Apparatus and method for a combination D/A converter and FIR filter employing active current division from a single current source
First Claim
1. An FIR filter for a digital-to-analog conversion circuit, comprising:
- (a) a shift register having a 1-bit digital input stream and a plurality of output taps, wherein each said output tap provides a 1-bit signal which has a value of a logic 1 or a logic 0;
(b) a single current source having a current output divided by a plurality of current paths, wherein each said path includes an active element having a high output impedance, each said active element being connected to a first terminal of an active high switch and a first terminal of an active low switch;
wherein a single said output tap of said shift register is used to control said active high switch and said active low switch for a single current path; and
wherein a second terminal of each said active high switch of each of said plurality of current paths is connected to a non-inverted output current path, and a second terminal of each said active low switch for each of said plurality of current paths is connected to an inverted output current path.
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Abstract
An active current steering semi-digital FIR filter for a digital-to-analog conversion circuit, which includes a shift register having a 1-bit digital input stream and a plurality of output taps, where each output tap provides a 1-bit signal which has a value of a logic 1 or a logic 0, and a plurality of current paths, where each path includes an active element, such as a transistor, having a relatively high output impedance, which is connected to a common current source, and to an op amp for current-to-voltage conversion. The relatively high output impedance of the active current steering element causes any error term resulting from offset at the op amp inputs to be minimized.
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Citations
23 Claims
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1. An FIR filter for a digital-to-analog conversion circuit, comprising:
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(a) a shift register having a 1-bit digital input stream and a plurality of output taps, wherein each said output tap provides a 1-bit signal which has a value of a logic 1 or a logic 0; (b) a single current source having a current output divided by a plurality of current paths, wherein each said path includes an active element having a high output impedance, each said active element being connected to a first terminal of an active high switch and a first terminal of an active low switch; wherein a single said output tap of said shift register is used to control said active high switch and said active low switch for a single current path; and wherein a second terminal of each said active high switch of each of said plurality of current paths is connected to a non-inverted output current path, and a second terminal of each said active low switch for each of said plurality of current paths is connected to an inverted output current path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of converting a 1-bit digital input signal to an analog output signal, comprising the steps of:
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(a) inputting said 1-bit digital input signal to a shift register; (b) shifting said 1-bit signal through said shift register; (c) providing, as a control bit, said shifted 1-bit signal to a plurality of output taps disposed along said shift register, wherein said control bit has a value of either a logic 1 or a logic 0; (d) controlling a plurality of non-inverted current switches and inverted current switches with said bit-values of said shift register output taps, wherein a single output tap value controls a single pair of switches comprised of a single non-inverted current switch and a single inverted current switch, and wherein said plurality of non-inverted current switches and inverted current switches are connected to a common current source; (e) producing a differential current from said plurality of non-inverting current switches and inverting current switches; and (f) inputting said differential current to a first and a second op amp circuit, wherein a differential voltage is output from said first and second op amp circuits. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method of converting a 1-bit digital input signal to an analog output signal, comprising the steps of:
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(a) inputting said 1-bit digital input signal to a shift register; (b) shifting said 1-bit signal through said shift register; (c) providing, as a control bit, said shifted 1-bit signal to a plurality of output taps disposed along said shift register, wherein said control bit has a value of either a logic 1 or a logic 0; (d) producing a differential current at a pair of current summing nodes by using said control bits to open or close switches disposed along a plurality of current paths connected to a common reference current source, wherein a DC offset current is subtracted from said differential current; and (e) inputting said differential current to a current-to-voltage conversion circuit, wherein a differential voltage is output from said current-to-voltage conversion circuit. - View Dependent Claims (23)
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Specification