Sine wave reference waveform generator

Claim 2

Apparatus for generating a sinusoidal voltage waveform comprising: an operational amplifier having first and second input terminals and an output terminal, said first input terminal being a signal polarity inverting terminal and said second input terminal being a signal polarity non-inverting terminal; means for applying to said first terminal a plurality of currents having mutual uniformly phase displaced, substantially symmetrical rectangular waveforms wherein the phase displacement of said current waveforms is substantially equal to 180.degree./N where N is an integer representing the number of said waveforms; means for maintaining at said second terminal a direct voltage to provide at said output terminal an output voltage having a waveform that is a combination of said rectangular current waveforms and is symmetrical about a voltage level substantially equal to that maintained at said second terminal.

Claim 3

The subject matter of claim 1 further comprising: a load coupled to said output terminal with isolation means, to remove direct current components from said output voltage waveform.

Claim 4

The subject matter of claim 1 where the said operational amplifier has a feedback capacitor connected between said output terminal and said first input terminal to provide integrator functions removing remaining harmonic components from said output voltage waveform.

Claim 5

The subject matter of claim 1 wherein: said means for applying a pluraltiy of currents to said first terminal comprises a direct voltage source connected through a plurality of circuit branches to said terminal; each said circuit branch comprising a pair of resistors having a midpoint therebetween; said pair of resistors having a resistance ratio to one another that is the same as the ratio of resistors in each of the other of said branches, said resistors in each of said branches having a value scaled in relation to that of the resistors of each other circuit branch to produce currents through said branches for harmonic neutralization of said combined waveform; said resistors in each branch having a midpoint connected to a switching device for each branch, said switches being connected between said midpoints and a ground potential; and means to control sequentially the operation of said switches in accordance with a predetermined pattern.

Claim 6

A reference generator for producing a desired time varying voltage waveform comprising: summing means for combining a plurality of individually developed current waveforms that are component parts of the desired waveform; a plurality of current sources for producing said current waveforms, said current sources comprising, for each current waveform to be developed, a circuit branch from a direct voltage source to said summing means, each said circuit branch having therein a pair of series connected resistors with a midpoint therebetween, said pair of resistors having a resistance magnitude ratio that is the same in each said branch, said resistors in an individual branch having a resistance magnitude in relation to said resistors in other branches in accordance with the required mathematical relation of said plurality of current waveforms to produce the desired waveform with minimum harmonics present; control means for each of said circuit branches for selectively forming a current path to ground from each said midpoint for a predetermined interval to produce said rectangular waveforms and to cause said waveforms to be uniformly phase displaced and each of said waveforms to have symmetrical positive and negative portions.

Claim 7

A reference generator for producing a desired time varying voltage waveform comprising: summing means for combining a plurality of individually developed current waveforms that are component parts of the desired waveform; a plurality of current sources for producing said current waveforms, said current sources comprising, for each current waveform to be developed, a circuit branch from a direct voltage source to said summing means, each said circuit branch having therein a pair of series connected resistors with a midpoint therebetween, said pair of resistors having a resistance magnitude ratio that is the same in each said branch, said resistors in an individual branch having a resistance magnitude in relation to said resistors in other branches in accordance with the required mathematical relation of said plurality of current waveforms to produce the desired waveform with minimum harmonics present; control means for each of said circuit branches for selectively forming a current path to ground from each said midpoint for a predetermined interval to produce said rectangular waveforms and to cause said waveforms to be uniformly phase displaced and each of said waveforms to have symmetrical positive and negative portions.

Claim 8

The subject matter of claim 5, wherein: said summing means is an amplifier with an input at which said waveforms are applied together and said amplifier has a capacitor connected between its output and said input to provide integrator functions and produce a smooth waveform.

Claim 9

The subject matter of claim 5 wherein: the relation of said resistors in said branches is determined by the following equations that determine the required current magnitudes:

Claim 10

The subject matter of claim 6 wherein: said amplifier is an operational amplifier whose inverting, summing terminal is said input and whose non-inverting input terminal is maintained at a direct voltage about which the output voltage is symmetrical.