A 12-bit 65 MS/s pipeline A/D converter in 0.18 μm SiGe BiCMOS
This work discusses the benefits of a SiGe BiCMOS implementation over a CMOS implementation for pipeline A/Ds. While various circuit blocks in a pipeline A/D can benefit from the higher transconductance (gm), higher unity gain frequency (fT) and lower noise of SiGe HBTs, this work focuses on the most critical block in a pipeline A/D, the operational transconductance amplifier (OTA). An OTA employing an all NMOS pre-amplifier followed by a cascoded SiGe HBT stage with actively cascoded PMOS loads is designed. A prototype 12-bit pipeline A/D achieves a measured SNDR of 62.6 dB and a SFDR of 73.4 dB at 65 MS/s with a power dissipation of 325 mW and operates from dual 1.8 V and 3.3 V supplies.