Amplifier performance enhancement methods using positive feedback techniques
The dramatic growth in the hi-tech sector of consumer market has created many unprecedented challenges in the area of integrated circuits. The present and future communication and entertainment systems including high speed cable and DSL modems, broadband wired and wireless systems, and high definition visual products require very fast and high accuracy amplifiers, data converters and filters. Analog design in the new digital CMOS submicron processes is becoming an economical necessity in the industry. The task of building fast Op-Amp with very high DC-gain is already a very difficult problem, and this task has become more difficult using these new submicron digital processes, where traditional gain enhancement techniques are loosing their ability to deliver amplifiers with sufficient gain. In this work three new methods of implementing the internal positive-feedback to build very high DC-gain amplifiers with very low gain sensitivity to signal swings are presented. Amplifiers proposed in the first method have very high current-controlled gain. A DC gain larger than 100dB is possible without limiting the speed of the amplifier. Amplifiers proposed in the second method exhibit both enhanced speed, i.e., unity gain frequency, and enhanced gain. Amplifiers proposed in the third method have self-adjusting gain without extra control block. An implementation of a 3 bit multiplying DAC in a 9-bit 165MS/s pipeline ADC built in a 1.8V, 0.21mu digital CMOS process using one of the proposed amplifiers is described. Test results show high gain with very fast settling.