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An operational transconductance amplifier (OTA), where its transconductance gain can be digitally controlled and linearly tuned, is proposed in this paper. The realization method is achieved by biasing the two fully balanced differential pairs with class AB current mirror and the current division network (CDN). gm of the proposed OTA can be linearly tuned by an external control current Iadj and the digitally controlled current gain α in the range of 0 to 500uS. The input-voltage range of about 200mVp-p with less than 1.0% nonlinearity is obtained. The performance of the proposed OTA is discussed and confirmed through an application example and PSPICE simulation results.