JPH0245370B2 - SHUHASUBUNRIKAIRO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency separation circuit that removes a fundamental wave component from an input signal containing a fundamental wave component and harmonic components.

[Prior Art and Problems to be Solved by the Invention] Distortion meters are widely used in the field of electronic technology. The harmonic component obtained by removing the fundamental component from an input signal having a fundamental component and a harmonic component is compared with the input signal. Conventional frequency separation circuits, for example, connect two T-type filters in series to two T-type bridge circuits connected in parallel, and manually adjust the pass frequency band of the filter. It was very difficult to match the fundamental wave component of the input signal. On the other hand, U.S. Patent No. 3,714,588 discloses a bandpass filter in which the pass frequency automatically follows the fundamental frequency of the input signal, but because the center frequency gain is not automatically controlled, There was a possibility that the center frequency gain would change. Therefore, even if this bandpass filter is used, it has not been possible to realize an automatic frequency separation circuit that reliably removes the fundamental wave component from the input signal.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a frequency separation circuit that automatically and reliably removes fundamental wave components from an input signal.

[Means for Solving the Problems] The frequency separation circuit of the present invention includes a pass frequency band adjustment section and an amplitude that receive an input signal including a fundamental wave component and a harmonic component, and adjust the frequency band to be passed and the amplitude thereof, respectively. It has an adjustment section, and when the pass frequency band adjustment section is tuned to the fundamental wave component of the input signal, it outputs a reference phase component and a quadrature phase component that have a reference phase relationship and a quadrature phase relationship, respectively, with the fundamental wave component of the input signal. a bandpass filter for removing the reference phase component of the output of the bandpass filter from the input signal, a removing means for removing the reference phase component of the output of the bandpass filter from the input signal, a paraphasing amplifier that receives the output of the removing means and generates a push-pull output, and a filter that responds to the reference phase component of the output of the bandpass filter. a multiplexer that selects one of the push-pull outputs according to the quadrature phase component, and a first integral that integrates the first output of the multiplexer selected according to the reference phase component; The vessel and
and a second integrator for integrating the second output of the selected multiplexer in accordance with the quadrature component.

Note that in this specification, a reference phase (inphase) relationship refers to a phase relationship of 0 degrees or ±180 degrees with respect to the input signal, and a quadrature phase relationship refers to a phase relationship of 0 degrees or ±180 degrees with respect to the input signal. This means that there is a phase relationship of ±90 degrees or ±270 degrees.

[Function] According to the frequency separation circuit of the present invention, the pass frequency band adjustment section of the bandpass filter is not completely tuned to the fundamental wave component, and the amplitude adjustment section does not properly adjust the amplitude of the fundamental wave component. If not, the removal means cannot completely remove the fundamental wave component, but in this case, the phase of the fundamental phase and quadrature phase of the output of the bandpass filter as the control signal of the multiplexer changes, and the phase of the output of the bandpass filter as the control signal of the multiplexer changes. The amplitude of the push-pull output of the paraphasic amplifier changes. Therefore, since the outputs of the first and second integrators also change, the amplitude adjustment section is controlled by the output of the first integrator, and the pass frequency band adjustment section is controlled by the output of the second integrator. Therefore, a signal obtained by removing the fundamental wave component from the input signal can be obtained at the output end of the removing means.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

(Overall Configuration) FIG. 1 is a block diagram for explaining the basic operation of the frequency separation circuit according to the present invention. An input signal is passed through an input terminal 10 to a bandpass filter 12 whose pass frequency band and amplitude can be controlled, and a removal means 1
4 and 16. In addition to receiving the input signal via the input terminal 10, the removing means 14 receives the reference phase of the fundamental wave component from the bandpass filter 12, and sends the output to the removing means 16, the output terminal 18,
is applied to the paraphasic amplifier 20. Removal means 1
The output of 6 is applied to a frequency discriminator 24 via a Schmitt circuit 22, and the output of the frequency discriminator 24 is applied to a band filter 12 and used for rough adjustment of the frequency band passed by the band filter 12. The push-pull output of the paraphasic amplifier 20 is applied to the analog multiplexer 26, and the multiplexer 26 receives the signal components (both have a phase difference of 90 degrees and 180 degrees with respect to the input signal, hereinafter the same) applied from the bandpass filter 12 ( That is, it is controlled by the quadrature phase component and the reference phase component). The two outputs from multiplexer 26 are connected to integrators 30 and 3, respectively.
The outputs of the integrators 30 and 32 are fed back to the bandpass filter 12 to control the amplitude of the filter output and the fine tuning of the filter pass frequency band.

