Power amplifier architectures with input power protection circuits
An RF power amplifier circuit and input power limiter circuits are disclosed. A power detector generates a voltage output proportional to a power level of an input signal. There is a directional coupler with a first port connected to a transmit signal input, a second port connected to the input matching network, and a third port connected to the power detector. A first power amplifier stage with an input is connected to the input matching network and an output is connected to the transmit signal output. A control circuit connected to the power detector generates a gain reduction signal based upon a comparison of the voltage output from the power detector to predefined voltage levels corresponding to specific power levels of the input signal. Overall gain of the RF power amplifier circuit is reduced based upon the gain reduction signal that adjusts the configurations of the circuit components.
1. A radio frequency power amplifier input power overload protection circuit having a transmit signal input and a transmit signal output, the circuit comprising:
an input matching network;
a power detector generating a voltage output proportional to a power level of an input signal;
a directional coupler with a first port connected to the transmit signal input, a second port connected to the input matching network, and a third port connected to the power detector;
a first power amplifier stage with an input connected to the input matching network and an output connected to the transmit signal output; and
a control circuit connected to the power detector, a gain reduction signal being generated thereby based upon a comparison of the voltage output from the power detector to predefined voltage levels corresponding to specific power levels of the input signal correlated to an overload condition in at least one component in a signal transmission chain between the transmit signal input and the transmit signal output, and overall gain of the radio frequency power amplifier circuit being reduced directly in response to the gain reduction signal being applied to at least one component in the signal transmission chain to reduce power overstress in each of the components in the signal transmission chain to below a predetermined threshold.
2. The circuit of claim 1 further comprising:
an inter-stage matching network connected to the output of the first power amplifier and the control circuit generating the gain reduction signal thereto; and
a second power amplifier stage with an input connected to the inter-stage matching network and an output connected to the transmit signal output.
3. The circuit of claim 2 further comprising:
an output matching network connected to the output of the second power amplifier stage and to the transmit signal output, the control circuit generating the gain reduction signal to the output matching network.
4. The circuit of claim 2 further comprising:
a bias control circuit connected to the second power amplifier stage, the control circuit generating the gain reduction signal to the bias control circuit.
5. The circuit of claim 1 further comprising:
an output matching network connected to the output of the first power amplifier stage and to the transmit signal output, the control circuit generating the gain reduction signal to the output matching network.
6. The circuit of claim 1 further comprising:
a bias control circuit connected to the first power amplifier stage, the control circuit generating the gain reduction signal to the bias control circuit.
7. The circuit of claim 1 wherein the control circuit generates the gain reduction signal to the input matching circuit.
8. The circuit of claim 1 further comprising a hysteresis circuit connected to the power detector and the control circuit.
9. The circuit of claim 1 wherein the input matching network, the power detector, the directional coupler, the first power amplifier stage, and the control circuit are fabricated on a single semiconductor die.
10. An input power limiter circuit for a power amplifier comprising:
an input directional coupler connected to a transmit signal input;
a first power amplifier stage connected to the input directional coupler;
an inter-stage matching network connected to the first power amplifier stage;
a second power amplifier stage connected to the inter-stage matching network;
an input power detector generating a voltage output proportional to a power level of an input signal;
a switching transistor connected to the inter-stage matching network and having an on state and an off state, the inter-stage matching network defining a first impedance with the switching transistor in the off state and a second impedance with the switching transistor in the on state; and
a control circuit connected to the input power detector, the switching transistor being set to the on state and the off state directly in response to an output generated by the control circuit that is based at least in part on a comparison of the voltage output from the input power detector to an input reference voltage correlated to an overload condition in at least one of the first power amplifier stage and the second power amplifier stage, and overall gain of the first power amplifier stage and the second power amplifier stage is reduced with the inter-stage matching network defining the second impedance, power overstress in at least one of the first power amplifier stage and the second power amplifier stage being reduced to below a predetermined threshold.
11. The circuit of claim 10 wherein the inter-stage matching network is an inductor-capacitor circuit.
12. The circuit of claim 10 wherein the input power detector is a peak envelope detector.
13. The circuit of claim 10 further comprising:
a first bias control circuit connected to the first power amplifier stage, the control circuit being connected to the first bias control circuit to regulate gain of the first power amplifier stage; and
a second bias control circuit connected to the second power amplifier stage, the control circuit being connected to the second bias control circuit to regulate gain of the second power amplifier stage.
14. The circuit of claim 10 further comprising an input matching network connected to input directional coupler and to the first power amplifier stage.
15. The circuit of claim 10 wherein the input directional coupler, the first power amplifier stage, the inter-stage matching network, the second power amplifier stage, the input power detector, the switching transistor, and the control circuit are fabricated on a single semiconductor die.
16. The circuit of claim 10 further comprising:
an output directional coupler connected to a transmit signal output; and
an output power detector generating a voltage output proportional to a power level of an output signal on the transmit signal output.
17. The circuit of claim 16 wherein the output power detector is connected to the control circuit.
18. The circuit of claim 17 wherein the switching transistor is set to the on state and the off state by the control circuit based at least in part on an evaluation of the voltage output from the output power detector.
19. The circuit of claim 17 wherein the control circuit includes:
a first comparator connected to the input power detector and an input reference; and
a second comparator connected to an output power detector and an output reference, the first comparator and the second comparator together triggering the switching transistor to the on state with either one or both of a voltage level of the transmit signal input exceeding a voltage level of the input reference and a voltage level of the transmit signal output exceeding a voltage level of the output reference.
20. The circuit of claim 17 wherein the output power detector is a peak envelope detector.