Power amplifier having analog pre-distortion by adaptive degenerative feedback

Power amplifier having analog pre-distortion by adaptive degenerative feedback. In some embodiments, a pre-distortion circuit for an amplifier can include a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit can further include a degeneration circuit implemented between the common node and the ground, with the degeneration circuit being configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level. The degeneration circuit can be further configured to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

BACKGROUND

Field

The present disclosure relates to power amplifiers such as radio-frequency power amplifiers.

Description of the Related Art

In radio-frequency applications, a signal to be transmitted is typically generated by a transceiver, and such a signal is amplified by a power amplifier. The amplified signal is then typically routed to an antenna through, for example, a transmit filter and a switching circuit, for transmission.

SUMMARY

In accordance with a number of implementations, the present disclosure relates to a pre-distortion circuit for an amplifier. The pre-distortion circuit includes a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit further includes a degeneration circuit implemented between the common node and the ground. The degeneration circuit is configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, and to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

In some embodiments, the transistor can be implemented as a bipolar-junction transistor having a base, an emitter, and a collector, such that the base provides the input node, the collector provides the output node, and the emitter provides the common node.

In some embodiments, the degeneration circuit can include a resistance implemented between the common node and the ground, and an antiparallel combination of first and second diodes implemented between the common node and the ground. The first and second diodes can be configured to turn on when the power level of the input signal exceeds the selected level. In some embodiments, the degeneration circuit can be further configured to provide a phase control functionality. The phase control functionality can include an AM-to-PM phase control functionality.

In some embodiments, the degeneration circuit can further include an inductance and a capacitance, each being implemented to be electrically parallel with the resistance, and between the common node and the ground. At least one of the inductance and the capacitance can be configured to provide the phase control functionality.

In some embodiments, the degeneration circuit can be further configured such that the selected level is compensated for a variation in temperature. The degeneration circuit can further include a voltage source configured to apply a bias to the first and second diodes. The voltage source can be implemented to be between each of the first and second diodes and the ground. The voltage source can be configured to provide a temperature-dependent voltage to each of the first and second diodes.

According to some teachings, the present disclosure relates to method for pre-distorting a signal for an amplifier. The method includes providing a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The method further includes introducing a feedback response, with a degeneration circuit implemented between the common node and the ground, such that the feedback response includes a reduction in the gain when the input signal has a power level at or below a selected level, and a disablement or a reduction of the feedback response when the input signal has a power level that exceeds the selected level.

In some implementations, the present disclosure relates to an amplifier that includes a pre-driver stage configured to receive an input signal and generate an output signal having a gain relative to the input signal. The amplifier further includes an amplification stage configured to receive an input signal representative of the output signal of the pre-driver stage and to generate an amplified signal. The amplifier further includes a pre-distortion circuit coupled to the pre-driver stage and configured to introduce a feedback response that reduces the gain when the input signal of the pre-driver stage has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal of the pre-driver stage has a power level that exceeds the selected level.

In some embodiments, the pre-driver stage can include a transistor having an input node for receiving the input signal, an output node for providing the output signal, and a common node for coupling to a ground. The pre-distortion circuit can include a degeneration circuit implemented between the common node and the ground. The degeneration circuit can include a resistance implemented between the common node and the ground, and an antiparallel combination of first and second diodes implemented between the common node and the ground. The first and second diodes can be configured to turn on when the power level of the input signal exceeds the selected level.

In some embodiments, the degeneration circuit can be configured to provide a phase control functionality. In some embodiments, the degeneration circuit can be configured such that the selected level is compensated for a variation in temperature.

In some embodiments, the amplifier can be a power amplifier.

In some implementations, the present disclosure relates to a method for amplifying a signal. The method includes pre-driving an input signal to generate an output signal having a gain relative to the input signal. The method further includes amplifying the output signal of the pre-driving to generate an amplified signal. The method further includes performing a pre-distortion operation with respect to the pre-driving to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

In some teachings, the present disclosure relates to a semiconductor die that includes a semiconductor substrate and a pre-distortion circuit implemented on the semiconductor substrate. The pre-distortion circuit includes a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit further includes a degeneration circuit implemented between the common node and the ground. The degeneration circuit is configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, and to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

In some embodiments, the semiconductor die can further include an amplifier stage configured to provide power amplification for the output signal generated by the transistor of the pre-distortion circuit.

