CIRCUIT AND METHOD FOR ADJUSTING AN OFFSET OUTPUT CURRENT FOR AN INPUT CURRENT AMPLIFIER

• US 20110148380A1
• Filed: 12/22/2010
• Published: 06/23/2011
• Est. Priority Date: 12/23/2009
• Status: Active Grant

• Current Assignee: Ateml Automotive GmbH, Arigna Technology Limited (Atlantic IP Services Limited)
• Original Assignee: Atmel Corporation (Microchip Technology Incorporated)
• Inventors: Prohaska, Armin, Saether, Terje, Vogelmann, Holger
• Granted Patent: US 8,289,082 B2
• Time in Patent Office: Days
• US Class Current: 323/284
• CPC Class Codes: H03F 2200/375 Circuitry to compensate the offset being present in an amplifier
• CPC Class Codes: H03F 2203/45648 the LC comprising two current sources, which are not cascode current sources
• CPC Class Codes: H03F 3/45179 using MOSFET transistors as the active amplifying circuit H03F3/45278 takes precedence

Abstract

A circuit and a method for correcting an offset is provided that includes a current amplifier and an adjusting circuit for correcting an offset of an output current of the current amplifier. Wherein the adjusting circuit has a controlled current source, an output of the controlled current source is connected to the current amplifier for impressing an output current of the controlled current source in the current amplifier, an input of the controlled current source to form a regulation element of a control loop is connected by a first switching device of the adjusting circuit to an output of the current amplifier and to form a holding element is disconnected from the output of the current amplifier by the first switching device. The controlled current source, acting as a regulation element in the control loop, is set up to regulate the offset to a minimum by setting of a current value of the output current, and the controlled current source, acting as a holding element, is set up to hold the current value, associated with the minimum, of the output current.

Claims

1. A circuit comprising:

a current amplifier; and

an adjusting circuit configured to correct an offset of an output current of the current amplifier, the adjusting circuit having a controlled current source and a first switching device,

wherein an output of the controlled current source is connectable to the current amplifier for impressing an output current of the controlled current source in the current amplifier,

wherein an input of the controlled current source is connectable by the first switching device of the adjusting circuit to an output of the current amplifier to form a regulation element of a control loop,

wherein the input of the controlled current source is disconnected from the output of the current amplifier by the first switching device to form a holding element,

wherein the controlled current source, acting as a regulation element in the control loop, is configured to regulate the offset to a minimum by setting a current value of the output current, and

wherein the controlled current source, acting as a holding element, is configured to hold the current value, associated with the minimum, of the output current.

2. The circuit according to claim 1, wherein the controlled current source has a capacitor.

3. The circuit according to claim 1, wherein the controlled current source is controllable by a control voltage.

4. The circuit according to claim 1, wherein the controlled current source has a transistor, which by means of a control voltage at the control input of the transistor controls the output current of the controlled current source.

5. The circuit according to claim 1, wherein the controlled current source has a storage device or a capacitor for storing the control voltage.

6. The circuit according to claim 5, wherein the capacitor of the controlled current source, which acts as a regulation element, is connectable to the output of the current amplifier by the first switching device for charging the capacitor until a steady state is attained for the minimum offset.

7. The circuit according to claim 1, wherein the current amplifier has a first current mirror and a second current mirror for current amplification, whose outputs are connected to the output of the current amplifier.

8. The circuit according to claim 1, wherein the adjusting circuit has a constant current source, which is connected to the current amplifier for impressing a constant current.

9. The circuit according to claim 8, wherein the current amplifier has a current summing node that is connectable to the output of the input current amplifier, wherein at least one first current and one second current are summed in the current summing node, wherein the first current is the output current of the controlled current source or is based on the output current of the controlled current source, and wherein the second current is the constant current of the constant current source or is based on the constant current of the constant current source.

10. The circuit according to claim 9, wherein the first current or the second current enters the summation with a negative sign.

11. The circuit according to claim 1, wherein the adjusting circuit has a second switching device that is connectable via an input of the adjusting circuit to the output of the current amplifier and to the circuit output.

12. The circuit according to claim 1, wherein the adjusting circuit has a third switching device, which is connectable to the capacitor and is configured to discharge a capacitor in a closed state.

13. The circuit according to claim 1, further comprising a control circuit that is configured to control the first switching device and is connectable to a first control terminal of the first switching device.

14. The circuit according to claim 11, further comprising a control circuit that is connectable to a second control terminal of the second switching device to control the second switching device.

15. The circuit according to claim 12, further comprising a control circuit that is connectable to a third control terminal of the third switching device to control the third switching device.

16. The circuit according to claim 1, further comprising a control circuit that is configured:

in a first step, to disconnect the output of the current amplifier from the circuit output by opening of the second switching device,

in a second step, to connect a capacitor of the controlled current source to the output of the current amplifier by closing the first switching device, after the second step the capacitor is charged by a charging current and by the charging of the capacitor an output current of the controlled current source is increased until the charging current attains a minimum,

in a third step, to disconnect the charged capacitor of the controlled current source from the output of the current amplifier by opening the first switching device, and

in a fourth step, to connect the output of the current amplifier to the circuit output by closing a second switching device.

17. A method for correcting an offset of an output current of a current amplifier of a circuit, the method comprising:

connecting a controlled current source to an output of the current amplifier via a first switching device, to form a regulation element of a control loop;

regulating an offset to a minimum by setting a current value of the output current of the controlled current source when an input signal of the current amplifier has a constant value, the controlled current source acting as the regulation element; and

disconnecting the controlled current source from the output of the current amplifier by the first switching device to form a holding element for holding the current value associated with the minimum of the output current.