Dynamic bias current adjustment for power amplifiers

In one embodiment, a circuit comprises a power amplifier. The circuit further comprises a memory that stores bias current values corresponding to a plurality of frequencies across a frequency band for setting the bias of a power amplifier based on selected frequencies, and a controller configured to provide at least one bias current value corresponding to a selected frequency from the memory to the power amplifier in response to a frequency selection signal. The bias current value at each frequency may be selected to maximize power efficiency or minimize adjacent channel leakage-power ratio of the power amplifier at said frequency. In one embodiment, the memory further stores bias current values corresponding to the plurality of frequencies across the frequency band at a plurality of temperatures for setting the bias of a power amplifier based on a temperature of the power amplifier and on selected frequencies.

BACKGROUND

The disclosure relates to power amplifiers, and in particular, to dynamic bias current adjustment for power amplifiers.

Unless otherwise indicated herein, the approaches described in this section are not admitted to be prior art by inclusion in this section.

As Envelope Tracking (ET) becomes more popular, power amplifiers (PAs) and duplexer modules (PADs) are being pushed to their operating limits for improved efficiency. As new PAs and PADs are improved, the main transmit metrics that are maintained in envelope tracking operation are maximum power, adjacent channel leakage ratio (ACLR) and current consumption. Conventional PAs optimize PA output matching based on the optimum PA parameters at one frequency.

SUMMARY

The present disclosure provides methods for dynamic bias current adjustment for power amplifiers and power amplifiers including dynamic bias current adjustment.

In one embodiment, the disclosure provides a circuit that comprises a power amplifier. The circuit further comprises a memory that stores bias current values corresponding to a plurality of frequencies across a frequency band for setting the bias of a power amplifier based on selected frequencies, and a controller configured to provide at least one bias current value corresponding to a selected frequency from the memory to the power amplifier in response to a frequency selection signal.

In one embodiment, the bias current value at each frequency is selected based on a power metric of the power amplifier at said frequency.

In one embodiment, the bias current value at each frequency is selected to minimize adjacent channel leakage-power ratio of the power amplifier at said frequency.

In one embodiment, the memory further stores bias current values corresponding to the plurality of frequencies across the frequency band at a plurality of temperatures for setting the bias of a power amplifier based on a temperature of the power amplifier and on selected frequencies.

In one embodiment, the bias current value is selected at different temperatures to maximize the power efficiency of the power amplifier at each temperature.

In one embodiment, the power amplifier further comprises a power transistor, and a bias controller that provides a bias current to the power transistor in response to the bias current value.

In one embodiment, the circuit further comprises an envelope digital-to-analog controller for envelope tracking.

In one embodiment, the disclosure provides a method comprising: receiving a frequency selection signal; retrieving from a memory a bias current corresponding to a channel based on the frequency selection signal, the memory stores bias current values corresponding to a plurality of frequencies across a frequency band for setting the bias of a power amplifier based on selected frequencies; and providing the retrieved bias current to the power amplifier.

In one embodiment, the method further comprises biasing at least one power transistor in response to the retrieved bias current.

In one embodiment, the method further selecting the bias current value at each frequency to maximize power efficiency of the power amplifier at said frequency.

In one embodiment, the method further comprises selecting the bias current value at each frequency to minimize adjacent channel leakage-power ratio of the power amplifier at said frequency.

In one embodiment, the memory further stores bias current values corresponding to a plurality of frequencies across a frequency band at a plurality of temperatures for setting the bias of a power amplifier based on a temperature of the power amplifier and on selected frequencies.

In one embodiment, the method further comprises selecting the bias current value at different temperatures to maximize the power efficiency of the power amplifier at each temperature.

In one embodiment, the method further comprises receiving a temperature signal indicative of the temperature of the power amplifier; and retrieving from the memory a bias current corresponding to a channel based on the frequency selection signal and the temperature signal.

In one embodiment, the power amplifier comprises a power transistor. The method further comprises providing a bias current to the power transistor in response to the bias current value.

In one embodiment, the method further comprises envelope tracking peak power of a radio frequency input to the power amplifier; and adjusting a supply voltage applied to the power amplifier in response to the enveloped tracked peak power.

