Abstract
This paper describes a novel technique for converting frequency into analog d. c. voltage. Its principle consists in the determination of frequency by a null method utilizing the relation that the product of the frequency and the period of a signal equals unity. The closed-loop configuration inherent in null methods is effective to eliminate errors resulting from crude components, thus achieving a static linearity of ±0.02% FS for input frequencies over two decades, a temperature coefficient of 100ppm/°C, a supply voltage sensitivity of 0.01%/%, and an output voltage fluctuation of 0.01%rms. The frequencies handled by the converter range from 0.01Hz to 10kHz. Having a linear characteristic normalized to be independent of the frequency inputted, the loop yields a response time approximately identical to one period of the input signal for any frequency shift, which is beyond the reach of conventional measurements by null methods. Another prominent feature is the negligible ripples in the stationary output afforded by the holder used at the output stage. The major devices employed in the prototype are about ten ICs consisting of OP amplifiers, an analog divider, analog gates, and logic SSIs.
