Abstract: The present application relates to the field of digital pre-distortion processing. Disclosed in an embodiment of the present application are a pre-distortion parameter obtaining method and pre-distortion system for simplifying calculating complexity of a model while achieving good signal processing effect. The method comprises: after the beginning of periodic filtering processing, obtaining a pre-distorted signal after pre-distortion processing and a first feedback signal after power amplification (S101); obtaining a second feedback signal by eliminating the rated linear gain of the first feedback signal (S102); determining a pre-distortion parameter according to a matrix formed by the second feedback signal and a matrix formed by the pre-distorted signal (S103); updating the pre-distortion parameter index table according to the determined pre-distortion parameter (104).

Abstract: An apparatus for controlling the gain and phase of an input signal input to a power amplifier comprises a gain control loop configured to control the gain of the input signal based on power levels of the input signal and an amplified signal output by the power amplifier, to obtain a predetermined gain of the amplified signal, and a phase control loop configured to obtain an error signal related to a phase difference between a first signal derived from the input and a second signal derived from the amplified signal, and control the phase based on the error signal, to obtain a predetermined phase of the amplified signal. The phase control loop delays the first signal, such that the delayed first signal and the second signal used to obtain the error signal correspond to the same part of the input signal. The apparatus may be included in a satellite.

Abstract: A distance measuring method includes: emitting a pulse of measuring light towards an object; receiving a pulse measuring light from the object and generating a pulse signal corresponding to the pulse of measuring light received from the object; delaying a first portion of the generated pulse signal for a predetermined time; generating an intensity signal indicative of an intensity of the generated pulse signal, while delaying the first portion of the generated pulse signal; amplifying the delayed first portion of the generated pulse signal using a gain dependent on the generated intensity signal; and determining a value representing a distance based on the amplified delayed first portion of the generated pulse signal.

Abstract: Method, apparatus, and article of manufacture for performing digital pre-distortion of wideband analog upconversion chains existing within communications systems. By pre-distorting for the deterministic non-linearities in an analog upconverter, a radiated passband signal will show an improved signal quality which will enhance the ability of a receiver to properly decode received data symbols, as well as perform equalization of the received signal constellation. It is desired that this pre-distortion technique will further improve the signal quality of communication systems who only implement pre-distortion techniques for compression effects due to power amplifiers.

Abstract: Methods and systems for optimizing amplifier operations are described. The described methods and systems particularly describe a feed-forward control circuit that may also be used as a feed-back control circuit in certain applications. The feed-forward control circuit provides a control signal that may be used to configure an amplifier in a variety of ways.

Abstract: An active optical combiner for a CATV network.

Abstract: This disclosure relates to adaptively reducing the peak power of harmonic distortions as a function of the operating conditions for transmission communications. Specifically, the bias of the amplifier is adaptively increased to reduce harmonic distortions when a small fraction of the resource blocks are active.

Abstract: Aspects of this disclosure relate to dynamic error vector magnitude (DEVM) compensation. In one embodiment, an apparatus includes an amplifier, a low pass filter, and a bias circuit. The amplifier, such as a power amplifier, can amplify an input signal. The low pass filter, such as an integrator, can generate a correction signal based at least partly on an indication of a duty cycle of the amplifier. The indication of the duty cycle of the amplifier can be an enable signal for the amplifier, for example. The bias circuit can generate a bias signal based at least partly on the correction signal and provide the bias signal to the amplifier to bias the amplifier.

Abstract: The present invention relates to the control of power amplifiers in order to enhance the efficiency of the amplifier by tracking the envelope of input signal and applying the same envelope into the drain voltage of a last stage power transistor. This invention can be used in each and every wireless communication transmitter, since there is definitely a power amplifier in the last part of the transmitter before the antenna, and every power amplifier has limited power performance, depending on type of modulation, due to its input-output curve. We are aiming to enhance the power utility of power amplifiers in different applications through introducing a new method and circuit for supplying power into a power amplifier, wherein the power supplied to the drain of the power amplifier is made to follow the envelope of the transmitted RF signal.

Abstract: A hybrid power module for supplying a power to a power amplifier is provided. The hybrid power module includes a DC-DC converter and a linear regulator. The DC-DC converter provides a first current to the power amplifier via a first inductor according to an operating frequency and an envelope tracking signal. The linear regulator provides a second current to the power amplifier via a first capacitor according to the envelope tracking signal. A switch-mode power supply (SMPS) ripple voltage caused by the DC-DC converter is reduced by the linear regulator.

Abstract: An apparatus for amplifying a transmit signal includes a power amplifier module arranged within a transmit path to be coupled to an antenna module. The power amplifier module is configured to amplify a transmit signal. Further, the apparatus includes a coupling module arranged between the power amplifier module and the antenna module. The coupling module is configured to provide a reverse feedback signal substantially generated by a part of the amplified transmit signal reflected by the antenna module. Further, the apparatus includes a determining module configured to determine a delay information on a delay between the transmit path and an envelope tracking path based on at least the reverse feedback signal. Additionally, the apparatus includes a power supply module arranged within the envelope tracking path configured to vary a power supply of the power amplifier module based on a transmit signal envelope information with a temporal alignment depending on the delay information.

