Amplifier performance stabilization through preparatory phase
View Patent ↗A method and related systems for amplifier performance stabilization of a digitally predistorted RF power amplifier are disclosed. The characteristics of power amplifiers change as a function of temperature making adaptive digital predistortion highly problematic during initial application of an RF signal to a power amplifier. Embodiments disclose a method and systems in which the power amplifier is taken through a preparatory phase before the RF signal is applied to the power amplifier and the digital predistortion calculation starts. This is achieved by increasing the quiescent current of the power stages beyond nominal values for a rapid warm up and readjusting to its normal bias point when the radio frequency signal is applied and the digital predistortion is turned on.
1. A method for stabilizing performance of a power amplifier comprising a first power amplifying device and a second power amplifying device, the method comprising the steps of:
determining an operating temperature of the first power amplifier device and an operating temperature of the second power amplifier device;
increasing a quiescent current of the first power amplifier device when the operating temperature of the first power amplifier device is less than a pre-defined level;
increasing a quiescent current of the second power amplifier device when the operating temperature of the second power amplifier device is less than a pre-defined level;
feeding an RF signal into the input of the power amplifier when the operating temperature of either or both of the first power amplifier device and the second power amplifier device is greater than or equal to the pre-defined level; and
adjusting the quiescent current of either or both of the first power amplifier device and the second power amplifier device to its normal bias point when the RF signal is applied.
2. The method for stabilizing performance of a power amplifier as set out in claim 1 , further comprising decoupling the RF signal from the input of the power amplifier during initialization.
3. The method for stabilizing performance of a power amplifier as set out in claim 1 , further comprising applying, predistortion to the RF signal after the operating temperature of either or both of the first power amplifier device and the second power amplifier device is greater than or equal to the pre-defined level.
4. The method for stabilizing performance of a power amplifier as set out in claim 1 , wherein the increased level of the quiescent current corresponds to full power or higher of either or both of the first power amplifier device and the second power amplifier device but within the safety range of drain current as defined by specifications at those power amplifier devices.
5. The method for stabilizing performance of a power amplifier as set out in claim 1 , further comprising
measuring a total time period in which the quiescent current of either or both of the first power amplifier device and the second power amplifier device has been increased;
comparing the total time period to a pre-defined time; and,
feeding the RF signal to the input of the power amplifier when the total time period is greater than or equal to the pre-defined time.
6. The method for stabilizing performance of a power amplifier as set out in claim 5 , further comprising maintaining the increased level of the quiescent current of either or both of the first power amplifier device and the second power amplifier device when the total time period is less than the pre-defined time.
7. The method for stabilizing performance of a power amplifier as set out in claim 5 , wherein the pre-defined time is determined based on an ambient temperature near the power amplifier.
8. The method for stabilizing performance of a power amplifier as set out in claim 1 , further comprising:
monitoring a current of the power amplifier;
communicating the value of the current of the power amplifier; and,
varying the quiescent current of either or both of the first power amplifier device and the second power amplifier device based on the value of the current.
9. A power amplifier system comprising:
a system controller;
a first power amplifying device amplifying a communication signal to provide a first output signal;
a first temperature sensor thermally coupled to the first power amplifying device and sensing and communicating the operating temperature of the first power amplifying device to the system controller;
a first bias circuit providing a first quiescent current to the first power amplifying device, the first bias circuit coupled to and controlled by the system controller;
a second power amplifying device amplifying a second portion of the communication signal to provide a second output signal;
a second temperature sensor thermally coupled to the second power amplifying device and sensing and communicating the operating temperature of the second power amplifying device to the system controller; and
a second bias circuit providing a second quiescent current to the second power amplifying device, the second bias circuit controlled by the system controller,
wherein the system controller controls the second bias circuit to increase the second quiescent current of the second power amplifying device when the operating temperature is less than a pre-defined level,
wherein the system controller controls the first bias circuit to increase the first quiescent current of the first power amplifying device when the operating temperature is less than a pre-defined level.
10. The power amplifier system as set out in claim 9 , further comprising:
a first current sensing circuit monitoring a first current of the first power amplifying device, the first current sensing circuit communicating the value of the first current to the system controller,
wherein the system controller varies the first quiescent current based on the value of the first current.
11. The power amplifier system as set out in claim 9 , wherein the first and second power amplifying devices are configured to form a balanced amplifier system.
12. The power amplifier system as set out in claim 9 , wherein the first and second power amplifying devices are configured to form a Doherty amplifier system.
13. The power amplifier system as set out in claim 9 , further comprising:
a variable attenuator stage having an input receiving an RF signal and an output coupled to a common input of the first and second power amplifying devices, the variable attenuator stage controlled by the system controller,
wherein the system controller controls the variable attenuator stage for selectively coupling and decoupling the RF signal to the first and second power amplifying devices.
14. The power amplifier system as set out in claim 9 , further comprising:
a first variable attenuator stage having an input receiving an RF signal and an output coupled to an input of the first amplifying device, the variable attenuator stage controlled by the system controller; and
a second variable attenuator stage having an input receiving an RF signal and an output coupled to an input of the second power amplifying device, the variable attenuator stage controlled by the system controller;
wherein the system controller selectively couples and decouples the RF signal to the first and second amplifying devices.