In one embodiment, the disclosure provides a method comprising: selecting, from a plurality of performance values of a power amplifier as a function of bias current corresponding to a plurality of frequencies across a frequency band, a bias current value for each frequency in response to a selection criteria of performance; and storing in a memory the selected bias current values in association with the corresponding frequencies.

In one embodiment, the selection criteria of performance is maximization of power efficiency of the power amplifier at said frequency.

In one embodiment, the selection criteria of performance is minimization of adjacent channel leakage-power ratio of the power amplifier at said frequency.

In one embodiment, the performance values further are a function of temperature of the power amplifier.

In one embodiment, the disclosure provides a method comprising: applying a radio frequency input signal having a frequency to a power amplifier; applying a plurality of bias currents to the power amplifier; detecting a radio frequency output signal from the power amplifier; determining a performance metric of the power amplifier from the radio frequency output signal for each bias current of the plurality of bias currents; and selecting a bias current to bias the power amplifier based on a criteria of the detected performance metrics.

DETAILED DESCRIPTION

FIG. 1illustrates a block diagram of a power amplifier (PA) system100according to an embodiment. In contrast to a system that provides a single bias value across the frequency range, the power amplifier systems herein may provide dynamic biasing of the power amplifier based on frequency and may also be based on temperature to maximize or optimize performance at each frequency. Performance may be quantified by, for example, power amplifier metrics, such as maximum power, adjacent channel leakage ratio (ACLR), or current consumption. PA system100comprises a radio frequency (RF) transceiver102, a power amplifier104, a modem106, and an envelope digital-to-analog converter (DAC) controller108. Modem106comprises an RF front end (RFFE) controller114and a memory116.

Memory116stores bias current (ICQ) values to bias PA104for different frequencies across a frequency band to improve the efficiency or performance of the power amplifier. In some embodiments, memory116also stores bias current (ICQ) values to bias PA104for different temperatures to improve the efficiency or performance of the power amplifier. In some embodiments, adjacent channel leakage-power ratio (ACLR) is one measure of amplifier efficiency of the power amplifiers described herein.

PA104generates an RF output (RFOut) in response to an RF input (RFin) from RF transceiver102. Envelope DAC controller108controls the supply voltage VCC to PA104for envelope tracking to change the supply voltage VCC based on the peak power of the RF input (RFIn).

The one or more bias values from memory116are programmed into a bias current (ICQ) register or registers in PA104to set a bias current (ICQ) for PA104. RF front end (RFFE) controller114generates clock and data for PA104including the ICQ register value for a selected RF channel in response to a frequency selection signal120from an external system (not shown).

Although memory116is described as external to PA104, memory116may be internal to PA104.

FIG. 2illustrates the ACLR as a function of channel/band of a power amplifier according to an embodiment. RFFE controller114selects a bias current value in the memory based on the particular channel (frequency) being used to minimize ACLR (or improve or maximize efficiency) for the channel. For example, RFFE controller114selects ICQ value244for channel27260and selects ICQ value248for channel27460.

The channels shown inFIG. 2includes an offset of plus one (+1) and minus one (−1). In this example, the +1 offset is 7.5 MHz above the carrier, and the −1 offset is 7.5 MHz below the carrier.

For each channel, the bias that provides the minimum ACLR is selected and stored in memory116. In some embodiments, the bias values are coded in memory116. The code is provided to PA104, where it is mapped to a bias current or currents for the power transistor or transistors in PA104.

For example, the code244is the number stored in memory116. When the corresponding channel is selected, the code244is stored in the register in PA104, and is mapped to a corresponding bias current.

A calibration procedure may be used to determine the ACLR function shown inFIG. 2. For each bias current value, the ACLR is measured for each channel, including positive and negative offsets from the carrier, across the frequency band. For each channel, the bias current value that has the minimum ACLR is selected, and stored, or a code associated with the bias current value is stored, in memory116in a table, such as shown inFIG. 3.

FIG. 3illustrates a table300of the channels and bias current values for the frequency band according to an embodiment. Table300is stored in memory116. Table300includes an ICQ value for each channel. Although only eight channels are shown inFIGS. 2 and 3, other numbers of channels may be used and stored in table300.

