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A compact class-AB variable gain amplifier has been proposed. The amplifier structure is based on twostage architecture comprising a linear transconductor cascaded by a current amplifier-based feedback transimpedance amplifier. The major advantage of such VGA circuit is its ability to offer a good degree of signal linearity without sacrificing the original advantages of its predecessor on both aspects of the power consumption and circuit complexity. Superiority of the proposed VGA has been confirmed by circuit simulation employing 0.18µm standard CMOS technology in designing a 10-MHz VGA under 0.5V voltage supply with MOS's minimum threshold voltage of 0.43V while draining static power consumption less than 25µW.

Low-voltage transconductor circuits suitable for G m -C filter are proposed. The proposed structures were developed from a well-known Nauta's inverter-type class-AB transconductor to improve common-mode rejection without sacrificing extra power consumption. The improvement relies on feed-forwarding both common-mode and differential mode signals, making it power efficient because additionally power has not be wasted only for suppressing common-mode signal. The concept has been confirmed by comparison with simulation on 1-V 5 th -order Chebyshev lowpass filters constructed from the proposed transconductors in 0.18µm CMOS process. The proposed transconductors offer improvement on common-mode rejection by 50dB with 20% less current consumption while still preserving dynamic range.

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