Here the WE-CNSW has been inserted in series with the circuit D+ and D- lines to cancel the noise within the USB / Opamp circuit. In addition, a surge protection device is also being used where D1 is connected in parallel with the lines for added surge protection from outside sources. The common mode device here, since being put on the input line of the signal, will clean the signal just as it enters the circuit, preventing any other noise from being generated later on. It is also protected from surges by D1.