Threshold detection circuit

• US 5,111,071 A
• Filed: 04/03/1991
• Issued: 05/05/1992
• Est. Priority Date: 10/19/1989
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kwan, Stephen C., Jones, Steven C.
• Primary Examiner(s): Zazworsky, John
• Application Number:
  US07/681,439
• Time in Patent Office: 398 Days
• Field of Search: 307/350, 307/362, 307/363
• US Class Current: 327/77
• CPC Class Codes: G01R 19/16576 comparing DC or AC voltage with one threshold G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533 and G01R19/1659 take precedence

Abstract

A threshold detection circuit (10) is provided which comprises an input node (12) and an output node (14). The input node (12) is coupled to a current mirror (22) through a resistor (32). The current mirror (22) is further coupled to another current mirror (16), which is arranged to receive a reference current proportional to absolute temperature. The reference current is mirrored and, having been increased by a multiplier is received by a current sink (28). When the voltage level at the input node (12) exceeds a predetermined voltage threshold level, the current exceeding the amount sinkable by the current sink (28) is directed to the base of a switching transistor (30) coupled to the output node (14), and produces an output voltage level at the output node (14) indicative of the threshold voltage level being reached an/or exceeded at the input node (12). The predetermined threshold voltage may be at a level exceeding the circuit supply voltage level and is independent of ambient operating temperature.

Claims

1. A threshold detection circuit comprising:

an input node for receiving an input voltage;

a first circuit coupled to a reference current;

a second circuit coupled to said first circuit, said second circuit producing a first current proportional to said reference current, wherein said first current is larger than said reference current;

a current sink coupled to said first current for sinking a portion of said current;

a resistive element coupled between said node and said second circuit; and

an output circuit coupled to said current sink, said output circuit providing an output voltage in response to said input voltage exceeding a predetermined threshold.

2. The threshold detection circuit, as set forth in claim 1, wherein said switching circuit is coupled to said output mode, said switching circuit being responsive to said first current having a magnitude larger than the current sinkable by said current sink.

3. The threshold detection circuit, as set forth in claim 1, wherein said switching circuit includes a first transistor having a base, a collector and an emitter, the base thereof coupled to said current sink and arranged to receive a portion of said first current.

4. The threshold detection circuit, as set forth in claim 3, wherein said switching circuit further comprises a second transistor having a base, a collector and an emitter, the collector thereof coupled to said output node, and the base thereof coupled to the collector of said first transistor, said second transistor being responsive to said first transistor receiving said portion of said first current and producing an output voltage at said output node.

5. The threshold detection circuit, as set forth in claim 1, further comprising at least one transistor having a base, a collector and an emitter, said collector and said base coupled to said second circuit and said emitter coupled to said current sink.

6. The threshold detection circuit, as set forth in claim 5, wherein said transistor base is coupled to said collector thereof.

7. The threshold detection circuit, as set forth in claim 5, further comprising:

a first resistor coupled between said base and collector of said transistor; and

a second resistor coupled between said base and emitter of said transistor.

8. The threshold detection circuit, as set forth in claim 1, wherein said reference current is proportional to absolute temperature.

9. The threshold detection circuit, as set forth in claim 1, wherein said predetermined threshold is proportional to a resistance of said resistive element.

10. The threshold detection circuit, as set forth in claim 1, wherein said input node exhibits high input impedance characteristics in response to the reference current being less than a predetermined value.

11. A threshold detection circuit comprising:

an input node;

a first current mirror for receiving a reference current and generating a first current having a magnitude of a first predetermined multiple of said reference current;

a second current mirror coupled to said first current mirror and generating a second current having a magnitude of a second predetermined multiple of said first current;

a current sink coupled to said second current mirror and arranged to sink a predetermined amount of said second current;

a resistor coupled between said input node and said second current mirror; and

a switching circuit coupled to said second current mirror and said current sink, said switching circuit being responsive to said input node having at least a predetermined threshold voltage level.

12. The threshold detection circuit, as set forth in claim 11, wherein said first current mirror comprises:

a first transistor having a base, an emitter and a collector, said base and collector coupled together;

a second transistor having a base, an emitter and a collector, said base coupled with said base of said first transistor; and

said second transistor emitter area being a first predetermined multiple of the area of said first transistor emitter.

