Continuous-time sigma-delta modulator with multiple feedback paths having independent delays
Apparatus are provided for continuous-time sigma-delta modulators. A sigma-delta modulator comprises a quantizer configured to convert an analog signal to a digital value. A main feedback arrangement is coupled to the quantizer, and the main feedback arrangement delays the digital value by a first delay period and generates a main feedback signal based on the delayed value. A compensation feedback arrangement is coupled to the quantizer, and compensation feedback arrangement delays the digital value by a second delay period and generates a compensation feedback signal based on the delayed value. A forward signal arrangement produces the analog signal at the quantizer based on an input signal, the main feedback signal, and the compensation feedback signal. The second delay period is independent of and is not influenced by the first delay period, and the second delay period is chosen such that the compensation feedback signal compensates for the first delay period.
1. A sigma-delta modulator comprising:
an input node for receiving an input signal;
a quantizer configured to convert a first analog signal to a digital value;
a main feedback arrangement coupled to the quantizer, the main feedback arrangement being configured to:
delay the digital value by a first delay period to obtain a first delayed value; and
generate a main feedback signal based on the first delayed value;
a compensation feedback arrangement coupled to the quantizer, the compensation feedback arrangement being configured to:
delay the digital value by a second delay period to obtain a second delayed value, wherein the second delay period is not equal to the first delay period and the second delay period is not influenced by the first delay period; and
generate a compensation feedback signal based on the second delayed value; and
a forward signal arrangement coupled between the input node and the quantizer, the forward signal arrangement being coupled to the main feedback arrangement and the compensation feedback arrangement, wherein:
the forward signal arrangement produces the first analog signal based on the input signal, the main feedback signal, and the compensation feedback signal; and
the compensation feedback signal compensates for the first delay period.
2. The sigma-delta modulator of claim 1 , wherein the compensation feedback arrangement comprises a non-return-to-zero digital-to-analog converter configured to generate the compensation feedback signal.
3. The sigma-delta modulator of claim 1 , wherein the compensation feedback arrangement comprises a return-to-zero digital-to-analog converter configured to generate the compensation feedback signal.
4. The sigma-delta modulator of claim 1 , wherein the forward signal arrangement comprises a circuit topology selected from a group consisting of a lowpass topology, a bandpass topology, a highpass topology, a feedback topology, a feedforward topology, a mixed feedforward-feedback topology, a cascade topology, a quadrature topology, and a complex topology.
5. The sigma-delta modulator of claim 1 , wherein:
the main feedback arrangement comprises a first non-return-to-zero digital-to-analog converter configured to generate the main feedback signal; and
the compensation feedback arrangement comprises a second non-return-to-zero digital-to-analog converter configured to generate the compensation feedback signal.
6. The sigma-delta modulator of claim 5 , wherein the main feedback arrangement generates the main feedback signal with a first gain and the compensation feedback arrangement generates the compensation feedback signal with a second gain, wherein a magnitude of the second gain is not equal to a magnitude of the first gain.
7. The sigma-delta modulator of claim 1 , wherein:
the main feedback arrangement comprises a non-return-to-zero digital-to-analog converter configured to generate the main feedback signal; and
the compensation feedback arrangement comprises a return-to-zero digital-to-analog converter configured to generate the compensation feedback signal.
8. An analog-to-digital converter comprising:
an input node for receiving an input signal;
a quantizer configured to convert a first analog signal to a digital value;
a forward signal path coupled between the input node and the quantizer;
a first delay element coupled to the quantizer, the first delay element being configured to delay the digital value by a first delay period resulting in a first delayed value;
a first digital-to-analog converter coupled between the first delay element and the forward signal path, the first digital-to-analog converter being configured to generate a first feedback signal based on the first delayed value;
a second delay element coupled to the quantizer, the second delay element being configured to delay the digital value by a second delay period different from the first delay period resulting in a second delayed value, wherein the first delay element and the second delay element are non-cascaded, such that the first delay period and the second delay period are uncorrelated; and
a second digital-to-analog converter coupled between the second delay element and the forward signal path, the second digital-to-analog converter being configured to generate a second feedback signal based on the second delayed value, wherein the forward signal path produces the first analog signal based on the input signal, the first feedback signal, and the second feedback signal, such that the second feedback signal compensates for the first delay period.
9. The analog-to-digital converter of claim 8 , wherein the forward signal path comprises a circuit topology selected from a group consisting of a lowpass topology, a bandpass topology, a highpass topology, a feedback topology, a feedforward topology, and a mixed feedforward-feedback topology.
10. The analog-to-digital converter of claim 8 , wherein the first digital-to-analog converter generates the first feedback signal with a first gain and the second digital-to-analog converter generates the second feedback signal with a second gain, wherein the second gain is not equal to the first gain.
11. The analog-to-digital converter of claim 8 , wherein the second digital-to-analog converter comprises a non-return-to-zero digital-to-analog converter.
12. The analog-to-digital converter of claim 8 , wherein the second digital-to-analog converter comprises a return-to-zero digital-to-analog converter.
13. The analog-to-digital converter of claim 8 , wherein the second delay period is less than the first delay period.
14. The analog-to-digital converter of claim 8 , wherein the second delay period is greater than the first delay period.
15. A sigma-delta modulator comprising:
an input node for receiving an input signal;
a first integrator having a first input and a first output, the first input being coupled to the input node;
a quantizer having a quantizer input and a quantizer output, the quantizer input being coupled to the first output, wherein the quantizer is configured to convert a first analog signal at the quantizer input to a digital value at the quantizer output;
a first delay element coupled to the quantizer output, the first delay element being configured to delay the digital value by a first delay period resulting in a first delayed value;
a first digital-to-analog converter coupled between the first delay element and the first input, the first digital-to-analog converter being configured to convert the first delayed value to a first analog value at the first input;
a second delay element coupled to the quantizer output, the second delay element being configured to delay the digital value by a second delay period resulting in a second delayed value, wherein the second delay period is not equal to the first delay period and the second delay period is independent of the first delay period; and
a second digital-to-analog converter coupled between the second delay element and the first input, the second digital-to-analog converter being configured to convert the second delayed value to a second analog value at the first input.
16. The sigma-delta modulator of claim 15 , further comprising:
a second integrator coupled between the input node and the first integrator, the second integrator having a second input and a second output, the second input being coupled to the input node and the second output being coupled to the first input;
a third digital-to-analog converter coupled between the first delay element and the second input, the third digital-to-analog converter being configured to convert the first delayed value to a third analog value at the second input.
17. The sigma-delta modulator of claim 16 , wherein the second delay period is less than the first delay period.
18. The sigma-delta modulator of claim 17 , the quantizer having a sampling period associated therewith, wherein the second delay period is equal to one quarter of the sampling period and the first delay period is equal to three quarters of the sampling period.
19. The sigma-delta modulator of claim 17 , the quantizer having a sampling period associated therewith, wherein the second delay period is equal to one half of the sampling period and the first delay period is equal to the sampling period.