In some implementations, the present disclosure relates to a radio-frequency module that includes a packaging substrate configured to receive a plurality of components, and a pre-distortion circuit implemented on the packaging substrate. The pre-distortion circuit includes a transistor having an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit further includes a degeneration circuit implemented between the common node and the ground. The degeneration circuit is configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, and to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

In some implementations, the present disclosure relates to a semiconductor die that includes a semiconductor substrate and an amplifier circuit implemented on the semiconductor substrate. The amplifier circuit includes a pre-driver stage configured to receive an input signal and generate an output signal having a gain relative to the input signal, and an amplification stage configured to receive an input signal representative of the output signal of the pre-driver stage and to generate an amplified signal. The amplifier circuit further includes a pre-distortion circuit coupled to the pre-driver stage and configured to introduce a feedback response that reduces the gain when the input signal of the pre-driver stage has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal of the pre-driver stage has a power level that exceeds the selected level.

According to some implementations, the present disclosure relates to a radio-frequency module that includes a packaging substrate configured to receive a plurality of components, and an amplifier circuit implemented on the packaging substrate. The amplifier circuit includes a pre-driver stage configured to receive an input signal and generate an output signal having a gain relative to the input signal, and an amplification stage configured to receive an input signal representative of the output signal of the pre-driver stage and to generate an amplified signal. The amplifier circuit further includes a pre-distortion circuit coupled to the pre-driver stage and configured to introduce a feedback response that reduces the gain when the input signal of the pre-driver stage has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal of the pre-driver stage has a power level that exceeds the selected level.

In some implementations, the present disclosure relates to a wireless device that includes a transceiver, an antenna, and an amplifier circuit implemented to be electrically between the transceiver and the antenna. The amplifier circuit includes a pre-distortion circuit having a transistor with an input node for receiving an input signal, an output node for providing an output signal having a gain relative to the input signal, and a common node for coupling to a ground. The pre-distortion circuit further includes a degeneration circuit implemented between the common node and the ground. The degeneration circuit is configured to introduce a feedback response that reduces the gain when the input signal has a power level at or below a selected level, and to be disabled or provide a reduced feedback response when the input signal has a power level that exceeds the selected level.

In some implementations, the present disclosure relates to a wireless device that includes a transceiver, an antenna, and an amplifier circuit implemented to be electrically between the transceiver and the antenna. The amplifier circuit includes a pre-driver stage configured to receive an input signal and generate an output signal having a gain relative to the input signal, and an amplification stage configured to receive an input signal representative of the output signal of the pre-driver stage and to generate an amplified signal. The amplifier circuit further includes a pre-distortion circuit coupled to the pre-driver stage and configured to introduce a feedback response that reduces the gain when the input signal of the pre-driver stage has a power level at or below a selected level, and to disable or provide a reduced feedback response when the input signal of the pre-driver stage has a power level that exceeds the selected level.

In some embodiments, the amplifier circuit can be a power amplifier circuit.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

FIG.1depicts a power amplifier102having an analog pre-distortion (APD) component100. Although various examples are described in the context of power amplifiers, it will be understood that one or more features of the present disclosure can also be implemented in other types of amplifiers.

FIG.2shows that in some embodiments, the APD component100ofFIG.1can be implemented to include, or be associated with, a pre-driver stage104and an associated degeneration APD circuit110. In some embodiments, an output of the pre-driver stage104can be provided to one or more amplification stages (collectively indicated as106) of the power amplifier102.

FIGS.3to5show more specific examples of the APD component100ofFIG.2. In each of the examples ofFIGS.3to5, an APD component100can include, or be associated with, a pre-driver stage104implemented with a bipolar junction transistor Q1having a base, a collector, and an emitter. Although various examples are described in the context of such a bipolar junction transistor, it will be understood that one or more features of the present disclosure can also be implemented utilizing other types of transistors, including a field-effect transistor having a gate, a drain, and a source.

Referring toFIGS.3to5, the base of the transistor Q1can receive a radio-frequency (RF) signal from an input node (RF_in), through an input signal path. In some embodiments, such an input signal path can include some or all of a transmission line (TL) (or a portion of the signal path behaving like a transmission line), an attenuator (Atten), a DC block capacitance C2, and a base resistance R2.

