VOLTAGE COMPARISON CIRCUIT, AND SEMICONDUCTOR INTEGRATED CIRCUIT AND ELECTRONIC DEVICE HAVING THE SAME

• US 20090206806A1
• Filed: 02/09/2009
• Published: 08/20/2009
• Est. Priority Date: 02/14/2008
• Status: Active Grant

• Current Assignee: RICOH Electronic Devices Co., Ltd. (Nisshinbo Holdings Incorporated)
• Original Assignee: Ricoh Company Limited
• Inventors: KAMATANI, Tomohiko
• Granted Patent: US 7,940,036 B2
• Time in Patent Office: Days
• US Class Current: 323/273
• CPC Class Codes: H03F 2203/45101 Control of the DC level being present
• CPC Class Codes: H03F 2203/45354 the AAC comprising offset means
• CPC Class Codes: H03F 2203/45392 the AAC comprising resistors in the source circuit of the AAC before the common source coupling
• CPC Class Codes: H03F 2203/45674 the LC comprising one current mirror
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence

Abstract

A disclosed voltage comparison circuit for detecting a voltage difference of two input signals includes one or more differential amplifier circuits, each of which has a differential pair of first and second input transistors each having an electrode to which a corresponding one of the input signals is input, a constant current circuit configured to generate constant current according to a control signal and supply the constant current to the first and second input transistors, and a first resistor connected between the constant current circuit and the first input transistor; and a current control circuit configured to control a value of the first constant current. The current control circuit controls the value so that a voltage difference between both ends of the first resistor becomes equal to a predetermined value.

Claims

1. A voltage comparison circuit for detecting a voltage difference of two input signals, the voltage comparison circuit comprising:

one or more differential amplifier circuit units, each of which includes a differential pair of a first input transistor and a second input transistor each input transistor having a control electrode to which a corresponding one of the input signals is input, a constant current circuit unit configured to generate a first constant current in accordance with an input control signal and supply the first constant current to the first input transistor and the second input transistor, and a first resistor connected between the constant current circuit unit and the first input transistor; and

a current control circuit unit configured to perform operational control on the constant current circuit unit to control a current value of the first constant current;

wherein the current control circuit unit controls the current value of the first constant current so that a voltage difference between both ends of the first resistor becomes equal to a predetermined value.

2. The voltage comparison circuit as claimed in claim 1, wherein the current control circuit unit includes a proportional current generating circuit configured to generate and output a proportional current proportional to the first constant current output from the constant current circuit unit;

a second resistor through which the proportional current output from the proportional current generating circuit flows;

a subtraction circuit configured to calculate and output a voltage difference between both ends of the second resistor; and

a control circuit configured to perform operational control on the constant current circuit unit and the proportional current generating circuit in such a manner that the voltage difference output from the subtraction circuit becomes equal to a predetermined reference voltage.

3. The voltage comparison circuit as claimed in claim 2, further comprising a load circuit unit functioning as a load of the differential pair and including a first load circuit connected in series to the first input transistor and a second load circuit connected in series to the second input transistor, wherein the current control circuit unit includes a third transistor connected in series to the second resistor and having a control electrode to which a signal is input so that the third transistor is always ON to be conductive, and a third load circuit configured to function as a load of the third transistor.

4. The voltage comparison circuit as claimed in claim 1, wherein the current control circuit unit includes a proportional current generating circuit configured to generate and output a proportional current proportional to the first constant current output from the constant current circuit unit;

a second resistor through which the proportional current output from the proportional current generating circuit flows; and

a control circuit configured to control a current value of the proportional current flowing through the second resistor so that a voltage difference between both ends of the second resistor becomes equal to a predetermined reference voltage.

5. The voltage comparison circuit as claimed in claim 4, wherein the proportional current generating circuit is an input transistor of a current mirror circuit, and the constant current circuit unit is an output transistor-of the current mirror circuit.

6. The voltage comparison circuit as claimed in claim 2, wherein the second resistor has a resistance value equal to a resistance value of the first resistor.

7. The voltage comparison circuit as claimed in claim 3, wherein the first input transistor, the second input transistor and the third transistor are MOS transistors of a same type, having a same transistor size.

8. The voltage comparison circuit as claimed in claim 3, wherein the first load circuit, the second load circuit and the third load circuit are MOS transistors of a same type, having a same transistor size.

9. The voltage comparison circuit as claimed in claim 2, wherein the constant current circuit unit is formed of a first transistor for outputting current in accordance with the input control signal which is input from the current control circuit unit to a control electrode of the first transistor, the proportional current generating circuit is formed of a second transistor for outputting current in accordance with the input control signal which is input from the current control circuit unit to a control electrode of the second transistor, and the second transistor outputs the proportional current proportional to the current output from the first transistor.

10. The voltage comparison circuit as claimed in claim 9, wherein the first transistor and the second transistor are MOS transistors of a same type, and the first transistor has twice a transistor size of the second transistor.

11. The voltage comparison circuit as claimed in claim 1, further comprising:

a third resistor connected between the constant current circuit unit and the second input transistor;

a first switching unit configured to short-circuit the first resistor; and

a second switching unit configured to short-circuit the third resistor;

wherein the first switching unit and the second switching unit perform opposite switching operations in accordance with the signal indicating the result of the detection, the signal being binary.

12. The voltage comparison circuit as claimed in claim 1, further comprising a fourth resistor connected between the second input transistor and the second load circuit.

13. The voltage comparison circuit as claimed in claim 1, wherein when two or more differential amplifier circuit units are disposed, the current control circuit unit controls the current value of the first constant current of each of the differential amplifier circuit units so that the voltage difference between the both ends of the first resistor becomes equal to the predetermined value.

14. A semiconductor integrated circuit having a voltage comparison circuit for detecting a voltage difference of two input signals, wherein the voltage comparison circuit includes one or more differential amplifier circuit units, each of which includes a differential pair of a first input transistor and a second input transistor each input transistor having a control electrode to which a corresponding one of the input signals is input, a constant current circuit unit configured to generate a first constant current in accordance with an input control signal and supply the first constant current to the first input transistor and the second input transistor, and a first resistor connected between the constant current circuit unit and the first input transistor;

and a current control circuit unit configured to perform operational control on the constant current circuit unit to control a current value of the first constant current, wherein the current control circuit unit controls the current value of the first constant current so that a voltage difference between both ends of the first resistor becomes equal to a predetermined value.

15. An electronic device having a predetermined function and including a semiconductor integrated circuit, wherein the semiconductor integrated circuit has a voltage comparison circuit for detecting a voltage difference of two input signals, wherein the voltage comparison circuit includes one or more differential amplifier circuit units, each of which includes a differential pair of a first input transistor and a second input transistor each input transistor having a control electrode to which a corresponding one of the input signals is input, a constant current circuit unit configured to generate a first constant current in accordance with an input control signal and supply the first constant current to the first input transistor and the second input transistor, and a first resistor connected between the constant current circuit unit and the first input transistor;

and a current control circuit unit configured to perform operational control on the constant current circuit unit to control a current value of the first constant current, wherein the current control circuit unit controls the current value of the first constant current so that a voltage difference between both ends of the first resistor becomes equal to a predetermined value.