Finnegan, Henderson, Farabow, Garrett & Dunner
Analog-to-digital converter
 A first reference voltage, a second reference voltage and an unknown analog signal with the same polarity with respect to that of the first reference voltage are applied in a given sequence to the second input of an integrator whose first input is supplied with a voltage which is half the difference between the first and second reference voltages. The output of the integrator is coupled with the second input of a comparator whose first input is supplied with a medium voltage between the second reference voltage and the input voltage at the first input of the integrator as a comparing reference voltage. At the beginning of conversion, the integrator initiates integration from the comparing reference voltage level. During first and second periods each having a given duration, the second reference voltage and the unknown analog signal are sequentially applied to the second input of the integrator. During a third period, the first reference voltage is applied to the second input of the integrator. A first counter counts clock pulses with a given frequency during the third period to thereby provide a digital value corresponding to the unknown analog signal. When the magnitude of the unknown analog signal is slightly smaller than the first reference voltage and when it is slightly larger than the second reference voltage, a digital value corresponding to the difference between the magnitudes of the unknown analog signal and the reference voltage is measured by a second counter. In another embodiment of the invention, one calibration cycle is executed for a series of conversion cycles of unknown analog signals. In the calibration cycle, a digital value, which includes an error due to an input offset voltage of the integrator, corresponding to the first of second reference voltage, is measured. The measured digital value of each unknown analog signal is calibrated depending on the difference between the measured digital value for a reference voltage including the error and a known correct digital value for the reference voltage. 
Tokyo Shibaura Denki Kabushiki Kaisha
H H
H03M H03M
additional inventional
Eiji Yasoji
Masuda Suzuki