Power amplifier having analog pre-distortion by adaptive degenerative feedback
Power amplifier having analog pre-distortion by adaptive degenerative feedback. In some embodiments, a pre-distortion circuit for an amplifier can include a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit can further include a degeneration circuit implemented between the common node and the ground, with the degeneration circuit being configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level. The degeneration circuit can be further configured to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.
1. A pre-distortion circuit for an amplifier, comprising:
a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground; and
a degeneration circuit implemented between the common node and the ground, the degeneration circuit configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, the degeneration circuit further configured to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level, the degeneration circuit including a resistance implemented between the common node and the ground, and an antiparallel combination of first and second diodes implemented between the common node and the ground, the first and second diodes configured to turn on when the power level of the input signal exceeds the selected level.
2. The pre-distortion circuit of claim 1 wherein the transistor is implemented as a bipolar-junction transistor having a base, an emitter, and a collector, such that the base provides the input node, the collector provides the output node, and the emitter provides the common node.
3. The pre-distortion circuit of claim 1 wherein the degeneration circuit is further configured to provide a phase control functionality.
4. The pre-distortion circuit of claim 3 wherein the phase control functionality includes an AM-to-PM phase control functionality.
5. The pre-distortion circuit of claim 3 wherein the degeneration circuit further includes an inductance and a capacitance, each implemented to be electrically parallel with the resistance, and between the common node and the ground.
6. The pre-distortion circuit of claim 5 wherein at least one of the inductance and the capacitance is configured to provide the phase control functionality.
7. The pre-distortion circuit of claim 1 wherein the degeneration circuit is further configured such that the selected level is compensated for a variation in temperature.
8. The pre-distortion circuit of claim 7 wherein the degeneration circuit further includes a voltage source configured to apply a bias to the first and second diodes.
9. The pre-distortion circuit of claim 8 wherein the voltage source is implemented to be between each of the first and second diodes and the ground.
10. The pre-distortion circuit of claim 8 wherein the voltage source is configured to provide a temperature-dependent voltage to each of the first and second diodes.
11. A method for pre-distorting a signal for an amplifier, the method comprising:
providing a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground; and
introducing a feedback response, with a degeneration circuit implemented between the common node and the ground, such that the feedback response includes a reduction in the gain when the input signal has a power level at or below a selected level, and a disablement or a reduction of the feedback response when the input signal has a power level that exceeds the selected level, the degeneration circuit including a resistance implemented between the common node and the ground, and an antiparallel combination of first and second diodes implemented between the common node and the ground, the first and second diodes configured to turn on when the power level of the input signal exceeds the selected level.
12. An amplifier comprising:
a pre-driver stage including a transistor having an input node for receiving an input signal, an output node for an output signal provided by the transistor and having a gain relative to the input signal, and a common node for coupling to a ground;
an amplification stage configured to receive an input signal representative of the output signal of the pre-driver stage and to generate an amplified signal; and
a pre-distortion circuit coupled to the pre-driver stage and configured to introduce a feedback response that reduces the gain when the input signal of the pre-driver stage has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal of the pre-driver stage has a power level that exceeds the selected level, the pre-distortion circuit including a degeneration circuit that includes a resistance implemented between the common node and the ground, and an antiparallel combination of first and second diodes implemented between the common node and the ground, the first and second diodes configured to turn on when the power level of the input signal exceeds the selected level.
13. The amplifier of claim 12 wherein the degeneration circuit is further configured to provide a phase control functionality.
14. The amplifier of claim 12 wherein the degeneration circuit is further configured such that the selected level is compensated for a variation in temperature.
15. The amplifier of claim 12 wherein the amplifier is a power amplifier.