JPH03178205A - Phase shift type cr oscillator - Google Patents

Abstract

PURPOSE:To prevent mutual interference between CR differentiating circuits caused by the connection, to easily set the constant remarkably and to facilitate the design of an oscillation circuit by connecting three lead phase shift circuits of the CR differentiating circuits having a maximum phase shift quantity of 90 deg. in cascade via a buffer. CONSTITUTION:Three lead phase shift circuits comprising CR differentiating circuits 23-25 having a maximum phase shift quantity of 90 deg. and buffers 26-28 connected to the output side of the CR differentiating circuits 23-25 are connected in cascade. Furthermore, a phase inverting amplifier circuit 21 is connected to the input of the 3 stages of lead phase shift circuits 22 and a feedback path from the output of the 3 stages of lead phase shift circuits 22 to the input side of the phase inverse amplifier circuit 21 is provided. Then the constant of the CR differentiating circuits 23-25 is set independently and a desired oscillating frequency is easily obtained and in the case of designing a variable frequency oscillator, the design of the oscillator such as decision of R, C constants and the setting of a desired oscillating frequency is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a phase-shifted CR oscillator, and particularly to setting constants in internal elements of the oscillator for a desired oscillation frequency.

2. Description of the Related Art As an example of a conventional phase-shifting type CR oscillator, FIG. 3 shows an example of a CR differential circuit in which three phase advance type phase shifters are connected in cascade.

In FIG. 3, the phase-shifting CR oscillator is composed of a phase-inverting amplifier circuit 1 and a phase-advance phase shift circuit 2, and circuit 2 is a phase-advanced phase shift circuit that shifts the phase by 180'. 3 and 4.5 are resistances, and the magnitudes of the resistances are R1, R, . . . R3, respectively. 6, 7.8 are capacitors, and their capacitances are C+, C2, and Ca, respectively.

9 is an arithmetic circuit, 10 is an output terminal, and a path is provided for feeding back the output of the 18o0 advance type phase shift circuit 2 to one input terminal of the arithmetic circuit 9 of the phase inversion amplifier circuit l.

FIG. 5 is a block diagram of the phase-shifted CR oscillator shown in FIG. 3. Reference numeral 11 denotes an input terminal, and its potential is set to Vl. Further, the potential at the connection point A between the phase inversion amplifier circuit 1 and the 180' phase advance type phase shift circuit 2 is assumed to be V. The conditions for this phase-shifted CR oscillator to oscillate are as follows.

Condition (1) The total gain of the phase inversion amplifier circuit 1 and the 180' phase advance type phase shift circuit 2 is 1 or more.

Condition (2) V+ and V are in phase.

FIG. 4 is a vector locus diagram of the transfer function obtained from the 180° advance type phase shift circuit 2 in FIG. 3, where ψ is the phase angle,
12 is a transfer function vector, and 13 is a vector locus.

Circuit 1 in Fig. 3 is a phase inversion amplifier circuit, and condition (2) is satisfied.
In order to satisfy the requirement, circuit 2 in FIG. 3 must be a 180° phase advance type phase shift circuit. The frequency at the 0 point in FIG. 4 is the oscillation frequency, and the magnitude D is the gain of the 1800-advanced phase shift circuit 2 in FIG.

Problems to be Solved by the Invention However, in the above configuration, it is difficult to make the phase-shifted CR oscillator shown in FIG. 3 oscillate at a desired frequency.
Internal elements of the phase inversion amplifier circuit 2 shown in FIG. 3 (1.
2. 3. 4. 5. When setting the constant 6), since the phase inversion amplifier circuit 2 has a configuration in which three CR differentiating circuits are connected in cascade, the three CR differentiating circuits act so as to interfere with each other. Therefore, there is a problem in that it is difficult to set the constants of the internal elements so as to satisfy the condition necessary for oscillation that the phase at point B at the output end in FIG. 3 leads by 180 degrees from point A.

Here, it is assumed that the total gain as an oscillator can be made greater than 1 by the phase inverting amplifier circuit l shown in FIG. 3 and is satisfied. The transfer function of the 180° advance phase shift circuit 2 shown in FIG. 2 is given by equation (1).

Gfii+1 ”ωR,C,・1ωR+　C1tωR,C.

(1+111R1c, l fl”i#RI Cal
[1”1liRI Cal ji, If”! vR1
c, l 'R+ C+ + (1+1llR+ Ca
l 'L C1+ 1tlR1RI C+ C+ However, G(iω) is the transfer function, ω is the angular frequency, j2=-4 Equations without the second term in the denominator of equation (1) are the transfer function of each CR differentiator circuit. The second term in the denominator is the product of three C
This term represents that the R differential circuits interfere with each other.

To obtain the desired oscillation frequency, find the frequency characteristics from equation (1) of the transfer function and solve the complex simultaneous equations.
The constants of internal elements are set, but they cannot be determined uniquely and are difficult. In addition, when a subsequent circuit is connected to the output terminal 10 in FIG. 3, the influence of the connected circuit must also be taken into consideration, and the constants of the internal elements of the 1800 phase advance type phase shift circuit 2 in FIG. 3 must be considered. becomes even more difficult.

The present invention solves the above-mentioned conventional problems, and aims to provide a phase-shifted CR oscillator that can be easily designed.

