PIN Diode basic Fundamentals and Applications

The PIN diode is a common microwave semiconductor device used in various applications. Unlike a standard PN junction diode, a PIN diode incorporates an insulating layer between the P-type and N-type materials. This unique structure distinguishes it from its PN junction counterpart. This page will cover the fundamentals of PIN diodes and their practical applications or use cases.

As mentined, PIN diode consists of P layer, undoped intrinsic (I) layer and N layer. Intrinsic layer is sandwidthed between P and N layers as shown. The figure depicts PIN diode structure and its forward and reverse biased equivalent circuits.

PIN diode is forward biased when positive voltage is applied to ‘P’ terminal with respect to ‘N’ terminal. In this case, current flows through the device as diode acts as small resistance device due to low resistivity of intrinsic region.

In another case, PIN diode is reverse biased when voltage on N-terminal is higher than P-terminal. In this condition, free charge carriers are swept out of intrinsic region and reactance of diode becomes very large. As shown in the equivalent circuit, the calculation of reactance depends on parallel values of resistance (R_p) and capacitance (C_T).

PIN Diode Applications

PIN diodes find applications in various domain areas which include RF & Microwave, Optical, power electronics, medical, automotive & aerospace, military and test equipments.

RF & Microwave applications

As PIN diode functions as variable resistors and switches at higher frequencies, it has extensive use in RF & Microwave systems as follows.

• RF Switches : PIN diode offers fast switching speeds and low insertion loss. Hence it is used in antenna switching, signal routing and Tx/Rx switches. The figure below illustrates how a PIN diode can be used to switch between transmit and receive operations using a single antenna. The switch position determines whether the antenna is used for transmitting or receiving.

• Attenuators : It is used for attenuation control in RF circuits which helps to vary signal amplitude as desired to meet link budget requirements of communication link.

• Phase Shifters : It is part of phased array antennas which helps to steer the direction of beam by changing phase of signal.

• Limiters : It limits amplitude of the incoming signals which helps to protect sensitive receiver from high power signals.

• Mixers/Modulators : Used in frequency conversion and modulation techniques.

Optical & Photonic applications

• It serves as efficient photo-detectors due to its intrinsic layer which helps to convert optical signals into electrical currents. Hence it is used in fiber optic communication systems.
• Used in optical sensing applications such as optical encoders, LiDAR etc.

Power Electronics

• Used as high voltage rectifiers as it withstands higher reverse voltages.
• Used in SMPS (Switch Mode Power Supplies) due to its fast switching functionalities.

Medical & Scientific instruments

• Used in X-Rays and MRI systems to detect radiation and switching of RF signals.
• Used in scientific research and medical diagnostics to detect ionizing radiation.

Automotive & Aerospace

• Used in collision avoidance and adaptive cruise control systems for signal modulation and switching.
• Used in aircraft and satellite systems for rf switching & control.

Military & Defense

• Used in jamming systems and radar counter measures due to its high power handling and switching capabilities
• Used in frequency hopping and encrypted systems for rapid switching

Industrial & test equipments

• Used in T&M instruments such as network analyzers and signal generators to control signal paths and amplitudes.
• Used in process control systems and material analysis systems to detect light and radiation.

Summary

PIN diodes offer unique electrical characteristics such as variable resistance under bias and high frequency performance. These characteristics enable their widespread use across multiple technological domains as described .