US3725673A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Switching circuit with hysteresis
Assignee: Motorola Solutions Inc
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Filing: 1971-08-16
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Granted: 1973-04-03
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Expires: 1991-08-16
Abstract
Abstract There is disclosed a switching circuit with a controllable hysteresis in which the hysteresis is introduced into the circuit through a feedback circuit which is connected to an internal node of the switching circuit. The input to the switching circuit is therefore independent of the hysteresis feedback circuit. The switching circuit is comprised first of a comparator which includes a differential amplifier, a differential-to-single-ended convertor, and ON-OFF biased output circuitry such that when an input signal is above a predetermined reference voltage, the switch is in an ''''open'''' condition and such that when the input signal falls below this predetermined reference voltage, the switch is in a ''''closed'''' or conducting condition. Hysteresis is introduced into the comparator circuit by selectively adding a predetermined amount of current to one or the other of the output nodes of the differential amplifier in the comparator circuit during times correlated with the operating condition of the switching circuit. This additional current raises or lowers the input voltage which is necessary to change the condition of the switching circuit and thus introduces a hysteresis into the circuit. The magnitude of the hysteresis is adjustable by controlling the amount of current delivered to the output nodes of the differential amplifier in the comparator. By the application of the hysteresis-producing current to the appropriate output nodes of the input differential amplifier, the hysteresis can be made to occur to one side or the other of the aforementioned reference voltage. Additionally, the hysteresis may be centered about this reference voltage.
Inventors
- 👤 T Frederiksen
- 👤 R Russell
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 15:30
CPC Classifications
H; H03; H03K; H03K3/00; H03K3/02; H03K3/26; H03K3/28; H03K3/281; H03K3/286; H03K3/2893; H03K3/2897
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
145 words
In a switching circuit, having a comparator, the comparator comprising a first differential amplifier having an input node for receiving an input signal and two output nodes connected to a first differential-to-single-ended-convertor, and output circuitry having associated with it two discrete states, connected to the first digital-to-single-ended-convertor and having a pair of output terminals for connection to a load, means for introducing hysteresis into the switching circuit comprising: a. selection means, having a pair of output legs, for monitoring the state of the output circuitry and selecting one of the output legs dependent upon the state; b. means, responsive to the selection means, for generating a current and causing the current to flow through the selected leg, the magnitude of the current determining the magnitude of the hysteresis; and c. means for connecting the selected leg to at least one of the two output nodes.
Claim 2
Dependent Claim
145 words
In a switching circuit, having a comparator, the comparator comprising a first differential amplifier having an input node for receiving an input signal and two output nodes connected to a first differential-to-single-ended-convertor, and output circuitry having associated with it two discrete states, connected to the first digital-to-single-ended-convertor and having a pair of output terminals for connection to a load, means for introducing hysteresis into the switching circuit comprising: a. selection means, having a pair of output legs, for monitoring the state of the output circuitry and selecting one of the output legs dependent upon the state; b. means, responsive to the selection means, for generating a current and causing the current to flow through the selected leg, the magnitude of the current determining the magnitude of the hysteresis; and c. means for connecting the selected leg to at least one of the two output nodes.
Claim 3
Dependent Claim
37 words
The switching circuit of claim 1 wherein the output circuitry further comprises a first saturable transistor, driven by the first differential-to-single-ended-convertor, the main electrodes for the first saturable transistor being the output terminals of the switching circuit.
Claim 4
Dependent Claim
107 words
The switching circuit recited in claim 2 wherein said selection means comprises: a current toggling circuit, coupled to said means for generating current for switching said current to one of two output legs; and means for sEnsing the condition of said first saturable transistor and for causing said current toggling circuit to switch current into a predetermined output leg thereof in response to a predetermined condition of said saturable transistor, whereby the direction of the hysteresis with respect to a reference potential applied to one of said input nodes is determined by to which output node of said first differential amplifier the current carrying leg is coupled.
Claim 5
Dependent Claim
56 words
The switching circuit as recited in claim 3 wherein that output leg of said current toggling circuit carrying current is coupled to that output node of said first differential amplifier, which due to an increase in current thereat has caused said switching circuit to change state, said hysteresis current thereby tending to preserve said changed state.
Claim 6
Dependent Claim
30 words
The switching circuit as recited in claim 4 wherein that output leg of said current toggling circuit not connected to an output node of said first differential amplifier is grounded.
Claim 7
Dependent Claim
51 words
The switching circuit as recited in claim 3 wherein one output leg of said current toggling circuit is permanently coupled to one of the output nodes of said first differential amplifier with the other of said output legs being grounded, whereby said hysteresis is to one side of said reference potential.
Claim 8
Dependent Claim
32 words
The switching circuit as recited in claim 3 wherein different output legs are coupled to different output nodes of said first differential amplifier whereby said hysteresis is centered about said reference potential.
Claim 9
Dependent Claim
89 words
The switching circuit as recited in claim 3 wherein said means for generating a current includes a second differential amplifier, a second differential-to-single-ended convertor, the output of said second differential-to-single-ended convertor being coupled to the input to said current toggle circuit, and means for applying a DC potential across the inputs to said second differential amplifier having a polarity so as to cause said current to flow, the magnitude of said hysteresis being dependent on the magnitude of the potential difference at the inputs to said second differential amplifier.
Claim 10
Dependent Claim
74 words
The switching circuit as recited in claim 8 wherein said first and second differential amplifiers have matched characteristics and include matched current sources for driving them, whereby the magnitude of the potential difference at the inputs of said second differential amplifier equals the magnitude of said hysteresis when only one of said output legs is connected to an output node of said first differential amplifier and whenever both of said differential amplifiers are balanced.
Claim 11
Dependent Claim
75 words
The switching circuit as recited in claim 8 wherein said current toggling circuit includes a third differential amplifier and a second saturable transistor coupled between one of the inputs to said third differential amplifier and ground, the state of said second saturable transistor controlling to which of said output legs said current is switched, the state of saturation of said second saturable transistor being controlled by the state of saturation of said first saturable transistor.
Claim 12
Dependent Claim
89 words
The switching circuit as recited in claim 10 wherein all of said differential amplifiers include two pairs of PNP transistors, the base of a first transistor in each pair coupled to the emitter of the second transistor in each pair, with the emitters of the first transistors of each pair being interconnected, the bases of the second transistors in each pair being the input nodes of each differential amplifier and the collectors of said first transistors of each pair being the output nodes or legs of said differential amplifiers.
Claim 13
Dependent Claim
40 words
The switching circuit as recited in claim 10 and further including means coupled to said first differential-to-single-ended convertor for adjusting the balance of said first differential amplifier thereby adjusting the offset of said hysteresis with respect to said reference potential.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-04-02 | 1976-10-02 | 1977-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-04-02 | 1980-10-02 | 1981-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-04-02 | 1984-10-02 | 1985-04-03 | $7700.00 | Window Closed / Lapsed |