Electronic system having common mode voltage range enhancement

• US 7,994,863 B2
• Filed: 12/31/2008
• Issued: 08/09/2011
• Est. Priority Date: 12/31/2008
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Hodapp, Stephen T., Kejariwal, Murari L., Melanson, John L., Schneider, Edmund M.
• Primary Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US12/347,155
• Publication Number:
  US 20100164631A1
• Time in Patent Office: 951 Days
• Field of Search: 330/297, 330/258, 330/69
• US Class Current: 330/297
• CPC Class Codes: H03F 3/005 using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers H03F3/45 takes precedence
• CPC Class Codes: H03F 3/45955 Measuring at the input circuit of the differential amplifier

Abstract

An electronic system generates at least one floating supply voltage, wherein during operation of the circuit the floating supply voltage tracks a common mode voltage of first and second differential input signals. By tracking the common mode voltage, in at least one embodiment, the floating supply voltage adjusts as the common mode voltage changes. Thus, the floating supply voltages can be based upon the peak-to-peak values of the first and second output signals without factoring in the common mode voltage. In at least one embodiment, the electronic system provides the floating supply voltages to an amplifier. The amplifier amplifies the first and second differential input signals and generates differential output signals. A differential sampling circuit samples the differential output signals to cancel the common mode voltage from the differential output signals. In at least one embodiment, an analog-to-digital converter converts the sampled differential output signals into a digital output signal.

Claims

1. An apparatus comprising:

a circuit to generate a floating first supply voltage, wherein during operation of the circuit the first supply voltage tracks a common mode voltage of first and second input signals, wherein the circuit is further configured to generate a second supply voltage and, during operation of the circuit, the second supply voltage tracks the common mode voltage;

a first amplifier having a first voltage input terminal coupled to the circuit to receive the first supply voltage and a second voltage terminal to receive the second supply voltage, wherein during operation the first amplifier receives and amplifies the first input signal to generate a first amplified input signal;

a second amplifier having a first voltage input terminal coupled to the circuit to receive the first supply voltage and a second voltage terminal to receive the second supply voltage, wherein during operation the second amplifier receives and amplifies the second input signal to generate a second amplified input signal; and

an analog-to-digital converter, the analog-to-digital converter comprising;

an input sampling circuit coupled to the first amplifier and the second amplifier to sample the first and second amplified input signals and substantially eliminate the common mode voltage from the first and second amplified input signals.

2. The apparatus of claim 1 further comprising:

a first amplifier having a voltage input terminal coupled to the circuit to receive the first supply voltage.

3. The apparatus of claim 1 wherein the circuit further comprises:

a power transfer circuit to transfer power from a first fixed voltage supply to a first power storage circuit to generate the first supply voltage, wherein the first power transfer circuit is referenced to the common mode voltage.

4. The apparatus of claim 3 wherein the power transfer circuit is further configured to transfer power from a second fixed voltage supply to a second power storage circuit to generate a second supply voltage that tracks the common mode voltage, wherein the second power storage circuit is referenced to the common mode voltage, the apparatus further comprising:

an amplifier having voltage input terminals to receive the first and second supply voltages.

5. The apparatus of claim 4 wherein the power transfer circuit comprises a switched capacitor network to transfer power from a first set of capacitors to a second set of capacitors, wherein the second set of capacitors are referenced to the common mode voltage.

6. The apparatus of claim 4 wherein the power transfer circuit comprises a transformer to transfer power from a supply voltage source to a floating voltage source, wherein the transformer includes a primary coil coupled to the supply voltage source, a secondary coil coupled to the floating voltage source, and a center tap referenced to the common mode voltage.

7. The apparatus of claim 1 further comprising:

a first input terminal to receive the first input signal;

a second input terminal to receive the second input signal;

a common mode detection circuit, coupled to the first and second input terminals, to generate the common mode voltage of the first and second input signals;

wherein the circuit to generate the first supply voltage includes a reference terminal coupled to the common mode detection circuit to receive the common mode voltage and the circuit further includes a first voltage supply terminal to receive the first supply voltage.

8. The apparatus of claim 7 wherein the first input signal includes a first signal component plus the common mode voltage, the second input signal includes a second signal component plus the common mode voltage, and the first and second signal components are differential signals.

9. The apparatus of claim 1 wherein the circuit is further configured to generate a floating second supply voltage, wherein the second supply voltage tracks the common mode voltage and the second supply voltage is an opposite polarity equivalent of the first input signal.

10. The apparatus of claim 1 wherein the input sampling circuit comprises:

a switched capacitor network to transfer first and second amplified input difference signals to a signal processor.

