Method and apparatus for optimizing output power levels in power amplifiers

Some embodiments discussed relate to an apparatus comprising a power amplifier module. The power amplifier module includes a plurality of sensors, and a first digital communication port configured to provide a monitor signal from at least one of the plurality of sensors. The apparatus includes a transceiver module coupled to provide an signal to an input of the power amplifier the transceiver module including a second digital communication port configured to receive the monitor signal from the first digital communication port, a processing unit configured to generate at least one of a bias control signal and a back-off signal dependent upon the monitor signal, and a power controller to receive the at least one of bias control signal and the back-off signal and provide at least one further input signal to the power amplifier based on at least one of the bias control signal and the back-off signal.

TECHNICAL FIELD

Embodiments described herein relate generally to power amplifiers and more particularly, to optimizing the output power levels in power amplifiers.

BACKGROUND

Global System for Mobile Communications (GSM) is one of the standards used for mobile phones. Gaussian Minimum Shift Keying (GMSK) is a type of continuous-phase frequency-shift keying used in GSM. Enhanced Data rates for GSM Evolution (EDGE) is a digital mobile technology used in conjunction with GSM to provide packet-switched applications such as internet connection. EDGE additionally uses 8 phase-shift keying (8PSK) as part of the modulation and coding scheme.

DETAILED DESCRIPTION

The growth and use of radio-frequency devices (such as hand-held devices) with increasing functional capabilities (e.g., voice, video, and data) has resulted in a greater demand for efficient power-saving techniques to increase the battery life in these devices. Energy-efficient linear power amplifiers are essential components in mobile battery operated systems having wireless connectivity, e.g cellular phones, personal digital assistants (PDAs).

Linearity in power amplifiers is a fundamental requirement for the operation of 8PSK based modulation schemes in mobile handsets. Any amplitude distortion of the signal envelope produces two unacceptable phenomena. Firstly, the spectrum of the signal is widened (also known as spectral re-growth). This widening effect can cause the signal to fail the prescribed modulation mask, a requirement set by the GSM standards to prevent interference to neighboring channels. Secondly, a simple distortion of the modulation constellation results in a lowered signal to noise ratio at the receiver. The GSM standards define an error vector magnitude (EVM) specification, which is a measure of the difference between the transmitted signal and an ideal one. In practice, imperfections in the modulator, other transmitter stages and non-linearity in the power amplifier can consume a significant fraction of the EVM budget.

In applications like the EDGE standard, a modified 8PSK modulation scheme is used where as a result of base-band filtering, the final modulation signal is also amplitude modulated which means a non-constant envelope is present. Consequently, due to the presence of a non-constant envelope, the spectrum at the output of power amplifier strongly depends on the linearity of the power amplifier used. Hence, it is desired to have power amplifiers used in applications having 8PSK modulation schemes to be optimized in order to meet the stringent linearity requirements. Moreover, it is desired to limit the maximum power amplifier current in applications using GMSK as the modulation scheme. Furthermore, it is also desired to prevent power amplifiers from breakdown due to excessive heat.

In some embodiments, since mobile devices using EDGE technology support two types of modulation schemes, the power amplifiers are also required to support two different working modes in such devices.

In a GMSK modulation scheme, the modulation is of constant envelope type. Here, the linearity of the power amplifier does not corrupt the modulation quality and it is therefore not an issue (as long as the harmonics stay below a certain threshold). However, the requirement on maximum power is important, because of the presence of (1) high peak currents and (2) greater heat generation within the power amplifier. Most handset manufacturers desire to have the maximum current drawn by the power amplifier to be limited. This would enable in maximizing the talk time and avoiding abrupt self switching-off of the mobile due to the drop in battery voltage.

On the other hand, in 8PSK the linearity plays a big role, since a non linear power amplifier generates unwanted side-lobes next to the active channel which can violate the European Telecommunications Standard Institute (ETSI) requirement on spectrum purity. It is therefore important to back-off the transmitting power when the power amplifier is operating in a region where the nonlinearity is too strong.

However, both maximum current (consequently, the heat generation) and linearity strongly depend upon the actual working conditions and parameters of the power amplifier, especially the parameters such as instantaneous load, temperature and supply voltage. In order to optimize the system performance, it is desirable to make the back-off dependent on actual load condition, so that an unnecessarily large back-off is avoided. Additionally, having a large back-off may lead to using bigger power amplifiers with lower efficiency.

In some embodiments, since the load condition depends heavily on the actual frequency, a system and method to pair the back-off or biasing conditions with the frequency is used. In some embodiments, such a system that pairs the back-off with the frequency is particularly useful when the mobile system is operating in frequency-hopping mode in which case the channel is continuously changed. In some embodiments, the system works on slot basis where the system detects the state of the power amplifier after a burst and takes appropriate action for the next set of bursts. By implementing this system, an improved power amplifier working condition along with a better switching spectrum is achieved.

In some embodiments the power amplifier has a power detector. In some embodiments, power amplifier has sensors including internal current sensors, temperature sensors, and linearity sensors. In some embodiments, a digital information from sensors is sent from the power amplifier to the transceiver using a digital communication link between digital communication ports located within the transceiver and power amplifier, respectively.

