Circuit and method for reducing driving losses in GAN switches

A device, comprising:

• a half bridge circuit including:
• a high side transistor;
• and
• a low side transistor coupled to the high side transistor at an intermediate node;
• a driver configured to generate a high side driver signal corresponding to a square wave and a low side driver signal corresponding to a square wave, wherein a first deadtime is a period between a falling edge of the low side driver signal and a rising edge of the high side driver signal, wherein the first deadtime includes a first portion and a second portion following the first portion;
• a half bridge adjustment circuit coupled between the driver and the half bridge circuit and configured to:
• generate a modified high side driver signal corresponding to the high side driver signal with a transition from a low voltage to an intermediate voltage at a beginning of the second portion of the first deadtime and a transition from the intermediate voltage to a high voltage at an end of the first deadtime, wherein the first modified driver signal remains flat at the low voltage during the first portion of the first deadtime;
• and
• drive a gate terminal of the high side transistor of a half bridge circuit with the modified high side driver signal, wherein:
• a second deadtime is a period between a falling edge of the first driver signal and a rising edge of the second driver signal;
• the half bridge adjustment circuit is configured to generate a modified low side driver signal corresponding to the low side driver signal with a transition from the low voltage to the intermediate voltage during the second deadtime and a transition from the intermediate voltage to the high voltage at an end of the second deadtime;
• and
• the half bridge adjustment circuit is configured to drive a gate terminal of the low side transistor with the modified low side driver signal.

A method, comprising:

• providing a first square wave from a driver to half bridge adjustment circuit coupled between the driver and a half-bridge resonant converter including a high side GaN high electron mobility transistor (HEMT) and a low side GaN HEMT, the first square wave having a high voltage value corresponding to a turn-on voltage of the HEMT and a low voltage value corresponding to a turn-off voltage of the HEMT and having a value less than 0 V;
• providing a second square wave from the driver to the half bridge adjustment circuit, the first and second square waves having a relative phase that provides a deadtime during which both the first square wave and the second square wave are at the low voltage value;
• and
• generating with the half bridge adjustment circuit, a first modified square wave in which the deadtime is divided into a first portion and a second portion, the first modified square wave being at the low voltage value during the first portion and at an intermediate voltage value during the second portion and including a transition from the low voltage value to the intermediate voltage value at a beginning of the second portion of the first deadtime, wherein the first modified driver signal remains flat at the low voltage value during the first portion of the first deadtime;
• applying the first modified square wave to a gate terminal of the high side GaN HEMT;
• generating, with the half-bridge adjustment circuit, a second modified square wave in which the deadtime is divided into a first half and a second half, the second modified square wave being at the low voltage value during the first portion and at the intermediate voltage value during the second portion;
• and
• applying the second modified square wave to a gate terminal of the low side GaN HEMT.