Unconditionally Stable Non-Foster Element Using Active Transversal-Filter-Based Negative Group Delay Circuit

Tiedi Zhang, Ruimin Xu, Chung Tse Michael Wu

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


This letter introduces a novel type of non-Foster element using a microwave transversal-filter-based negative group delay (NGD) circuit that can exhibit unconditional stability. The proposed device is realized by a distributed amplifier, in which the NGD response is synthesized by adjusting the ratio of transconductance of transistors in each stage. On top of this, by properly amending the in-band magnitude and phase characteristics, the NGD circuit can realize non-Foster elements within the operating band. Furthermore, thanks to the distributed topology, the proposed network has very good input and output matching characteristics. As proof-of-concept, a prototype of the proposed non-Foster element is built to validate the proposed scheme. The experimental results show that the proposed circuit can realize a unilateral non-Foster element composed of a -1 pF shunt capacitor and a -1.25 nH series inductor.

Original languageEnglish (US)
Article number8031279
Pages (from-to)921-923
Number of pages3
JournalIEEE Microwave and Wireless Components Letters
Issue number10
StatePublished - Oct 2017

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Electrical and Electronic Engineering


  • Distributed amplifier (DA)
  • negative capacitance
  • negative group delay (NGD)
  • negative inductance
  • non-Foster element


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