Patent ID: 6249239
Filing Date: 2001-06-19
Classification: H03M

Abstract:
A potentiometric DAC comprising:a string of n serially connected resistors having first and second end portions,first, second, third and fourth switches and first and second voltage supplies, the first switch connected to the first voltage supply and the first end portion, the second switch connected to the second voltage supply and the second end portion, the third switch connected to the first end portion and the second voltage supply and the fourth switch connected to the second end portion and the first voltage supply,a first tap connected at a selected location of the string of resistors and a second tap connected to a selected location of the string of resistors at an inverse location symmetrical about the average voltage of the voltages at the first and second switches,first and second capacitors and an operational amplifier having a non-inverting and an inverting input and an output,a circuit for connecting the first capacitor to the first tap when the first and second switches are closed and for connecting the second capacitor to the second tap when the third and fourth switches are closed and to average the voltages on the first and second capacitors and input the average of the voltages to the non-inverting input of the operational amplifier, anda logic circuit for closing the first and second switches to charge the first capacitor, then to open the first and second switches and close the third and fourth switches to charge the second capacitor.