An active filter composed of an operational amplifier, a resistor, a capacitor, etc. has a very high Q value and the resonant frequency can be easily controlled, so it is suitable for use as a bandpass filter. Note that if the band filter 12 is an inverting filter (input/output signals have opposite phases), the removing means 14 is an adding circuit, and the band filter 12
If is an in-phase filter (input and output signals have the same phase), the removing means 14 is a subtraction circuit. On the other hand, if the two input signals to the removal means 16 are in phase, the removal means 16 is a subtraction circuit, and if the two input signals are in opposite phases, it is an addition circuit. In this embodiment, the band filter 12 is an inversion filter, and the removal means 14 and 16 are both phase inversion adder circuits. Note that the amplification factor of the removal means 14 is less than 1.

(Overall operation) When the frequency of the bandpass filter 12 is tuned to the fundamental wave component of the input signal, the inverted fundamental wave component is applied to the removal means 14, so that the removal means 14, which is an inverting adder, is tuned to the input signal. Outputs harmonic components of opposite phase. That is, the band filter 12 and the removing means 14 constitute a so-called notch filter (the center frequency of the pass-blocking frequency band of the notch filter is called the notch frequency).

Next, automatic adjustment of the pass frequency band of the band filter 12 will be explained. An input signal is applied to the removal means 16 via the input terminal 10, and a harmonic component is applied from the removal means 14. Since the removing means 14 is an inverting adder, the harmonic components of the input signal are inverted and output. Since this anti-phase harmonic component is added to the input signal by the removal means 16, the harmonic component of the input signal is reduced. Removal means 16
Even if the output includes harmonic components, their amplitude is sufficiently small compared to the amplitude of the fundamental wave component, so the harmonic components are ignored by the hysteresis of the Schmitt circuit 22. The frequency discriminator 24 discriminates the frequency of the output pulse of the Schmitt circuit 22, detects the frequency band of the fundamental wave component, and roughly adjusts the center frequency of the band filter 12. Note that the band filter 12 is an active filter, and as described later, an operational amplifier,
It is composed of a plurality of resistors, a plurality of capacitors, and a switch means for selectively switching the resistors and capacitors according to the output from the frequency discriminator 24.

The bandpass filter 12 outputs a quadrature phase component and a reference phase component of the fundamental wave component having a phase difference of 90 degrees (advanced phase) and 180 degrees from the input signal while being tuned to the fundamental wave component. The phase difference with respect to the input signal corresponding to these phases is determined by the characteristics of the bandpass filter 12, and as the frequency of the fundamental wave component becomes lower than the tuning frequency of the bandpass filter 12, that is, the pass frequency (corresponding to the notch frequency), the input signal The phase changes as the quadrature phase component approaches 0 degrees, and changes as the reference phase component approaches 90 degrees. Furthermore, as the frequency of the fundamental wave component becomes higher than the pass frequency of the band filter 12, the phase relative to the input signal changes as the reference phase portion moves toward 270 degrees, but the quadrature phase portion changes as it moves toward 180 degrees. . Furthermore, if the pass frequency band is adjusted correctly, a signal with a phase difference of 90 degrees between the fundamental wave components will not be output to the output end of the notch filter, that is, the output end of the removal means 14. If the amplitude is adjusted correctly, the fundamental wave component will not be output. The paraphasic amplifier 20 removes a signal having a phase difference of 180 degrees from the input signal by means 1
4 and applies in-phase and anti-phase harmonic component signals to the multiplexer 26 at the next stage. The multiplexer 26 outputs the paraphasing amplifier 2 according to two types of signals having a phase difference of 90 degrees (advanced phase) and 180 degrees from the fundamental wave component signal of the input signal applied from the bandpass filter 12, that is, a reference phase component and a quadrature phase component.
The signal from 0 is selectively applied to integrators 30 and 32. To explain in more detail, multiplexer 2
6 is controlled by the period and phase determined by the fundamental wave component signal (reference phase portion) with a phase difference of 180 degrees from the bandpass filter 12, and is connected to the paraphasing amplifier 2.
The in-phase or anti-phase harmonic component signal from 0 is selectively applied to the integrator 30, while the multiplexer 2
6 is controlled by the period and phase determined by the fundamental wave component (quadrature phase component) with a phase difference of 90 degrees from the bandpass filter 12, and selectively outputs the in-phase or anti-phase harmonic component signal from the paraphasing amplifier 20. is applied to the integrator 32. The integrator 30 integrates the output of the multiplexer 26 and outputs a signal that controls the amplitude adjustment section of the bandpass filter 12, while the integrator 32 integrates the output of the multiplexer 26 to adjust the pass frequency band of the bandpass filter 12. Outputs a signal to finely adjust the area. Specifically, referring to FIG. 2, the outputs of the integrators 30 and 32 control the amplification factor and pass frequency band of the bandpass filter 12 by controlling the resistance of the photocoupler. The polarity of the DC level of the output of the multiplexer 26 is determined by the integrators 30 and 32.
The passing frequency band of the bandpass filter 12 and the changing direction of the amplification degree are controlled through the notch filter 12 to set the notch filter to an appropriate value and to prevent fundamental wave components from leaking from the notch filter.

