High precision voltage-to-frequency converter

A bipolar high precision voltage-to-frequency converter is described. The circuit includes an input voltage-to-current conversion stage followed by current-controlled multivibrator. The multivibrator trigger includes a window comparator with a limiter of the output voltage swing, and the timing capacitor discharge current is switched simultaneously with the window comparator bias. This allows to obtain high resolution near both trigger thresholds. The circuit simulation shows that the converter provides an accuracy better than 2% in the range 100 Hz-100 kHz of the output frequency. The breadboarded circuit was tested in the temperature range -25°C to 75°C and provided the temperature coefficient of the output frequency less than 60 ppm/°C. The converter can be fabricated using an ASIC process