For simplicity and clarity, the ACLR as a function of frequency is shown inFIG. 2for only one temperature, and the table of the channels and ICQ values is shown inFIG. 3for only one temperature. The ACLR may be determined as a function of frequency over a temperature range, such as an expected operating temperature range of the power amplifier. The table300may be expanded to include ICQ code values for a plurality of different temperatures for each channel.

FIG. 4illustrates a Smith chart400of impedance variation as a function of frequency and temperature for an example power amplifier. A line402illustrates the impedance of the example power amplifier for a frequency range at 25° C. A line404illustrates the impedance of the example power amplifier for a frequency range at 60° C. A point406illustrates the error vector magnitude (EVM) of the power amplifier. A point408illustrates the efficiency of the power amplifier. A point410illustrates the gain of the power amplifier. A point412illustrates the output power (Pout) of the power amplifier. A point414illustrates the ACLR of the power amplifier.

FIG. 5illustrates a block diagram of a power amplifier (PA) system500according to an embodiment. PA system500comprises a radio frequency (RF) transceiver102, a modem106, a power amplifier502, a power amplifier supply voltage module504, and a temperature sensor505. In some embodiments, power amplifier supply voltage module504is an envelope DAC controller108.

PA502generates an RF output (RFOut) in response to an RF input (RFin) from RF transceiver102. Power amplifier supply voltage module504controls the supply voltage VCC to PA502, which may include envelope tracking for changing the VCC based on the peak power of the RF input (RFIn). Temperature sensor505senses or detects the temperature of PA502or of a component therein (such as a power transistor) and generates a temperature signal507that may be provided to RFFE controller114or modem106.

PA502comprises a plurality of power transistors506and508, a plurality of inductors510and512, an RFFE controller516, a bias controller518, an input match circuit520, an inter-stage match circuit522, and an output match circuit524. Although memory116is described as external to PA502, memory116may be internal to PA502.

Input match circuit520provides impedance matching between RF receiver102and first stage power transistor506. Inter-stage match circuit522provides impedance matching between first stage power transistor506and second stage power transistor508. Output match circuit524provides impedance matching between second stage power transistor508and an external circuit, such as an antenna.

RFFE controller516receives clock and data including the ICQ register value for a selected RF channel for the PA502from RFFE controller114of modem106. RFFE controller516provides the ICQ bias values to bias controller518, which applies the selected bias to the respective bases of first stage power transistor506and second stage power transistor508. In some embodiments, bias controller518comprises a plurality of registers (not shown) for storing the ICQ bias values provided by RFFE controller516.

FIG. 6illustrates a simplified diagram of a process flow600for controlling bias of a power amplifier according to an embodiment. Although process flow600is described for PA system500, process flow600may be applied to other PA systems.

At602, a frequency selection signal120is received to select a frequency of an RF input signal (RFIn) from RF transceiver102. At604, a temperature signal507indicative of the temperature of power amplifier502is received. In some embodiments, the process flow600does not include process part604.

At606, a bias current value corresponding to a channel is retrieved from memory116in response to the temperature signal507and the frequency selection signal116. In some embodiments, the process flow600does not include process part604, and at606retrieves a bias current value based on the frequency selection signal116.

At608, the retrieved bias current value is provided to power amplifier502. At610, a bias current corresponding to the retrieved bias current code is provided to bias a power transistor (or power transistors506and508for power amplifier502).

FIG. 7illustrates a simplified diagram of a process flow700for selecting bias values of a power amplifier according to an embodiment.

Although process flow700is described for PA system100, process flow700may be applied to other PA systems.

At702, a bias current value is selected for each frequency of a plurality of frequencies across a frequency band in response to a selection criteria of performance. The bias current value is selected from a plurality of performance values of a power amplifier as a function of bias current corresponding to the frequencies. The performance values can be, for example, the values from an ACLR as a function of channel, such as shown inFIG. 2. The selection criteria of performance may be, for example, maximization of power efficiency or minimization of ACLR of the power amplifier at said frequency.

