Signal processing system with analog-to-digital converter using delta-sigma modulation having an internal stabilizer loop
AssigneeCirrus Logic, Inc.
InventorJohn L. Melanson
Life of this patent
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Abstract
A signal processing system includes an analog-to-digital delta sigma modulator with a duty cycle modulator and a finite impulse response (FIR) filter in a main loop feedback path of the delta sigma modulator. The duty cycle modulator and FIR filter can provide high performance filtering in the main loop feedback path. To prevent instability in the main loop caused by the duty cycle modulator and FIR filter, the delta sigma modulator also includes a stabilizer loop. Transfer functions of the main loop and the stabilizer loop combine to achieve a target transfer function for the analog-to-digital delta sigma modulator that provides for stable operation of the analog-to-digital delta sigma modulator.
Claims21
A signal processing system comprising an analog-to-digital converter, the analog-to-digital converter comprising:
- a main loop filter having a transfer function HMAIN, the main loop filter comprising:
- a signal input to receive an input signal;
- a quantizer;
- a first digital-to-analog converter coupled to an output of the quantizer, the first digital-to-analog converter comprising a duty cycle modulator;
- a finite impulse response filter coupled to an output of the first digital-to-analog converter;
- an integrator coupled to the signal input, to an output of the finite impulse response filter, and to an input of the quantizer;
- and
- a stabilizer loop coupled to an output of the quantizer and an input to the quantizer, the stabilizer loop having a transfer function HST;
- wherein a target transfer function of the analog-to-digital converter is HT, and HT comprises a combination of HMAIN and HST.
A signal processing system comprising an analog-to-digital converter having a target transfer function of HT, the analog-to-digital converter comprising:
- a delta sigma modulator comprising:
- a main loop filter to process input data and quantization feedback data in accordance with a transfer function HMAIN, wherein the main loop filter comprises components for:
- receiving the input data;
- generating the quantization feedback data from quantizer output data using (i) pulse width modulation to generate pulse width modulated output data and (ii) finite impulse response filtering of the pulse width modulated output data;
- combining the input signal with the quantization feedback data to generate an input_feedback signal;
- and
- processing the input_feedback signal using at least one integrator;
- and
- a stabilizer loop to process the quantizer output data in accordance with a transfer function HST;
- wherein the target transfer function HT comprises a combination of HMAIN and HST.
A method for converting an analog input signal into a digital signal, the method comprising:
- converting the analog input signal into a digital output signal using a delta sigma modulator having a target transfer function HT, wherein the delta sigma modulator includes a main loop having a transfer function HMAIN and a stabilizer loop having a transfer function HST, and the target transfer function HT comprises a combination of HMAIN and HST;
- wherein converting the analog input signal comprises:
- determining a first signal from the analog input signal using a main loop of a delta sigma modulator, wherein the main loop includes (i) a quantizer feedback path comprising a duty cycle modulator coupled to a first finite impulse response filter and (ii) a signal path comprising an integrator;
- determining a stabilizer signal using a stabilizer loop of the delta sigma modulator, wherein the stabilizer loop is coupled across a quantizer of the delta sigma modulator and the stabilizer loop includes a digital-to-analog converter coupled to a second finite impulse response filter;
- generating a quantizer input signal from the first signal and the stabilizer signal;
- and
- quantizing the quantizer input signal.
A method for converting an analog signal into a digital signal, the method comprising:
- receiving an input signal;
- processing the input signal using delta sigma modulation in accordance with a target transfer function HT, wherein the target transfer function HT is a function of a main loop transfer function HMAIN and a stabilizer loop transfer function HST, wherein processing the input signal using delta sigma modulation in accordance with a target transfer function HT further comprises:
- in a main loop of the delta sigma modulator:
- generating quantization feedback data from quantizer output data, wherein generating quantization feedback data from quantizer output data comprises:
- duty cycle modulating quantizer output data to generate pulse width modulated output data;
- and
- filtering the pulse width modulated output data with finite impulse response filter;
- combining the input signal with the quantization feedback data to generate an input_feedback signal;
- and
- processing the input_feedback signal using at least one integrator to generate a main loop output signal;
- in a stabilizer loop of the delta sigma modulator:
- processing the quantizer output data to generate a stabilizer feedback signal using a digital-to-analog converter;
- and
- combining the main loop output signal and the stabilizer feedback signal to generate a main loop_stabilizer signal;
- and
- generating a quantization output signal using the main loop_stabilizer signal.
Dependencies are inferred from the claim text.