JPS60237704A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To stop parasitic vibrations of higher-order frequency and to perform oscillations by composing a filter means of the 1st low-pass filter connected to the output side of an oscillator and the 2nd low-pass filter which is connected to the output side of the filter remove higher harmonic components. CONSTITUTION:The oscillation circuit 30 consists of an oscillating means 31 which oscillates at a desired frequency and an amplifying means 33 which amplifies the output of the means 31 through the filter means 32. The 1st low-pass filter 32a of this filter means 32 suppresses a DC vomponent and the 2nd low- pass filter 36b connected to the output side of the filter 32a remove higher harmonic components of the oscillation output. This low-pass filter 32a consists of the parallel circuit of a capacitance C3 and a resitance R3 and its one terminal is grounded. Further, the 2nd low-pass filter 32b is composed of a resistance R4 whose one terminal is connected to the output side of the low-pass filter 32a and a capacitance C4 connected between the other terminal of the resistance R4 and the ground. Then, parasitic vibrations of higher-order frequency of the oscillating means 31 are inhibited from passing and the DC component is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an oscillation circuit that oscillates using a piezoelectric vibrator.

[Prior art]

Conventionally, two types of oscillation circuits using piezoelectric vibrators are known.

First, a first conventional example will be explained with reference to FIGS. 1 and 2.

In the figure, 1 and 2 are a pair of piezoelectric vibrators that vibrate at a desired frequency, and these piezoelectric vibrators 1 and 2 have electrode plates ta, 1b, 2a, and 2b at both ends, respectively.
is grounded via conductor 3. 4 is piezoelectric vibrator 1
A phase shift circuit 5 connected to the electrode plate 1a is an amplifier circuit which amplifies the output of the phase shift circuit 4 and feeds it back to the piezoelectric elements 1 and 2.

6 is an equivalent circuit of the piezoelectric vibrators 1 and 20, and high-frequency waves f, . resonant circuit A, ~A
n, a coupling circuit M for electromagnetically coupling the resonant circuit An to the input/output side, and an input/output capacitor located on the input/output side. In addition, T.I.

■, and T8. T and T are the input and output terminals of the piezoelectric vibrators 1 and 20, respectively, which are represented by the circuit 6.

In the conventional oscillation circuit configured as described above, when the power is turned on, the piezoelectric vibrators 1 and 2 generate mechanical vibrations due to the piezoelectric strain effect. , so-called spurious vibrations such as harmonic vibrations having a frequency that is an integral multiple of this oscillation frequency are parasitic, but when this vibration is amplified by the amplifier circuit 5, there is a problem that harmful harmonic oscillations are caused. . In particular, when the amplifier circuit 5 connected to the piezoelectric vibrators 1 and 2 is made to maintain a sufficiently large amplification gain in order to perform oscillation smoothly, harmonic oscillation becomes significant in accordance with the amplification gain.

Therefore, in order to prevent this harmonic oscillation, conventional structures have been constructed using elements for preventing harmonic oscillation (such as mechanical filters) having a reduced i-pole corresponding to the frequency of harmonic oscillation, and active elements such as transistors. Active filters were used as appropriate.

However, the use of an element having such an attenuation pole or an active filter has the disadvantage that the oscillation circuit becomes expensive.

Further, as a second conventional example, oscillation circuits shown in FIGS. 3 and 5 have been proposed.

Next, this oscillation circuit will be explained. However, the same or equivalent parts as in the first conventional example are given the same reference numerals, and the details thereof are omitted.

In the figure, a circuit 20 indicates the output side of the piezoelectric vibrators 1 and 2, and consists of a current source 21 and an output capacitor C0 connected in parallel to the current source 21. It shows the output of the vibrator 1.2, and has a peak output corresponding to each oscillation frequency fo to fn.

22 is a filter connected to the output side of the piezoelectric vibrators 1 and 2 to remove harmonics, and is connected to the amplifier circuit 5.

The filter 22 includes resistors R, R, and capacitors C, .
A pair of low-pass filters 22a formed by C.

22b to prevent harmonics by providing the wave leakage characteristics shown in FIG.
The capacitors c, ,c are sufficiently smaller than l.

The capacitance of C0 is set to be sufficiently larger than the output capacitance C0.By the way, in the conventional oscillation circuit as described above,
Harmful oscillation is prevented by attenuating the harmonics f1 to fn, but in order to smooth oscillation at the fundamental oscillation frequency t0, the amplification gain of the amplifier circuit 5 is normally set to 3.
Since it is necessary to set the value to 0 (11 or more), two low-pass filters 22a and 22b are used to provide a second-order characteristic.

However, when the filters 22a and 22b are used to attenuate the harmonics f1 to fn, the amount of attenuation becomes excessive, making it difficult to oscillate at the fundamental oscillation frequency fo, or making it difficult to oscillate at the fundamental oscillation frequency f0. There is a problem in that it is extremely difficult to match the phase to achieve this, and stable oscillation cannot be maintained.

Furthermore, the output voltage of the filter 22 V,GfC,=C,Ei
If Cφ, R1=R, =iii'Rφ, then Cφ> C
Since o + Rφ<lt/jωco, it is expressed as , and only the DC component is output. On the other hand, the phase of the output side during oscillation is as shown in Figure 5 (b
), but the phase difference with the input side cannot be made zero, so the phase cannot be perfectly matched, and therefore the oscillation circuit is not stable. The drawback is that oscillation cannot be maintained.

