How to Bias GaN Transistors Without Damaging the Device: A Video Tutorial

Are you an RF or microwave engineer who’s never worked with gallium nitride (GaN) or depletion mode FETs? Do you keep damaging your sampled GaN parts or evaluation boards but don’t know why?

GaN is a relatively new semiconductor technology, particularly in commercial applications. Due to GaN’s superior properties over incumbent technologies like LDMOS, it’s being used in more applications every day. Although engineers may assume that GaN is similar to LDMOS, it’s not.

This blog post and our brief tutorial video give you tips for how to bias GaN products for the best results.

Key things to remember about GaN

GaN HEMTs are depletion mode devices, which means the device is normally on when the gate source voltage is zero. If you’re new to GaN, it's important to realize these two key points:

  • You need a positive and negative voltage when working with GaN — a positive, high drain voltage and a lower, negative gate voltage.
  • The bias sequencing for GaN must be conducted in a certain sequence — even before the RF signal is applied to the circuit — or else you risk damaging the device.

 
In contrast, LDMOS is an enhancement mode device and needs a positive, high drain voltage and a lower, positive gate voltage. For LDMOS, the gate voltage may be applied at the same time as drain voltage.
 

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You'll Learn:

  • The proper turn-on and turnoff sequence for GaN
  • An example procedure using Qorvo's QPD1004, a 25-watt input-matched GaN-in-SiC HEMT

Watch the Video >

Proper biasing sequence for GaN: The right way to turn GaN on and off

If you have experience with depletion mode FETs, you’ll see that GaN biasing is very similar. For GaN, the correct bias sequences for powering up and down are as follows:

  • For turn on: gate, drain, gate adjust, RF
  • For turnoff, the sequence is reversed: RF, gate adjust, drain, gate
Correct Biasing Sequence for GaN Transistors