output circuit 40. In order to provide VCO output characteristics with good linearity, the VCO 4 utilizes the load capacitance-oscillation frequency characteristics of the oscillator, and uses a variable capacitance diode 42 having characteristics that match these characteristics.

[For production]

In FIG. 1(a), the phase comparator 2, low-pass filter 3, VCO 4, and programmable frequency divider 5 have a general PLL circuit configuration. By providing the multiplier 6 in the circuit, circuits 2 to 5 only need to operate at a frequency of 1/M, and basically they can be used with conventional circuit elements whose operating frequency is not very high, such as the aforementioned LS-TTL. , N-TTL, etc.

VCO4 is connected to variable capacitance diode 4 by control voltage VC.
2 changes, and in response to this change, the oscillation frequency of the piezoelectric vibrator 43 changes, and the output frequency f VC
(1 is obtained.Here, the characteristic of the variable capacitance diode 42 is V
An output frequency tvco that matches the load capacitance-oscillation frequency characteristic of the CO is used to obtain an output frequency tvco with good linearity with respect to changes in the control voltage V. Furthermore, a piezoelectric vibrator 43 is used, and the output frequency tvc is determined by a change in the control voltage V. - The range of change is small, less than 0.5%.

This provides a stable output frequency that is less susceptible to the effects of voltage fluctuations, noise, etc.

By using such a VCO, the entire PLL circuit
It operates stably as

〔Example〕

FIG. 2 shows a circuit diagram of an embodiment of the VCO shown in FIG. 1(b). This circuit, like a mycelium, constitutes a Colpitts-type oscillator. In FIG. 2, the Colpitts type oscillator includes a variable capacitance diode 42, an 'EE oscillating electron oscillator, and a lithium tantalate (LiTaOs) oscillator 43.
, transistor 47, resistors 41, 44.4B, and capacitors 45, 46, 49 are connected as shown.

FIG. 3 shows the capacitance characteristics of the variable capacitance diode 42 with respect to the input voltage vt'.

The capacitance of the variable capacitance diode 42 changes according to the input voltage as shown in the characteristics shown in FIG. The characteristics of the output oscillation frequency t vco with respect to , are shown in FIG.

As is clear from FIG. 4, it can be seen that the linearity of the output frequency j9CQ is good. Also, the output frequency change range is approximately 50.9 for a control voltage change of 0 to 5V.
The rate of change is approximately 0.3 between 9MHz and 51.14MHz.
It is small, about %. Therefore, it is less susceptible to fluctuations in the power supply voltage vce.

On the other hand, the fact that the amount of change in the output frequency fVC6 is small can be considered a disadvantage, but for example, a CB of 27 MO2
Multi-channel PLL for (Citizen Band)
When applied to circuits, there is no particular problem since the number of permissible channels is limited. Rather, it has the advantage of not emitting illegal radio waves.

As an example of the PLL circuit shown in FIG. 1(a) using the VCO shown in FIG. The frequency j is 13.5 MHz, and in this fr, N-TTL and LS-TTL.

A high-speed 0MO3 or the like can be used as the programmable frequency divider 5. The frequency division ratio M can be arbitrary, but in the case of a digital format, it can be set to a power of two. The magnification of the multiplier 6 is generally 1/1/
Make it M.

〔Effect of the invention〕

As described above, according to the present invention, first, a voltage controlled oscillator (VCO) with good linearity and stable operation can be obtained.

In addition, when the vCO of the present invention is used, the frequency characteristics of the PLL circuit are stabilized, and it is not affected by disturbances such as noise (VHF band P
An LL type multi-channel frequency oscillator is obtained.

Furthermore, according to the present invention, a PLL circuit can be constructed using conventional circuit elements whose operating frequencies are not very high.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the present invention, Fig. 2 is a circuit diagram of a VCO as an embodiment of the present invention, Fig. 3 is a characteristic diagram of a variable capacitance diode in the circuit of Fig. 2, and Fig. 4 is a diagram of a VCO as an embodiment of the present invention. The figure shows the output characteristics of the circuit. (Explanation of symbols) 1... Frequency divider, 2... Phase comparator, 3... Low pass filter, 4... Voltage controlled oscillator, 5... Programmable frequency divider, 6... Tei Multiplier. (a) °6...multiplier Fig. 2 vCO circuit diagram of an embodiment of the present invention Fig. 3 Input voltage-capacitance characteristics of variable capacitance diode

Claims (1)

[Claims] 1. A piezoelectric vibrator whose oscillation frequency changes in response to a change in capacitance of a variable capacitance diode and a capacitance of the variable capacitance diode, wherein the capacitance of the variable capacitance diode is equal to the load capacitance. - An oscillation circuit characterized in that it has characteristics matching the oscillation frequency characteristics. 2. The oscillation circuit according to claim 1, wherein the piezoelectric vibrator is a lithium tantalate piezoelectric element. 3. The oscillation circuit according to claim 1 or 2, wherein the oscillation circuit is configured as a Colpitts type oscillation circuit.