ΔΣ modulator and program of ΔΣ modulator

1. A ΔΣ modulator for converting an m-value (m: an integer of 3 or more) digital signal into an n-value (n: an integer of 2 or more smaller than m) digital signal and outputting the n-value output signal, the ΔΣ modulator comprising:

a loop filter including a plurality of cascaded integrators each having a subtractor at its input, for inputting the m-value digital signal into the subtractor at a first integrator in the plurality of cascaded integrators;

an n-value quantizer for inputting a first output signal output from the loop filter and outputting a second output signal that is the n-value digital signal, the first output signal based on an output of a last integrator in the plurality of cascaded integrators; and

a selecting device for inputting the first output signal and the second output signal therein and selecting between feeding back the first output signal and the second output signal based on the first output signal and not based on outputs of the first integrator to next-to-last integrator in the plurality of cascaded integrators, and feeding back the first output signal to all of the subtractors of the loop filter when an absolute value of the first output signal is a predetermined value or more, and feeding back the second output signal to all of the subtractors of the loop filter when the absolute value of the first output signal is less than a predetermined value, wherein

the predetermined value in the selecting device is set to be larger than a maximum value of an absolute value of a quantization value to be obtained by the n-value digital signal.

2. The ΔΣ modulator according to claim 1 , wherein when n=2, in the n-value quantizer, a threshold with respect to the input signal for deciding a signal value of a binary digital signal to be output to a first quantization value or a second quantization value is set to zero.

3. The ΔΣ modulator according to claim 2 , wherein when n=2, the first quantization value and the second quantization value of the n-value quantizer are set as positive and negative quantization values of which absolute values are equal to each other.

4. A non-transitory computer readable medium storing a program for causing a computer to execute ΔΣ modulation signal processing for converting an m-value (m: an integer of 3 or more) digital signal into an n-value (n: an integer of 2 or more smaller than m) digital signal and outputting the n-value digital signal, the program causing a processor of the computer to execute:

a step of executing signal processing in a loop filter for inputting the m-value digital signal into a subtractor, the loop filter including a plurality of cascaded integrators each having a subtractor at its input, wherein the m-value digital signal is input into the subtractor at a first integrator in the plurality of cascaded integrators, and the loop filter outputs a first output signal based on an output of a last integrator in the plurality of cascaded integrators;

a step of executing n-value quantization signal processing for inputting the first output signal to be output from the loop filter and outputting a second output signal as the n-value digital signal; and

a step of executing selection processing for inputting the first output signal and the second output signal and selecting between feeding back the first output signal and the second output signal based on the first output signal and not based on outputs of the first integrator to next-to-last integrator in the plurality of cascaded integrators, feeding back the first output signal to all of the subtractors of the loop filter when an absolute value of the first output signal is a predetermined value or more, and feeding back the second output signal to all of the subtractors of the loop filter when the absolute value of the first output signal is less than a predetermined value, wherein

the predetermined value in the selection processing is set to be larger than a maximum value of an absolute value of a quantization value to be obtained by the n-value digital signal.

5. A ΔΣ modulator for converting an m-value (m: an integer of 3 or more) digital signal into an n-value (n: an integer of 2 or more smaller than m) digital signal and outputting the n-value output signal, the ΔΣ modulator comprising:

a loop filter including a plurality of cascaded integrators each having a subtractor at its input, for inputting the m-value digital signal into the subtractor at a first integrator in the plurality of cascaded integrators;

a y-value quantizer for inputting a first output signal to be output from the loop filter and outputting a second output signal as a y-value (y: an integer of 2 or more that satisfies m≧y≧n) digital signal, the first output signal based on an output of a last integrator in the plurality of cascaded integrators;

a selecting device for inputting the first output signal and the second output signal therein and selecting between feeding back the first output signal and the second output signal based on the first output signal and not based on outputs of the first integrator to next-to-last integrator in the plurality of cascaded integrators, feeding back the first output signal to all of the subtractors of the loop filter when an absolute value of the first output signal is a predetermined value or more, and feeding back the second output signal to all of the subtractors of the loop filter when the absolute value of the first output signal is less than a predetermined value; and

a ΔΣ modulating unit for inputting a signal fed back to the loop filter by the selection device and outputting the n-value digital signal, wherein

the predetermined value in the selection device is set to be larger than a maximum value of an absolute value of a quantization value to be obtained by the n-value digital signal.

6. The ΔΣ modulator according to claim 5 , wherein when n=2, the ΔΣ modulating unit is a first order ΔΣ modulating unit for executing first order ΔΣ modulation signal processing or a second order ΔΣ modulating unit for executing second order ΔΣ modulation signal processing.

7. The ΔΣ modulator according to claim 5 , wherein when n=y=2, a threshold with respect to an input signal for deciding a signal value of a binary digital signal output by the y-value quantizer is set to a first quantization value or a second quantization value.

8. The ΔΣ modulator according to claim 7 , wherein when n=y=2, the first quantization value and the second quantization value of the y-value quantizer are set as positive and negative quantization values of which absolute values are equal to each other.

9. A non-transitory computer readable medium storing a program for causing a computer to execute ΔΣ modulation signal processing for converting an m-value (m: an integer of 3 or more) digital signal into an n-value (n: an integer of 2 or more smaller than m) digital signal and outputting the n-value digital signal, the program causing a processor of the computer to execute:

a step of executing signal processing in a loop filter for inputting the m-value digital signal into a subtractor, the loop filter including a plurality of cascaded integrators each having a subtractor at its input, wherein the m-value digital signal is input into the subtractor at a first integrator in the plurality of cascaded integrators, and the loop filter outputs a first output signal based on an output of a last integrator in the plurality of cascaded integrators;

a step of executing y-value quantization signal processing for inputting the first output signal to be output from the loop filter and outputting a second output signal as a y-value digital signal;

a step of executing selection processing for inputting the first output signal and the second output signal and selecting between feeding back the first output signal and the second output signal based on the first output signal and not based on outputs of the first integrator to next-to-last integrator in the plurality of cascaded integrators, feeding back the first output signal to all of the subtractors of the loop filter when an absolute value of the first output signal is a predetermined value or more, and feeding back the second output signal to all of the subtractors of the loop filter when the absolute value of the first output signal is less than a predetermined value; and

a step of executing ΔΣ modulation processing for inputting a signal to be fed back to the loop filter by a selecting device and outputting the n-value digital signal, wherein

the predetermined value in the selection processing is set to be larger than a maximum value of an absolute value of a quantization value to be obtained by the n-value digital signal.