Continuous-Time Filters from 0.1Hz to 2.0GHz

caroline11

Abstract.-The bipolar transconductance amplifier (OTA) was commercially introduced in 1969 by RCA. Designers began using OTAs in the middle 80’s, since then the CMOSOTA has becoming a vital component in a number of electronic circuits, both in open loop and in closed loop applications. Here, we will focus on open loop applications. Continuous-time filters implemented with transconductance amplifiers and capacitors known as Gm-C or OTA-C are very popular for a host of applications. These applications involve frequency of operation from a few tents of a hertz up to several gigahertz. Several of those applications are in medical electronics and seismic area where the frequency range is between 0.1Hz up to 20Hz. Other applications in the audio range do not commonly use OTA-C filters because switched-capacitor techniques excel in this range. But for frequency range of a few MHz like in Intermediate Frequency (IF) filters in RF receivers OTA-C implementations are very attractive. For a few GHz range applications where the OTA becomes a simple differential pair there is number of researchers investigating LC-oscillators and filters. In this tutorial we discuss practical implementations of transconductance amplifiers oriented for wide range of applications for example in medical, IF filters, hard disk drive linear phase filters, LC-oscillators and RF filters. Furthermore the unavoidable tuning scheme to compensate the Gm/C deviations due to process technology variations is discussed. OTA single ended, fully differential and pseudo differential versions are introduced together with the commonmode feedback circuits needed for proper operation of differential architectures.