Sigma delta modulator
AssigneeAudioasics A/S
InventorsHenrik Thomsen, Claus Erdmann Fuerst
Life of this patent
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Abstract
A method of controlling a sigma delta modulator with a loop which establishes a signal transfer function, STF, and a quantization noise transfer function, NTF, of the sigma delta modulator, wherein the sigma delta modulator receives an input signal, x(n), and provides a modulated output signal, y(n) in response to the input signal. The method is characterized in comprising the step of controlling the sigma delta modulator to change the quantization noise transfer function, NTF, in response to a signal feature, A(n), which is correlated with the input signal.
Claims33
A method of controlling a sigma delta modulator with a loop which establishes a signal transfer function and a noise transfer function of the sigma delta modulator, wherein the sigma delta modulator receives an input signal and provides a modulated output signal in response to the input signal;
- wherein the noise transfer function establishes a maximum stable amplitude for the input signal;
- wherein the sigma-delta modulator comprises a loop filter and operates at a clock frequency that sets an over-sampling ratio;
- the method controlling the sigma delta modulator to change the noise transfer function in response to an output signal of the modulator or a state variable of the loop filter, and comprising steps of:
- processing the output signal of the modulator or a state variable of the loop filter with a peak detector to determine a peak detector output,
- storing a running window of N previous samples of the peak detector output, where N is less than the oversampling ratio,
- selecting a maximum of the N previous samples to provide an intermediate control signal,
- deriving the control signals for controlling the noise transfer function from the intermediate control signal such that the noise transfer function is changed to suppress quantization noise to a smaller extent when the output signal of the modulator or a state variable of the loop filter represents a relatively large amplitude, whereas when the output signal of the modulator or a state variable of the loop filter represents a relatively small amplitude, the noise transfer function is changed to suppress quantization noise to a larger extent.
A sigma delta modulator with a loop which establishes a signal transfer function and a quantization noise transfer function of the sigma delta modulator, where the sigma delta modulator receives an input signal, x(n), and provides a modulated output signal, y(n) in response to the input signal;
- wherein the noise transfer function establishes a maximum stable amplitude for the input signal;
- wherein the sigma-delta modulator comprises a loop filter and operates at a clock frequency that sets an over-sampling ratio;
- wherein the sigma delta modulator is configured to:
- change the quantization noise transfer function, NTF, in response to an output signal of the modulator or a state variable of the loop filter,
- process the output signal of the modulator or a state variable of the loop filter with a peak detector to determine a peak detector output,
- store a running window of N previous samples of the peak detector output, where N is less than the oversampling ratio,
- select a maximum of the N previous samples to provide an intermediate control signal, and
- derive the control signals for controlling the noise transfer function from the intermediate control signal such that the noise transfer function is changed to suppress quantization noise to a smaller extent when the output signal of the modulator or a state variable of the loop filter represents a relatively large amplitude, whereas when the output signal of the modulator or a state variable of the loop filter represents a relatively small amplitude, the noise transfer function is changed to suppress quantization noise to a larger extent.
Dependencies are inferred from the claim text.