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A simple nA/V CMOS transconductor for low-frequency gm-C filters is presented. To benefit from the lowest gm/ID ratio, input transistors operate in the triode region, with gm adjusted by their (W/L) and VDS, the latter a tuning-voltage replica. Since VDS surmounts the equivalent noise of the replica circuit, excellent control of gm is attained. Simulations support theoretical analysis. A 5Hz bandpass filter was designed, featuring SNR=59.2 dB for THD<1% at 150 mV and 17 nW consumption.