FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
METHOD AND CIRCUIT FOR REDUCTION OF HARMONIC DISTORTION AND PRODUCING SINUSOIDAL WAVE FROM SQUARE WAVE
2. APPLICANT(S)
(a) NAME: SANDEEP V RODE
(b) NATIONALITY: INDIAN
(c)ADDRESS: 202, Shubham Apartment, B/H Hanuman Madir, Gadge nagar,
Amravati-444603 (Maharashtra State) INDIA
3.PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification
particularly describes the
invention and the manner
in which it is to be
performed.
4. DESCRIPTION (Description shall start from next page)
5. CLAIMS (not applicable for provisional specification. Claims should start with the preamble "I/we claim" on separate page)
6. DATE AND SIGNATURE (to be given at the end of last page of specification)
7. ABSTRACT OF THE INVENTION (to be given along with complete specification on separate page)

METHOD AND CIRCUIT FOR REDUCTION OF HARMONIC DISTORTION AND PRODUCING SINUSOIDAL WAVE FROM SQUARE WAVE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing sinusoidal wave with less than 2% harmonic distortion as well as a circuit for implementing the method.
2. Description of the Prior Art
In square wave to sine wave converter, the need for a low harmonic distortion factor, i.e., the signal power of all the output harmonics together shall be small with respect to the signal power of the fundamental output wave. Sine wave generator with a low distortion factor simplifies the control of electrical motors and sensitive application. Furthermore, it is known form the technique of inverter to convert DC voltages into square wave voltages by means of switching devices and to convert those square wave voltages into sinusoidal output voltage. Conventionally passive LC filters have been used to eliminate harmonics and improve power factor. However, passive LC filters are bulky, load dependent, and inflexible. They can also cause resonance in to the system. Therefore, conventional passive filter cannot provide a complete solution. According ,it would desirable to provide a method and circuit for producing sinusoidal wave which would produce very low distortion sine wave utilizing a novel method and circuit which overcomes the aforesaid shortcoming of the prior art.

SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for producing sinusoidal waves from square wave forms.
Another object of the present invention is to provide a circuit utilizing a novel method for producing sinusoidal waves from square wave forms.
In accomplishing these and other objects, there has been provided, in accordance with the present invention, a method for producing sinusoidal waves includes reference signal source such as the Wien bridge oscillator or any type of circuit which would provide a low distorted output sine wave. This reference signal is used for adaptive filter in signal processing operation and modifies the output. An adaptive filter utilizing this method uses multiplier, an amplifier, and integrator and subtractor circuit. First multiplier multiply the input square wave and reference sine wave signal of fundamental frequency and then output of first multiplier is applied to integrator as input, after integrating the dc signal it is multiplied to reference signal using second multiplier, output of second multiplier generate the error signal for first multiplier as well as it also provide the output of the circuit.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 schematically shows the square wave to sine wave converter circuit of the
present invention.
FIG. 2 shows the square wave input voltage as a function of time and spectrum of
the square wave input voltage as a function of frequency.
FIG. 3 is a graph of a waveform and spectrum of an output voltage of the circuit of
FIG.l
FIG. 4 schematically shows the circuit for attenuation of fundamental frequency
signal from square waveform of 50Hz.
FIG. 5 is a graph of a waveform and spectrum of an output voltage of the circuit of
FIG.4
FIG. 6 schematically show the square wave to sine wave converter circuit with low
pass filter.
FIG. 7 is spectrum of: a) an output voltage of the circuit of FIG.6 and b) an output
voltage of Low pass filter present in circuit of FIG.6