The base of the transistor Q1can be provided with a bias signal from a biasing circuit120. In some embodiments, such an example biasing circuit can include a current mirror arrangement of transistors Q11and Q12, where the base of Q12is coupled to the collector of Q11, and the base of Q11is coupled to the emitter of Q12through a resistance R12. The collector of Q11is shown to be coupled to a supply voltage node V_supply through a resistance R11, and the collector of Q12is coupled to the supply voltage node V_supply. The collector of Q11is shown to be coupled to ground through a capacitance C11, and the emitter of Q11is shown to be coupled to ground through a resistance R13. The emitter of Q12is shown to be coupled to ground through a series arrangement of a resistance R14and a diode X11.

With the foregoing example biasing circuit120, the bias signal can be provided to the base of Q1through an inductance L2and the base resistance R2. In some embodiments, a node between C2and R2can be coupled to ground through a series arrangement of the inductance L2and a capacitance C4.

In some embodiments, and referring toFIGS.3to5, a feedback circuit can be provided between the output114of Q1and the input112of Q1. Such a feedback circuit can include a series arrangement of a capacitance C5and a resistance R3. Values of C5and/or R3can be selected to provide a gain-setting functionality for the transistor Q1.

Referring toFIGS.3to5, a supply voltage can be provided to the collector of the transistor Q1from the supply voltage node V_supply, through an inductance L3. The collector of the transistor Q1can also provide an output signal having a gain relative to the input signal, to an output node (Out) through an output signal path. In some embodiments, such an output signal path can include a DC block capacitance C3.

In each of the examples ofFIGS.3to5, an APD component100is shown to include a degeneration APD circuit110that couples the emitter of the respective transistor Q1to ground. For example,FIG.3shows that in some embodiments, a degeneration APD circuit110can include an electrically parallel arrangement of a resistance R1, a first diode X1, and a second diode X2, and such a parallel arrangement can be implemented to be electrically between the emitter of Q1and the ground. In some embodiments, the first diode X1can be arranged so that its anode is coupled to the emitter of Q1, and its cathode is coupled to the ground. The second diode X2can be arranged so that its cathode is coupled to the emitter of Q1, and its anode is coupled to the ground.

Configured in the foregoing manner, the degeneration APD circuit110can introduce a non-linear feedback response by way of an emitter degeneration that reduces gain of the transistor Q1when the input RF signal has low power. When the input RF signal has high power, the anti-parallel arrangement of the first and second diodes X1, X2can provide a shunt path between the emitter of Q1and the ground, and thereby disable the degeneration APD circuit110.

It is noted that gain expansion provided by the transistor Q1can be steep with the use of the degeneration APD circuit110(e.g., on the order of 1 dB expansion per 1 dB increase in power of the input RF signal). As the power (Pin) of the input RF signal reaches a selected level (e.g., Pin=0 dBm), DC voltage across emitter resistor R1becomes sufficiently high to turn on the diodes X1, X2. After such turning on of the diodes X1, X2, the gain-reducing effect of the degeneration APD circuit110diminishes, and the gain provided by the transistor Q1increases. Accordingly, power of the input signal (i.e., the output of Q1) provided to the one or more amplification stages (106inFIG.2) of the power amplifier increases rapidly.

In some embodiments, the foregoing rapid gain expansion provided by the APD component100can be configured to compensate for gain compression of the one or more amplification stages of the power amplifier. In some embodiments, such a rapid gain expansion compensation can result in an increased range of linear power amplification capability (e.g., an increase by approximately 1 dB).

It is noted that in some embodiments, an APD component having one or more features as described herein can provide a rate of gain expansion that is much higher than that of conventional diode pre-distorters.

In some embodiments, the above-described selected level of the power (Pin) of the input RF signal at which the diodes (X1, X2) turn on to result in gain expansion can be selected as Pexp=(Vdiode2/Re)*(Rload/Re)2, where Pexpis gain expansion threshold power, Vdiodeis turn-on voltage for the diodes (X1, X2), Reis the emitter resistance (R1inFIG.3), and Rloadis load resistance associated with the transistor Q1.

In some embodiments, initial gain of the transistor Q1can be Gv=Rload/Re. In some embodiments, such an initial gain of the transistor Q1can be adjusted by selecting the above-described resistance R3of the feedback circuit between the output114and input112of the transistor Q1.

