Parasitic Compensation and Hence Isolation Improvement of PIN Diode-Based Switches

This brief presents a transmission line based resonant technique to nullify the parasitic effect of a PIN diode used to design a narrowband high frequency switch. Resonant condition is obtained by using a section of transmission line in series with a single PIN diode in a shunt branch. The method guarantees isolation improvement at any design frequency lower than the series resonant frequency of a diode. It does not use any lumped component other than those required for biasing. Thus, the method greatly improves the high frequency performance of a PIN diode as a switch. A transmission line based analysis is carried out to obtain the design equations. The theoretical prediction is verified by fabrication and measurement. A single-pole-single-throw (SPST) switch using just one single PIN diode provides measured isolation of 40 dB and insertion loss of 1.5 dB at 10.55 GHz. The return loss is more than 20 dB over 10.2-10.8 GHz. A low cost NXP semiconductors BAP64-02 PIN diode with high parasitic and the manufacturer specified highest frequency as 6 GHz is used to show the competency of the proposed method. A second SPST switch using two diodes provides isolation of 72 dB, insertion loss of 1.8 dB and return loss of 35 dB at 10.55 GHz. An SP4T switch is also fabricated and tested. Measured 1 dB compression point for all the switches is higher than 23 dBm.