Emitter ballast bypass for radio frequency power transistors

US5684326A · kind A · utility

Assignee

• Telefonaktiebolaget LM Ericsson (Publ) · SE

Inventors

• Ted Johansson · Djursholm, SE
• Larry Leighton · Scottsdale, US

Key dates

• Filing date: Feb 24, 1995
• Grant date: Nov 4, 1997
• Expiry date: Feb 24, 2015

Classification

• Technology area (CPC H): Electricity
• CPC primary: H10D84/615

Abstract

An apparatus and method are provided for bypassing the emitter ballast resistors of a power transistor, thereby increasing transistor gain. In a power transistor of the interdigitated type, bypassing the emitter ballast resistors requires bypassing each individual ballast resistor with a capacitor in parallel. Bypassing is therefore done on the silicon chip. More particularly, in accordance with one embodiment of the invention, an RF power transistor includes a silicon die, an emitter ballast resistor formed on the silicon die, and a bypass capacitor formed on the silicon die and connected in parallel with the emitter ballast resistor. The resistor may be a diffused resistor, and the capacitor may be a metal-on-polysilicon capacitor. In accordance with another embodiment of the invention, a method is provided for increasing the gain of an RF transistor formed on a silicon chip and having an emitter ballast resistor formed on the silicon chip, in which a capacitor is formed on the silicon chip and connected in parallel with the ballast resistor.