| 摘要 |
<p>In a bipolar mark-space analogue-to-digital converter, two opposed-polarity reference voltages are applied to an integrator during a first conversion interval to balance a square-wave forcing-function signal and an input signal whose magnitude is to be measured, and a counter receives clock pulses at up and down inputs during application of the positive and negative reference voltages respectively. Subsequently, zero input signal is applied during a second conversion interval, and the inputs to the counter are interchanged, so that up- and down-counted pulses correspond to the negative and positive reference voltages respectively. At the end of the second conversion interval, the counter contains a digital representation of the input signal, corrected for zero drift. The application of the reference voltages is controlled by two level detectors which compare the integrator output with fixed detector levels, the magnitudes of which are chosen so that at zero input each reference voltage is applied for substantially half the period of the square-wave forcing-function signal. The operation of the converter may be coordinated by a microprocessor which is arranged to aggregate the counts of clock pulses accumulated by the counter during each cycle of the forcing-function signal.</p> |
