CMOS current-mode active transformer sigma-delta modulators

This paper presents a new current-mode sigma-delta modulator for Blue-tooth base-band applications. The modulator employs a current-mode ADC, a current-mode DAC, and a new active transformer loop filter to provide the desired noise shaping characteristics. The modulator provides the advantages of tunable filter bandwidth and an extremely small silicon area consumption. The modulator has been implemented in TSMC's 0.18μm 1.8V CMOS technology and analyzed using SpectreRF from Cadence Design Systems with BSIM3V3-RF device models. The simulation results have demonstrated that the modulator exhibits a SNR of 65 dB and a dynamic range of 50 dB at a sample rate of 500 M/s and a bandwidth of 5 MHz while occupying 0.0073mm² silicon area.