Direct Conversion Analog to Digital Converter.
DEPARTMENT OF THE ARMY WASHINGTON DC
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A four bit subtractor analog to digital converter provides direct conversion of analog voltage signals into binary or binary coded decimal output signals for digital display or digital signal processing. The analog to digital converter utilizes a plurality of signal processing sections, each section being designed to provide a binary output with the composite output bits being indicative of the analog input signal. In processing the analog signal an operational amplifier compares the input analog signal with a reference voltage in each section. Each section either passes or rejects the analog signal input in response to this comparison voltage. If the signal is rejected by a section it is passed to the next section where the same type of comparison takes place, if the signal is accepted by the operational amplifier and operated on, a comparator responsive to the amplifier output changes state providing a binary one output instead of a binary zero. A change in the comparator output signal to a binary one causes a field effect transistor switch to change states thereby supplying the operational amplifier output signal to subsequent signal processing sections instead of the originally supplied analog signal input. Subsequent sections operate in an identical manner with a systematic reduction in the comparison or reference voltage for providing digital signal processing. An amplifier at the end of each signal processing stage operates on the residual analog signal input to that amplifier to prepare the signal for processing in subsequent stages and thereby maintain signal integrity with no loss of signal level. Author
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