Active RC resonators with enhanced Q factor

• US 8,410,962 B2
• Filed: 01/19/2011
• Issued: 04/02/2013
• Est. Priority Date: 01/19/2011
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Shibata, Hajime, Schreier, Richard
• Primary Examiner(s): NGUYEN, LINH V
• Application Number:
  US13/009,015
• Publication Number:
  US 20120182168A1
• Time in Patent Office: 804 Days
• Field of Search: 341/143, 341/155, 327/336, 327/551, 327/553, 327/559
• US Class Current: 341/143
• CPC Class Codes: H03H 11/1204 Distributed RC filters
• CPC Class Codes: H03H 11/1252 Two integrator-loop-filters
• CPC Class Codes: H03H 11/1291 Current or voltage controlled filters
• CPC Class Codes: H03M 3/396 among different frequency bands
• CPC Class Codes: H03M 3/406 by the use of a pair of integrators forming a closed loop

Abstract

An active RC resonator includes a first operational amplifier having first and second inputs and first and second outputs, a second operational amplifier having first and second inputs and first and second outputs, a first resistor coupled between the first input of the first operational amplifier and the second output of the second operational amplifier, a second resistor coupled between the second input of the first operational amplifier and the first output of the second operational amplifier, a third resistor coupled between the first output of the first operational amplifier and the first input of the second input of the second operational amplifier, a fourth resistor coupled between the second output of the first operational amplifier and the second input of the second operational amplifier, and at least one of 1) a first capacitor coupled between the first input of the first operational amplifier and the first output of the second operational amplifier, and a second capacitor coupled between the second input of the first operational amplifier and the second output of the second operational amplifier, 3) a third capacitor coupled between the second output of the first operational amplifier and the first input of the second operational amplifier, and a fourth capacitor coupled between the first output of the first operational amplifier and the second input of the second operational amplifier.

Claims

1. An active RC resonator, comprising:

a first differential integrator;

a second differential integrator, wherein first and second inputs of the first differential integrator are respectively coupled to second and first outputs of the second differential integrator via first and second signal paths, and first and second outputs of the first differential integrator are respectively coupled to first and second inputs of the second differential integrator via third and fourth signal paths, each of the first, second, third, and fourth signal paths including a respective resistor; and

at least one of;

1) a first capacitor coupled from the first output of the second differential integrator to the first input of the first differential integrator, and a second capacitor coupled from the second output of the second differential integrator to the second input of the first differential integrator,

2) a third capacitor coupled from the first output of the first differential integrator to the second input of the second differential integrator, and a fourth capacitor coupled from the second output of the first differential integrator to the first input of the second differential integrator.

2. The active RC resonator of claim 1, wherein each of the resistors in the first, second, third, and fourth signal paths is a tunable resistor, and wherein the tunable resistors in the first and the second signal paths have a first resistance, and the tunable resistors in the third and the fourth signal paths have a second resistance.

3. The active RC resonator of claim 2, wherein the tunable resistors in the first, second, third, and fourth signal paths vary the resistance by switching a set of MOSFET switches, and wherein the switching generates parasitic capacitances to each of the tunable resistors in the first, second, third, and fourth signal paths.

4. The active RC resonator of claim 3, wherein the first, second, third, and fourth capacitors are tunable capacitors.

5. An active RC resonator, comprising:

a first differential integrator;

a second differential integrator, wherein first and second inputs of the first differential integrator are respectively coupled to second and first outputs of the second differential integrator via first and second signal paths, and first and second outputs of the first differential integrator are respectively coupled to first and second inputs of the second differential integrator via third and fourth signal paths; and

at least one of;

1) a first capacitor coupled from the first output of the second differential integrator to the first input of the first differential integrator, and a second capacitor coupled from the second output of the second differential integrator to the second input of the first differential integrator,

2) a third capacitor coupled from the first output of the first differential integrator to the second input of the second differential integrator, and a fourth capacitor coupled from the second output of the first differential integrator to the first input of the second differential integrator,

wherein capacitances of the first and second capacitors are set to a level such that the set capacitances of the first and the second capacitors equal or substantially equal the parasitic capacitance in the first and second signal paths, wherein capacitances of the third and fourth capacitors are set to a level such that the set capacitances of the third and fourth capacitors equal or substantially equal the parasitic capacitances in the fourth and third signal paths.

6. An active RC resonator, comprising:

a first differential integrator;

a second differential integrator, wherein first and second inputs of the first differential integrator are respectively coupled to second and first outputs of the second differential integrator via first and second signal paths, and first and second outputs of the first differential integrator are respectively coupled to first and second inputs of the second differential integrator via third and fourth signal paths; and

at least one of;

1) a first capacitor coupled from the first output of the second differential integrator to the first input of the first differential integrator, and a second capacitor coupled from the second output of the second differential integrator to the second input of the first differential integrator,

2) a third capacitor coupled from the first output of the first differential integrator to the second input of the second differential integrator, and a fourth capacitor coupled from the second output of the first differential integrator to the first input of the second differential integrator,

wherein capacitances of the first and second capacitors are set to a level such that the set capacitances of the first and the second capacitors are larger than the parasitic capacitance in the first and second signal paths, wherein capacitances of the third and fourth capacitors are set to a level such that the set capacitances of the third and fourth capacitors are larger than the parasitic capacitances in the fourth and third signal paths.

