Sigma-delta modulator
Proposed is a sigma-delta modulator circuit. The circuit comprises a loopfilter having at least one integrator or resonator section; and a feed-forward path adapted to provide a feed-forward signal to the output of the at least one integrator or resonator section via a filter.
1. A sigma-delta modulator circuit comprising:
a loopfilter having at least one integrator or resonator section, and an output summation node after the integrator or resonator section;
a feed-forward path configured to provide a feed-forward signal to the output summation node via a filter configured to implement a specific phase shift and compensate peaking behavior in a signal transfer function of the sigma-delta modulator, the feed-forward signal being taken from a circuit node before the at least one integrator or resonator section; and
an ADC; wherein the output summation node is directly coupled to the ADC.
2. The circuit of claim 1 , wherein the feed-forward signal is the sigma-delta modulator circuit input signal.
3. The circuit of claim 1 , further comprising:
a feedback path configured to combine an output signal of the sigma-delta modulator circuit with an input signal of the sigma-delta modulator circuit so as to provide the loopfilter input signal, wherein the feed-forward signal is the loopfilter input signal.
4. The circuit of claim 1 , wherein the circuit node is within the loopfilter.
5. The circuit of claim 1 , wherein the sigma-delta modulator circuit is a discrete-time sigma-delta modulator circuit, and wherein the filter is configured to implement a time delay.
6. The circuit of claim 1 , wherein the ADC is a quantizer configured to quantize an output signal from the loopfilter.
7. The circuit of claim 1 , further comprising:
a second feed-forward path configured to provide a second feed-forward signal via a second filter, the second feed-forward path being different from the feed-forward path.
8. A circuit arrangement comprising:
the sigma-delta modulator circuit as claimed in claim 1 .
9. A switched-mode power supply comprising the sigma-delta modulator circuit as claimed in claim 1 .
10. A method of operating a sigma-delta modulator circuit comprising a loopfilter having at least one integrator or resonator section, and an output summation node after the integrator or resonator section, wherein the output summation node is directly coupled to an ADC, the method comprising:
providing a feed-forward signal to the output summation node via a filter configured to implement a specific phase shift and compensate peaking behavior in a signal transfer function of the sigma-delta modulator, wherein the feed-forward signal is taken from a circuit node before the at least one integrator or resonator section.
11. The method of claim 10 , wherein the feed-forward signal is the sigma-delta modulator circuit input signal.
12. The method of claim 10 , further comprising:
combining an output signal of the sigma-delta modulator circuit with an input signal of the sigma-delta modulator circuit so as to provide the loopfilter input signal, wherein the feed-forward signal is the loopfilter input signal.
13. The method of claim 10 , wherein the circuit node is within the loopfilter.
14. The circuit of claim 1 , wherein the feed-forward signal is filtered but not amplified.
15. The circuit of claim 1 , wherein the output summation node follows all of the integrator or resonator sections.
16. The circuit of claim 1 , wherein the specific phase shift is implemented using a weighted vector summation of quadrature signals.