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Abstract

An analog-to-digital converter circuit is disclosed that is capable of converting both positive and negative analog input signals, and that is capable of operating as either an analog-to-digital converter or a digital-to-analog converter. The converter includes a modifying filter, a series of substantially identical converter stages, and a restoring filter. An original reference signal is provided, coupled to a resistor array to provide a stage reference signal to each converter stage that is equivalent to the value of the bit of an N-bit binary word corresponding to that stage. An incoming analog signal is modified to ensure that it is positive before applying it in parallel to the converter stages. Each converter stage compares the modified analog signal to the sum of its own reference signal and the value of all stage reference signals for prior converter stages where the digital output of the stage was a binary '1.' When the modified signal is larger than or equal to the stated sum, the converter stage outputs a binary '1', and when the modified signal is smaller than the sum, a binary '0' is output. In digital-to-analog mode, binary inputs to each stage determine the reference signals to be summed in order to produce an analog output. The restoring filter may be used to restore the original incoming analog signal, including its sign.

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