(Band Filter and Removal Means) FIG. 2 is a detailed circuit diagram of the band filter 12 and the removal means 14 and 16 shown as blocks in FIG. 1. The bandpass filter 12 includes an operational amplifier 34,
Resistors 36 and 38, capacitors 40 to 56, relays 58 to 64, transistors (hereinafter abbreviated as TR) 66 to 72 that drive the relays 58 to 64,
Photocouplers 74 to 78, operational amplifiers 80 and 8
2. It is composed of resistors 84 to 112, etc.
Filter 12 is a combination of a high frequency pass filter and a low frequency pass filter. The high frequency pass filter consists of an operational amplifier 34, resistors 36, 38 and capacitors 48-54, and the low frequency pass filter consists of a capacitor 40-46, a photocoupler 74 and an electronic resistor (photocoupler 76, operational amplifier 80 and associated resistors). consists of). The feedback resistors 36 and 38, the photocoupler 74, and the input resistors 84 and 86 constitute an attenuator. The pass frequency band of the filter 12 can be adjusted by appropriately switching both the resistors 36 and 38 and the capacitors 40 to 54, for example, 5-10-50-100-...
It is done in steps like this. This switching operation transfers the output pulse of the frequency discriminator 24 to the terminal 114.
~120 to TR66~72, TR
Controlling on/off of relays 66 to 72 and relays 58 to 72
64 is selectively driven. Incidentally, switching for each decade is performed by appropriately switching the capacitors 40 to 54. For example, when the fundamental wave component frequency of the input signal applied to the input terminal 10 is approximately 10 KHz or less, the relay 64 operates, and when it is approximately 1 KHz or less, the relays 64 and 62 operate, and the frequency is approximately 100 Hz.
Relays 64, 62, and 60 operate in the following cases. Relay 58 is a relay that controls the upper half of the frequency between switching decades, and its operation reduces the resistance within bandpass filter 12 to increase (eg, triple) the notch frequency.

The outputs of integrators 30 and 32 are connected to terminals 122, respectively.
and 124. As mentioned above, the step adjustment of the notch frequency is performed by switching the capacitors 40 to 54 and the resistor 36, but the continuous adjustment between each step is performed using the electronic resistor impedance whose main components are the operational amplifier 80 and the photocouplers 76 and 78. is controlled according to the output of the integrator 32. That is, when the resistance of photocouplers 76 and 78 increases due to the output of integrator 32 applied to terminal 124, the impedance between the midpoint of photocoupler 76 and resistor 108 and ground decreases, causing the notch frequency to increase. move it to Therefore, this electronic resistor becomes a pass frequency band adjusting section. On the other hand, terminal 1
The output of the integrator 30 applied to the notch filter 22 changes the resistance of the photocoupler 74, which together with the resistors 36 and 38 constitute an attenuator, to finely adjust the gain of the bandpass filter 12, that is, the input signal amplitude. The fundamental wave component is effectively removed from the output. Therefore, the attenuator made of this photocoupler 74 and the like becomes an amplitude adjustment section. In this way, the reference phase component and the quadrature phase component of the fundamental wave component signal are obtained from the output terminals 126 and 128 of the bandpass filter 12, respectively.

