Low-distorted waveform generating method and waveform generator using the same

Claim 2

The waveform generator of claim 1, wherein said computation and control part includes temporary storage means and Fourier transform analysis means, and wherein said computation and control part fetches thereinto via said distortion measuring part a waveform signal which is provided from said waveform generating part when reading out a reference signal waveform from said memory means, determines amplitudes and phases of distortion components in the output waveform signal of said waveform generating part by performing a Fourier transform analysis of said fetched waveform signal with said Fourier transform analysis means and writes said amplitudes and phases of said distortion components into said memory means, fetches thereinto said output waveform signal of said waveform generating part via said A/D converter means without passing through said filter means, determines an amplitude and a phase of a fundamental frequency component of said reference signal waveform by performing a Fourier transform analysis of said fetched output waveform signal with said Fourier transform analysis means and writes said amplitude and phase of said fundamental frequency component into said temporary storage means, fetches thereinto via said distortion measuring part output waveform signal of said waveform generating part when reading out of said memory means a composite waveform composed of harmonic components each having a predetermined amplitude and phase and the frequency of corresponding one of said distortion components, determines amplitude/phase characteristics of said waveform generating part with respect to each of said harmonic components by performing a Fourier transform analysis of said fetched output waveform signal with said Fourier transform analysis means and writes said amplitude/phase characteristics into said temporary storage means, computes amplitudes and phases of said distortion canceling harmonic components for canceling said distortion components, based on said determined amplitudes and phases of said distortion components, said determined amplitude and phase of said fundamental frequency component and said determined amplitude/phase characteristic written in said temporary storage means, and writes into said memory means waveform data composed of said canceling harmonic waveform components determined by said computed amplitudes and phases and said reference signal waveform.

Claim 3

The waveform generator of claim 2, wherein said memory means includes a first memory for storing said reference signal waveform when a low-distortion waveform is generated, and a second memory for storing said canceling harmonic component waveform; said D/A converter means includes a first D/A converter for converting said reference signal waveform read out of said first memory into an analog waveform and a second D/A converter for converting said canceling harmonic component waveform read out of said second memory into an analog waveform; and said amplifier means includes first and second amplifiers for amplifying the outputs of said first and second D/A converters, respectively, and adder means for adding the output of said second amplifier to the input to said first amplifier and for inputting the added output into said first amplifier.

Claim 4

The waveform generator of claim 3, further comprising an attenuator provided between the output of said second amplifier and the input of said adder means, for attenuating the output signal of said second amplifier by a predetermined rate.

Claim 5

A waveform generator comprising: memory means wherein there are written waveform data; a read control part for controlling the readout of said memory means; D/A converter means for converting said waveform data read out of said memory means into an analog waveform signal; and amplifier means for amplifying said analog waveform signal from said D/A converter means; wherein said waveform data is one that contains a signal waveform component to be generated and a distortion canceling waveform for canceling distortion components which are caused when said signal waveform component is amplified by said amplifier means.

Claim 6

The waveform generator of claim 5, wherein there is written in said memory means composite waveform data composed of said signal waveform component to be generated and said distortion canceling waveform.

Claim 7

The waveform generator of claim 5, wherein said memory means includes a first memory in which there is written waveform data of said signal waveform component to be generated, and a second memory in which there is written said distortion canceling waveform data; said D/A converter means includes a first D/A converter for converting said signal waveform component data from said first memory into an analog waveform, and a second D/A converter for converting said distortion canceling waveform data from said second memory into an analog distortion canceling waveform; and said amplifier means includes adder means for adding said analog distortion canceling waveform from said second D/a converter to said analog signal waveform from said second D/A converter, and a first amplifier for amplifying the output of said adder means to produce a distortion-reduced signal waveform.

Claim 8

The waveform generator of claim 7, wherein said amplifier means further includes a second amplifier for amplifying said analog signal waveform from said second D/A converter, and an attenuator for attenuating the output of said second amplifier by a predetermined rate and then applying said attenuated output to said adder means.

Claim 9

A waveform generating method in which waveform data read out of a memory by a computation and control part is converted by a D/A converter to an analog waveform, said analog waveform is amplified by an amplifier and a waveform signal is generated as the output of a waveform generating part, said method comprising the steps of: writing into said memory data of a multi-sine waveform which is a composite waveform composed of n sine waves respectively having a fundamental frequency ω of a signal waveform to be generated and two-fold, three-fold, ..., n-fold harmonic frequencies and each having a predetermined amplitude; reading out said multi-sine waveform from said memory, converting said multi-sine waveform by said D/A converter to an analog waveform and amplifying said analog waveform by said amplifier to thereby output said multi-sine waveform; applying said multi-sine waveform form said amplifier to a filter to attenuate the component of said fundamental frequency ω, converting the output of said filter by an A/D converter to digital multi-sine waveform data and fetching said digital multi-sine waveform data into said computation and control part; measuring amplitude/phase characteristics of said waveform generating part, inclusive of the influence of said filter, by obtaining the amplitude and phase of each of said harmonic frequency components through a Fourier transform analysis of said fetched digital multi-sine waveform data; writing said signal waveform data of said fundamental frequency to be generated into said memory; reading out said signal waveform data of said fundamental frequency ω from said memory, converting said read-out signal waveform data by said D/A converter to an analog waveform, amplifying said analog waveform by said amplifier and outputting said amplified analog waveform; applying said analog signal waveform from said amplifier to said filter to attenuate the component of said fundamental frequency, converting the output of said filter by said D/A converter to a digital signal waveform and fetching said digital signal waveform into said computation and control part; measuring a distortion characteristic of said waveform generating part, inclusive of the influence of said filter, by obtaining amplitudes and phases of harmonic distortion components with respect to said fundamental frequency ω through a Fourier transform analysis of said fetched digital signal waveform; determining, based on said measured amplitude/phase characteristics and said measured distortion characteristic, the amplitude and phase of each of distortion canceling sine signal waveforms of frequencies 2ω, 3ω, ..., nω for canceling distortion components which are generated in said waveform generating part with respect to said signal waveform of said fundamental frequency to be generated; computing composite waveform data composed of said distortion canceling sine signal waveforms and said fundamental frequency signal waveform and writing said composite waveform data into said memory; and reading out said composite waveform data from said memory, converting said read-out composite waveform data by said D/A converter to an analog waveform, amplifying said analog waveform by said amplifier and outputting said amplified analog waveform as said signal waveform to be generated.