Filter Loop Reduction in DT BP Sigma-Delta Modulator Assisted by Noise Coupling Technique

Abstract

In bandpass modulators, a 2N-order loop filter can lead to an N-order noise shaping in the band of interest. This caused a bandpass modulator with more complex structure than a lowpass modulator and increased the power consumption and area of the modulator. In this paper, we proposed a discrete-time bandpass modulator using the noise-coupling technique that only needs to a second-order loop filter to have a second-order noise shaping. To realize a noise coupled bandpass modulator, we need to implement Z -2 delay block in the analog domain, but the proposed modulator uses only Z -1 delay blocks to apply the noise coupling technique. This simplifies the structure of the modulator and reduces the power consumption, area, and nonlinearity of the modulator. The error in the coupling path is considered and the effect of it on the modulator resolution is analyzed. According to the simulation results, the proposed modulator results in SNR = 84.9 dB at 80 MHz sampling frequency, 200 KHz bandwidth and OSR = 200.