Burr-brown Corporation

Burr-brown Research Corporation

Lewis R Smith

David M Thomas

In one embodiment, a successive approximation analog-to-digital converter having a main CDAC and a trim CDAC includes resistors in the main CDAC connected in series with various bit switch FETs. The resistors are precisely matched to equivalent resistances of trimmable voltage divider circuits connected in series with various corresponding bit switch FETs in the trim DAC, to prevent non-linear parasitic capactiance and voltage-current properties of first and second clamping FETs from 'unbalancing' the voltages on the charge summing conductors of the main DAC and the trim DAC during turn-off of the first and second clamping FETs after they have been turned on to equalize the voltages of the charge summing conductors. In another embodiment, separate trim and dummy DACs are provided to improve the accuracy to which the resistances in the main CDAC and trim CDAC can, as a practical matter, be matched.

Dummy/trim DAC for capacitor digital-to-analog converter

An isolation amplifier includes an electrically floating comparator having inputs coupled to inputs of the isolation amplifier. Operating power is supplied to the isolation amplifier by an electrically floating rectifier circuit. A triangular waveform generator produces a triangular output signal which is combined by means of a first coupling capacitor with a differential input signal applied to the inputs of the isolation amplifier. A second coupling capacitor couples the triangular waveform to the floating rectifier circuit. The floating comparator circuit produces a pulse width modulated output signal representative of the magnitude of the differential input signal. A demodulator circuit inverts the pulse width modulated signal to an analog output signal which is an amplified replica of the differential input signal. The analog output signal is electrically isolated from the differential input signal.

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Tucson, AZ, United States of America

Lewis R Smith