In another example,FIG.4shows that in some embodiments, a degeneration APD circuit110can be similar to the example ofFIG.3, and also include an optional phase control functionality (e.g., AM-to-PM). For example, an inductance L1and a capacitance C1can be provided to be electrically parallel with the emitter resistance R1, between the emitter of Q1and the ground. Either or both of L1and C1can be selected to provide the phase control functionality.

In the example ofFIG.4, other parts of the APD component100can be similar to the example ofFIG.3.

In some embodiments, an APD component having one or more features as described herein can be configured so that gain expansion threshold of a degeneration APD circuit can be compensated for variations in temperature. For example,FIG.5shows that in some embodiments, a degeneration APD circuit110can be configured to provide temperature compensation by applying an external bias to the diodes X1, X2.

For example, a voltage source130can be provided between each of the diodes X1, X2and the ground, and such a voltage source can be configured to provide a voltage that depends on temperature. For example, such a temperature-dependent voltage can be Vdc=(T−25)(0.001), where T is temperature associated with operation of Q1in ° C., and Vdc is in volts.

In the foregoing example, implementation of the Vdc can be supported by an approximately 1 mV/° C. added to the bias signal provided to the base of Q1. In some embodiments, such a temperature-dependent bias signal can be provided by an appropriately configured biasing circuit120.

For example, and referring toFIG.5, a biasing circuit120can include a field-effect transistor Q12′ implemented as a source follower, replacing the transistor Q12ofFIGS.3and4. With such a transistor (Q12′), the gate, drain, and source of Q12′ can correspond to the base, collector, and emitter of Q12. The biasing circuit120can further include a current source121implemented between the collector of Q11and ground. Configured in the foregoing example manner, the biasing circuit120can support the temperature-dependent bias signal provided to the transistor Q1.

In some embodiments, gain of one or more power amplification stages coupled to the output of the APD component100ofFIG.5can be approximately uniform over a desired temperature range associated with operation of Q1.

FIG.6shows examples of AM-AM and AM-PM plots for power amplifiers with an analog pre-distortion (APD) and without (baseline) an APD component as described herein. Among others,FIG.6shows (baseline AM-AM vs APD AM-AM plots) that gain expansion provided by the APD component compensates for gain compression of the respective power amplifier, and thereby desirably pushes out (arrow150) the compression transition point to a higher power value. In the example ofFIG.6, such an extension of the compression transition point is shown to be approximately 1.5 dB.

FIG.7shows examples of figure-of-merit (FOM) for power amplifiers with an APD and without (baseline) an APD component as described herein. The curve indicated as Baseline1is for a power amplifier without an APD component, and the curves indicated as APD_VBIAS_2P4 and APD_VBIAS_3P4 are for a power amplifier with an APD component operated at different bias voltages. One can see that each of the FOM plots for the two bias settings of the APD component shows an improvement of 6 points in FOM (arrows152,154).

FIG.8shows examples of ACLR for power amplifiers with an APD and without (baseline) an APD component as described herein. The curve indicated as Baseline1is for a power amplifier without an APD component, and the curves indicated as APD_VBIAS_2P4 and APD_VBIAS_3P4 are for a power amplifier with an APD component operated at different bias voltages. One can see that each of the ACLR plots for the two bias settings of the APD component shows an approximately 1 dB increase in power headroom (arrow158), and an approximately 5 dB improvement in ACLR (arrow156).

FIGS.9A and9Bshow examples of responses of the APD component100ofFIG.4in which the emitter degeneration APD circuit110includes the inductance L1and the capacitance C1, as a function of input power. It is noted that in the examples ofFIGS.9A and9B, the threshold power level for inducing gain expansion is at approximately 0 dBm.

InFIG.9A, one can see that when the input power is less than 0 dBm (in region160), the gain of the APD component100remains at a reduced level. When the input power exceeds the example threshold value of 0 dBm, the diodes (X1, X2inFIG.4) of the emitter degeneration APD circuit110are turned on, and the APD component100provides a steep gain expansion response (in region162).