At704, the selected bias current values and the associated frequencies are stored in memory116. The performance values may be a function of temperature, and the selected bias current values and the associated frequencies and temperatures are stored in memory116.

FIG. 8illustrates a block diagram of a power amplifier (PA) system800according to an embodiment. PA system800may provide dynamic biasing of the power amplifier based on frequency and may also be based on temperature to maximize or optimize performance at each frequency in a similar manner as PA system100. PA amplifier system800further provides a feedback system for detecting and analyzing performance online or in real time and determine bias values for a selected frequency. PA system800comprises a radio frequency (RF) transceiver802, a power amplifier104, a modem806, an envelope digital-to-analog converter (DAC) controller108, a duplexer808, an antenna switch810, and a coupler812. RF transceiver802comprises a feedback receiver820. Modem806comprises an RF front end (RFFE) controller824, a feedback (FB) sample processing circuit826, and a memory116.

Memory116stores bias current (ICQ) values to bias PA104for different frequencies across a frequency band to improve the efficiency or performance of power amplifier104and otherwise operates in a similar manner as described above for PA system100.

PA104generates an RF output (RFOut) in response to an RF input (RFin) from RF transceiver802. Envelope DAC controller108controls the supply voltage VCC to PA104for envelope tracking to change the supply voltage VCC based on the peak power of the RF input (RFIn). Duplexer808provides the RF output (RFOut) to antenna switch810and provides a received RF signal from antenna switch810to RF transceiver802(not shown inFIG. 8for simplicity and clarity). Antenna switch810provides the RF output (RFOut) to coupler812, which provides the RF output to an antenna (not shown) and to feedback receiver820of RF transceiver802. Feedback receiver820provides mixing, down conversion, and processing of the feedback signal, which is at a frequency of the RF output. Feedback sample processing circuit826takes samples of the processed feedback signal from feedback receiver820and determines bias values for PA104in response to the processed samples, and provides the bias values to RFFE controller824.

In response to an online mode signal820from an external system (not shown), PA system800executes a procedure to determine bias values at a selected frequency indicated by the frequency section signal120. Bias values are selected based on the performance metric (such as those used in PA system100) that is being evaluated. For example, PA system800may use ACLR as the performance metric. RFFE controller820provides a sequence of bias values to PA104that generates the RF output in response to the sequence of bias values applied to bias the power transistors in PA104. Feedback receiver820receives the coupled power from coupler812, and mixes, downconverts, and processes the coupled power to provide a processed feedback signal to feedback sample processing circuit826. For each bias value, feedback sample processing circuit826analyzes the processed feedback signal for the performance metric (in this example, ACLR) and determines the bias value that provides the minimum ACLR at the selected frequency.

Referring again toFIG. 2, feedback sample processing circuit826generates the data for a selected frequency (channel inFIG. 2) for the bias values, and selects the bias value that minimizes the ACLR. This allows the PA amplifier system800to determine during normal system operation the appropriate bias value from the online measurements. The determined bias values may be stored in memory116for later use, such as in the operation described inFIG. 6.

FIG. 9illustrates a simplified diagram of a process flow900for determining and controlling bias of power amplifier104according to an embodiment. At902, a frequency selection signal120is received. At904, RFFE controller824generates a bias current value and provides the value to PA104. At906, coupled power is detected by feedback receiver820. At908, the processed feedback signal from feedback receiver820is analyzed for a performance metric. At910, the loop returns to at904unless the last bias current value has been generated and the performance metric for the value is analyzed. At912, a bias value is selected for the frequency based on the performance metric, such as minimizing ACLR.

The power amplifier system may change the biasing ICQ current to improve performance while keeping the transmit metrics the same or substantially the same. The ACLR may be improved by dynamically changing the bias without significantly changing the maximum power across the frequency range. Accordingly, the power amplifier system may be used in an external system, such as a phone, while maintaining the output power and keeping the total system current constant.

The power amplifier systems optimize a performance characteristic, such as ACLA or maximum power, at each frequency or channel across the frequency range. The optimization may also account for temperature. Although the systems are described for providing biasing at a specific channel or a specific channel at a specific temperature using the data in a table, the biasing may also be based on interpolation of values in the table.