In some embodiments, after the transmission of either a GMSK or 8PSK slot, the transceiver activates the digital link to the power amplifier in order to monitor its status. In some embodiments, the status report indicates the temperature at power amplifier and whether a maximum current threshold has been overtaken (e.g., in the case of GMSK) or whether the linearity of power amplifier was not good enough (e.g., in the case of 8PSK). In some embodiments, the status report may also include the amount of battery power remaining. In some embodiments, information regarding the amount of remaining battery power is evaluated directly at the transceiver.

In some embodiments, one of two modes are available (i) either to set a maximum current or (ii) to provide linearity. In some embodiments, for subsequent transmission operations on a particular channel, the maximum power is limited (e.g., in the case GMSK) or the bias condition of the power amplifier is changed (e.g., in the case of 8PSK).

In some embodiments, it may also be necessary to back off the power if the temperature of the power amplifier is too high (to avoid burn up of the device) or if the battery voltage is below a certain threshold (this could happen regardless of the particular frequency being used).

FIG. 1is a schematic view of apparatus100for optimizing the output power level of power amplifiers, according to some embodiments of the invention. Apparatus100includes an RF transceiver module102, and a power amplifier module130. Power amplifier module130is electrically coupled to an antenna142using a link140. RF transceiver102includes a processing circuit104, a power controller110, a summing circuit115and a digital port interface120. Processing circuit104includes a processor106and a memory108. Power amplifier130includes a digital port interface132, a temperature sensor134, an internal current sensor135, a linearity sensor136, and a power detector137. Digital port interface120of RF transceiver102and the digital port interface132of power amplifier130are coupled using a digital communication link122.

Sensor information related to conditions experienced by power amplifier module130as measured by134,135,136, and137is communicated from power amplifier130to RF transceiver102using digital port interfaces120,132and digital communication link122. In some embodiments, digital port interface120is a serial port interface (SPI).

Summing circuit115receives an initial signal on line114generated at a baseband circuit module (not shown) and a back-off signal on line116generated at processing circuit104. Summing circuit115combines the signals on lines114and116and sends the combined signal to power controller110, which in turn provides an input signal on line126to power amplifier module130. Input signal on line126is received at an input terminal of power amplifier130. Additionally, processing circuit104generates a bias control signal on line118based on power amplifier operating information received at processing circuit104from sensors134,135,136, and137. A bias control signal provided on line118is received at power controller110. Based on the bias control signal on line118, power controller110communicates to power amplifier130a VRAMP/Biasvoltage signal on line124. Additionally, power amplifier130provides a feedback signal VDETon line128back to power controller110. In some embodiments the VDETsignal is a feedback signal and VRAMP/Biaschanges the gain of RF power amplifier130.

FIG. 2illustrates a table200showing various power control parameters stored for each transmission channel, according to some embodiments of the invention. Row202shows the temperature of power amplifier130sensed by temperature sensor134. Row204lists channels used for frequency-hopping. Row206corresponds to the back-off voltages to be applied to the initial signal on line114for each corresponding channel listed in row204. Row208lists the bias voltages of bias control signal in line118for each corresponding channel listed in row204. In some embodiments, the output power of power amplifier130is controlled based on the values of bias voltages and back-off voltages.

In some embodiments, the RF transceiver102maintains a table200(shown inFIG. 2) with the necessary back-off and biasing conditions determined for each of the channels used for transmission. In some embodiments, the dimension of this table (maximum number of channels) depends on the maximum number of the different frequencies used in a frequency hopping scenario. In some embodiments, the back-off can be gradually increased or reduced over many bursts (with or without hysteretic behavior) according to whether the sensors measuring the linearity, the over-current, or the over-temperature remain active or not.

In some embodiments, the transceiver optimizes the power amplifier output power and/or the power amplifier biasing conditions according to digital information gathered through a digital link between power amplifier and transceiver. In some embodiments (e.g., in the case of GMSK), the output power of the power amplifier is reduced depending on the status of the current sensor, or if the maximum temperature is exceeded. In some embodiments (e.g., in the case of 8PSK), the bias voltage to the power amplifier is changed upon sensing an increase in quiescent current and the linearity sensor reports bad linearity. In some embodiments, a table is used to store the necessary back off and biasing condition for different channels. Storing the back-off and biasing conditions improves system performances in a frequency-hopping scenario. In some embodiments, the back off or biasing increase is performed only on those channels where it is really necessary.

FIG. 3shows a method300for optimizing the output power levels of power amplifiers, according to some embodiments of the invention.

At block302, the apparatus is generating a monitor signal at a sensor in a power amplifier. At block304, the action is sending the monitor signal using a digital communication port to a transceiver. At block306, the action is receiving the monitor signal at a transceiver using a digital communication port. At block308, the action is processing the monitor signal to generate a bias control signal and a back-off signal. At block310, the action is receiving the bias control signal and the back-off signal at a power controller. The power controller is generating a power amplifier input signal based on an initial signal, the back-off signal, and the bias control signal.

The system for controlling output power disclosed in this invention is suitable for applications in various wireless data and voice communications standard and protocols, including GSM, General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), IEEE 802.11 and others. In addition, the system discussed may be used in a wide range of wireless communication devices such as cellular phone, mobile computers, and other handheld wireless digital devices.

Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. In the previous discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”.