Companding Realizations of the Nonlinear Energy Operator

Realizations of the nonlinear energy operator (NEO), using the concept of companding filtering, are introduced and compared in this work. For this purpose, the Log-Domain and Sinh-Domain filtering techniques have been followed. Both topologies are constructed from differentiator and multiplier blocks which have been realized through the utilization of nonlinear transconductor cells. Both of the proposed topologies offer the capability of ultra-low voltage operation, thanks to the employment of MOS transistors in the weak inversion. Considering a single power supply voltage of 0.5？V, the behavior of the proposed NEO realizations has been simulated using the Analog Design Environment of the Cadence software and the design kit of the TSMC 130？nm process. Comparison results show that the Sinh-Domain realization offers a more power efficient design than that offered by the Log-Domain realization. 1. Introduction Owing to its efficiency for estimating the instantaneous product of amplitude and frequency of a signal, the NEO is a very powerful tool for handling biomedical signals. A number of NEO realizations have been already introduced in the literature [1–4]. The topology in [1] operates in a supply voltage 1.8？V, while a dual ±1.65？V supply voltage scheme has been used in [3]. A power supply voltage 2？V has been utilized in the topology in [4], while the topology in [2] operates at 0.6？V. Conventional linear Operational Transconductance Amplifiers (OTAs) have been utilized for realizing the topologies in [1, 3]. A drawback of these realizations is the restriction for handling signals with relatively low amplitude, so that the conditions for small-signal operation are fulfilled, and the transconductance parameter of the corresponding MOS transistors can be employed. The same restriction is also valid for the realization in [2], where the small-signal transconductance parameter of current mirror has been utilized for realizing the required resistors. Companding realizations do not suffer from the aforementioned limitation, due to the fact that an externally linear system could be constructed from nonlinear active blocks. Thus, there is an absence of employment of linearization techniques and/or small-signal operation conditions for achieving the linear operation of the whole system. Therefore, for given amplitude of the input current, the bias current could be chosen smaller than that in the case of the conventional linear systems [5–13]. In the Log-Domain implementation in [4], the required nonlinear transconductors have been constructed from translinear