The removal means 14 is composed of an operational amplifier 130, input resistors 132 and 134, and a feedback resistor 136, and receives the output of the bandpass filter 12 via the resistor 132 and applies the output to the input terminal 10 via the resistor 134. The input signal is received and the output is sent to an external circuit (not shown) via the output terminal 18.
It is applied to the paraphasing amplifier 20 at the next stage via the terminal 18'. On the other hand, the removing means 16 includes an operational amplifier 148 and resistors 140 to 1.
44 and resistor 142 with an input signal applied to input terminal 10 via resistor 140.
It receives the output of the removal means 14 via. The output of the removal means 16 is applied to the Schmitt circuit 22 via a terminal 146. Resistors 132-13
The respective resistances of 6,140 to 144 are, for example, as follows.

Resistor 132: 5.90KΩ Resistor 134: 2.00KΩ Resistor 136: 1.00KΩ Resistor 140: 10KΩ Resistor 142: 10KΩ Resistor 144: 10KΩ (Schmitt circuit and frequency discriminator) Figure 3 shows the Schmitt circuit 22 and 2 is a circuit diagram of a frequency discriminator 24. FIG. The Schmitt circuit 22 is
This is a conventional circuit consisting of emitter coupled TRs 150, 152 and associated resistors. Frequency discriminator 24
is a D-type flip-flop (hereinafter referred to as a flip-flop).
The circuit is composed of timing circuits 170 to 176 having different time constants each having a resistor and a capacitor, a multiplexer (MUX) 178, and comparators 180 to 186.

The removing means 16 (FIGS. 1 and 2) sends its output to the Schmitt circuit 22 via a terminal 146.
and the Schmitts circuit 22 outputs an output synchronized with the fundamental wave component of the input signal to the frequency discriminator 24.
Apply to the clock terminals of FFs 154-160.
The terminal of FF160 is connected to each D terminal of FF154-160, so FF154-16
The Q of 0 and the output of the terminal are connected to the Schmitt circuit 22.
The phase is reversed every time the output rises. Each of the timing circuits 170 to 176 is an integrator, and the output level of each is determined by the respective time constant and FF 154 to 16.
It is determined by the frequency of the output of the corresponding FF within 0. Therefore, the frequency of the fundamental wave component can be detected based on the output level of the timing circuits 170 to 176. Incidentally, as an example, the timing circuit 170,1
The time constants of 72, 174, and 176 are 16 μs, respectively.
200μs, 2ms, 20ms.

Comparators 182-186 connect the output levels of corresponding timing circuits 172-176 to resistors 18
Compare with a reference value (threshold) from a voltage divider consisting of 8 to 192. The outputs of the corresponding comparators 182 to 186 are applied to the D terminals of FFs 164 to 168, and the outputs of the terminals of FF 160 are applied to the clock terminal C, so the outputs of the Q terminals of FFs 164 to 168 are applied to the terminals of FF 160. is updated every output cycle and represents the frequency of the fundamental wave component.
The output of the Q terminal of FF164 to 168 is the terminal 11
6 to 120 for driving the relay in Figure 2.
Applied to TR68-72.

Analog multiplexer 178 receives analog outputs from timing circuits 170-176 and the outputs of comparators 182-186 as control signals. The analog output of multiplexer 178 is connected to resistor 18 at comparator 180.
The output of comparator 180 is compared with a reference value (threshold) from a voltage divider consisting of FF1 to FF192.
62 is applied to the D terminal. Since the output of the FF160 terminal is applied to the clock terminal of FF162, the output of the FF162 terminal is applied to the clock terminal of FF160.
It is updated every cycle of the output of the terminal and applied to TR66 in FIG.

The relationship between the inputs of the multiplexer 178 according to the control inputs A, B, and C is as follows.

