A square-rooting current-to-frequency converter

A square-rooting current-to-frequency converter (CFC) is presented in this paper. It has been designed by using the current controlled resistor (CCR) in CMOS technology with bisection of the input voltage, and one relaxation oscillator. CCR is used-instead of the resistor within the relaxation oscillator. In this way, the time constant of the relaxation oscillator is current-controlled. There is no need for a high stable voltage or current references in the proposed circuit. By appropriate setting of the process, parameters of the MOSFETs used, the temperature variations of the output frequency can be made smaller than 7/spl times/10/sup -3/%/K. Experimental results confirm that the behavior of the proposed square-rooting CFC is in good agreement with the predictions of the analysis performed. According to these results, relative errors are less than 1% for the input current range from 35 /spl mu/A to 15 mA, and for the output frequency range from 1.45 kHz to 9.80 kHz.