Electrical transmission or interconnection systems – Personnel safety or limit control features – Interlock
Patent
1992-08-06
1995-04-04
Wolfe, Willis R.
Electrical transmission or interconnection systems
Personnel safety or limit control features
Interlock
307290, 328 28, H03K 524
Patent
active
054040540
ABSTRACT:
The present invention provides dynamic hysteresis for threshold detection circuitry. The hysteresis decay pattern, rate of decay, and minimum separation between the HSP and LSP are programmable. In particular, the hysteresis decay pattern may be programmed, in any manner, so that it has a better correlation to the amplitude of the input signal. The preferred embodiment of the present invention includes a comparator circuit, digital logic, and a digital-to-analog converter circuit. The comparator circuit has a fixed LSP and a programmable HSP for detecting threshold crossings of the input signal in order to accurately generate a pulse train. The HSP includes hysteresis for providing greater immunity to noise for an input signal having an amplitude which varies with frequency. The hysteresis of the HSP decays linearly at a programmable rate unlike prior art threshold detectors having a fixed rate of exponential decay determined by resistor and capacitor values. The magnitude of hysteresis decays until either the input signal crosses an intermediate HSP value or it reaches a last value and stops decreasing. Also, the minimum separation between the HSP and LSP is controlled by a digital-to-analog conversion circuit having digitally programmable levels. While the preferred embodiment provides a linearly decreasing hysteresis pattern, the digital logic of the present invention may be implemented with a memory device for storing programmable hysteresis patterns.
REFERENCES:
patent: 3718864 (1973-02-01), Kelly et al.
patent: 4755951 (1988-07-01), Hollister
patent: 4800500 (1989-01-01), Tanaka
patent: 4926068 (1990-05-01), Fujita
Silicon Systems Inc.
Wolfe Willis R.
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