Digital non-integer sample/hold implemented using virtual filtering
First Claim
1. A sigma-delta digital-to-analog converter system for performing a non-integer sample rate conversion, comprising:
- an interpolation filter having an input to receive a digital input signal with a first sampling rate and to generate a digital output signal with a second sampling rate on its output, said second sampling rate being increased by a predetermined upsampling integer;
a polyphase filter circuit coupled to the output of said interpolation filter and being used to upsample the digital output signal with the second sampling rate by a predetermined non-integer upsample ratio of a relatively large number so as to produce a third sampling rate;
a modulator coupled to receive the digital output signal with the third sampling rate from said polyphase filter circuit and to generate a digital signal having the third sampling rate with the non-integer upsampling rate such that quantization noise is moved substantially beyond the band of the digital input signal; and
said polyphase filter circuit being formed of a long zero-order hold and a short FIR filter so that only several branches associated with said polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated.
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Abstract
A method and apparatus for implementing non-integer sample hold operations in a sigma-delta digital-to-analog converter system includes an interpolation filter, a polyphase filter circuit, and a modulator. The polyphase filter circuit is used to virtual upsample a digital input signal by a predetermined non-integer upsample ratio of a relatively large number. The polyphase filter circuit is formed of a long zero-order hold and a short FIR filter so that only several branches associated with the polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated, thereby reducing the need to store a large number of filter coefficients and eliminating complex computations.
14 Citations
20 Claims
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1. A sigma-delta digital-to-analog converter system for performing a non-integer sample rate conversion, comprising:
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an interpolation filter having an input to receive a digital input signal with a first sampling rate and to generate a digital output signal with a second sampling rate on its output, said second sampling rate being increased by a predetermined upsampling integer; a polyphase filter circuit coupled to the output of said interpolation filter and being used to upsample the digital output signal with the second sampling rate by a predetermined non-integer upsample ratio of a relatively large number so as to produce a third sampling rate; a modulator coupled to receive the digital output signal with the third sampling rate from said polyphase filter circuit and to generate a digital signal having the third sampling rate with the non-integer upsampling rate such that quantization noise is moved substantially beyond the band of the digital input signal; and said polyphase filter circuit being formed of a long zero-order hold and a short FIR filter so that only several branches associated with said polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An interpolation filter for performing a non-integer sample rate conversion, said interpolation filter comprising:
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a polyphase filter circuit being used to upsample a digital input signal with a first sampling rate by a predetermined non-integer upsample ratio of a relatively large number so as to produce a second sampling rate; and said polyphase filter circuit being formed of a long zero-order hold and a short FIR filter so that only several branches associated with said polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal is required to be calculated. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A method for performing a non-integer sample rate conversion in a sigma-delta digital-to-analog converter system, comprising:
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receiving a digital input signal with a first sampling rate on an input of an interpolation filter and generating a digital output signal with a second sampling rate on the output thereof, the second sampling rate being increased by a predetermined upsampling integer; upsampling the digital output signal with the second sampling rate through a polyphase filter circuit coupled to the output of the interpolation filter by a predetermined non-integer upsample ratio of a relatively large number so as to produce a third sampling rate; receiving the digital output signal with the third sampling rate from the polyphase filter circuit on an input of a modulator and generating a digital signal having the third sampling rate with the non-integer upsampling rate such that quantization noise is moved substantially beyond the band of the digital input signal; and calculating only several branches associated with the polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal so as to reduce the need to store a large number of filter coefficients and to eliminate complex computations. - View Dependent Claims (14, 15, 16)
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17. A method for performing a non-integer sample rate conversion comprising:
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upsampling a digital input signal with a first sampling rate through a polyphase filter circuit by a predetermined non-integer upsample ratio of a relatively large number so as to produce a second sampling rate; and calculating only several branches associated with said polyphase filter circuit corresponding to output samples immediately after a transition of the digital input signal so as to reduce the need to store a large number of filter coefficients and to eliminate complex computations. - View Dependent Claims (18, 19, 20)
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Specification