Amplifier feedback switch configuration with improved PSRR

Abstract

A circuit including a first sensitive node, a first component connected between the first sensitive node and a first terminal of a first switch, said first switch controlled by a first control signal variable between a supply voltage level and a second voltage level, and a second switch including a first terminal connected to the first terminal of said first switch, and a second terminal connected to a clean voltage supply, said second switch controlled to connect the first node of said first switch to said clean voltage supply when said first switch is in a non-conducting state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, discussed above, illustrates a known switch;

FIG. 2 illustrates the switch of FIG. 1 in more detail;

FIG. 3 illustrates an inversing amplifying circuit comprising a number of switches arranged according to the present invention;

FIG. 4 illustrates one of the switches of FIG. 3 in more detail according to one embodiment;

FIGS. 5A and 5B illustrate the feedback switches of FIG. 3 in more detail according to an embodiment of the present invention;

FIG. 6 illustrates a circuit for generating a common mode voltage reference;

FIG. 7 illustrates an amplifying circuit according to another embodiment of the present invention; and

FIG. 8 illustrates switches of FIG. 7 in more detail.

Claims

1. A circuit comprising: a first sensitive node;a first component connected between the first sensitive node and a first terminal of a first switch, said first switch controlled by a first control signal variable between a supply voltage level and a second voltage level; anda second switch comprising a first terminal connected to the first terminal of said first switch, and a second terminal connected to a clean voltage supply, said second switch controlled to connect the first node of said first switch to said clean voltage supply when said first switch is in a non-conducting state.

2. The circuit of claim 1 wherein a second terminal of said first switch is connected to an output node of an amplifier, and said first sensitive node is connected to an input node of said amplifier.

3. The circuit of claim 2 wherein said component is a resistor.

4. The circuit of claim 2 wherein said component is a switch.

5. The circuit of claim 4 further comprising a resistor connected between said first sensitive node and said output node of said amplifier.

6. The circuit of claim 1 wherein said second switch comprises a first transistor comprising a first main terminal connected to the first terminal of said first switch, and a second main terminal connected to said clean voltage supply, and a control terminal for receiving a second control signal.

7. The circuit of claim 6 further comprising control means for providing said second control signal, said control means arranged to connect said control terminal to one of said clean voltage supply and said second voltage level.

8. The circuit of claim 1 wherein said first transistor further comprises a well terminal connected to switching means arranged to connect said well terminal to one of said supply voltage and said clean voltage supply.

9. The circuit of claim 6 wherein said switching means comprises a pair of transistors connected in series and each comprising a control terminal for receiving said second control signal.

10. The circuit of claim 3 further comprising: a second resistor connected between said first sensitive node and the first terminal of a third switch, said third switch controlled by a third control signal variable between a supply voltage level and a second voltage level; anda fourth switch comprising a first terminal connected to the first terminal of said third switch, and a second terminal connected to said clean voltage supply, said fourth switch arranged to connect the first node of said third switch to said clean voltage supply when said third switch is in a non-conducting state.

11. The circuit of claim 10 further comprising a resistor connected between said first sensitive node and said output node of said amplifier.

12. The circuit of claim 1 wherein said first switch comprises a complementary pair of MOS transistors.

13. An audio device comprising: a first sensitive node;a first component connected between the first sensitive node and a first terminal of a first switch, said first switch controlled by a first control signal variable between a supply voltage level and a second voltage level; andand a second switch comprising a first terminal connected to the first terminal of said first switch, and a second terminal connected to a clean voltage supply, said second switch controlled to connect the first node of said first switch to said clean voltage supply when said first switch is in a non-conducting state.

14. A method of reducing noise at the output of a circuit, the circuit comprising a sensitive node and a first component connected between a first sensitive node and a first terminal of a first switch, said first switch controlled by a first control signal variable between a supply voltage level and a second voltage level, the method comprising: when said first switch is in a non-conducting state, controlling a second switch to connect the first terminal of said first switch to a clean voltage supply.

15. The method of claim 14 wherein said second switch comprises a first transistor comprising a well, and method further comprising connecting said well to one of said supply voltage level and said clean voltage supply.