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.
Pin diode switch schematic.
There is a 50 ohm coax from tx to antenna.
Rf switch with pin diodes circuit diagram.
The operated diodes block the disconnected antennas by about 30 db.
The pin diode makes an ideal rf switch.
Figure 5 shows a single pole double throw spdt rf switch and its bias circuit.
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.
The pin diode can be used as a high voltage rectifier.
There are many unique market applications such as the wireless communications market where new.
What is the frequency range of the pin diode as an rf switch.
Take a look at the diagram below which is a schematic of a simple single pole single throw rf switch using a pin diode.
The signal to noise ration of the receiver deteriorates somewhat up to 1 db.
This high impedance coax has an inner conductor with a diameter of 3 mm.
The circuit uses back to back pin diodes in the paths from antenna to transmitter and again from antenna to receiver.
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.
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.
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.
For example the capacitance of an off state discrete pin diode might be 1 pf.
At each t a high impedance quarter wave coax cable is connected.
At 320 mhz the capacitive reactance of 1 pf is 497 ohms.
Signal losses at the closed diode is negligible.
Along this cable there are two t connections separated by one quarter wavelength.
These biasing conditions are swapped to switch between transmit and receive.
The intrinsic region provides a greater separation between the pn and n regions allowing higher reverse voltages to be tolerated.
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.
Figure d 1 is a typical circuit and figure d 2 is the same circuit with.
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.
It is really very straight forward.
The bias circuit typically uses a low pass filter between the rf circuit and the switch driver.
The pin diode switch can be used for antennas with impedances of from 50 ω up to 75 ω.
Schematic diagram of high power pin diode switch.
