What is an Operational Transconductance Amplifier (OTA) and how is it used in integrated circuits?

An OTA outputs current proportional to differential input voltage, with transconductance (gm) controllable via bias current. Key characteristics: gm = Ibias/(2*VT) for BJT, Output is high-impedance current source, Gain is gm*Rload. IC applications include: Gm-C filters (OTA + capacitor creates integrator, tunable by bias current), Voltage-controlled amplifiers, PLL loop filters, and Continuous-time sigma-delta modulators. Design considerations include linearity (limited input range before gm degradation), noise (proportional to sqrt(gm)), and power-bandwidth trade-off. Linearization techniques include source degeneration and cross-coupled differential pairs.