Pin Diode Switch Schematic

Figure 5 shows a single pole double throw spdt rf switch and its bias circuit.

Pin diode switch schematic. One pair is biased to conduct in pin diode mode with forward current while the other is reverse biased with high voltage to the off or blocking condition. The pin diode makes an ideal rf switch. Applying both rf and dc bias at the same time as can be seen in the diagram the rf is fed into and out of the diode through 0 01uf blocking capacitors. Thus a pin diode is a dc controlled high frequency resistor and if no dc current is present the diode is just like an open circuit.

This high impedance coax has an inner conductor with a diameter of 3 mm. These biasing conditions are swapped to switch between transmit and receive. Rf switch with pin diodes circuit diagram. There are many unique market applications such as the wireless communications market where new.

It is really very straight forward. Figure d 1 is a typical circuit and figure d 2 is the same circuit with. At 320 mhz the capacitive reactance of 1 pf is 497 ohms. Chapter 2 the common pin diode switch configurations are presented followed by sections comparing those features of pin diode switch designs for unique to high power microwave switches and high power lower frequency rf band switches.

What is the frequency range of the pin diode as an rf switch. The operated diodes block the disconnected antennas by about 30 db. Driver circuits for high power pin diode switches the information in this chapter is presented as a guide for the rf switch switch driver interface. For example the capacitance of an off state discrete pin diode might be 1 pf.

There is a 50 ohm coax from tx to antenna. The bias circuit typically uses a low pass filter between the rf circuit and the switch driver. Take a look at the diagram below which is a schematic of a simple single pole single throw rf switch using a pin diode. References 1 2 provide a fuller treatment of this subject and can be used as a basis for rf switch switch driver.

Along this cable there are two t connections separated by one quarter wavelength. The intrinsic layer between the p and n regions increases the distance between them. The pin diode switch can be used for antennas with impedances of from 50 ω up to 75 ω. The pin diode can be used as a high voltage rectifier.

Schematic diagram of high power pin diode switch. At each t a high impedance quarter wave coax cable is connected. It is primarily a function of the thickness of the i region and thicker diodes can operate down to 1 mhz while thinner ones can function into. Connecting the switch driver control circuit to a pin diode such that it can turn diodes on and off by applying a forward or reverse bias is a challenging task.

The signal to noise ration of the receiver deteriorates somewhat up to 1 db. A pin diode switch can switch much more quickly e g 1 microsecond although at lower rf frequencies it isn t reasonable to expect switching times in the same order of magnitude as the rf period.