A 2.8-V Multibit Complex Bandpass ΔΣAD Modulator in 0.18μm CMOS

A second-order multibit switched-capacitor (SC) complex bandpass ΔΣ AD modulator has been designed, fabricated and tested for application to low-IF receivers in wireless communication systems. We have employed two new algorithms there to improve the signal-to-noise-and-distortion (SNDR) of the modulator, (i) A complex bandpass filter with I, Q dynamic matching to reduce the mismatch influence between I, Q paths. As its by-product, the complex modulator can be divided into two separate parts without signal line crossing between the upper and lower paths. Therefore, the layout design of the modulator can be greatly simplified; (ii) A new complex bandpass data-weighted averaging (DWA) algorithm is implemented to suppress nonlinearity effects of multibit DACs in complex form to achieve high accuracy. Implemented in a 0.18-μm CMOS process and at 2.8V supply, the modulator achieves a measured peak SNDR of 64.5dB at 20MS/s with a signal bandwidth of 78kHz while dissipating 28.4mW and occupying an area of 1.82mm².