Basic configuration using N-mosfet. (Not too different from common base
operation in transistors.) Gate is held to an unchanging bias level. An incoming signal is applied to the source leg, in such a manner that it changes the gate-source relative voltage. (Thus operation is similar to changing base-to-emitter voltage in a transistor.)
Play with values to obtain a reasonable range of output. Saturation might be indicated when output goes to an extreme, either supply V or 0V gnd.