TRANSFORMER-ISOLATED ANALOG-TO-DIGITAL CONVERTER (ADC) FEEDBACK APPARATUS AND METHOD

• US 20090212759A1
• Filed: 02/26/2008
• Published: 08/27/2009
• Est. Priority Date: 02/26/2008
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Melanson, John L.
• Granted Patent: US 7,796,076 B2
• Time in Patent Office: Days
• US Class Current: 324/76.110
• CPC Class Codes: G01R 31/2844 using test interfaces, e.g. adapters, test boxes, switches, PIN drivers G01R31/2889 takes precedence
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 17/691 using transformer coupling
• CPC Class Codes: H03M 3/41 combined with modulation to or demodulation from the carrier
• CPC Class Codes: H03M 3/466 Multiplexed conversion systems

Abstract

A transformer-isolated analog-to-digital converter (ADC) feedback apparatus and method provides reduction of circuit complexity in high power/high voltage systems having a transformer-isolated sensing circuit. The feedback apparatus is a circuit including an ADC for receiving an analog input signal and a transformer having a first winding that receives a modulated output of the analog-to-digital converter. A second winding of the transformer provides an isolated data output of the ADC. A demodulator is coupled to the second winding of the transformer and demodulates the isolated output to generate a digital representation of the analog input signal. The ADC may be a delta-sigma converter and the demodulator may be the corresponding decimation filter. The circuit further includes an isolation circuit for introducing a clock signal and/or power supply waveform at the second winding of the transformer, so that the ADC circuit is supplied with an isolated clock and/or an isolated power supply.

Claims

1. A circuit, comprising:

an analog-to-digital converter for receiving an analog input signal;

a transformer having at least one first winding for receiving a modulated output of the analog-to-digital converter and at least one second winding for providing an isolated data output;

a demodulator coupled to the at least one second winding of the transformer for demodulating the isolated output to generate a digital representation of the analog input signal; and

an isolation circuit coupled to the at least one second winding of the transformer for coupling at least one of a clock signal or power supply through the transformer to the analog-to-digital converter, whereby the analog-to-digital converter is supplied with at least one of an isolated clock or an isolated power supply.

2. The circuit of claim 1, wherein the isolation circuit applies an alternating current at the at least one second winding of the transformer and wherein the analog-to-digital conversion circuit further comprises a rectifier for rectifying a voltage impressed on the at least one first winding by the isolation circuit to provide the isolated power supply to the analog-to-digital converter.

3. The circuit of claim 2, wherein the isolation circuit further applies a clock signal at the at least one second winding of the transformer, and wherein the analog-to-digital conversion circuit further comprises a clock extraction circuit coupled to the at least one first winding for providing the isolated clock to the analog-to-digital converter by extracting the clock signal from the at least one first winding.

4. The circuit of claim 1, wherein the isolation circuit applies a clock signal at the at least one second winding of the transformer and wherein the analog-to-digital conversion circuit further comprises a clock extraction circuit coupled to the at least one first winding for providing the isolated clock to the analog-to-digital converter by extracting the clock signal from the at least one first winding.

5. The circuit of claim 1, wherein the analog-to-digital converter comprises a delta-sigma modulator, and wherein the modulated output of the analog-to-digital converter is an output of a quantizer of the delta-sigma modulator and wherein the demodulator includes a decimator that decimates the isolated data output.

6. The circuit of claim 1, wherein the analog-to-digital converter comprises a delta-sigma modulator, and wherein the modulated output of the analog-to-digital converter is a data stream provided by a decimation filter of the analog-to-digital converter having an output coupled to the at least one first winding.

7. The circuit of claim 1, wherein the analog-to-digital converter comprises a delta-sigma modulator, and wherein the modulated output of the analog-to-digital converter is an output of a quantizer of the delta-sigma modulator and wherein the demodulator is coupled to a digital-to-analog converter for providing an analog output indicative of a value of the analog input signal.

8. The circuit of claim 1, further comprising:

a switching power stage control circuit having a modulator output coupled to the at least one second winding for providing an isolated drive signal at the at least one first winding, wherein the modulator output has a rate substantially higher than the switching power stage control circuit control rate;

another demodulator having an input coupled to the first winding of the transformer for demodulating the isolated drive signal; and

a switching transistor having a gate coupled to an output of the another demodulator, whereby the switching transistor is controlled at the switching power stage control rate.

