Sub-miniature common mode filter with integrated ESD protection

A miniaturized common mode filter (CMF) for the USB 2.0 interface is presented. This novel design is built in a planar copper/polyimide process, allowing its combination with Electrostatic Discharge (ESD) protection diodes fabricated in bipolar semiconductor technology. This filter design provides strong common mode rejection in the GSM spectrum and the ESD protection diodes feature a very low dynamic resistance. The small size (1.34 mm × 0.95 mm) of the device makes it well suited for integration in modern mobile phone applications, to suppress electromagnetic interference (EMI) between a USB transmitter and the GSM receiver. Measurement data of mixed-mode S-Parameters and experimental results underline the EMI protection in the GSM downlink spectrum. The dynamic resistance is derived in transmission line puls (TLP) measurements. This combination of EMI filter and ESD protection outperforms conventional ferrite CMF with varistors.