REALIZATION OF SIGNAL PROCESSING & GENERATING CIRCUITS USING OTRA

Abstract

With the evolution of submicron technologies such as 0.18 micron and 0.13 micron, the supply voltages have been reduced to 1.5 volts and lower. This makes it difficult to design a voltage mode CMOS circuit with high linearity and wide dynamic range. Also as signal processing extends to higher frequencies, the traditional design methods based on voltage operational amps are no longer adequate. To overcome these problems circuits operating in current mode are preferred. Various analog building blocks operating in the current mode are available. Operational Trans-Resistance Amplifier (OTRA) is one of them. OTRA is a current controlled voltage source. Both its input and output terminals are characterized by low impedance, therefore eliminating response limitations incurred by capacitive time constants. Its bandwidth is independent of closed loop voltage gain. Thus using the OTRA as the active building block various signal processing and generating circuits can be realized with more flexibility in controlling the frequencies of waveforms. The Operational Trans-Resistance Amplifier (OTRA) is though not available as a single IC but various CMOS circuit realizations are available in literature and can also be implemented using two standard CFOAs. One such CFOA that can be used is the commercially available AD844AN IC 5 manufactured by Analog Devices Inc., US. The AD844AN has current feedback architecture. In this project Operational Trans-Resistance Amplifier (OTRA) based different analog signal processing and generating circuits such as Filters, Multiphase Sinusoidal Oscillators (MSO), Voltage Controlled Oscillator (VCO) and LC oscillator based on active realization of inductor have been realized. The theoretical results have been verified through PSPICE simulations and experimental work by assembling practical circuits of the above and testing them to give near theoretical results. For practical circuits the OTRA has been realized using the AD844AN CFOA ICs manufactured by Analog Devices.