JPH0531321B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sine wave oscillation circuit, and more particularly to a sine wave oscillation circuit that obtains a sine wave oscillation output by applying positive feedback to a multiple feedback band filter or the like.

Conventionally, in this type of sine wave oscillator circuit, when adjusting the amplitude, a gain adjustment amplifier is connected after the sine wave oscillator and the gain adjustment amplifier is used to adjust the amplitude. An automatic gain adjustment circuit was installed to adjust the gain. However, in any of these conventional methods, since an amplitude adjustment means is provided outside the positive feedback loop formed for oscillation, it is difficult to perform stable amplitude adjustment for various oscillation states. For this reason, it was not possible to achieve a dynamic range up to the maximum amplitude adjustment amount.

The present invention has been made in view of the above points, and provides a sine wave oscillator circuit that can obtain a sine wave output with a wide dynamic range and little distortion, and also stabilizes the oscillation frequency of the sine wave output. The purpose is to provide. In order to achieve this object, the present invention includes means for converting the output signal into a square wave and controlling the amplitude of this square wave in a positive feedback loop formed for a bandpass filter that obtains the fundamental wave as an output signal. The present invention is characterized in that the present invention is characterized in that the center frequency of the band filter is switched in accordance with the output of the phase comparison output of a square wave and a predetermined square wave from the converting means through a low pass filter.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing the basic configuration of a sine wave oscillation circuit according to the present invention. 1 is a comparator that generates a square wave from the output signal (sine wave signal);
2 is an amplitude adjustment circuit that adjusts the amplitude of the square wave from the comparator 1; 3 is a band filter that extracts the fundamental wave component of the square wave; the output signal of the band filter 3 is applied to the comparator 1 in order to cause oscillation; Positive feedback is provided to the input side. 4 is an automatic gain adjustment circuit that compares the amplitude of the output signal with a reference voltage and feeds it back to the amplitude adjustment circuit 2 to adjust the amplitude to be constant. Further, 5 is a phase comparator that compares the phase difference between the square wave signal from comparator 1 and the output of reference oscillators 7 and 8 selected by switch _S1 , and 6 extracts the DC component from the compared signal. This is the low-pass filter that is taken out.

FIG. 2 is a circuit diagram showing an embodiment of the present invention based on the basic configuration of FIG. 1. Comparator 1 is
It is composed of resistors R ₁ , R ₂ and an operational amplifier Q ₁ , and the resistance value of resistor R ₂ is selected to be much larger than that of resistor R ₁ . Further, the amplitude adjustment circuit 2 is composed of resistors R ₃ , R ₄ and a diode D ₁ , where
_S2 is a switch for stopping oscillation. Further, the bandpass filter 3 is composed of an operational amplifier Q ₂ , resistors R ₅ to R ₉ , a FET Q ₃ , and capacitors C ₁ and C ₂ . In addition, the automatic gain adjustment circuit 4 includes resistors R ₁₀ to R ₁₅ and variable resistors.
It consists of VR ₁ , capacitors C ₃ and C ₄ , diode D ₂ , operational amplifier Q ₄ , and Zener diode ZD ₁ . Further, the reference oscillators 7 and 8, which output square waves of a predetermined frequency, are configured to output a highly accurate oscillation frequency obtained by dividing the output of a crystal oscillator that provides a stable oscillation frequency. Furthermore, the low-pass filter 6 is composed of resistors R ₁₇ to R ₁₉ , capacitors C ₅ and C ₆ , and an operational amplifier Q ₅ , and extracts the DC component from the phase-compared signal in the phase comparator 5 and outputs it to the FETQ 3 of the band filter _{3 .} is configured to change the gate bias of.

The configuration of one embodiment of the present invention is as described above, and prior to explaining its operation, the oscillation principle of the sine wave oscillation circuit according to the present invention will be explained.

The bandpass filter 3 is composed of a multiple feedback type, for example, a second-order bandpass filter, and the transfer function of the bandpass filter ₃ is expressed by the following equation, where R' is the combined resistance value of the resistance of FETQ 3 and resistors R ₆ and R ₇ . expressed.

F(jω)=−Aα(jω/ω ₀ )/(jω/ω ₀ ) ² +α
(jω/ω ₀ )+1 …(1) Here When positive feedback is applied to the bandpass filter 3 to cause it to oscillate, the imaginary part of the transfer function becomes zero, and oscillation occurs at ω=ω ₀ , that is, frequency f ₀ . Further, the gain of the fundamental wave component at this time is A. As described above, in the oscillation circuit of this embodiment, distortion occurs because the square wave signal is passed through the bandpass filter 3 to obtain a sine wave. Now let the voltage of the square wave be E ₁ V _pp , and perform Fourier expansion: V ₁ (t)=a ₀ /2+ ^∞ 〓 ⁿ⁼⁰ (2/π)E ₁ /2n+1 sin(2n+1)ω ₀ t (a ₀ / 2 is the DC component)...(2) When this square wave is passed through the above band filter 3, the output V ₀ (t) is That is, a sine wave of 4/πAE ₁ V _pp is obtained as the fundamental wave component, and the amplitude of the sine wave can be easily adjusted by adjusting the voltage E ₁ of the square wave. Also, the strain rate γ is If α=0.1, the distortion rate will be approximately 1%, and a sine wave with little distortion will be obtained.

