Systematic Design of Current-Mode Multiple-Loop Feedback Filters Based on a Single CDCTA

In this paper, a new current differencing cascaded transconductance amplifier (CDCTA) is presented. The CDCTA circuit consists of a current differencing unit and n cascaded highly linear voltage-controlled transconductance amplifiers, and it possesses wide bandwidth and linear-tunable feature. Based on this CDCTA, a systematic design method generating current-mode (CM) multiple-loop feedback filter is proposed. By altering the parameters of the design matrix, multiple nth-order CM all-pole low pass filters structures can be synthesized without changing internal circuit. The nth-order filters have low complexity and meet the requirement of no active and passive element matching conditions as adopting only a single CDCTA and n grounded capacitors. Furthermore, the frequency of the nth-order filters can be linearly tuned by the bias voltage. A fourth-order Butterworth filter is designed as an example, and its Cadence simulation results have good agreement with the theoretical analysis.