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A thermal technique of rms measurement is described which uses the base-emitter junction of a bipolar transistor to sense the temperature change of a monolithic chip due to the power dissipation of a companion diffused resistor. An analysis is presented which provides: 1) design equations for performing error compensation to minimize the nonlinearity of the rms-to-dc conversion, and 2) ac feedback network design to optimize the low frequency cutoff and settling time product. Resulting rms converters had midband accuracies of /spl plusmn/0.05 percent of full scale over a dynamic range of 30 dB, high frequency limits of 100 MHz for 2 percent accuracy, and settling times less than 1 s.
Date of Publication: Dec. 1974