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

ABSTRACT

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 80 MHz, and its bandwidth could be more than 20 MHz. With ± 1.25 V supply, two examples of the proposed filter are introduced. Their bandwidths are from 46.1 to 68.5 MHz and from 22.3 to 48.4 MHz, respectively. Their image rejection ratios could be more than 59 and 39 dB, respectively. Meanwhile, both the IIP3s are over 18 dBm. The theoretical results are demonstrated by using SPECTRE simulation in CHRT 0.18 μm standard complementary metal oxide semiconductor (CMOS) process.

KEYWORDS:

• Current-mode
• Complex filter
• Image rejection
• Tunable independently, high centre frequency
• Leapfrog
• MOCDTA

ACKNOWLEDGMENTS

This work was supported in part by the National Natural Science Foundation of China (No. 61274020). We would like to thank the authors whose works we have cited throughout our paper and also thank the individuals who reviewed this article and gave valuable comments.

DISCLOSURE STATEMENT

No potential conflict of interest by reported by the authors.

Additional information

Funding

National Natural Science Foundation of China [grant number 61274020].

Notes on contributors

Hao Peng

Hao Peng received the BS degree in 2013. Now he is studying towards the MS degree at the Hunan University. His research includes design and simulation of current-mode integrated circuits.

E-mail: [email protected]

Chunhua Wang

Chunhua Wang was born in Yongzhou, China, in 1963. He received the PhD degree from Beijing University of Technology, Beijing, China. He is currently a professor of Hunan University, Changsha, China. His research includes current-mode circuit design and RFIC design. He is the corresponding author.

E-mail: [email protected]

Xiaotong Tian

Xiaotong Tian is studying towards the BS degree at the Hunan University.

E-mail: [email protected]

Jun Liu

Jun Liu is a professor of engineering. He is an engineer at the STATE GRID HUNAN electric power company. His main research interests include optical communications༌ wireless communications༌ next-generation networking, and internet.

E-mail: [email protected]