Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Patent
1994-06-15
1995-10-31
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
327205, 327344, 327517, 327 89, H03K 3037, H03K 5153, G06G 764
Patent
active
054633338
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a combined integrator and level detector circuit with switched hysteresis and temperature compensation, which is suitable for implementation in an integrated circuit. This configuration is usable in sensors and in particular, inductive proximity switches.
According to one aspect of the invention there is provided a proximity switch including an integrator arranged to provide a supplementary current source which is responsive to an output from a sensing circuit of the proximity switch to provide switched hysteresis.
According to a second aspect of the present invention there is provided an integrator with switched hysteresis for inductive proximity switches comprising a reference current source connected between a reference voltage supply rail and a first side of a current mirror, a second side of the current mirror being connected to a proximity switch rectifier, the first side of the current mirror further being connected with a capacitor and also to one input of a two input comparator, the other input of the comparator being held at a threshold level, wherein a fixed hysteresis current source is provided in parallel with the reference current source, the fixed hysteresis current source producing a switchable current which is a fixed proportion of the current of the reference current source, the fixed hysteresis current source being switched on (off) when a target is detected and off (on) when no target is detected.
The reference current source may be provided by a current mirror comprising two transistors having a predetermined area ratio.
The hysteresis current source may be provided by a second output of the reference current mirror comprising a third transistor having an n:l area ratio with a first of the two transistors, wherein n is any number.
Emitter resistors may be provided on an input side and/or an output side of the current mirrors, which permits large current ratios to be achieved without the cost of larger transistor area ratios. This also allows the temperature coefficient to be preset in magnitude and direction to offset the intrinsic temperature coefficient of the sensor disclosed in co-pending GB 91 27 570.1.
The comparator may have a first output used to drive an output from the sensor.
The comparator may further have a second output which controls a switch which is used to switch the detection hysteresis current on or off.
The comparator may have a third output which modifies the comparator threshold to improve electrical noise immunity and be less affected by ripple on the signal current.
Preferably, the second and third outputs are connected to first and second saturating transistors.
Preferably, a diode is provided, the cathode of which is connected to the hysteresis current source, and the anode of which is connected to the capacitor.
Preferably, the voltage across the integrating capacitor is limited close to the comparator threshold. This may be done by providing PNP and NPN transistors, their bases being connected to the comparator threshold, while their emitters are connected to the capacitor, their collectors being connected to respective reference supply rails. This increases the operating speed of the proximity switch.
According to another aspect of the present invention there is provided an integrated circuit for use in an integrator as hereinbefore described.
Various embodiments of the invention will now be described by way of example only with reference to the accompanying drawings which are:
FIG. 1. A schematic circuit diagram of a typical basic integrator;
FIG. 2. A schematic circuit diagram of an integrator according to the present invention;
FIG. 3. A curve showing hysteresis achieved by switching the oscillator operating point;
FIG. 4. A curve showing hysteresis as employed in the present invention;
FIG. 5. A first embodiment of reference and hysteresis current sources for use in an integrator according to the present invention;
FIG. 6. A second embodiment of reference and hysteresis current sources for use in an integrator according to the
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patent: 3440448 (1969-04-01), Dudley
patent: 3889200 (1975-06-01), Tyau
patent: 4414512 (1983-11-01), Nelson
patent: 4421995 (1983-12-01), Gottschalk
patent: 4766335 (1988-08-01), Shiraishi et al.
patent: 5397946 (1995-03-01), Truong et al.
Bizley Arthur J.
Calder Douglas W.
Callahan Timothy P.
Femal Michael J.
Golden Larry I.
Shrout Larry T.
Square D Company
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