1. Introduction
Low frequency oscillators are important for many applications and particularly for biomedical, electronic and instrumentation devices [1,2]. The design of such oscillators is difficult mainly due to the large values of capacitors and resistors required to achieve low oscillation frequencies [3]. Several circuit design techniques and structures have been reported in the literature to avoid the use of such impractically large component values [4–9]. However, recent developments in material science and mainly in carbon-based energy storage devices have resulted in capacitors with values exceeding 1 Farad, which are commercially available from several vendors. These capacitors are known as supercapacitors [10] and are also referred to as ultra-capacitors or electric double layer capacitors [11]. They are energy storage devices with diverse applications ranging from energy storage for wind turbines [12], and other renewable energy sources [13], hybrid and electric vehicles [14], to wireless sensor nodes [15]. The impedance of super-capacitors usually shows frequency-dependent behavior that can be modeled by a capacitance dispersion phenomena (due to distributed surface reactivity, inhomogeneity