13. The threshold detection circuit, as set forth in claim 12, wherein said second current mirror comprises:

a third transistor having a base, an emitter and a collector, said base and collector coupled together, and said collector coupled to said second transistor collector;

a fourth transistor having a base, an emitter and a collector, said base coupled with said third transistor base; and

said fourth transistor emitter area being a second predetermined multiple of the area of said third transistor emitter.

14. The threshold detection circuit, as set forth in claim 12, wherein said current sink comprises a third transistor having a base, an emitter and a collector, said third transistor base coupled with said first and second transistor bases.

15. The threshold detection circuit, as set forth in claim 11, further comprising at least one transistor having a base, a collector and an emitter, said transistor coupled between said second current mirror and said current sink.

16. The threshold detection circuit, as set forth in claim 15, wherein said transistor base is coupled to the collector thereof.

17. The threshold detection circuit, as set forth in claim 15, further comprising:

a first resistor coupled between said base and collector of said transistor; and

a second resistor coupled between said base and emitter of said transistor.

18. The threshold detection circuit, as set forth in claim 11, wherein said switching circuit includes a first transistor having a base, a collector and an emitter, the base thereof coupled to said current sink and arranged to receive a portion of said second current.

19. The threshold detection circuit, as set forth in claim 18, further comprising a second transistor having a base, a collector and an emitter, the collector thereof coupled to the collector of said first transistor, and the emitter thereof coupled to a supply voltage.

20. The threshold detection circuit, as set forth in claim 19, further comprising a third transistor having a base, a collector and an emitter, the base thereof coupled to the collector of said first transistor, and said output node coupled to the collector of said third transistor.

21. The threshold detection circuit, as set forth in claim 11, wherein said reference current is proportional to absolute temperature.

22. The threshold detection circuit, as set forth in claim 11, wherein said threshold voltage level is adjustable by varying the value of said resistor.

23. The threshold detection circuit, as set forth in claim 11, being operable to detect a threshold voltage level exceeding a circuit supply voltage level.

24. The threshold detection circuit, as set forth in claim 11, wherein said input node exhibits high input impedance characteristics in response to said reference current being less than a predetermined value.

25. A threshold detection circuit comprising:

an input node for receiving an input voltage;

a first resistor coupled in series with said input node;

a first current mirror arranged to receive a reference current and to reproduce and sink a first current having a magnitude of a multiple of said reference current;

a second current mirror coupled to said first current mirror and adapted to reproduce and source a second current having a magnitude of a multiple of said first current magnitude, said second current mirror coupled with said resistor;

a first transistor having a base, a collector and an emitter, said collector coupled with said second current mirror, said first transistor adapted to sink a predetermined amount of said second current;

a second transistor having a base, a collector and an emitter, said base coupled to said first transistor collector and adapted to receive any of said second current in excess of current sinkable by said first transistor;

a third transistor having a base, a collector and an emitter, said base coupled with said second transistor collector; and

an output node coupled to said third transistor collector, said output node providing an output voltage responsive to said input voltage exceeding a predetermined threshold.

26. A method for detecting a threshold, said method comprising the steps of:

supplying an input voltage to an input node;

providing a resistive element coupled to said input node;

receiving a reference current;

producing a first current which is a predetermined multiple of said reference current;

drawing a second current through said resistive element which is a predetermined multiple of said first current;

sinking a predetermined portion of said second current;

driving a switching circuit with a portion of said first current in excess of said sink portion; and

producing an output voltage at an output node coupled to said switching circuit, said output voltage being responsive to said input voltage exceeding said threshold.

27. The method, as set forth in claim 26, wherein said step of providing a resistive element comprises selecting a resistance value whereby said threshold is proportional to said resistance value.

28. A method for constructing a threshold detecting circuit, said method comprising the steps of:

providing an input node having an input voltage;

providing a resistive element coupled to said input node;

forming a first circuit for receiving a reference current and producing a first current proportional to said reference current in magnitude;

forming a second circuit coupled to said resistive element for receiving said first current and drawing a second current through said resistive element proportional to said first current in magnitude;

forming a current sink arranged to sink a portion of said second current; and

providing an output node coupled to said current sink, said output node providing an output voltage responsive to said input voltage exceeding a predetermined threshold.