Analog-to-digital converting apparatus

Apparatus for converting the amplitude of an analog signal to a digital signal including in combination

• a signal input terminal for receiving an analog input signal;
• a plurality of N stages arranged in series;
• each stage including a comparator means having a first input terminal connected to said signal input terminal, a second input terminal, and an output terminal;
• each comparator means being operable to produce a first output condition at its output terminal when the voltage at one of the input terminals is greater than that at the other input terminal and to produce a second output condition at its output terminal when the voltage at the other of the input terminals is greater than that at the one input terminal;
• a source of reference voltage connected to the second input terminal of the comparator means of the first stage in the series;
• each stage except the last stage in the series including
• resistance means connected between the second input terminal of the associated comparator means and the second input terminal of the next comparator means in the series;
• first constant current means for producing a constant current connected to the juncture of the associated resistance means and the second input terminal of the associated comparator means;
• second constant current means for producing a constant current equal to the constant current produced by the associated first constant current means connected to the juncture of the associated resistance means and the second input terminal of the next comparator means in the series;
• switching means coupled to the output terminal of the associated comparator means, the associated first and second constant current means, and the associated resistance means;
• the switching means being operable when the associated comparator means is producing the first output condition to provide a path for current from the first constant current means bypassing the associated resistance means, and to provide a path for current from the second constant current means flowing through the associated resistance means in the direction from the second input terminal of the next comparator means in the series toward the second input terminal of the associated comparator means, whereby the voltage at the second input terminal of the next comparator means in the series is greater than that at the second input terminal of the associated comparator means by the voltage drop across the associated resistance means;
• and
• the switching means being operable when the associated comparator means is producing the second output condition to provide a path for current from the second constant current means bypassing the associated resistance means, and to provide a path for current from the first constant current means flowing through the associated resistance means in the direction from the second input terminal of the associated comparator means toward the second input terminal of the next comparator means in the series, whereby the voltage at the second input terminal of the next comparator means in the series is less than that at the second input terminal of the associated comparator means by the voltage drop across the associated resistance means;
• whereby the output conditions of the comparator means in the series provide a digital representation corresponding to the analog input signal.