Means for Solving the Problems In order to solve the above problems, the phase shift type CR oscillator of the present invention has the following features: In cascading three phase advance type phase shift circuits of CR differentiating circuits having a maximum phase shift amount of 90 degrees. , connected via a buffer.

Effect: The above configuration eliminates mutual interference between CR differential circuits caused by connection, and even when a subsequent circuit is connected to the output terminal, there is no need to consider the influence of the connected circuit. Therefore, when obtaining the desired oscillation frequency,
It is only necessary to consider the constants of the internal elements for each CR differential circuit, which greatly simplifies the setting of the constants and facilitates the design of the oscillation circuit.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram of a phase-shifted CR oscillator according to an embodiment of the present invention. In FIG. 1, the phase-shift type CR oscillator is composed of a phase inversion amplifier circuit 21 and an 18G' phase advance type phase shift circuit 22.
It consists of cascade connection of CR differentiating circuits 23, 24, 25 and buffers 26, 27, 28 connected to the subsequent stage of each. The CR differentiating circuits 23, 24, and 25 are the same as the conventional one shown in FIG. 3, but the 180° phase advance type phase shift circuit 22 has buffers 26, 27, and 28 so that the CR differentiating circuits 23, 24, and 25 do not interfere with each other. It is composed of 24.25. 2
9 is an arithmetic circuit, and 30 is an output terminal.

The differentiating circuits 23, 24, and 25 in FIG. 1 each have a simple transfer function, which is given by the following equation (2).

1+jωRC where R is the resistance size, C is the capacitance, ω
is the angular frequency In this embodiment, the difference from the conventional example is that the buffer 26
．． 27.28, the CR differential circuits 23, 24, and 25 can be treated as one independent circuit without interfering with each other. The oscillation conditions in the phase-shifted CR oscillator shown in FIG. 1 are also the same as conditions (1) and (2) already described in the prior art.

In other words, condition (1) is satisfied when the phase inversion amplifier circuit 1 of FIG.
In this case, the total gain can be made more than 1, which is satisfactory. Condition (2) is three CR differential circuits 23°24, 25
Calculate the advanced phase shift amount of each separately, and the sum of the three is 1.
If you set it so that it is 80 degrees, you will be satisfied.

Constants of internal elements are set so that the phase-shifted CR oscillator shown in FIG. 1 oscillates at a desired frequency.

In FIG. 1, the advance type phase shift amounts of the CR differentiating circuits 23, 24, and 25 are shown as θ□, θ2. Let it be θ3. Here, the phase advance type maximum phase shift amount is 90° and θ.

θ2. Considering that the sum of θ3 is 180°, θ
1. θ2. Although the value of θ3 can be arbitrarily determined, it is preferably around 60° per stage since the total of the three stages of the CR differential circuit must be 180°.

FIG. 2 is a vector locus diagram obtained from the transfer function of equation (2), where 31 is a transfer function vector and 32 is a vector locus. The range of θ represents the phase angle, and the magnitude of θ represents the amount of advance phase shift.

Constants of R1 and C1 of the CR differentiation circuit 23 shown in FIG. 1 are set. From equation (2), the frequency characteristic representing the phase angle is shown in equation (3).

θ=jan-1... (3) 2πfRIC However, 0°≦θ≦90° f is the oscillation frequency Substitute the desired oscillation frequency and arbitrary θ1 into equation (3), and calculate the constants of R1 and 01. Set. Similarly, R2°C3, Ra, and Cs can be easily calculated and set.

Effects of the Invention As described above, according to the present invention, by connecting a buffer after the CR differentiating circuit of each stage, the constant of the CR differentiating circuit of each stage can be set independently, and it is possible to easily set the constant of the CR differentiating circuit of each stage as desired. The oscillation frequency is obtained.

Furthermore, when designing a variable frequency oscillation device, it is possible to facilitate the design of the oscillation device, such as determining the constant of R2C and setting a desired oscillation frequency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a phase-shifting CR oscillator according to an embodiment of the present invention, FIG. 2 is a vector locus diagram obtained from the transfer function of the CR differential circuit of the phase-shifting CR oscillator, and FIG. A circuit diagram of a conventional phase-shifted CR oscillator, Fig. 4 is similar to 18 in Fig. 3.
FIG. 5 is a vector locus diagram obtained from the transfer function of the 0° phase advance type phase shift circuit, and FIG. 5 is a block diagram of the phase shift type CR oscillator shown in FIG. 3. 2I... Phase inversion amplifier circuit, 22... 180° advance type phase shift circuit, 23.24.25... CR differentiation circuit, 26.27°28... Buffer. Agent Yoshihiro Morimoto Figure 23-2s CR chart X-axis

Claims (1)

[Claims] 1. A CR differentiating circuit with a maximum phase shift of 90° and a phase advance type phase shift circuit configured by connecting a buffer to the output side of the CR differentiating circuit are connected in cascade, and the three stages are further connected in series. A phase-shifting CR, in which a phase-inverting amplifier circuit is connected to the input side of the phase-shifting phase-shifting circuit, and a path is provided for feedback from the output side of the three-stage phase-advancing phase-shifting circuit to the input side of the phase-inverting amplifier circuit. Oscillation device.