The oscillation principle of the present invention is as described above, and the operation will be explained next. First, when power is supplied to the entire circuit, a signal appears at the output terminal OUT and is input to the comparator 1. This results in an operational amplifier
The output of Q ₁ becomes a square wave when the inverted and amplified signal is saturated. Here, as understood from equation (3) above, the amplitude value E ₁ of the square wave is adjusted according to the amplification value of the desired output signal. That is, the square wave signal from the operational amplifier Q ₁ is supplied to the bandpass filter 3 through resistors R ₃ and R ₄ . Here, from the output of the operational amplifier Q4 of the automatic gain adjustment circuit ₄ , when the voltage of the square wave is high, the diode _D1 conducts and the amplitude is limited, and when the voltage of the square wave is low, it is affected by the diode _D1 . do not have. To explain in detail the operation of the automatic gain adjustment circuit 4 in this case, the output sine wave signal is half-wave rectified by the diode _D2 , and is charged to the capacitor _C3 through the resistor _R10 . Here, the resistor _R11 connected in parallel with the capacitor _C3 is a discharge resistor. The voltage charged on capacitor C ₃ is connected to resistor R ₁₃ and Zener diode
The power supply voltage configured by ZD ₁ is compared with the voltage adjusted by variable resistor VR ₁ , and differentially amplified by operational amplifier Q ₄ . Since the amplitude of the square wave of the amplitude adjustment circuit 2 is adjusted based on the output amplified by the operational amplifier _Q4 , the amplitude of the output sine wave becomes constant. Further, to explain in detail the operation of the phase comparator 5 mentioned above, the phase of the output of the comparator 1 and the output of either the reference oscillator 7 or 8 selected by the switch _S1 is compared in the phase comparator 5. The DC component is extracted by a filter 6. Since the gate bias of FETQ ₃ changes according to this DC component, the combined resistance value R′ including this FETQ ₃ changes, as understood from equation (1) above.
The center frequency of the bandpass filter 3 can be changed. That is, in this case, since the sine wave oscillation circuit is operated as a PLL as a voltage controlled oscillator (VCO) based on the output of the phase comparator 5, the oscillation of the sine wave oscillation circuit is performed at the frequency of either the reference oscillator 7 or 8. Frequency can always be tracked with high precision.

One embodiment of the present invention is as described above, and since the amplitude adjustment means is provided in the positive feedback loop for oscillation, it is possible to oscillate a sine wave with a wide dynamic range and little distortion. Also, change the oscillation frequency to PLL
The frequency characteristics are stable because the frequency can always be matched to the reference frequency through operation. Further, by turning on the switch _S2 as necessary, the amplitude limit amount can be maximized (amplitude zero) and oscillation stop control can be easily performed. Furthermore, since the amplitude of the amplitude adjustment circuit 2 is adjusted by the automatic gain adjustment circuit 4, the amplitude of the sine wave output can always be kept constant. Furthermore, by controlling the amplitude of the square wave as necessary, the output amplitude can be changed linearly, and AM modulation is also possible using the center frequency of the bandpass filter 3 as a carrier frequency.

The present invention is as described above, and it is possible to obtain a sine wave output with a wide dynamic range and no distortion, and to stabilize the oscillation frequency of the sine wave output.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of a sine wave oscillation circuit according to the present invention, and FIG. 2 is a circuit diagram of an embodiment based on the basic configuration of FIG. 1...Comparator, 2...Amplitude adjustment circuit, 3
...bandwidth filter, 4...automatic gain adjustment circuit, 5
...Phase comparator, 6...Low pass filter, 7, 8...
...Reference oscillator.

Claims (1)

[Scope of Claims] 1. A band filter that obtains a fundamental wave as an output signal, means for converting the output signal into a square wave, and means for controlling the amplitude of the square wave from the converting means, In order to form a positive feedback loop including the conversion means and the amplitude control means, the output of the amplitude control means is input to the band filter, and the square wave from the conversion means and a predetermined square wave output are input to the band filter. 1. A sine wave oscillation circuit characterized in that the sine wave oscillation circuit has means for performing a phase comparison, and is configured to switch the center frequency of the band filter based on the output of the phase comparison means. 2. The sine wave oscillation circuit according to claim 1, further comprising an automatic gain adjustment circuit that adjusts the amount controlled by the amplitude control means based on the feedback output of the bandpass filter. 3. The sine wave oscillation circuit according to claim 1, wherein oscillation is stopped by maximizing the amount of amplitude limitation by the amplitude control means. 4. The sine wave oscillation circuit according to claim 1, wherein the center frequency of the band filter is changed by switching the predetermined square wave output.