Ciena Corporation
Extremely-fine resolution sub-ranging current mode Digital-Analog-Converter using Sigma-Delta modulators

Abstract:

A X-bit Digital-to-Analog Converter (DAC) circuit includes an effective X/2-bit coarse DAC configured to produce a coarse bitstream (CBS) from a digital input DC.sub.1 using an n.sup.th order Sigma-Delta (.SIGMA..DELTA.) modulator, and to provide a coarse current source based on the CBS, wherein X is an even integer and n is an integer; an effective X/2-bit fine DAC configured to produce a fine bitstream (FBS) from a digital input DC.sub.2 using a 1.sup.st order .SIGMA..DELTA. modulator, and to provide a fine current source based on the FBS; and an output configured to form a voltage from the combination of the coarse current source and the fine current source.