7. An active RC resonator, comprising:

a first operational amplifier having first and second inputs and first and second outputs;

a second operational amplifier having first and second inputs and first and second outputs;

a first resistor coupled between the first input of the first operational amplifier and the second output of the second operational amplifier;

a second resistor coupled between the second input of the first operational amplifier and the first output of the second operational amplifier;

a third resistor coupled between the first output of the first operational amplifier and the first input of the second input of the second operational amplifier;

a fourth resistor coupled between the second output of the first operational amplifier and the second input of the second operational amplifier; and

at least one of;

1) a first capacitor coupled between the first input of the first operational amplifier and the first output of the second operational amplifier, and a second capacitor coupled between the second input of the first operational amplifier and the second output of the second operational amplifier,

2) a third capacitor coupled between the second output of the first operational amplifier and the first input of the second operational amplifier, and a fourth capacitor coupled between the first output of the first operational amplifier and the second input of the second operational amplifier.

8. The active RC resonator of claim 7, wherein the first and second resistors are tunable resistors and have a first resistance, and the third and fourth resistors are tunable resistors and have a second resistance.

9. The active RC resonator of claim 8, wherein the first, second, third, and fourth tunable resistors vary the resistance by switching a set of MOSFET switches, and wherein the switching generates parasitic capacitances to each of the first, second, third, and fourth tunable resistors.

10. The active RC resonator of claim 9, wherein the first, second, third, and fourth capacitors are tunable capacitors.

11. The active RC resonator of claim 10, wherein capacitances of the first and second capacitors are set to a level such that the set capacitances of the first and the second capacitors equal or substantially equal the parasitic capacitances associated with the first and second resistors, wherein capacitances of the third and fourth capacitors are set to a level such that the set capacitances of the third and fourth capacitors equal or substantially equal the parasitic capacitances associated with the third and fourth resistors.

12. The active RC resonator of claim 10, wherein capacitances of the first and second capacitors are set to a level such that the set capacitances of the first and the second capacitors are larger than the parasitic capacitances associated with the first and second resistors, wherein capacitances of the third and fourth capacitors are set to a level such that the set capacitances of the third and fourth capacitors are larger than the parasitic capacitances associated with the third and fourth resistors.

13. A loop filter, comprising:

an active RC resonator that includes;

a first differential integrator;

a second differential integrator, wherein first and second inputs of the first differential integrator are respectively coupled to second and first outputs of the second differential integrator via first and second signal paths, and first and second outputs of the first differential integrator are respectively coupled to first and second inputs of the second differential integrator via third and fourth signal paths, each of the first, second, third, and fourth signal paths including a respective resistor; and

at least one of;

1) a first capacitor coupled from the first output of the second differential integrator to the first input of the first differential integrator, and a second capacitor coupled from the second output of the second differential integrator to the second input of the first differential integrator,

2) a third capacitor coupled from the first output of the first differential integrator to the second input of the second differential integrator, and a fourth capacitor coupled from the second output of the first differential integrator to the first input of the second differential.

14. A loop filter, comprising:

an active RC resonator that includes;

a first operational amplifier having first and second inputs and first and second outputs;

a second operational amplifier having first and second inputs and first and second outputs;

a first resistor coupled between the first input of the first operational amplifier and the second output of the second operational amplifier;

a second resistor coupled between the second input of the first operational amplifier and the first output of the second operational amplifier;

a third resistor coupled between the first output of the first operational amplifier and the first input of the second input of the second operational amplifier;

a fourth resistor coupled between the second output of the first operational amplifier and the second input of the second operational amplifier; and

at least one of;

1) a first capacitor coupled between the first input of the first operational amplifier and the first output of the second operational amplifier, and a second capacitor coupled between the second input of the first operational amplifier and the second output of the second operational amplifier,

2) a third capacitor coupled between the second output of the first operational amplifier and the first input of the second operational amplifier, and a fourth capacitor coupled between the first output of the first operational amplifier and the second input of the second operational amplifier.

15. An analog-to-digital converter, comprising:

at least one loop filter, wherein the at least one loop filter includes;

an active RC resonator that includes;

a first differential integrator;

a second differential integrator, wherein first and second inputs of the first differential integrator are respectively coupled to second and first outputs of the second differential integrator via first and second signal paths, and first and second outputs of the first differential integrator are respectively coupled to first and second inputs of the second differential integrator via third and fourth signal paths, each of the first, second, third, and fourth signal paths including a respective resistor; and

at least one of;

1) a first capacitor coupled from the first output of the second differential integrator to the first input of the first differential integrator, and a second capacitor coupled from the second output of the second differential integrator to the second input of the first differential integrator,

2) a third capacitor coupled from the first output of the first differential integrator to the second input of the second differential integrator, and a fourth capacitor coupled from the second output of the first differential integrator to the first input of the second differential integrator.

16. An analog-to-digital converter, comprising:

at least one loop filter, wherein the at least one loop filter includes;

an active RC resonator that includes;

a first operational amplifier having first and second inputs and first and second outputs;

a second operational amplifier having first and second inputs and first and second outputs;

a first resistor coupled between the first input of the first operational amplifier and the second output of the second operational amplifier;

a second resistor coupled between the second input of the first operational amplifier and the first output of the second operational amplifier;

a third resistor coupled between the first output of the first operational amplifier and the first input of the second input of the second operational amplifier;

a fourth resistor coupled between the second output of the first operational amplifier and the second input of the second operational amplifier; and

at least one of;

1) a first capacitor coupled between the first input of the first operational amplifier and the first output of the second operational amplifier, and a second capacitor coupled between the second input of the second operational amplifier and the first output of the second operational amplifier,

2) a third capacitor coupled between the second output of the first operational amplifier and the first input of the second operational amplifier, and a fourth capacitor coupled between the first output of the first operational amplifier and the second input of the second operational amplifier.