Power amplifier system with a current bias signal path
Power amplifier (PA) systems are typically comprised of a signal path integrated circuit (IC) and a power control IC. Advanced CMOS technologies may allow smart integration of such ICs into a single IC and provide an opportunity to improve performance and cost. Specifically, the radio frequency (RF) signal path is designed to enable local biasing of the gain stages that comprise the RF signal path. By using current-mode biasing instead of the prior art voltage-mode biasing significant area reduction is achieved as well as better isolation between the stages which reduces noise, and improves stability.
1. A power amplifier (PA) system comprising:
a radio frequency (RF) signal path comprising a plurality of gain stages;
an output stage the input of which is coupled to the output of the last gain stage of the RF signal path;
one or more current-mode bias sources, each of the one or more current-mode bias sources comprising a transistor with a drain contact coupled to a DC power supply and a source contact coupled to a different one of the plurality of gain stages, each of the one or more current-mode bias sources adapted to supply a biasing current to a respective gain stage of the RF signal path; and
a power control unit adapted to control the biasing current of a first one of the one or more current-mode bias sources responsive to sensing an output signal of the output stage.
2. The PA system of claim 1 , wherein the first current-mode bias source is adapted to bias the last gain stage of the RF signal path.
3. The PA system of claim 1 , wherein each of the one or more current-mode bias sources is isolated from other current-mode bias sources of the PA system.
4. The PA system of claim 1 , wherein each of the one or more current-mode bias sources is one of: a constant g m bias current source, a constant gain bias current source, a constant f τ bias current source.
5. The PA system of claim 1 , wherein the PA system is implemented as a single integrated circuit (IC) in a CMOS process technology.
6. A method of operating a power amplifier (PA) system comprising:
providing an RF signal path having a plurality of gain stages connected in series, each gain stage having a signal input and a signal output;
providing a power output stage having an input signal and an output signal, wherein the input signal of the power output stage is coupled to the output signal of the last gain stage of the plurality of gain stages;
selecting a current-mode bias source comprising a transistor with a drain contact coupled to a DC power supply and a source contact coupled to a different one of the plurality of gain stages and adapted to supply a biasing current to a first gain stage of the RF signal path of the PA system for optimization of the first gain stage for at least one of: gain, noise performance; and
controlling the biasing current of the current-mode bias source responsive to sensing an output signal of an output stage of the PA system.
7. The method of claim 6 , further comprising:
selecting an input resistance of the first gain stage of the RF signal path to control noise contribution of following stages of the RF signal path.
8. The method of claim 6 , further comprising:
adjusting of the current-mode bias source by one of: a current digital-to-analog (DAC) controlled adjustment, continuous current variation.
9. The method of claim 6 , further comprising:
providing at least a current-mode bias source to at least one other of the plurality of gain stages of the RF signal path.
10. The PA system of claim 1 wherein the power control unit is coupled to the one or more current-mode bias sources via a gate contact.
11. The PA system of claim 10 wherein the power control unit is configured to control the biasing current of the one or more current-mode bias sources by altering a voltage presented to the gate contact of the one or more current-mode bias sources.