A B C Output 1 1 1 Input 7 1 1 0 Input 3 1 0 0 Input 1 0 0 0 Input 0 The frequency discrimination operation of the circuit of FIG. 3 will be described in more detail with respect to this embodiment. As mentioned above, the input signal applied to the input terminal 146 of the Schmitt circuit 22 is a fundamental signal with reduced harmonic components. Even if the output of the removing means 14 contains a quadrature component of the fundamental wave component, the removing means 14
The frequency of the fundamental wave output of No. 6 does not change. Accordingly, a square wave having a fundamental frequency is obtained from the Schmitt circuit 22. This square wave is FF154~
160 clock terminals C, and a 1/2 square wave is output from each Q output terminal.
At the rise of this square wave, each timing circuit 170~
176 starts integration at a speed corresponding to each time constant. The integrated voltage of the timing circuit with a small time constant rises steeply, and the integrated voltage of the timing circuit with a small time constant rises slowly. Therefore, timing circuits 170-176 having different time constants output different voltage waveforms even when receiving the same square wave. Comparators 18 corresponding to each timing circuit
Whether or not a high (logic 1) signal is output at the falling edge of the Q output square wave of FF154-160 from 0 to 186 depends on the size of the threshold, the time constant of the timing circuit, and the square wave. Depends on frequency.

In the time constant example described above, when the input frequency is sufficiently low (for example, about 100 Hz or less), the period of the square wave is long, and the timing circuit 172 at the falling edge of the square wave.
~176 output levels are all comparators 182~1
The threshold of 86 has been reached. Therefore, the outputs of comparators 182-186 will be 111, and multiplexer 178 will select its input 7 (i.e., the output level of timing circuit 176) to output comparator 180.
Output to. The threshold of comparator 180 is set higher than the other comparators 182-186, as seen from resistive voltage dividers 188, 190, and 192 in FIG. Therefore, when the output level of timing circuit 176 is selected as the input to comparator 180, comparator 186 will output 1 if the input frequency is less than about 100 Hz, but comparator 180 will output 1 if the input frequency is less than about 100 Hz, for example, 30 Hz. The following outputs 1. That is,
This configuration allows identification of the upper and lower halves of one day. Since the output of FF160 rises at the falling edge of the output square wave of FF154-160, the output of comparators 180-186 is FF1, respectively.
It is latched from 62 to FF168. At the same time, the accumulated charge in the timing circuits 170-176 is transferred to the diode 17 at the falling edge of the square wave in preparation for the next integration operation.
It is rapidly discharged through 0-176.

When the input signal frequency is in the range of approximately 100Hz to 1KHz,
The outputs of comparators 182-186 will be 110, and input 3 of multiplexer 178 (timing circuit 1
74 output level) is provided to comparator 180. In this case, as in the case described above, comparator 180 will produce an output of 1 at input frequencies below about 300 Hz. Input frequency is higher than 1K
In the range Hz to 10 KHz, the outputs of comparators 182-186 will be 100 and input 1 of multiplexer 178 is selected, so the input to comparator 180 will be the output level of timing circuit 172. Comparator 180 outputs 1 when the input frequency is about 3KHz or less. When the input frequency ranges from about 10K to 100KHz,
Since the outputs of the comparators 182 to 186 become 000 and the input 0 of the multiplexer 178 is selected, the output level of the timing circuit 170 is input to the comparator 180. Comparator 180 outputs a 1 for input frequencies below approximately 30 KHz. In addition, each FF16
Q output of 2 to 168 is connected to comparator 1 through a resistor.
The reason why the frequency range is fed back to 80 to 186 is to provide a slight hysteresis to frequency range switching so that the frequency range does not switch randomly with respect to the input frequency around the switching frequency of the frequency range. In this manner, each output pattern of FFs 162-168 changes depending on the input frequency to control the corresponding relay in FIG.

(Push-pull amplifier, multiplexer, and integrator) FIG. 4 is a circuit diagram of the push-pull amplifier 20, analog multiplexer 26, and integrators 30 and 32. Bandwidth filter 12 and removal means 14
The output of the notch filter is applied via a terminal 18' to an amplifier 20 whose main components are operational amplifiers 194-198. Incidentally, the gain of the amplifier 20 is, for example, about 50 dB.
Since operational amplifiers 194 and 196 are voltage followers and operational amplifier 198 is a unity gain inverter, a push-pull output is applied from amplifier 20 to the X, Y inputs of multiplexer 26.
Note that a part of the output of the amplifier 20 is connected to the diode 20.
After being rectified by 0 and 202, further amplified by TR204, and smoothed by capacitor 206, the FET
(field effect transistor) 208 and controls the attenuator constituted by this FET 208 and resistor 209 to control the gain of the amplifier 20. This gain control loop allows multiplexer 26
The input level to, for example, is maintained at about 5V or less.

