Gilbert cell
In electronics, the Gilbert cell is a type of mixer. It produces output signals that are proportional to the product of two input signals. Such circuits are widely used for frequency conversion in radio systems. The advantage of this circuit is the output current is an accurate multiplication of the (differential) base currents of both inputs. As a mixer, its balanced operation cancels out many unwanted mixing products, resulting in a "cleaner" output. It is a generalized case of an early circuit first used by Howard Jones in 1963, invented independently and greatly augmented by Barrie Gilbert in 1967. It is actually a specific example of “translinear” design, a current-mode approach to analog circuit design. The specific property of this cell is that the differential output current is a precise algebraic product of its two, differential analog current inputs. (Wikipedia).
