A four quadrant multiplier suitable for neural networks is presented. The product of two analogue voltages Vx and Vw is achieved by performing the difference of two currents, I1 and I2, that are nonlinearly related to Vx and Vw. Both currents are passed through the same transistor in two different time slices, eliminating, thereby, problems due to component mismatch.
Mekkaoui, A., & Jespers, P. (1991). 4 Quadrant Multiplier for Neural Networks. Electronics Letters, 27(4), 320-322. https://doi.org/10.1049/el:19910202 (Original work published 1991)