The quadrature component of the fundamental component from the bandpass filter 12 is applied via terminal 128 and an inverting amplifier 210 to the control signal input C1 of the multiplexer 26, while the reference phase component of the fundamental component from the bandpass filter 12 is applied to the control signal input C1 of the multiplexer 26. is applied to the control signal input C2 of the multiplexer 26 via the terminal 126 and the inverting amplifier 212. multiplexer 26
acts as a phase detector, and the control signal input terminal C
1 and C2, the signals applied to input terminals X and Y are selectively output to output terminals A and B.
Output to. The following table shows the input/output relationship of the multiplexer 26.

C1 C2 A B 0 0 X X 1 0 X Y 0 1 Y An in-phase (with respect to input terminal 10) harmonic component (terminal In this case, the in-phase harmonic component signal (X terminal) from the paraphasing amplifier 200 or An inverted harmonic component signal (terminal Y) is selectively applied.
Note that the integrators 30 and 32 are the inverting amplifiers 21 and 32, respectively.
4 and a capacitor 218, and an inverting amplifier 216 and a capacitor 220 as the main components.

The output of integrator 30 is connected to TR222 and terminal 12.
2 to the photocoupler 74 in FIG.
The amplification degree of the bandpass filter 12 is controlled by controlling its resistance value, and the output of the integrator 32 is applied to the photocouplers 76 and 78 in FIG. 2 via the TR 224 and the terminal 124 to control their resistance value. to control the pass frequency band of the bandpass filter 12. The polarity of the DC signal output to the output terminals A and B of the multiplexer 26 determines the pass frequency band and the direction of change in the amplification degree of the bandpass filter 12, respectively, and sets the notch frequency correctly and blocks the fundamental wave component. It is something. Variable resistors 226 and 228 are each
The resistors 226 and 228 are used to remove offsets from the operational amplifiers 214 and 216, and by appropriately adjusting the resistors 226 and 228, the fundamental wave component can be efficiently removed from the output of the notch filter.

Note that when the adjustment of the notch filter is completed, the average output voltage of the output terminals A and B of the multiplexer 26 becomes substantially 0V.

Next, the operation of the circuit shown in FIG. 4 will be explained with reference to FIGS. 5A to 5C. In order to simplify the explanation, the input signal supplied to the input terminal 10 is Asinωt+(A/4)sin2ωt, that is, the fundamental wave component is Asinωt, and the second harmonic component is (A/4)sin2ω. Therefore, in the figure, the zero crossing point of the input waveform is 0 degrees of the fundamental wave component,
180 degrees and 360 degrees. Furthermore, the amplitudes of each waveform do not correspond to each other in order to make the waveform easier to understand.

FIG. 5A shows a case where the pass frequency band of the bandpass filter 12 is higher than the fundamental wave component frequency of the input signal. Control signal input terminal C1 of multiplexer 26
The control signal is the quadrature component of the fundamental component of the input signal, but because the amplifiers 82 and 210 are of the inverting type, it is in phase with the quadrature component of the output of the operational amplifier 80, ie, the electronic resistor. As described above, when the pass frequency band of the bandpass filter 12 is high, the phase difference with respect to the quadrature input signal is smaller than 90 degrees. Furthermore, the control signal at the control input terminal C2 of the multiplexer 26 is an inversion of the reference phase component of the fundamental wave component of the input signal at the terminal 126, but this reference phase component is within the pass frequency band of the band filter 12 as described above. When is high, the phase difference with respect to the input signal is less than 180 degrees. The signals at the inputs X and Y of the multiplexer 26 are
This is the output signal of the filter, which is equal to the difference from the reference phase C2 of the input signal. Therefore, the phase relationship between the signals at the terminals C1, C2, X and Y of the multiplexer 26 with respect to the input signal is as shown in the figure.
If the signals at terminals C1 and C2 are logic "1" when higher than the zero crossing and logic "0" when low, the signals at outputs A and B of multiplexer 26 will be as shown. These output terminals A and B
The signals are integrated by integrators 30 and 32, and
The notch filter controls the amplitude adjustment section and the pass frequency band adjustment section of the bandpass filter 12 in a direction that completely removes the fundamental wave component.

