A 30 kHz/√V Sensitivity Square-Rooting Voltage-to-Frequency Converter

This article presents a highly sensitive square-rooting (SQRT) voltage-to-frequency converter (VFC). The proposed circuit is based on an asynchronous charge-balanced VFC consisting of an integrator, comparator, and monostable multivibrator (MM), in addition to the circuit for the SQRT of the input voltage. The sensitivity of the proposed SQRT VFC can be controlled digitally, or by changing the resistance ratio of two passive resistors, or by changing the control voltage of a voltage-controlled resistor (VCR). The output signal frequency is independent of the temperature variations and the process parameters variations of the MOSFETs used. The prototype made by discrete of-the-shelf components has been experimentally validated, with a single supply voltage of 3 V. Sensitivities up to 15.79 kHz/
$\surd \text{V}$
and 30.1 kHz/
$\surd \text{V}$
for the input voltage ranges up to 1.7 V and up to 1.4 V, respectively, have been achieved. For the input voltage range from 1 mV to 1.7 V, the full-scale error is less than 0.5% for the highest sensitivity.