Modified-Nauta Operational Transconductance Amplifier for 400 MHz High-Q VHF Filter

This paper proposes an efficient transconductor structure nearly free from the serious drawback of common- mode signal amplification at its output found in the conventional Nauta-OTA widely used for the implementation of VHF filter. A newly developed method mathematically clarifies the transfer characteristic of the proposed OTA and reveals the essential features of OTA/gyrator. In order to verify this scheme, we implemented a transconductor circuit and a lowpass filter based on the proposed concepts, using a compact circuit design that avoids CMFB circuit and parasitic poles. The measurement results of a 7^th order Gm-C Chebyshev lowpass filter with cutoff frequency of 400 MHz, are shown.