Method for varying the interpolation ratio of a digital oversampling digital-to-analog converter system and apparatus therefor
AssigneeAnalog Devices, Inc.
InventorJames Wilson
Life of this patent
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Abstract
A digital oversampling digital-to-analog converter system includes an interpolator, a sigma-delta modulator, a digital-to-analog converter and a low pass filter. The interpolator receives a digital input signal and upsamples the input signal by certain upsampling factor. The upsampled signal is processed by the sigma-delta modulator, converted to an analog signal by the digital-to-analog converter and then filtered by the low pass filter. The interpolator includes control circuitry, preferably a central processor, which controls the upsampling factor and increases the upsampling factor upon a decrease in the frequency of the input signal.
Claims20
A digital oversampling DAC system comprising:
- an interpolator receiving a digital input signal having an input sampling frequency and upsampling the digital input signal to produce an upsampled signal, the interpolator having an interpolation ratio, and including control circuitry to set the interpolation ratio such that quantization noise is moved substantially outside of a passband of the input signal;
- a noise shaping modulator, coupled to the interpolator, operating at a clock rate, receiving the upsampled signal and outputting a noise-shaped n-bit digital stream;
- an n-bit DAC, coupled to the modulator, receiving the n-bit digital stream and converting the n-bit digital stream to an analog signal;
- and
- a low pass filter, coupled to the n-bit DAC, receiving the analog signal and reducing high frequency quantization noise.
A variable upsampling interpolator for a digital oversampling DAC system including a noise shaping modulator and a low pass filter, the interpolator comprising:
- upsampling circuitry receiving a digital input signal having an input sampling frequency and upsampling the digital input signal by an upsampling factor;
- and
- control circuitry, coupled to the upsampling circuitry, setting the upsampling factor such that quantization noise is moved substantially outside of a passband of the digital input signal.
A variable upsampling interpolator for a digital oversampling DAC system including a noise shaping modulator and a low pass filter, the interpolator comprising:
- means for receiving a digital input signal having an input sampling frequency;
- means, coupled to the means for receiving, for upsampling the digital input signal by an upsampling factor;
- and
- means, coupled to the means for upsampling, for setting the upsampling factor such that quantization noise is moved substantially outside of a passband of the digital input signal.
A method for varying the interpolation ratio of an interpolator within a digital oversampling DAC system, comprising the steps of:
- receiving a digital input signal having an input sampling frequency;
- upsampling the digital input signal by an upsampling factor;
- and
- setting the upsampling factor such that quantization noise is moved substantially outside of a passband of the digital input signal.
Dependencies are inferred from the claim text.