11. The apparatus of claim 10 wherein the analog-to-digital converter further includes the signal processor.

12. A method comprising:

generating a floating first supply voltage that tracks a common mode voltage of first and second input signals, wherein generating the floating first supply voltage further comprises;

transferring first power from a first fixed voltage supply using a primary transformer coil coupled to a secondary transformer coil, wherein the secondary transformer coil includes a center tab coupled to the common mode voltage;

providing the first supply voltage to a first circuit;

generating a floating second supply voltage that tracks the common mode voltage; and

providing the second supply voltage to the first circuit.

13. The method of claim 12 wherein the first circuit is a first amplifier, the method further comprising:

providing the first and second supply voltages to the first circuit and to a second amplifier;

amplifying the first input signal with the first amplifier to generate a first amplified input signal; and

amplifying the second input signal with the second amplifier to generate a second amplified input signal.

14. The method of claim 13 further comprising:

converting a difference between the first and second amplified signals into a digital signal.

15. The method of claim 13 wherein the first input signal includes a first signal component plus the common mode voltage, the second input signal includes a second signal component plus the common mode voltage, and the first and second signal components are differential signals.

16. The method of claim 12 wherein generating the floating first supply voltage further comprises:

transferring first power from a first fixed voltage supply to a first power storage circuit, wherein the first power storage circuit is referenced to the common mode voltage; and

transferring second power from a second fixed voltage supply to a second power storage circuit, wherein the second power storage circuit is referenced to the common mode voltage.

17. The method of claim 16 wherein transferring first power comprises transferring power from a first capacitor referenced to a ground voltage to a second capacitor referenced to the first fixed voltage supply and the common mode voltage and transferring second power comprises transferring power from a third capacitor to a fourth capacitor referenced to the second fixed voltage supply and the common mode voltage.

18. The method of claim 12 further comprising:

detecting the common mode voltage.

19. An apparatus comprising:

a circuit to generate a floating first supply voltage, wherein during operation of the circuit the first supply voltage tracks a common mode voltage of first and second input signals;

a power transfer circuit to transfer power from a first fixed voltage supply to a first power storage circuit to generate the first supply voltage, wherein the first power transfer circuit is referenced to the common mode voltage;

wherein;

the power transfer circuit is further configured to transfer power from a second fixed voltage supply to a second power storage circuit to generate a second supply voltage that tracks the common mode voltage, wherein the second power storage circuit is referenced to the common mode voltage; and

the power transfer circuit comprises a transformer to transfer power from a supply voltage source to a floating voltage source, wherein the transformer includes a primary coil coupled to the supply voltage source, a secondary coil coupled to the floating voltage source, and a center tap referenced to the common mode voltage; and

an amplifier having voltage input terminals to receive the first and second supply voltages.

20. The apparatus of claim 19 further comprising:

a first amplifier having a voltage input terminal coupled to the circuit to receive the first supply voltage.

21. The apparatus of claim 19 further comprising:

a first input terminal to receive the first input signal;

a second input terminal to receive the second input signal;

a common mode detection circuit, coupled to the first and second input terminals, to generate the common mode voltage of the first and second input signals;

wherein the circuit to generate the first supply voltage includes a reference terminal coupled to the common mode detection circuit to receive the common mode voltage and the circuit further includes a first voltage supply terminal to receive the first supply voltage.

22. The apparatus of claim 21 wherein the first input signal includes a first signal component plus the common mode voltage, the second input signal includes a second signal component plus the common mode voltage, and the first and second signal components are differential signals.

23. The apparatus of claim 19 wherein the circuit is further configured to generate a floating second supply voltage, wherein the second supply voltage tracks the common mode voltage and the second supply voltage is an opposite polarity equivalent of the first input signal.

24. The apparatus of claim 19 wherein the circuit is further configured to generate a second supply voltage and, during operation of the circuit, the second supply voltage tracks the common mode voltage, the apparatus further comprising:

a first amplifier having a first voltage input terminal coupled to the circuit to receive the first supply voltage and a second voltage terminal to receive the second supply voltage, wherein during operation the first amplifier receives and amplifies the first input signal to generate a first amplified input signal; and

a second amplifier having a first voltage input terminal coupled to the circuit to receive the first supply voltage and a second voltage terminal to receive the second supply voltage, wherein during operation the second amplifier receives and amplifies the second input signal to generate a second amplified input signal.

25. The apparatus of claim 24 further comprising:

an analog-to-digital converter, the analog-to-digital converter comprising;

an input sampling circuit coupled to the first amplifier and the second amplifier to sample the first and second amplified input signals and substantially eliminate the common mode voltage from the first and second amplified input signals.

26. The apparatus of claim 25 wherein the input sampling circuit comprises:

a switched capacitor network to transfer first and second amplified input difference signals to a signal processor.

27. The apparatus of claim 26 wherein the analog-to-digital converter further includes the signal processor.