Integrated systems
The unique island topology that we use provides for diodes, normally-off and normally-on transistors to be integrated. This allows complex structures to be built on a single chip. A commonly required structure is the half bridge shown below.
This can easily be built using the island topology and the layout is highly efficient in terms of function per unit area, and the layout matrixes perfectly to allow a very large structure to be built. However, when used in very high power, high voltage applications the half bridge drive requirements become difficult due to Miller capacitance. Using multiple, dispersed direct drivers and totally isolated input circuits as shown – a very much more practical and useful integration is achieved.
Since our island structure is designed to be totally compatible with conventional RF GaN processes, the entire MMIC fabrication capability and components are available. Microwave, digital and power devices can all be integrated on one chip. These structures are used in the patented on-chip driver design.
Another useful integrated structure is the 3-level neutral point clamped (3-Level NPC) converter element shown below. The EMI requirements are very stringent because these structures are used in aircraft applications.
The integrated GaN structure reduces the stray inductance problem and improves the switching speed and efficiency. The new on-chip drivers and isolation circuits, with their ease of use, transform the value of the circuit.
It has been shown that a 3-level NPC converter, built with 600V devices has lower losses than a 2-level converter built with 1200V devices if the switching frequency is high enough. This is due to the reduced switching and conduction losses of the low-voltage devices which overcompensate for the increased conduction losses caused by the higher number of series connected devices in the current path. Additionally, the 3-level converter generates a better voltage and current spectrum compared to the 2-level converter. This has the ability to reduce the additional pulse width modulation losses in electrical motors.
The future of GaN in power applications is closely linked to the integration that can be easily achieved using the GaN Systems patented island topology.