Ultra Low Power Switched Current Finite Impulse Response Filter Banks Realized in CMOS 0.18 μm technology

摘要

Ultra low power circuits are in high demand in many applications especially in wireless sensor networks (WSN), where energy is scavenged from environment. WSN systems contain different blocks, such as: sensors, filters, analog-to-digital converters, very often a simple processor and the RF front end block. This paper concerns ultra low power finite impulse response (FIR) filters and filter banks implemented in a switched current (SI) technique. In this paper new SI FIR filter structures and filter banks have been proposed. These circuits operate in the current mode and do not use operational amplifiers, what enables very low power dissipation on the level of several μW. Proposed filters incorporate transistors working under threshold level for the voltage supply that is in the range 0.5 - 0.7 V. The simulated attenuation in the stopband of the frequency response is limited to about 45 dB, what is due to different nonidealities, but such value is usually sufficient in WSN applications. The SI technique features many interesting mechanisms that simplify realization of analog filter banks. The signal samples that are stored in the delay lane are in SI filters copied to the filter coefficients using current mirrors. As a result, there exists the possibility to connect many sets of filter coefficients to a single delay line without the speed limitation. Ultra low power operation of proposed filters is also possible due to a special structure of the clock generator that only consists from switches and NOT gates.