FIG. 5B shows a case where the pass frequency band of the bandpass filter 12 is lower than the fundamental wave component frequency of the input signal. In this case, as mentioned above, the band filter 12
The phase difference with respect to the quadrature phase input signal is greater than 90 degrees, and the phase difference with respect to the reference phase input signal is greater than 180 degrees. The signals at the inputs C1, C2, X and Y of the multiplexer 26 and the resulting signals at the outputs A and B are thus as shown. The signals at outputs A and B are integrated in the same manner as in FIG. 5A, and the notch filter controls the bandpass filter 12 in a direction that completely removes the fundamental component.

FIG. 5C shows a case where the pass frequency band of the bandpass filter 12 is equal to the fundamental wave component frequency of the input signal and the amplitude adjustment of the bandpass filter 12 is optimal.
When the pass frequency band of the bandpass filter 12 is equal to the fundamental wave component frequency, the phase difference of the quadrature phase component and the reference phase component of the bandpass filter 12 with respect to the input signal is 90 degrees and 180 degrees, respectively, as described above.
The signals at the inputs C1, C2, X and Y and the outputs A and B of the multiplexer 26 are as shown in the figure. It should be noted that the input signals, the signals at terminals C1, C2, X and Y, coincide with each other at 0 degrees, 90 degrees, 180 degrees, 270 degrees or 360 degrees. Therefore, the harmonic components supplied to the input terminals X and Y appear as they are at the output terminals A and B one cycle at a time at the output terminals A and B, so that these signals become substantially zero. That is, even if these signals are integrated and averaged by the integrators 30 and 32, their outputs will not change. Note that the outputs of the integrators 30 and 32 at this time are determined by the values charged in the capacitors 218 and 220 in the previous process.

Although the preferred embodiment of the present invention has been described above, those skilled in the art can easily modify the present embodiment according to the intended use. For example, in FIG. 2, a voltage-to-resistance converter may be used instead of a photocoupler, and a voltage-to-capacitance converter such as a variable cap may be used instead of a relay and a capacitor. Further, if the frequency of the fundamental wave component of the input signal is limited to a relatively narrow range, a configuration related to coarse adjustment of the bandpass filter 12 is not necessary.

[Effects of the Invention] As explained above, the frequency separation circuit according to the present invention can automatically and accurately adjust the pass frequency band of the bandpass filter to the frequency of the fundamental wave of the input signal, so that the notch of the distortion meter can be adjusted. Extremely useful for filters. The notch filter section of the present invention consists of a bandpass filter and a removal means, and since the notch frequency is determined by the center frequency of the bandpass filter, adjustment of the notch frequency is very easy.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of the bandpass filter and removal means shown as blocks in FIG. 1, and FIG. 3 is a circuit diagram of the Schmitt circuit and removal means shown as blocks in FIG. 4 is a circuit diagram of the paraphasing amplifier, multiplexer, and integrator shown as blocks in FIG. 1, and FIGS. 5A to 5C are circuit diagrams for explaining the circuit operation of FIG. 4. It is an explanatory diagram. In the figure, 12 is a band filter, 14 is a removal means,
20 is a paraphrase amplifier, 26 is a multiplexer, 30 is a first integrator, and 32 is a second integrator.

Claims (1)

[Scope of Claims] 1. A frequency separation circuit that removes the fundamental wave component from an input signal containing fundamental wave components and harmonic components, comprising: a pass frequency band adjustment section that adjusts the pass frequency band; and a pass frequency band adjustment section that adjusts the amplitude of the input signal. and generates two output signals whose phases are perpendicular to each other in response to the input signal, and when the pass frequency band adjustment section is tuned to the fundamental wave component of the input signal, One of the output signals is a reference phase component that has a reference phase relationship with the fundamental wave component of the input signal, and the other signal of the two output signals is a quadrature phase component that has a quadrature phase relationship with the reference wave component of the input signal. a bandpass filter that removes the reference phase of the output of the bandpass filter from the input signal; a paraphasing amplifier that receives the output of the removal unit and generates a push-pull output; a multiplexer that selects one of the push-pull outputs according to the reference phase component and selects one of the push-pull outputs according to the quadrature phase component; a first integrator that integrates a first output of the multiplexer; and a second integrator that integrates a second output of the multiplexer selected according to the quadrature component; By controlling the amplitude adjustment section and the pass frequency band adjustment section using the output of the second integrator,
A frequency separation circuit that obtains a signal obtained by removing the fundamental wave component from the input signal at an output end of the removing means.