Analog-to-digital converter employing an electromagnetic resolver

Claim 1

In an analog-to-digital converter system including an electromagnetic transducer having first and second reference windings, a voltage generator for providing stepped voltages to said first and second reference windings, said voltages having fundamental sinusoidal frequency components in phase quadrature with respect to each other and low harmonic content, comprising an impedance element having first and second ends and having at least first and second groups of spaced taps thereon, first switching means connected to said impedance element for alternately connecting reference voltages of opposite polarity and constant value across said first and second groups of spaced taps, said taps being located on said impedance element to provide a voltage at each tap within a group which is a sinusoidal function of said location with respect to a tap maintained at a fixed potential, said first switching means further comprising an input terminal and first, second, third and fourth output terminals, a clock generator for generating pulses, a counter having an input coupled to said clock generator and a first output coupled to said first switching means, said counter resetting after receiving a predetermined number of pulses from said clock generator, a decoder having an input coupled to a second output of said counter and a plurality of output terminals, each of said output terminals being coupled to the control terminals of a corresponding tap switch in said first and second groups, said decoder energizing sequentially said tap switches in accordance with pulses received by said counter means from said clock generator, said first switching means further comprising a first multivibrator having an input coupled to the input terminal of said first switching means and a pair of outputs coupled to said first and second output terminals of said first switching means, said first multivibrator receiving a pulse each time said counter resets and reversing the states of the voltages at its first and second outputs, a second multivibrator having an input coupled to an output of said first multivibrator and a pair of outputs, said second multivibrator reversing the states of the voltages at its outputs for every second pulse received by said first multivibrator, first and second switching elements each having an input coupled to a corresponding output of said second multivibrator and an output coupled to said third and fourth output terminals of said first switching means and to a corresponding end of said impedance element, said first and second switching elements being driven alternately into conduction each time the output of said second multivibrator changes states, second switching means connected to said impedance element and having first and second output terminals, said second switching means coupling sequentially and selectively the taps in each of said first and second groups Respectively to said first and second output terminals to provide stepped output voltages thereat, said voltages having fundamental sinusoidal components in phase quadrature with each other, said second switching means including first and second groups of said tap switches, each tap switch having a first terminal, a second terminal and a control terminal, the first terminal of each of the switches in said first and second groups being coupled to a corresponding tap in said first and second groups of spaced taps respectively; and a switching circuit having a first input terminal coupled to the second terminals of said first group of tap switches and a second input terminal coupled to the second terminals of said second group of tap switches, said switching circuit further comprising third and fourth input terminals coupled to the first and second output terminals of said first switching means, first, second, third, fourth, fifth and sixth switches, each of said switches having first, second and control electrodes, the control electrodes of said first, third and fifth switches being coupled to the third input terminal of said switching circuit and said second, fourth and sixth switches being coupled to the fourth input terminal of said switching circuit, means coupling the second and first electrodes of said first and second switches respectively to the second input terminal of said switching circuit and means coupling the second and first electrodes of said third and fourth switches respectively to the first input terminal of said switching circuit, first, second and third operational amplifiers, each of said amplifiers having first and second input terminals and an output terminal; the first input terminal of said first amplifier being coupled to the first electrode of said first switch and the second electrode of said fourth switch, the second input terminal and the output terminal of said first amplifier being coupled together; the first input terminal of said second amplifier being coupled to the second electrode of said fifth switch and the first electrode of said sixth switch, the second input terminal of said second amplifier being coupled to the first electrode of said fifth switch, the second input and output terminals of said third amplifier and the output terminal of said second amplifier; and the first input terminal of said third amplifier being coupled to the second electrode of said second switch and the first electrode of said third switch, the second electrode of said sixth switch being coupled to a reference point, means coupling the outputs of said first and second amplifiers to the second and first output terminals respectively of said second switching means, and means coupling the first and second output terminals of said second switching means to the first and second input windings of said transducer respectively.