Application of network transposition in the design of OTA-C filters and oscillators

Recent advances in analog integrated circuit and signal processing have shown that the current-mode approach is superior to the voltage-mode in terms of its wide bandwidth, high speed, low voltage and power. As a wide range of voltage-mode analogue circuits already exist, a straightforward method of converting these voltage-mode circuits to current-mode circuits would be very useful. The network transposition, introduced by Bhattacharyya and Swamy as early as in 1971, provides a perfect solution to this question of conversion from voltage-mode to current-mode circuits. A vast body of literature already exists concerning voltage-mode OTA-C filter structures. At the same time, many current-mode OTA-C filter structures are being reported in the literature. These two apparently independent areas of research and development could be unified by the application of the principle of network transposition. For this reason, an intensive investigation on the OTA-C structures is conducted. The result of this investigation shows that transposition relationship could be used to advantage in deriving current-mode filter structures from the voltage-mode filter structures and vice versa. The principle of transposition has been extended to oscillator circuits to derive new OTA-C oscillator structures from known ones. The concept of transposition has been extended to differential input dual-output (DIDO) structures, since such structures can increase the common-mode rejection ratio, eliminate the even-order harmonic distortion components and reduce the effects of power supply noise. The theoretical work presented in the thesis is verified by simulation results as well as by practical circuits using discrete resistors, capacitors and OTA devices. In addition, an oscillator is fabricated in a 0.18 om CMOS process to further verify the validity of network transposition. The measurement result shows good agreement with the theoretical analysis