9. A method for measuring an analog input signal, comprising:

converting the analog input signal to digital values using an analog-to-digital converter circuit;

first providing the digital values as modulated information to a first winding of a transformer;

demodulating the modulated information at a second winding of the transformer;

second providing at least one of a clock signal or a power supply waveform to the second winding of the transformer;

receiving at least one of the clock signal or the power supply waveform at the first winding of the transformer; and

supplying the received clock signal or power supply waveform to the analog-to-digital converter circuit, whereby the analog-to-digital converter circuit is provided with at least one of operational clock or power.

10. The method of claim 9, wherein the second providing provides the power supply waveform and the receiving receives the power supply waveform, and wherein the method further comprises rectifying the power supply waveform to provide operational power to the analog-to-digital converter circuit.

11. The method of claim 10, wherein the second providing further provides the clock signal and the receiving receives the clock signal, and wherein the method further comprises extracting the clock signal from a signal at the first winding of the transformer and supplying clock information to the analog-to-digital converter circuit in conformity with the clock signal.

12. The method of claim 9, wherein the second providing provides the clock signal and the receiving receives the clock signal, and wherein the method further comprises extracting the clock signal from a signal at the first winding of the transformer and supplying clock information to the analog-to-digital converter circuit in conformity with the clock signal.

13. The method of claim 9, wherein the analog-to-digital converter circuit comprises a delta-sigma modulator, and wherein the first providing provides output values of a quantizer of the delta-sigma modulator to the first winding of the transformer, and wherein the receiving further comprises decimating the output values of the transformer that are received at the first winding of the transformer.

14. The method of claim 9, wherein the analog-to-digital converter circuit comprises a delta-sigma modulator, wherein the method further comprises decimating the output of a quantizer of the delta-sigma modulator, and wherein the first providing provides a result of the decimating to the first winding of the transformer.

15. The method of claim 9, wherein the analog-to-digital converter circuit comprises a delta-sigma modulator, and wherein the first providing provides output values of a quantizer of the delta-sigma modulator to the first winding of the transformer, and wherein the method further comprises converting the output values that are received at the first winding of the transformer to an analog output signal indicative of a value of the analog input signal.

16. The method of claim 9, further comprising:

providing a modulated switching power stage control signal at the second winding of the transformer having a rate substantially higher than a control rate of a switching power stage; and

demodulating the modulated switching power stage control signal at the first winding of the transformer to generate a control signal for the switching power stage.

17. An integrated circuit, comprising:

a pair of terminals for connection to a second winding of a transformer having digital output information from an analog-to-digital converter integrated circuit connected to a first winding of the transformer; and

a modulator for generating at least one of a power waveform or a clock waveform, wherein the output of the modulator is coupled to the pair of terminals for supplying the at least one power waveform or clock waveform to the analog-to-digital converter by coupling the at least one power waveform or clock waveform through the transformer.

18. The integrated circuit of claim 17, further comprising a switching power stage control circuit having an output coupled to the modulator for further providing modulated switching power stage control information to the pair of terminals for controlling a switching power stage coupled to analog-to-digital converter integrated circuit.

19. An integrated circuit, comprising:

an analog-to-digital converter circuit;

a pair of terminals for connection to a first winding of a transformer and coupled to an output of the analog-to-digital converter circuit for providing digital values to a receiver integrated circuit connected to a second winding of the transformer; and

a clock or power reception circuit for deriving at least one of a clock signal or power from the first winding of the transformer and having an output coupled to the analog-to-digital converter circuit for providing at least one of power or clock information to the analog-to-digital converter circuit.

20. The integrated circuit of claim 19, further comprising:

a switching power stage control demodulator having an input coupled to the pair of terminals for decoding modulated switching power stage control information provided by the receiver integrated circuit; and

at least one switching power stage output terminal coupled to an output of the switching power stage control demodulator for providing a switching power control signal to at least one power switching device.

21. The integrated circuit of claim 19, further comprising a rectifier having an input coupled to the pair of terminals and an output coupled to a power supply input of the analog-to-digital converter circuit for providing power to the analog-to-digital converter circuit.

22. The integrated circuit of claim 21, further comprising a clock extractor circuit having an input coupled to the pair of terminals and an output coupled to a clock input of the analog-to-digital converter circuit for providing clock information to the analog-to-digital converter circuit.

23. The integrated circuit of claim 19, further comprising a clock extractor circuit having an input coupled to the pair of terminals and an output coupled to a clock input of the analog-to-digital converter circuit for providing clock information to the analog-to-digital converter circuit.