The elimination of offset errors in dual-slope analog-to-digital converters

A new method of eliminating offset error from a dual-slope analog-to-digital converter is described. Two dual-slope cycles, each with the same fixed time period, are needed for a complete conversion. The converter differs from other converters in that the sum and difference of the unknown and reference voltage, as well as the voltages themselves are integrated. Different combinations yield a number of error-free converters in which the ratio of the two voltages is equal to the ratio of the sum or difference of two time periods. The converters also have a limited computational capability In that useful outputs other than the ratio of the unknown and reference voltages can be obtained. For some of the converters the sum or difference of two time periods yields an output with greatly reduced offset error. Another sum or difference provides a correction factor. In addition, some of the converters require a single reference voltage for the entire positive and negative range of the unknown voltage.