Multi-stage digital to analog conversion circuit and method
First Claim
Patent Images
1. A digital-to-analog conversion (DAC) circuit, comprising:
- (a) an multi-stage interpolation filter circuit, having a multi-bit input and a multi-bit output;
(b) a noise shaper circuit, having a multi-bit input and a 1-bit output, said noise shaper input being connected to said multi-bit output from said multi-stage interpolation filter circuit; and
(c) a semi-digital FIR filter circuit, having a digital input and an analog output, with said FIR filter digital input being connected to said 1-bit output from said noise shaper circuit, wherein said FIR filter circuit further comprises a shift register having output taps and an input, said shift register input being connected to said FIR filter digital input, a plurality of current sinks, a plurality of DC offset current sources and a first and a second current summing operational amplifier, wherein said current sinks and DC offset current sources are selectively connected to inputs to said first and second current summing operational amplifiers and wherein said inputs of said first and second current summing operational amplifiers are also selectively connected to said output taps of said shift register.
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Abstract
This invention is for a digital-to-analog conversion circuit (DAC) which includes an interpolation filter circuit, a noise shaper circuit and a semi-digital FIR filter circuit. The entire DAC circuit provides noise shaping, analog filtering and oversampling functions.
82 Citations
20 Claims
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1. A digital-to-analog conversion (DAC) circuit, comprising:
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(a) an multi-stage interpolation filter circuit, having a multi-bit input and a multi-bit output; (b) a noise shaper circuit, having a multi-bit input and a 1-bit output, said noise shaper input being connected to said multi-bit output from said multi-stage interpolation filter circuit; and (c) a semi-digital FIR filter circuit, having a digital input and an analog output, with said FIR filter digital input being connected to said 1-bit output from said noise shaper circuit, wherein said FIR filter circuit further comprises a shift register having output taps and an input, said shift register input being connected to said FIR filter digital input, a plurality of current sinks, a plurality of DC offset current sources and a first and a second current summing operational amplifier, wherein said current sinks and DC offset current sources are selectively connected to inputs to said first and second current summing operational amplifiers and wherein said inputs of said first and second current summing operational amplifiers are also selectively connected to said output taps of said shift register. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of converting an n-bit digital signal to an analog signal, comprising the steps off
(a) inputting said n-bit signal to a multi-stage interpolator filter circuit; -
(b) interpolating said input n-bit digital signal to 64 times the sample rate of said n-bit signal; (c) outputting said interpolated signal to a noise shaper circuit; (d) converting said interpolated signal to a 1-bit output signal; (e) inputting said 1-bit output signal to a semi-digital FIR filter circuit, wherein said FIR filter circuit comprises a shift register having output taps and an input, said shift register input being connected to said FIR filter digital input, a plurality of current sinks, a plurality of DC offset current sources and a first and a second current summing operational amplifier, wherein said current sinks and DC offset current sources are selectively connected to inputs to said first and second current summing operational amplifiers and wherein said inputs of said first and second current summing operational amplifiers are also selectively connected to said output taps of said shift register; and (f) converting said 1-bit signal to an analog output signal.
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16. A method of converting an n-bit digital audio signal to an analog audio signal, comprising the steps of:
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(a) inputting said n-bit audio signal to a three-stage interpolator filter circuit; (b) interpolating said input n-bit digital signal in a first stage interpolator circuit to twice the sample rate of said n-bit digital audio signal; (c) outputting said first stage interpolated signal to a second stage interpolator circuit; (d) interpolating said first stage interpolated signal to four times the sample rate of said n-bit digital audio signal; (e) outputting said second stage interpolated signal to a third stage interpolator circuit; (f) interpolating said second stage interpolated signal to 64 times the sample rate of said n-bit digital audio signal; (g) outputting said third stage interpolated signal to a 1-bit noise shaper circuit; (h) converting said third stage interpolated signal to a 1-bit signal; (i) outputting said 1-bit signal to a semi-digital FIR filter circuit, wherein said FIR filter circuit comprises a shift register having output taps and an input, said shift register input being connected to said FIR filter digital input, a plurality of current sinks, a plurality of DC offset current sources and a first and a second current summing operational amplifier, wherein said current sinks and DC offset current sources are selectively connected to inputs to said first and second current summing operational amplifiers and wherein said inputs of said first and second current summing operational amplifiers are also selectively connected to said output taps of said shift register; and (j) converting said 1-bit signal to an analog audio output signal. - View Dependent Claims (17, 18, 19, 20)
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Specification