Negative current feedback OTA with application to 250 MHz Gm-C filter

A 4th-order low-pass Gm-C filter for high speed wireless/wireline system is realized in 0.18 μm CMOS process. The high speed filter is designed based on operational transconductance amplifier (OTA) biquad sections. As well known, large transconductance is required for high speed applications, and thus the conventional source degeneration topology, which operates with the trade-off between linearity and transconductance, should be improved. In this paper, the proposed OTA uses negative current feedback topology to maintain linearity while increasing transconductance for high speed application, and a 4th-order low-pass filter is realized by using the OTA as a building block. Fabricated in 0.18 μm CMOS technology, the -3 dB filter frequency response at 250 MHz is obtained. The measured HD3 performance is about -40 dB while the filter consumes 32 mW power at a 1.8 V supply voltage.