Bias circuit for a radio frequency power-amplifier and method therefor
View Patent ↗A wireless communication unit comprises a transmitter having a power amplifier biased by a bias circuit and a controller operably coupled to the bias circuit for setting one or more bias levels of the power amplifier. The bias circuit is a single bias circuit and is configured to provide either a current mode bias control of the power amplifier or a voltage mode bias control of the power amplifier in response to a control signal from the controller. In this manner, a single bias control circuit can be used to support applications that benefit from both current mode bias control and voltage mode bias control of the power amplifier.
1. A wireless communication unit comprising:
a transmitter having a power amplifier biased by a bias circuit connected to a base of the power amplifier and a controller operably coupled to the bias circuit for setting one or more bias levels applied to the power amplifier, wherein the bias circuit is configured to provide either a current to the base to implement a current mode bias control of the power amplifier or a voltage to the base to implement a voltage mode bias control of the power amplifier in response to a control signal from the controller, wherein the bias circuit comprises a current source operably coupled to an input port of the power amplifier via a first switch that is configured by the controller to be in a closed position when biasing the power amplifier in a current mode and in an open position when biasing the power amplifier in a voltage mode.
2. The wireless communication unit of claim 1 wherein the controller configures the bias circuit to provide current mode biasing of the power amplifier to operate the power amplifier in a saturated mode.
3. The wireless communication unit of claim 2 wherein the power amplifier is configured to operate in the saturated mode to support a constant envelope modulation scheme used by the wireless communication unit.
4. The wireless communication unit of claim 3 wherein the constant envelope modulation scheme used by the wireless communication unit is a GSM constant envelope modulation scheme.
5. The wireless communication unit of claim 1 wherein the controller configures the bias circuit to provide the voltage mode biasing of the power amplifier to operate the power amplifier in a linear mode.
6. The wireless communication unit of claim 5 wherein the linear mode is a non-constant envelope modulation scheme used by the wireless communication unit.
7. The wireless communication unit of claim 5 wherein the power amplifier is configured to operate in the linear mode to support the wireless communication unit transmitting Edge or WCDMA communication.
8. The wireless communication unit of claim 5 , wherein the bias circuit comprises a current-to-voltage converter circuit that is activated when biasing the power amplifier in the voltage mode.
9. The wireless communication unit of claim 8 , wherein the current-to-voltage converter circuit is located between a biasing current source and the input port of the power amplifier, wherein the current-to-voltage converter circuit comprises a second switch located between the biasing current source and a reference transistor and a third switch located between a base port of the reference transistor and the input port of the power amplifier wherein the second switch and third switch are configured by the controller to be in a closed position when biasing the power amplifier in the voltage mode.
10. An integrated circuit comprising:
a power amplifier; and
a bias circuit for biasing a power amplifier in response to a control signal, the bias circuit is configured to set one of a bias current for the power amplifier to provide current mode bias control of the power amplifier and a bias voltage for the power amplifier to provide voltage mode bias control of the power amplifier in response to the control signal, wherein the bias circuit comprises a current source operably coupled to an input port of the power amplifier via a first switch that is configured by a controller to be in a closed position when biasing the power amplifier in a current mode and in an open position when biasing the power amplifier in a voltage mode.
11. The integrated circuit of claim 10 wherein an output signal from the bias circuit provides the current mode biasing to operate the power amplifier in a saturated mode.
12. The integrated circuit of claim 11 wherein an output signal from the bias circuit provides the current mode biasing to support a constant envelope modulation scheme used by the power amplifier.
13. The integrated circuit of claim 12 wherein the constant envelope modulation scheme is a GSM constant envelope modulation scheme.
14. The integrated circuit of claim 10 wherein output signal from the bias circuit provides the voltage mode biasing to operate the power amplifier in a linear mode.
15. The integrated circuit of claim 14 wherein the linear mode is a non-constant envelope modulation scheme.
16. The integrated circuit of claim 14 wherein the non-constant envelope modulation scheme supports Edge or WCDMA communication.
17. The integrated circuit of claim 10 , wherein the bias circuit comprises a current-to-voltage converter circuit that is activated by the control signal when biasing the power amplifier in the voltage mode.
18. The integrated circuit of claim 17 , wherein the current-to-voltage converter circuit comprises a second switch located between a biasing current source and a reference transistor and a third switch located between a base port of the reference transistor and a bias output of the bias circuit wherein the second switch and the third switch are configured by the control signal to be in a closed position when biasing the power amplifier in the voltage mode.
19. The integrated circuit of claim 10 , wherein the control signal is applied to a control pin of the integrated circuit to configure the bias circuit.
20. A method of biasing a power amplifier in a wireless communication unit, the method comprising:
receiving a bias control signal from a controller;
configuring, in response to the bias control signal having a first state, a first switch of a single bias circuit having a current source to be in a closed position to provide a current mode bias control of the power amplifier to a base of the power amplifier; or
configuring, in response to the bias control signal having a second state, the first switch to be in an open position to provide a voltage mode bias control of the power amplifier to the base of the power amplifier.
21. The method of claim 20 wherein the step of configuring comprises configuring a bias circuit to provide current mode biasing of the power amplifier to operate the power amplifier in a saturated mode.
22. The method of claim 20 wherein the step of configuring comprises configuring a bias circuit to provide voltage mode biasing of the power amplifier to operate the power amplifier in a linear mode.
23. The method of claim 20 , wherein the step of configuring comprises switching a plurality of switches to an open position or a closed position to bias the power amplifier.