New Log-Domain First-Order Multifunction Filter Using MOSFETs in Weak Inversion
Circuits and Systems
In 1979, Adams  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   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
... 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  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  in 1990. Abstract A new current-mode first-order log-domain multifunction filter is presented in this paper. This filter has single input and provides three outputs (low-pass, high-pass and all-pass) using a first-order low-pass filter and five of current mirrors as building blocks. The proposed filter employs only MOSFETs and a grounded capacitor. The first-order filters are used in audio and video applications extensively. The MOS-FETs of the core section are operated in weak inversion thereby making the circuit suitable for low-voltage, low-power applications. The SPICE simulations have shown good performance of the proposed filter.