Power amplifier with close-loop adaptive voltage supply
View Patent ↗A two-(or multi)stage power amplifier receives a variable RF input signal, and outputs an optimized. RF output signal from, for example, a mobile handset. The output power level from the handset is predetermined, as known in the art, by the received control signal from a base station. The first power amplifier stage amplifies the variable RF input signal and outputs an RF signal, Vin, to a power detector circuit and an RF signal to the second or next amplifier stage. The power detect circuit amplifies the Vin signal and rectifies that signal with a linearly biased diode and provides a detect signal to a DC to DC converter. The converter responds by providing an optimum voltage bias, which is linearly related to the DC voltage detect signal from the power detector, to the output stage, and, if desired, to the first and/or other stages of the power amplifier that optimizes the output power level while meeting the required linearity specification. The battery current consumption is optimized through this automatic, dynamically control of the supply voltage for the power amplifier at each output power level through the DC to DC converter.
1. An RF power amplifier system comprising:
at least a first and a second power amplifier;
where a first RF signal is input to the first power amplifier that outputs a second RF signal, and wherein the second RF signal couples to the second power amplifier that outputs an RF output signal;
an RF power detector that receives the second RF signal and provides a linearly related DC voltage detect signal;
a DC to DC converter that receives the DC detect signal and outputs a corresponding supply voltage that is coupled to the second power amplifier, and wherein the second RF signal from the first power amplifier determines the optimum supply voltage for the second power amplifier, and the supply voltage determines the optimum output power from the second power amplifier; and
the DC voltage detect signal from the power detector is linearly related to the optimum supply voltage for the second power amplifier.
2. The RF power amplifier system of claim 1 wherein the supply voltage is also coupled to the first power amplifier.
3. The RF power amplifier system of claim 1 wherein the RF power detector includes a diode peak detector that rectifies the second RF signal and which diode is forward biased in a substantially linear range.
4. The RF power amplifier system of claim 1 further comprising:
a bypass switch, wherein when the bypass switch is activated the output of a battery is directly coupled to the second power amplifier.
5. The RF power amplifier system of claim 4 further comprising a threshold setting, wherein when the threshold is met the bypass switch is activated.
6. A process for optimizing the RF output signal from an RF power amplifier system, the process comprising the steps of:
receiving a first RF signal at a first power amplifier that outputs a second RF signal;
receiving the second RF signal at a second power amplifier, and wherein the second power amplifier outputs an RF output signal;
detecting the second RF signal and providing a DC voltage detect signal to a DC to DC converter;
generating a supply voltage from the DC to DC converter that is linearly related to the DC voltage detect signal; and
coupling the supply voltage to the second power amplifier, and wherein the supply voltage determines the optimum output power from the second power amplifier.
7. The process of claim 6 further comprising the step of coupling a changed supply voltage to the first power amplifier activates a feedback loop of operations, wherein the gain of the first power amplifier changes causing, in turn: a change in the second RF signal, the related DC voltage detect signal, the supply voltage from the DC to DC converter, and finally back to the gain of the first power amplifier, wherein the feedback loop continues until a new supply voltage stabilizes at the optimum output power.
8. The process of claim 6 wherein the step of detecting includes passing the RF signal through a peak detector diode that is forward biased in a substantially linear region and that detects and rectifies the second RF signal.
9. The process of claim 6 further comprising the step of:
activating a bypass switch that connects a battery directly to the second power amplifier.
10. The process of claim 9 further comprising the step of thresholding the DC voltage detect signal, wherein when the threshold is met the bypass switch is activated.