Tracking and holding in a dac the peaks in the field-proportional

Abstract

In a proximity-detector, a Hall transducer produces a signal Vsig. Two counters, P-counter and N-counter count pulses from a clock and produce count signals respectively to two DACs, PDAC and NDAC. The DACs output signals track and hold, respectively, the positive pulses and negative pulses in Vsig. These output signals are compared with Vsig to produce a proximity-detector binary output voltage Vout that becomes high when a tracking voltage V.sub.DAC-P produced by PDAC rises to each peak positive voltage V.sub.pk in Vsig, and that becomes low when a tracking voltage V.sub.DAC-P falls to each peak negative voltage in Vsig. The peak V.sub.DAC-P is held until Vsig drops by a fixed amount below V.sub.pk to produce an output pulse that resets the counter connected to PDAC at a time shortly following the actual peak in Vsig. Similarly, the peak V.sub.DAC-N is held until Vsig rises a fixed amount above V.sub.DAC-N to produce an output pulse that resets the counter connected to NDAC. The N-counter is reset at t.sub.npk by the negative-peak indicating signal V.sub.Ncomp and is enabled at t.sub.ppk by the positive-peak indicating signal V.sub.Pcomp, while the P-counter reset by the positive peak indicating signal V.sub.Pcomp and enabled by V.sub.Ncomp. This proximity detector detects articles passing at rates down to zero.