Bipolar mark-space analogue-to-digital converter

A bipolar mark-space analogue-to-digital converter comprising:

• integrating means for receiving an analogue input signal to be converted;
• means for including a periodic signal component in the output signal produced by the integrating means in addition to the output signal component of the integrating means due to the analog input signal;
• first and second level detectors connected to compare the output signal from the integrating means with first and second detector levels respectively, whereby analogue input signals of one polarity cause the magnitude of the output signal from the integrating means to exceed the first level by crossing it in a direction away from the second level, while analogue input signals of the other polarity cause the magnitude of the output signal from the integrating means to fall below the second level by crossing it in a direction away from the first level, the first and second level detectors being arranged to produce first and second control signals respectively when the magnitude of the output signal from the integrating means exceeds the first level and falls below the second level respectively;
• first and second reference signal sources of opposite polarity;
• switch means responsive to the first control signal to apply one of said reference signal sources, opposite in polarity to said one polarity of the analogue input signal, to the integrating means, said switch means being also responsive to the second control signal to apply the other of said reference signal sources to the integrating means;
• means for defining a conversion interval equal in duration to the duration of an integral number of cycles of said periodic signal;
• a source of clock pulses;
• and
• counter means for counting the clock pulses during the application of either of the reference signal sources to the integrating means, whereby the count in the counter means at the end of the conversion interval is a digital representation of the magnitude of the integral of the analogue signal over the conversion interval.