Current comparator

• US 5,446,397 A
• Filed: 02/25/1993
• Issued: 08/29/1995
• Est. Priority Date: 02/26/1992
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Yotsuyanagi, Michio
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): LAM, TUAN THIEU
• Application Number:
  US08/022,290
• Time in Patent Office: 915 Days
• Field of Search: 307/354, 307/355, 307/358, 307/362, 307/363, 307/490, 307/494, 307/296.1, 307/296.6, 307/296.5, 323/313, 323/315, 327/58, 327/60, 327/62, 327/63, 327/66, 327/68, 327/70, 327/72, 327/77-79, 327/82, 327/85, 327/88, 330/288
• US Class Current: 327/66
• CPC Class Codes: H03K 5/2472 using field effect transistors H03K5/2436 takes precedence

Abstract

Current output terminals of first and second current mirror circuits are connected. An input terminal of a third current mirror circuit is connected to a node of the current output terminals of the first and second current mirror circuits. A load circuit is connected between a current output terminal of the third current mirror circuit and a first voltage. An output terminal is connected to the load circuit. First and second currents to be compared with each other are supplied to current input terminal of the first and second current mirror circuits.

Claims

1. A current comparator, comprising:

first and second input terminal to which first and second currents to be compared are supplied;

a first current mirror circuit, whose current input terminal is coupled to the first input terminal;

a second current mirror circuit, whose current input terminal is coupled to the second input terminal and whose current output terminal is coupled to an current output terminal of the first current mirror circuit;

a third current mirror circuit, whose current input terminal is coupled to a node of the current output terminals of the first and second current mirror circuits;

a load circuit coupled between a current output terminal of the third current mirror circuit and a terminal to which a first voltage is applied; and

a comparison result output terminal coupled to the load circuit.

2. The current comparator circuit according to claim 1, wherein the first current mirror circuit is comprised of a first-conductivity-type transistor and the second current mirror circuit is comprised of a second-conductivity-type transistor, the second-conductivity-type being different from the first-conductivity-type.

3. The current comparator according to claim 1, wherein the load circuit is comprised of any one of a resistor, a variable resistor and a transistor.

4. The current comparator according to claim 1, wherein the load circuit is comprised of a switch coupled to the third current mirror circuit and a load coupled between the switch and the terminal to which the first voltage is applied, and the comparison result output terminal is coupled to a node of the switch and the load.

5. The current comparator according to claim 1, wherein the load circuit is comprised of:

a first transistor of a first conductivity type having a current path whose one terminal is coupled to the current output terminal of the third current mirror circuit; and

a second transistor of a second conductivity type different from the first conductivity type and having a current path whose one terminal is coupled to the terminal to which the first voltage is applied and the other terminal thereof is coupled to the other terminal of the current path of the first transistor;

and wherein a common control signal is supplied to the first and second transistors.

6. A current comparator, comprising:

first circuit means, having a first input terminal and a first output terminal, for flowing through the first output terminal a current equivalent to a current supplied to the first input terminal;

second circuit means having a second input terminal to which a second current is supplied and a second output terminal coupled to the first output terminal, for flowing the second current through the second output terminal when the first current is larger than the second current and for flowing the first current through the second output terminal when the first current is smaller than the second current;

third circuit means having a third output terminal and a third input terminal coupled to a node of the first and second output terminals, for receiving at the third input terminal the difference of the first and second currents and flowing a current equivalent to the difference through the third output terminal when the first current is larger than the second current, and for receiving no current at the third input terminal and for setting the third output terminal to an open state when the first current is smaller than the second current; and

a load circuit coupled between the third output terminal and a terminal to which a predetermined voltage is supplied; and

a comparison result output terminal coupled to the load circuit.

7. The current comparator according to claim 6, wherein the first current mirror circuit is comprised of a first-conductivity-type transistor and the second current mirror circuit is comprised of a second-conductivity-type transistor, the second-conductivity-type being different from the first-conductivity-type.

8. The current comparator according to claim 7, wherein the first through third circuit means comprise first through third current mirror circuits, respectively.

9. The current comparator according to claim 6, wherein the load circuit is comprised of any one of a resistor, a variable resistor, and a transistor.

10. The current comparator according to claim 6, further comprising a switch coupled between the load circuit and the third circuit means and wherein the comparison result output terminal is coupled to a node of the switch and the load circuit.

11. The current comparator according to claim 6, wherein the load circuit comprises:

a first transistor of a first conductivity type having a current path whose one terminal is coupled to the third output terminal; and

a second transistor of a second conductivity type different from the first conductivity type and having a current path whose one terminal is coupled to the terminal to which the predetermined voltage is applied and the other terminal thereof is coupled to the other terminal of the current path of the first transistor;

and wherein a common control signal is supplied to the first and second transistors.