Tracking and holding in a DAC the peaks in the field-proportional voltage in a slope activated magnetic field sensor

摘要

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 VDAC-P produced by PDAC rises to each peak positive voltage Vpk in Vsig, and that becomes low when a tracking voltage VDAC-P falls to each peak negative voltage in Vsig. The peak VDAC-P is held until Vsig drops by a fixed amount below Vpk 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 VDAC-N is held until Vsig rises a fixed amount above VDAC-N to produce an output pulse that resets the counter connected to NDAC. The N-counter is reset at tnpk by the negative-peak indicating signal VNcomp and is enabled at tppk by the positive-peak indicating signal VPcomp, while the P-counter reset by the positive peak indicating signal VPcomp and enabled by VNcomp. This proximity detector detects articles passing at rates down to zero.