An improved biasing scheme for NMOS cascode structures for linear voltage regulators is proposed for mixed-signal communication systems. The proposed regulator achieves approximately 40 dB power supply rejection over wide frequency range, 15 mA load current regulation, and a regulated voltage temperature coefficient of 6 ppm/°C. This paper also presents a modified Gilbert cell SiGe-based HBT voltage reference circuit for the proposed regulator. The bandgap circuit demonstrates a simulated line regulation of 95 dB at DC, 70 dB at 1 MHz, and a reference voltage temperature coefficient of 2 ppm/°C. The proposed regulator has been designed for the IBM SiGe BiCMOS 0.35-μm process.