Design and analysis of the quadfferential amplifier

This paper presents a design and analysis of a quadfferential amplifier for a CAT5 cable. A quadfferential amplifier consists of four inputs, four outputs, and a Vocm pin which controls the output common-mode voltage (Erdi, 1970 [1]). It is similar to the differential amplifier in that it amplifies differences and rejects overall input common-mode. The transfer function shows that quadfferential amplifier requires symmetry of feedback and gain resistors to approach its ideal behavior. Using a graphical approach the amplifier is compensated to drive a capacitive load of 50 pF. The output current drive is designed for minimum load resistance of 150Ω. Performing Monte Carlo simulations to evaluate offset voltage and common-mode rejection shows the mean offset voltage of 265μV and a common-mode rejection of 126 dB.