Explicit design formulas for current-mode leap-frog OTA-C filters and 300 MHz CMOS seventh-order linear phase filter

Yichuang Sun*, Xi Zhu, James Moritz

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


The leap-frog (LF) configuration is an important structure in analogue filter design. Voltage-mode LF OTA-C filters have recently been studied in the literature; however, general explicit formulas do not exist for current-mode LF OTA-C filters and there is also need for current-mode LF-based OTA-C structures for realization of arbitrary transmission zeros. Three current-mode OTA-C structures are presented, including the basic LF structure and LF filters with an input distributor or an output summer. They can realize all-pole characteristics and functions with arbitrary transmission zeros. Explicit design formulas are derived directly from these structures for the synthesis of, respectively, all-pole and arbitrary zero filter characteristics of up to the sixth order. The filter structures are regular and the design formulas are straightforward to use. As an illustrative example, a 300 MHz seventh-order linear phase low-pass filter with zeros is presented. The filter is implemented using a fully differential linear operational transconductance amplifier (OTA) based on a source degeneration topology. Simulations in a standard TSMC 0.18 μm CMOS process with 2.5 V power supply have shown that the cutoff frequency of the filter ranges from 260 to 320 MHz, group delay ripple is about 4.5% over the whole tuning range, noise of the filter is 420nA/.√Hz, dynamic range is 66 dB and power consumption is 200 mW.

Original languageEnglish
Pages (from-to)367-382
Number of pages16
JournalInternational Journal of Circuit Theory and Applications
Issue number4
Publication statusPublished - May 2010
Externally publishedYes


  • Active filters
  • Analog circuits
  • Circuit theory
  • OTA-C filters


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