A Tunable Leapfrog Complex Filter for High Frequency and Wide Bandwidth Using Multi-Output Current Differencing Transconductance Amplifiers

摘要

In this paper, a new fourth-order complex (polyphase) filter is realized with the leapfrog structure. The proposed filter is based on the first-order stage using multi-output current differencing transconductance amplifiers (MOCDTAs). The design procedures for the realization of the first-order stage and fourth-order leapfrog polyphase filter are presented. In the procedures, the signal flow diagrams are also presented. The proposed design using MOCDTA simplifies the circuit of the current-mode leapfrog complex filter, where there are no resistors and with minimum number of active components. Besides, its centre frequency and bandwidth could be electrically tunable independently. The centre frequency of the proposed filter could be adjusted from 20 to 80MHz, and its bandwidth could be more than 20MHz. With +/- 1.25V supply, two examples of the proposed filter are introduced. Their bandwidths are from 46.1 to 68.5MHz and from 22.3 to 48.4MHz, respectively. Their image rejection ratios could be more than 59 and 39dB, respectively. Meanwhile, both the IIP3s are over 18dBm. The theoretical results are demonstrated by using SPECTRE simulation in CHRT 0.18 m standard complementary metal oxide semiconductor (CMOS) process.