Design of Low Power Electronic Circuits for Bio-Medical Applications

The operational transconductance amplifier, OTA is one of the basic building blocks in many analogue circuit applications. The low power consumption is an essential parameter in modern electronic designs for many areas particularly for portable devices and biomedical applications. For biomedical applications, the low-power low-voltage OTA-C filters operating at low-frequency ranges are desired. The low-power, low-voltage operation of electronic devices is very important for applications such as hearing aids, pacemakers, and EEG. The importance of such operation is due to the need to implant these electronic circuits inside the body of the patient for long times before re-charging or replacing the batteries as for pacemakers and future hearing aids. The small size lightweight wearable EEG systems are preferable for applications ranging from epilepsy diagnosis to brain-computer interfaces. The low power consumption is achieved by operation at very small levels of current. So, in such applications the operation in the nano-ampere current range is essential to ensure power consumption of nW or few µW. Such very small currents are obtained through the operation of MOS transistors in their sub-threshold regime. The design space in such applications is restricted by their specifications which in turn based on the nature of the application. In this work, the design and implementation of OTA-C filter topologies for two bio-medical applications are made and discussed. Those applications are represented by hearing aids and EEG applications. In hearing aids, the work focused on cochlear implant and specifically on its most important stage represented by the filter. Four OTA-C filter topologies are proposed and two of them are tested experimentally. For the filter in a hearing aid system, besides its low power operation, it is required to operate with a relatively high dynamic range of 60dB and above. The dynamic range is the operation space of the filter that specified by the range of signals which can process properly. It is bounded by the maximum power signal less than its distortion overhead level to the minimum power signal more than its noise floor. The maximum signal level the filter can perform properly represents its input linear range. The challenge in CMOS OTA sub-threshold operation is the very small input linear range which makes it extremely difficult to build low-power consumed OTA-C filters with a wide dynamic range, DR. In this work, an OTA with an input linear range of ±900mV for total harmonic distortion, THD