An asynchronous short word length Delta-Sigma FIR filter for low power DSP

Asynchronous design techniques such as NULL Convention Logic (NCL) are of increasing interest for ultra low power designs used in portable body wearable Digital Signal Processing (DSP) applications such as pacemakers, ECG monitors, speech filtering for hearing aids and the like. Their primary advantages are their intrinsic tolerance to process, voltage and temperature variations at lower supply voltage operation, the potential for reduced power consumption, along with simplified timing analysis efforts. Furthermore, Short Word-Length (SWL) filter systems that operate, for example, on single bit Sigma-Delta encoded data have also been suggested for low-power and portable systems. Synchronous short word length filters using over sampling of both data and coefficients and operating in this domain have already been shown to be typically more hardware efficient and give better performance than their equivalent multi-bit counterparts. This work explores whether the highly pipelined organization of SWL systems can be exploited to produce usable ultra-low-power asynchronous DSP applications. A single-bit binary delta sigma domain finite impulse response filter is implemented in hardware using asynchronous NCL technique and its performance is measured in terms of average power and speed of operation. Our results show that the filtering performance required by the applications requiring low power such as speech filtering applications can be obtained using ultra low supply SWL NCL operated down to 400mV.