Patent ID: 8284085
Filing Date: 2012-10-09
Classification: H03M

Abstract:
1. An apparatus comprising: a first continuous-time (CT) sigma-delta modulator (SDM) that receives an analog input signal; a first digital-to-analog converter (DAC) that is coupled to the first CT SDM; a first summing circuit that receives the analog input signal and that is coupled to the first DAC, wherein the first summing circuit determines a difference between the analog input signal and an output from the first DAC; an amplifier that is coupled to the first summing circuit, wherein the amplifier has a first gain, and wherein the amplifier includes a filter; a second CT SDM that is coupled to the amplifier, wherein the second CT SDM includes: a digital gain circuit that is coupled to the second CT SDM, wherein the digital gain circuit has a second gain, and wherein the second gain is substantially the inverse of the first gain, and wherein the amplifier, the second CT SDM, and the first DAC collectively have a first transfer function; a digital filter that is coupled to the first CT SDM, wherein the digital filter has a second transfer function, wherein the second transfer function substantially matches the first transfer function, and wherein the first DAC has a third gain, and wherein the digital filter has a fourth gain, and wherein the second DAC has a fifth gain, and wherein the ratio of the third gain to the fifth gain is approximately equal to the fourth gain; and a second summing circuit that is coupled to the digital filter and the digital gain circuit.