New Log-Domain First-Order Multifunction Filter Using MOSFETs in Weak Inversion

Abstract

In 1979, Adams [1] proposed the concept of log-domain signal processing but this concept did not receive much attention of the researchers at that time. The power of log-domain technique came into popular focus only when Frey [2] [3] gave a generalized method to synthesize log-domain filters by using state-space technique. The principle of log-domain signal processing is to first compress (logarithmic) the input signal and then process it and finally expand (exponential) the signal at output stage. The working nature of log-domain filters is the same as that of companding circuits which were proposed by Tsividis, Gopinathan and Toth [4] independently in 1990. Thus, the log-domain circuits fall into the class of externally linear and internally nonlinear (ELIN) circuits. Adams circuit was the first ELIN circuit. The log-domain filters are also recognized as translinear (TL) filters (or dynamic translinear filters). The TL filter concept was reinvented by Seevinck [5] in 1990.