flow through two voltage dividers of similar impedance the first comprises r12 the balancing impedance of r18 r22 and c14 and finally r17 the second comprises r8 the transmission pair between r1 and r2 and r11 the transmitted signal is not however seen at the input terterminals 31 and 32 this occurs because the line differential voltage and the balance impedance differential voltage are both connected to the summing inputs 31 and 32 of the summing differential amplifier 3a the differential line voltage is connected by r9 and r10 to the inputs 32 and 31 respectively and the balance impedance voltage is connected to the inputs 31 and 32 by r13 and r15 connections from the line voltage to the differential amplifier have been reversed so that this voltage is subtracted from the balance impedance voltage thus the differential amplifier amplifies the difference of the two differential voltages which is effectively zero for transmitted signals because the termination impedance connected to the terminals r1 and r2 is the same and also the impedance between the terminals r1 and r2 and the inputs 31 and 32 is the same common mode voltages do not cause a differential voltage to be applied across the inputs 31 and 32 and hence they are ignored by the amplifier 3a if common mode signals were presented to an unbalanced termination differential voltages would result at the amplifier 3a and hence would result as an output from the receiver at the rxd terminal more specifically terminal r1 sees ground through resistors r9 and r15 and sees the input 32 through.