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the square -to-sine wave converter circuit of the present invention. This circuit includes a two multiplier 1 and 2, an integrator 3, amplifier 4 and subtracter circuit 5. A square wave signal is applied to terminal 6, and a reference signal is applied to terminal 7. The sine wave signal of fundamental frequency appears at output terminals 10. Resistorsll (10k ohm) and 12(lk ohm) are determined the gain of non-inverting amplifier 4. This amplifier consists of an operational amplifier LM 741.Resisitors 14,15,16 and 17 are of same value IK ohm for subtractor 5. Multiplier 1 and 2 are four- quadrant multiplier AD633JN. An output of the first multiplier 1 is connected to an integrator circuit 3. This integrator, as is well known, consists of an operational amplifier having an appropriate capacitive element 26 in a feedback path. To avoid the saturation problem capacitor is shunted by a resistor 24.Resistor 33 is minimize the effect of the input bias circuit. The resulting output 20 of integrator is applied to an input Y2 of the second multiplier 2 and the second multiplier 2 produces an output Vo at 10.
When a reference sine wave of fundamental frequency with 1V peak amplitude is applied at 7 to the non-inverting amplifier 4, it get amplified by the factor of 11 and square wave of 12V with 50Hz frequency is applied to terminal 6 of subtractor 5, initially the square wave signal appears at output terminal 21 of subtractor.
The multiplier 1, multiply two signal connected at inputs X1 and Yl, reference signal 30 after amplification is connected to X1 and output signal 21 of subtractor is connected to Yl and produces a parabolic wave at 19. The parabolic wave, output of first multiplier get integrated using integrator circuit 3 and applies an output signal 20 of integrator to the input Y2 of the second multiplier 2. Since the input X2 of the second multiplier concurrently receives the amplified reference signal 22, the second multiplier produces an output voltage as sine wave of fundamental frequency. At output of second multiplier said fundamental frequency signal of square wave being so modified by applying to said subtractor at input terminal 23 that the amplitude of said fundamental frequency signal in said subtractor output 21 is minimized.
FIG.2 shows the square wave of 50Hz with 12 V input voltage as a function of time and spectrum of the square wave input voltage. Square wave spectrum represent it contain fundamental frequency 50Hz signal of peak amplitude 15.28V (27.3% greater than peak amplitude of square wave) and other harmonics (third harmonic 5.09V, fifth harmonic 3.06V, seventh harmonic 2.18V etc). Total harmonics distortion of square wave is 47.82%.

FIG.3 is a graph of sinusoidal signal of 50Hz frequency with amplitude of 15.28 V as a function of time and spectrum of an output voltage of the circuit of FIG.l. Spectrum of this wave represent it contain fundamental frequency (15.28V), third harmonic (0.24V), fifth harmonic (0.03V), and reduction in harmonic distortion (1.60%).
FIG.4 shows the circuit for attenuation of fundamental frequency signal from square waveform of 50Hz. Output of subtractor circuit 5 is waveform where the fundamental frequency signal is attenuated. To attenuate particular frequency from the periodic waveform applied to terminal 6, apply the reference signal of same frequency to terminal 7.
FIG. 5 is a graph of a waveform and spectrum of an output voltage of the circuit of FIG.4. This spectrum represents attenuation of fundamental frequency of 50Hz square wave. Peak amplitude of fundamental frequency sine wave 15.28V is attenuated to 0.2025 V.
FIG. 6 shows the circuit for the square -to-sine wave converter with RC low pass filter 32. Here reference signal 7 is generated from square wave applied to terminal 6 using RC low pass filter 32.
FIG. 7 is spectrum of: a) an output voltage of the circuit of FIG 6 and b) output voltage of Low pass filter of FIG.6. Spectrum shown in FIG 7 -a) is of output waveform of circuit in FIG.6 for square wave of 12V with 50Hz frequency; contain fundamental frequency (15.27V), third harmonic (0.48V), fifth harmonic (0.03V), and reduction in harmonic distortion (3.16%). Spectrum shown in FIG. 7 -b) is of output waveform 7 of low pass filter 32 if input is square wave of 12V with 50Hz frequency, it contain fundamental frequency signal of amplitude 0.78Vand other harmonics.

We claim:
1. A method and circuit for minimization of harmonic distortion from
square wave to produce in phase sinusoidal wave. Comprising the
steps of:
a) reference signal of fundamental frequency to be amplified;
b) applying said reference signal to first multiplier as first input XI;
c) applying square wave signal Vi to first multiplier through subtractor as second input Yl;
d) deriving from the output of said multiplier is a parabolic wave ;
e) so applying said parabolic wave to integrator to produce ramp signal;
f) multiplying said ramp signal to reference signal of fundamental frequency using second multiplier;
g) at output of second multiplier said fundamental frequency signal of square wave being so modified by applying to said subtractor that the amplitude of said fundamental frequency signal in said subtractor output is minimized. ,

2. An adaptive filter as mentioned in claim 1.utilising multiplier, an amplifier, an integrator, and subtractor circuit and produces a sine wave output of fundamental frequency of input square wave and has less than 2 percent harmonic distortion.
3. Method and Circuit given in claim 2 for attenuation of periodic sine wave of particular frequency from square waveform.
4. Method and circuit given in claim 2 for minimization of harmonic distortion from periodic waveform like triangular, sawtooth etc. to produce in phase sinusoidal wave.
5. Method and Circuit given in claim 2 for attenuation of periodic sine wave of particular frequency from periodic waveform like triangular, sawtooth etc.