〔the purpose〕

This invention was made with attention to the above points, and it is possible to prevent parasitic oscillations having frequencies different from the fundamental oscillation frequency, especially harmonic oscillations having higher-order frequencies, and to suppress DC components. The purpose is to provide circuits.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 6 and 7. Note that the same reference numerals are given to the same or equivalent parts as in the conventional example, and the details thereof are omitted.

In the figure, reference numeral 30 denotes an oscillation circuit of the present invention, which comprises an oscillation means 31 that vibrates at a desired frequency, and an amplification means 33 that amplifies the output of the oscillation means 31 via a wave leakage means 32. The wave means 32 is a first wave means capable of suppressing the DC component.
It consists of a low-pass filter 32a and a second low-pass filter 32b connected to the output side of this low-pass filter 32a.

The first low-pass filter 32a is formed by a parallel circuit of a capacitor C1 and a resistor R3, and one end is grounded.

The second low-pass filter 32b includes a resistor having one end connected to the output side of the first low-pass filter 32a, and a capacitor C4 connected between the other end of the resistor and ground.

In the leakage means 32 formed by the above-mentioned low-pass filters 32a and 32b, the low-pass portion P0 where the fundamental oscillation frequency f0 exists is almost flat, as shown in FIG. A high frequency section P8 having a higher frequency than this low frequency section P0
has a damping characteristic with a steep slope, and as shown in the seventh axis), the phase difference in the low frequency region P0 is 0 degrees and the phase in the high frequency region P1 is 0 degrees, and the phase in the high frequency region P1 is It has a phase characteristic that is approximately 180 degrees out of phase, and is configured to remove harmonics and suppress DC components.

Note that the values of the resistors R, , R, constituting the wave leakage means 32 are the same, and the capacitors C, , C are also of the same -o value, and the resistors R, , R4 are equal to the output capacitance C6 of the oscillating means 31. The capacitors C3 and C4 are set to have a sufficiently larger value than the output capacitance C8.

That is, R3=R,=-Hφ, c, 2C,=Cφ, and Rφ< (1/ JllCo (, Cφ>c).

In the oscillation circuit 30 configured as described above, when harmonics f1 to fn are parasitic to the fundamental oscillation output from the oscillation means 31, the harmonics existing in the high frequency region P1 of the attenuation characteristic of the leakage means 32 Since f1 to fn are significantly attenuated by the action of the wave leakage means 32, oscillation due to harmonics is prevented.

On the other hand, the fundamental oscillation frequency f0 existing in the low frequency region P0 of the attenuation characteristic is transmitted to the amplifying means 33 without being attenuated, and the phase difference is also in the order phase with almost zero degree (see Fig. 7(b)). ), it is possible to perform phase matching frequently and easily, and stable oscillation can be firmly maintained.

Furthermore, the output voltage V of the wave leakage means 32 is R3=R4miR
φ, c, = C4-cφ, and Rφ large / jωco l
@Cjv C4) Since C0, it can be expressed as (however, t+% is a time constant), and in the low frequency region P0 where the fundamental oscillation frequency f0 exists, the output voltage of the wave leakage means 32 is accepts the almost flat Is property, and in particular, at the Hadaura value, V, = (Rφ, which is a finite value, and therefore the DC component is suppressed to this value, ensuring stable oscillation of the oscillation circuit 30. It can be held as

〔effect〕

As explained above, according to the present invention, vibrations having frequencies different from the fundamental oscillation frequency, especially harmonic oscillations that are high-order parasitic vibrations, can be significantly prevented, and the direct current component can be suppressed, resulting in stable This has the remarkable effect of being able to firmly maintain the oscillation.

[Brief explanation of drawings]

Fig. 1 is a first conventional oscillation circuit diagram, Fig. 2 is an equivalent circuit diagram of the piezoelectric vibrator shown in Fig. 1, Fig. 3 is an equivalent circuit diagram of Fig. 1,
Figure 4 is a circuit diagram showing details of the filter in Figure 3, Figure 5 (&), (b) is a characteristic diagram of the filter in Figure 3, Figure 6
The figure shows the oscillation circuit diagram of this invention, Figure 7 (IL), (b
) is the characteristic factor of the wave leakage means shown in FIG. 30... Oscillation circuit 31... Oscillation means 32... Leakage means 32a... First low pass filter 32b... Second low pass filter 33.・・・・・・Amplification means

Claims (3)

[Claims] (1) In an oscillation circuit in which the output of an oscillation means that vibrates at a desired frequency is input to an amplification means via a wave leakage means, the wave leakage means is connected to the output side of the oscillation means. An oscillation circuit comprising a low-pass filter and a second low-pass filter connected to the output side of the first low-pass filter to remove harmonic components. (2) The oscillation circuit according to claim M1, wherein the first low-pass filter is formed by a parallel circuit of capacitance and resistance, and one end is grounded. (3) The second low-pass filter has an input terminal grounded through a parallel circuit of a resistor and a capacitance, and this input terminal is grounded to the second resistor, and the other terminal of the second resistor is grounded. The oscillation circuit according to claim 1, wherein the oscillation circuit is connected to the second capacitance, the other terminal 01a of the second capacitance is grounded, and the output is the voltage across the second capacitance. .