A Negative R-Assisted Amplifier on the Virtual Ground and Its Applications

An active network with the property that the impedance on a terminal pair is negative is called as a negative impedance, and many active circuits, such as amplifiers, filters and oscillators, contain the negative impedance. In particular, a negative resistor (negative R) has been used since the days of the vacuum tube oscillators, in which the negative R compensates for resistive leakage of an inductor. In the late 1970s and early 1980s, significant research efforts were made to expand the bandwidth of amplifiers and apply them to integrated filters and oscillators [1-4]. Among these, an amplifier with a negative R on its virtual ground was proposed in [1] and described in [2-5]. The idea of using the negative R-assisted amplifier has been used in recent state-of-the-art works [6-19], as it turns out that the negative R compensates for the finite gain, bandwidth, noise and distortion of the amplifier. Despite many advantages, the negative R-assisted amplifier did not get the attention it deserves. The aim of this paper is, therefore, to reconsider some of these early concepts [1-5], and in particular to evaluate the benefits of negative R-assisted amplifiers in the light of recent advances [6-19]. The rest of the paper is organized as follows. First, the operation principle of fundamental building blocks with negative R such as inverting amplifier and integrator is described. Second, several negative-R assisted amplifiers in the signal chain are discussed. Third, the design benefit of continuoustime delta-sigma modulators (CTDSMs) with negative R-assisted integrators is evaluated. The negative R lmplementation is also discussed. Finally, an interesting option is described to proceed this concept.