Method and apparatus for converting a/d nonlinearities to random noise

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 2.sup.N-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.times.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.