Conference Paper

A 1 GHz OTA-Based low-pass filter with a high-speed automatic tuning scheme

Nat. Chiao Tung Univ., Hsinchu
DOI: 10.1109/ASSCC.2007.4425717 Conference: Solid-State Circuits Conference, 2007. ASSCC '07. IEEE Asian
Source: IEEE Xplore


A continuous-time 4th-order equiripple linear phase G m -C filter with an automatic tuning circuit is presented. A high speed OTA based on the inverter structure is realized. The combined CMFF and CMFB circuit ensures the input and output common-mode stability. The gain performance could be maintained by combining a negative resistor at the output nodes. Transconductance tuning can be achieved by adjusting the bulk voltage by using the Deep-NWELL technology. Through the use of the OTA as a building block with a modified automatic tuning scheme, the filter -3 dB cutoff frequency is 1 GHz with the group delay less than 4% variation up to 1.5 fc frequency. The -43 dB of IM3 at filter cutoff frequency is obtained with -4 dbm two tone signals. Implemented in 0.18-mum CMOS process, the chip occupies 1mm2 and consumes 175 mW at a 1.5-V supply voltage.

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    ABSTRACT: A class-AB, dual path building block for Gm-C filter that has high linearity and high PSRR is presented. The class-AB action provides good linearity and gm/Id while the dual path approach solves the PSRR problem associated with conventional class-AB OTA. A current-mode 4<sup>th</sup> order Butterworth filter designed using the proposed building block in 0.13 mum CMOS technology provides 54.2 dB IM3 and 52 dB SNR in 1.3 GHz bandwidth while consuming as low as 24 mW. It occupies 0.1 mm<sup>2</sup>.
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