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Advantages of LDMOS | Disadvantages of LDMOS

This page covers advantages and disadvantages of LDMOS. It mentions LDMOS advantages or benefits and LDMOS disadvantages or drawbacks. LDMOS (Laterally Diffused Metal Oxide Semiconductor) transistor structure is also mentioned.

What is LDMOS and its structure

Introduction:
There are two types of power MOSFETS used in RF/Microwave domain viz. DMOS and LDMOS. They have their unique structures and semiconductor processes. These devices are constructed in two variants viz. NMOS (n-type MOSFET) and PMOS(p-type MOSFET).

LDMOS structure

LDMOS is pre-dominately lateral and surface effect device. In LDMOS channel current is being controlled by vertical electric field (E). This E-field is induced by gate and lateral field which exists between S (Source) and D (Drain). In LDMOS device, channel is determined by three parameters viz. gate length, drain diffusion and source diffusion. The figure-1 depicts cross section view of LDMOS structure.

Benefits or advantages of LDMOS

Following are the benefits or advantages of LDMOS:
➨It operates upto 2.2 GHz and used for cost effective Power Amplifier Solutions.
➨With its excellent performance in class-AB, it is used in the design of linear amplifier with higher gain and better efficiency.
➨It delivers highly rugged devices with good VSWR
➨It delivers consistent thermal behaviour.
➨Used for broadband applications below 1 GHz
➨Delivers highest power upto 1.5 GHz
➨It is used in systems (CDMA, WCDMA) requiring higher crest factors due to its high PAPR capability.

Drawbacks or disadvantages of LDMOS

Following are the disadvantages of LDMOS:
➨The current drift due to elavated temperature is a concern. This can be eliminated in future generations of the LDMOS.
➨Layout and packaging, in combination with gold top metallization and gold bonding wires (a long-proven concept for RF power semiconductors), are considered critical to ensuring long-term reliability of the device and thus of the RF power amplifier and basestation.
➨ In order to ensure long term reliability of LDMOS devices, layout, packaging and gold top metallization are critical factors.



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