Low-voltage fully differential switched-opamp bandpassΣΔ modulator

摘要

The paper deals with the design of a low-voltage bandpassnΣΔ modulator implemented with the switched-capacitorntechnique. To use standard technology (no low-threshold devices) andnwithout an on-chip voltage multiplier, the switched-opamp technique hasnbeen adopted. The basic building blocks for the construction of anΣΔ modulator (SC integrator, quantiser, and feedback DAC)nare proposed in a fully differential version. In addition, they havenbeen improved with respect to those previously reported to give a largernoutput swing at a higher sampling frequency and without any voltagenreference. The validity of the proposed circuits is demonstrated by thenrealisation of a second-order bandpass ΣΔ modulatornoperating with a single 1 V supply within a standard 0.5 Μm CMOSntechnology (VTHn=0.65 V, VTHp=0.7 V). Thenmodulator operates at a sampling frequency of 1.8 MHz with a full-scaleninput range of 2 Vpk-pk and achieves a 45 dB dynamic range inna 20 kHz bandwidth