Hocheffiziente CMOS-Schaltverstärkerstufen im Mikrowellenbereich

• Applicant: Professor Dr.-Ing. Manfred Berroth
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 222284409

Nowadays radio frequency power amplifiers are usually working in class-AB mode. In class-A mode efficiencies of 50 %, in class-B mode efficiencies of 78 % can be reached. A PA in class-AB mode has an efficiency in between. In comparison there are switching mode amplifiers, which can reach in theory a maximum efficiency of 100 % and therefore seem applicable for broadband mobile radio frequency applications. In this project a CMOS-power amplifier with high output voltage swing for radio applications in mobile devices shall be developed. A broadband switching mode amplifier with sharp slopes can be used with different forms of signal shaping, for example with pulse-width-modulation or with a delta-sigma-modulated phase modulation, and can reach very high power efficiencies above 70 %. With the digital approach the switching mode amplifier is applicable for all frequency ranges up to a maximum frequency. Due to the missing analog components the migration to advanced CMOS-technologies is eased and the yield increases. The concept of stacked MOSFETs with a digital driver allows a high output voltage swing with very high bandwidth. Due to the high output voltage swing the output current can be reduced at the same output power. Hence the resistive losses of the wiring on chip and the requirements for the blocking capacitors are reduced. In the first part of this project a switching mode amplifier with a digitally driven MOSFET-stack and a 3-V-output voltage swing was designed, built and measured. The rise and fall times are 100 ps. The high bandwidth is shown with a pseudo random bit sequence up to 3 GBit/s. The output signal shape can be optimized by analog control voltages. The input interface is compatible to circuits with current mode logic. The use with already designed circuits is possible. The second part of the project pursues the following goals: -The analog control voltages shall be replaced by digital control logic. -The delays for the digital driver of the stacked MOSFETs cannot be determined directly in the first part of the project. An analysis circuit shall be designed. With it the relative delays of all driving signals can be determined. -Starting from the existing 3-V-switching mode amplifier a 6-V-amplifier with simple structure shall be designed. At the same output current the output power is doubled. -One of the main problems in mobile radio signals is the high peak to average power ratio. An amplifier with adjustable output voltage swing (1V, 2V, 3V) shall lead to a crucial increase of efficiency for amplifying mobile radio signals. Especially the latter two goals address important problems in todays mobile communications and they improve the state of the art significantly.

• DFG Programme: Research Grants