Method and apparatus for converting A/D nonlinearities to random noise
First Claim
1. A circuit comprising:
- a plurality of capacitors, each having a capacitance of approximately C;
a first switch coupled to a first number x of said capacitors;
a second switch coupled to a second number y of said capacitors;
a switching matrix coupled to said plurality of capacitors and to said first and second switches for selectably coupling said plurality of capacitors to each of said first and second switches such that the time-averaged ratio of the amount of time one of said capacitors is coupled to said first switch compared to the amount of time said one of said capacitors is coupled to said second switch is approximately equal to x/y.
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Abstract
A method and apparatus for removing the effects of mismatched components in an A/D converter is described. The present invention dynamically rearranges the capacitors of an A/D converter so that physical mismatch is averaged out. In the preferred embodiment of the present invention, an array of equally-sized capacitors is coupled to a switching network. A successive approximation scheme is implemented in which the input signal is coupled through SAR switches to the capacitor array. Each switch is coupled to 2N-1 capacitors where N is the switch number. For example, in an 8-bit scheme, there are 3 switches with switch 1 coupled to one capacitor, switch 2 coupled to two capacitors, and switch 3 coupled to four capacitors. In this manner, eight levels of capacitance values can be defined. The present invention adds a scramble control code to control the switching array so that the physical capacitors themselves are coupled to different SAR switches at different times. This requires a scramble matrix of switches, which in the present invention requires N×2N switches where N equals the number of bits of control code. In this manner, the effects of any variations in the capacitance ratios is averaged out and converted to noise which can be filtered out of the signal.
80 Citations
34 Claims
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1. A circuit comprising:
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a plurality of capacitors, each having a capacitance of approximately C; a first switch coupled to a first number x of said capacitors; a second switch coupled to a second number y of said capacitors; a switching matrix coupled to said plurality of capacitors and to said first and second switches for selectably coupling said plurality of capacitors to each of said first and second switches such that the time-averaged ratio of the amount of time one of said capacitors is coupled to said first switch compared to the amount of time said one of said capacitors is coupled to said second switch is approximately equal to x/y. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A method of reducing the effects of component mismatch in an analog to digital (A/D) converter having a plurality of capacitors each having a capacitance of approximately C, said plurality of capacitors coupled to a plurality of switches, said method comprising the steps of:
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defining at least first and second groups of said capacitors, said first group comprising x capacitors and said second group comprising y capacitors; selectively coupling a first of said switches to said first group and a second of said switches to said second group; switching each of said plurality of capacitors into said first group or said second group; controlling said switching of said capacitors such that the time-averaged ratio of the amount of time one of said capacitors is coupled to said first of said switches compared to the amount of time said one of said capacitors is coupled to said second of said switches is approximately equal to x/y. - View Dependent Claims (9, 10, 11, 12)
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13. A circuit comprising:
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a plurality of impedance elements, each having an impedance which is approximately equal; a first switch coupled to a first number x of said elements; a second switch coupled to a second number y of said elements; a switching matrix coupled to said elements and to said first and second switches for selectably coupling said plurality of impedance elements to each of said first and second switches such that the time-averaged ratio of the amount of time one of said elements is coupled to said first switch compared to the amount of time said one of said elements is coupled to said second switch is approximately equal to x/y. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A method of switching elements in a circuit having a plurality of impedance elements, each having an impedance which is approximately equal, coupled to a plurality of switches, said method comprising the steps of:
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defining at least first and second groups of impedance elements, said first group comprising x impedance elements and said second group comprising y impedance elements; selectively coupling a first of said switches to said first group and a second of said switches to said second group; switching each of said plurality of impedance elements into said first group or said second group; controlling said switching of said impedance elements, such that the time averaged ratio of the amount of time one of said impedance elements is coupled to said first of said switches compared to the amount of time said one of said impedance elements is coupled to said second of said switches is approximately equal to x/y. - View Dependent Claims (22, 23, 24, 25)
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26. A circuit comprising:
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a plurality of impedance elements; a plurality of switches; a switching matrix coupled to said impedance elements and to said switches for selectively coupling said impedance elements to said switches such that each of said impedance elements is coupled to not more than one of said switches at any instant, but that each of said impedance elements is eventually coupled to each of said switches. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34)
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Specification