Analog to digital conversion with charge balanced voltage to frequency converter having polarity responsive offset

摘要

A bipolar analog voltage is converted into a digital signal by sensing the polarity of the voltage and selectively supplying a bias voltage to an analog-to-digital converter, which can preferably be a charge balanced voltage to frequency converter, as a function of the sensed polarity. The voltage to frequency converter has a double valued variable frequency output with a discontinuity at zero volt such that the converter derives a maximum output frequency for a maximum positive voltage and also for a negative value slightly displaced from zero; the voltage to the frequency converter minimum output frequency is derived from positive voltages slightly greater than zero and for maximum negative voltages. The converter output frequency and the sensed polarity are supplied to a frequency to digital converter which derives an output signal having a bit representing the polarity of the analog voltage and additional bits indicative of the magnitude of the analog voltage.