InFIG.9B, an example AM-to-PM response is shown for a corresponding set of L1and C1of the emitter degeneration APD circuit110ofFIG.4. In some embodiments, values of L1and/or C1can be selected to control at least a portion (164) of the AM-to-PM response corresponding to the steep gain expansion region162. For example, the phase response portion164can be tailored to be opposite, or approximately opposite, of an AM-to-PM response of one or more power amplification stages downstream of the APD component100.

FIG.10shows an example of how direction and amount of phase pre-distortion (such as the example ofFIG.9B) can be controlled by appropriately selecting values of L1and C1of the emitter degeneration APD circuit110ofFIG.4. InFIG.10, various phase responses are shown for respective capacitance values (Cpd, in pF) of C1, for a given value of L1. As described herein, such a functionality can be utilized to provide phase control while providing the emitter degeneration APD functionality.

FIGS.11A to11Dshow examples of AM-AM plots (FIG.11A), AM-PM plots (FIG.11B), gain plots (FIG.11C), and power added efficiency (PAE) plots (FIG.11D), as functions of output power Pout, for different supply voltage levels of an envelope tracking power amplifier without an APD component.FIGS.12A to12Dshow examples of AM-AM plots (FIG.12A), AM-PM plots (FIG.12B), gain plots (FIG.12C), and power added efficiency (PAE) plots (FIG.12D), as functions of output power Pout, for different supply voltage levels of an envelope tracking power amplifier with an APD component.

Among others,FIGS.11and12show that the power amplifier without an APD component has a relatively soft compression profile (e.g., profile170inFIG.11C), while the power amplifier with an APD component has a sharper compression profile (e.g., profile180inFIG.12C). It is also noted that the power amplifier without an APD component can have a sub-optimal PAE profiles (e.g., profile172inFIG.11D), while the power amplifier with an APD component can have a PAE profile that ride on tops of some or all of the various PAE curves (e.g., profile182inFIG.12D).

FIG.13shows that in some embodiments, one or more features of the present disclosure can be implemented in a packaged module400. Such a module can include a packaging substrate402configured to receive a plurality of components. Some or all of such components can be implemented to provide a power amplifier102with an APD component100having one or more features as described herein.

In some implementations, an architecture, device and/or circuit having one or more features described herein can be included in an RF device such as a wireless device. Such an architecture, device and/or circuit can be implemented directly in the wireless device, in one or more modular forms as described herein, or in some combination thereof. In some embodiments, such a wireless device can include, for example, a cellular phone, a smart-phone, a hand-held wireless device with or without phone functionality, a wireless tablet, a wireless router, a wireless access point, a wireless base station, etc. Although described in the context of wireless devices, it will be understood that one or more features of the present disclosure can also be implemented in other RF systems such as base stations.

FIG.14schematically depicts an example wireless device500having one or more advantageous features described herein. In some embodiments, such advantageous features can be implemented in, for example, a power amplifier module (PAM)400.

In the example ofFIG.14, power amplifiers (PAs) in the PA module400can receive their respective RF signals from a transceiver510that can be configured and operated to generate RF signals to be amplified and transmitted, and to process received signals. At least some of the power amplifiers can include an APD component as described herein.

The transceiver510is shown to interact with a baseband sub-system508that is configured to provide conversion between data and/or voice signals suitable for a user and RF signals suitable for the transceiver510. The transceiver510is also shown to be connected to a power management component506that is configured to manage power for the operation of the wireless device500. Such power management can also control operations of the baseband sub-system508and other components of the wireless device500.

The baseband sub-system508is shown to be connected to a user interface502to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system508can also be connected to a memory504that is configured to store data and/or instructions to facilitate the operation of the wireless device, and/or to provide storage of information for the user.

In the example wireless device500, a front-end module514can be configured to support transmit and/or receive operations utilizing one or more antennas. For example, one or more primary antennas520a,520bcan be provided, and each antenna can support transmit and/or receive operations through the front-end module514. In another example, a diversity antenna530can be provided, and such an antenna can support at least a receive operation through a diversity receive module516coupled to the front-end module514through a path532.

In some embodiments, at least some of the signals received through the front-end module514can be routed to the transceiver510. Such received signals may or may not be amplified by low-noise amplifiers.

A number of other wireless device configurations can utilize one or more features described herein. For example, a wireless device does not need to be a multi-band device. In another example, a wireless device can include additional antennas such as diversity antenna, and additional connectivity features such as Wi-Fi, Bluetooth, and GPS.