70-MHz IF 10-MHz bandwidth bandpass Sigma Delta modulator for WCDMA applications
A MASH bandpass Sigma Delta modulator for wideband code division multiple access (WCDMA) applications is presented. The signal bandwidth of the proposed modulator is 10 MHz centered around an intermediate frequency (IF) of 70.5 MHz. Two two-path second-order bandpass Sigma Delta modulators make the MASH architecture, which realizes a noise transfer function with four couples of complex conjugate zeros. The proposed circuit, fabricated with a 0.18 mu m CMOS technology, uses a sampling frequency of 180 MHz to obtain a resolution of about 12 bits in the 10 MHz bandwidth around the IF. The measured modulator power consumption is 95 mW with a supply voltage of 1.8 V. The achieved figure-of-merit (FoM(Bp)) is 0.37 pJ/conversion-level.
bandpass analog-to-digital conversion sigma-delta modulation