Details for Patent: 8,624,678

Title:	Output stage of a power amplifier having a switched-bulk biasing and adaptive biasing
Abstract:	A power amplifier (PA) using switched-bulk biasing to minimize the risk of output stage snapback effect is disclosed. An adaptive biasing of the output stage prevents device breakdown while accommodating large voltage swings. These protection techniques can be applied to all types of cascode configurations of a PA, including single-ended, differential, quadrature, segmented and any combination thereto.
Inventor(s):	Scott; Baker (San Jose, CA), Maxim; George (Milpitas, CA), Franck; Stephen (Felton, CA)
Assignee:	RF Micro Devices (Cayman Islands), Ltd. (Greensboro, NC)
Filing Date:	Dec 02, 2011
Application Number:	13/310,623
Claims:	1. A power amplifier system comprising: a radio frequency signal path comprising a plurality of cascaded gain stages of which at least one gain stage has a cascode configuration; and a switching bias network to control the potential of a bulk terminal of at least one metal-oxide semiconductor field effect transistor in the at least one gain stage having the cascode configuration, the switching bias network being controlled to provide different potentials to the bulk terminal. 2. The power amplifier system of claim 1, wherein the radio frequency signal path comprises at least one of: a pre-driver, a driver, an output stage. 3. The power amplifier system of claim 1, wherein the radio frequency signal path architecture is at least one of: single-ended, differential, segmented, quadrature. 4. The power amplifier system of claim 1, wherein the switching bias network switches the bulk terminal between a first potential and at least one second potential. 5. The power amplifier system of claim 4, wherein the first potential is a ground reference potential. 6. The power amplifier system of claim 1, wherein the switching bias network comprises at least one of: an auxiliary leg driven by a source input used by the at least one gain stage having the cascode configuration, an auxiliary leg driven by a separate clock signal, an arbitrary switching network driven by an input RF signal, an arbitrary switching network driven by a separate clock. 7. The power amplifier system of claim 6, further comprising a constant resistance connected to the bulk terminal. 8. The power amplifier system of claim 1, further comprising a variable gate biasing network having its voltage dependent on an output voltage of the power amplifier system. 9. A power amplifier system comprising: a radio frequency signal path comprising a plurality of cascaded gain stages of which at least one gain stage has a cascode configuration; and a variable gate biasing network having its voltage dependent on an output voltage of the power amplifier system, the variable gate biasing network coupled to a gate of a metal-oxide semiconductor field effect transistor of the at least one gain stage having the cascode configuration, wherein the variable gate biasing network is configured to provide a biasing voltage at the gate of the metal-oxide semiconductor field effect transistor such that the relationship of a gate voltage of the metal-oxide semiconductor field effect transistor to the output voltage of the power amplifier system is non-linear. 10. The power amplifier system of claim 9, further comprising a switching bias network to control the potential of a bulk terminal of at least one device comprising the at least one gain stage having the cascode configuration, the switching bias network controlled to provide different potentials to the bulk terminal. 11. The power amplifier system of claim 9, wherein the radio frequency signal path architecture is at least one of: single-ended, differential, segmented, quadrature. 12. The power amplifier system of claim 9, wherein a peak output voltage level of the output voltage of the power amplifier system is sensed with one of: rectifier, charge pump, DC-DC converter, mixer, sampler. 13. The power amplifier system of claim 9, wherein the variable gate biasing network is driven by at least one of: a temperature detector, a process detector, a supply voltage detector, a load detector, a voltage standing wave ratio detector, a phase angle detector. 14. A power amplifier system comprising: a radio frequency signal path comprising a plurality of cascaded gain stages of which at least one gain stage has a cascode configuration; a phase shift unit coupled to an output of at least one of the plurality of cascaded gain stages to provide a phase shift unit radio frequency output that is phase shifted with respect to a radio frequency signal in the radio frequency signal path; and a switching bias network to control the potential of a bulk terminal of at least one metal-oxide semiconductor field effect transistor in the at least one gain stage having the cascode configuration, the switching bias network being coupled to an output of the phase shift unit to provide different potentials to the bulk terminal responsive to the output of the phase shift unit. 15. The power amplifier of claim 14, wherein a last gain stage of the plurality of cascaded gain stages is the at least one gain stage having the cascode configuration.