Overload protection for look-ahead delta sigma modulators

A method of quantizing an input signal using a look-ahead delta-sigma modulator having quantizer overload protection, wherein a look-ahead depth of the look-ahead delta sigma modulator equals n1, the method comprising:

• determining a set of state variables for a loop filter of the look-ahead delta sigma modulator for at least n1 elements ofan input signal vector X(n) and at least n1 elements of each output candidate vector Y(n)i, wherein “i” is an element of at least a subset ofthe set {0, 1, . . . , 2n1−1}, n1 is a positive integer greater than one, and the n1 elements of input signal vector X(n) represent n1 input signal samples;
• substituting a quantizer of the look-ahead delta sigma modulator with a gain stage to provide a closed loop feedback path in the look-ahead delta sigma modulator;
• determining closed loop output responses of the look-ahead delta sigma modulator for n2 input samples using at least one set of determined state variables, wherein n2 represents a number of input samples to anticipate quantizer overload of the look-ahead delta sigma modulator;
• determining which closed loop output response has a lowest maximum absolute value closed loop output response;
• and
• if overload of the look-ahead delta-sigma modulator is anticipated, selecting an output of the look-ahead delta sigma modulator from the output candidate vector corresponding to the determined closed loop output response having the lowest maximum absolute value closed loop output response.

A signal processing system to quantize an input signal using a look-ahead delta-sigma modulator with quantizer overload protection module, wherein a look-ahead depth of the look-ahead delta sigma modulator equals n1, the signal processing system comprising:

• an input to receive an input signal vector X(n), wherein the input signal vector X(n) has n1 elements and n1 is a positive integer greater than one and equals a look-ahead depth of the look-ahead delta-sigma modulator;
• a loop filter coupled to the input;
• a quantizer coupled to the loop filter;
• a gain stage coupled to the loop filter;
• and
• a memory to store a set of state variables for the loop filter of the look-ahead delta sigma modulator for at least n1 elements of an input signal vector X(n) and at least n1 elements of each output candidate vector Y(n)i, wherein “i” is an element of at least a subset of the set {0, 1, . . . , 2n1−1}, n1 is a positive integer greater than one, and the n1 elements of input signal vector X(n) represent n1 input signal samples;
• wherein the overload protection module is configured to:
• substitute the quantizer with the gain stage to provide a closed loop feedback path in the look-ahead delta sigma modulator;
• determine closed loop output responses of the look-ahead delta sigma modulator for n2 input samples using at least one set of determined state variables, wherein n2 represents a number of input samples to anticipate overload of the quantizer;
• determine which closed loop output response has a lowest maximum absolute value closed loop output response;
• and
• if overload of the look-ahead delta-sigma modulator is anticipated, select an output of the look-ahead delta sigma modulator from the output candidate vector corresponding to the determined closed loop output response having the lowest maximum absolute value closed loop output response.

An apparatus to quantize an input signal using a look-ahead delta-sigma modulator with quantizer overload protection, wherein a look-ahead depth of the look-ahead delta sigma modulator equals n1, the apparatus comprising:

• means for determining a set of state variables for a loop filter of the look-ahead delta sigma modulator for at least n1 elements of an input signal vector X(n) and at least n1 elements of each output candidate vector Y(n)i, wherein “i” is an element of at least a subset of the set {0, 1, . . . , 2n1−1}, n1 is a positive integer greater than one, and the n1 elements of input signal vector X(n) represent n1 input signal samples;
• means for substituting a quantizer of the look-ahead delta sigma modulator with a gain stage to provide a closed loop feedback path in the look-ahead delta sigma modulator;
• means for determining closed loop output responses of the look-ahead delta-sigma modulator for n2 input samples using at least one set of determined state variables, wherein n2 represents a number of input samples to anticipate quantizer overload of the look-ahead delta sigma modulator;
• means for determining which closed loop output response has a lowest maximum absolute value closed loop output response;
• and
• means for selecting an output of the look-ahead delta sigma modulator from the output candidate vector corresponding to the determined closed loop output response having the lowest maximum absolute value closed loop output response if overload of the look-ahead delta-sigma modulator is anticipated.

A method comprising:

• substituting a gain stage for a quantizer in a look-ahead delta sigma modulator, wherein the look-ahead delta sigma modulator has a look-ahead depth of n1 and n1 is a positive integer greater than one;
• providing a first input signal to the gain stage;
• determining a feedback signal from the gain stage;
• providing the feedback signal to a loop filter of the look-ahead delta sigma modulator;
• providing a second input signal to the loop filter;
• determining an output of the loop filter from a combination of the input signal and the feedback signal;
• substituting the quantizer for the gain stage in the look-ahead delta sigma modulator;
• and
• selecting a quantization output using the loop filter.

A signal processing system comprising:

• a look-ahead delta sigma modulator, wherein the look-ahead delta sigma modulator has a look-ahead depth of n1 and n1 is a positive integer greater than one, the look-ahead delta sigma modulator comprising:
• a loop filter to filter a combination of an input signal and a feedback signal;
• a quantizer coupled to an output of the loop filter to select a quantization output using an output of the loop filter;
• a gain stage coupled to the output of the loop filter to generate the feedback signal;
• and
• a module to substitute the gain stage for the quantizer to allow the gain stage to receive an output signal from the loop filter and generate the feedback signal for the loop filter.