Abstract: A current bypass circuit that passes part of a photocurrent output from a photodetector is connected to an input terminal of a current-to-voltage conversion amplifier circuit. A voltage obtained by level conversion of an output voltage by a voltage level conversion circuit is input into the current bypass circuit so that the current bypass circuit is turned on at a photocurrent that is smaller than the photocurrent at which a diode connected in parallel to a feedback resistor of the current-to-voltage conversion amplifier circuit is turned on. Consequently, the current-to-voltage conversion gain is switched in three stages according to the intensity of the photocurrent corresponding to an optical signal level.

Abstract: A buffer circuit includes an amplifying unit suitable for comparing an input voltage of an input terminal with an output voltage of an output terminal, a current sinking unit suitable for controlling a sinking current of the amplifying unit when the input voltage is varied, and a current compensation unit suitable for uniformly maintaining a sinking current amount of the current sinking unit.

Abstract: A transmitter's operation is characterized using components having relatively low cost and low complexity. A device includes comparator(s) that compare a transmitter's analog output to predetermined level(s) to generate count(s) associated with analog output range bin(s). Each of the predetermined levels is associated with a corresponding one of the analog output range bins. A transfer function of the transmitter is generated using the comparison count values associated with the analog output range bin(s). A histogram may be generated from the comparison count values associated with the various analog output range bins. An equalizer is implemented to process data that will be transmitted by the transmitter. The equalizer uses equalizer parameter(s) that are selected based on the characterization of the transmitter (e.g., its transfer function, its histogram, etc.). The equalizer may use default or start up parameters until the transmitter's operation is characterized.

Abstract: One embodiment of the present invention provides a system for controlling operations of a power amplifier in a wireless transmitter. During operation, the system receives a baseband signal to be transmitted, and dynamically switches an operation mode of the power amplifier between a high power back-off mode having a first power back-off factor and a normal mode having a second power back-off factor based on a level of the baseband signal.

Abstract: A comparator 13 that detects the difference between a high frequency signal detected by a detector 12 and a feedback signal A output from a comparator 11; a comparator 14 that detects the difference between the difference detected by the comparator 13 and a feedback signal B output from an adder 18; and a loop filter 15 that passes only a prescribed low frequency band of the output signal of the comparator 14 are provided, in which an amplitude sensitivity adjuster 16 adjusts the amplitude sensitivity of a variable gain amplifier 3 in accordance with the rate of change of the signal passing through the loop filter 15, thereby controlling the gain of the variable gain amplifier 3.

Abstract: Radio frequency (RF) transmitters and methods of their operation are disclosed. An exemplary RF transmitter includes an RF power amplifier (RFPA), a dynamic power supply (DPS), and a baseband processing unit. The baseband processing unit generates an amplitude modulation (AM) signal that the DPS follows to generate a DPS voltage VDD(t). The DPS voltage VDD(t) serves as a power supply for an output stage of the RFPA. Under most operating conditions the output stage is configured to operate in a compressed mode (C-mode), but is reconfigured to operate in a product mode (or “P-mode) during times low-magnitude events in the AM signal are conveyed to the DPS and become present in the DPS voltage VDD(t) produced by the DPS. Operating the output stage in P-mode overcomes the inability of C-mode operation to reproduce low-magnitude events contained in the AM signal at the RF output of the RFPA.

Abstract: There is disclosed a method of controlling an input to an envelope modulated power supply of an envelope tracking amplification stage, comprising: generating an envelope signal representing the envelope of a signal to be amplified; applying a shaping function to the envelope signal to generate a shaped envelope signal, including: clipping the shaped envelope signal at high input envelope values; and providing the shaped envelope signal as an input signal to the envelope modulated power supply.

Abstract: The present disclosure includes envelope tracking circuits and methods with adaptive switching frequency. In one embodiment, a circuit comprising an amplifier to receive an envelope tracking signal having an envelope tracking frequency and output voltage and current to a power supply terminal of a power amplifier circuit. A programmable comparator receives an output signal from the amplifier and generates a switching signal having a switching frequency. A switching regulator stage receives the switching signal and outputs a switching current to the power supply terminal. A frequency comparison circuit configures the programmable comparator based on the envelope tracking frequency and the switching frequency so that the switching frequency tracks the envelope tracking frequency.

Abstract: A high performance and cost effective method of RF-digital hybrid mode power amplifier systems with high linearity and high efficiency for multi-frequency band wideband communication system applications is disclosed. The present disclosure enables a power amplifier system to be field reconfigurable and support multiple operating frequency bands on the same PA system over a very wide bandwidth. In addition, the present invention supports multi-modulation schemes (modulation agnostic), multi-carriers and multi-channels.

Abstract: A high-frequency amplifier circuit (10) includes a high-frequency amplifying element (11), a bias circuit (12), and a bias adjusting circuit (13). The high-frequency amplifying element (11) includes an input end and an output end. The bias circuit (12) is connected to the high-frequency amplifying element (11) and supplies a first bias voltage to an input side of the high-frequency amplifying element (11). The bias adjusting circuit (13) is connected between the input end and the bias circuit (12) and adjusts the first bias voltage based on a high-frequency signal inputted to the input end. The bias adjusting circuit (13) includes a lumped element and an active element.

Abstract: Methods and apparatus, including computer program products, are provided for hybrid DC-DC converters. In one aspect, there is provided a method. The method may include tracking, by an envelope detector, an envelope of a signal being amplified by an amplifier. The method may further include supplying, by a first direct-current to direct-current converter, power to the amplifier, the power supplied by the first direct-current to direct-current converter including one or more high-frequency components of the envelope tracked by the envelope detector. The method may further include supplying, by a second direct-current to direct-current converter, power to the amplifier, the power supplied by the second direct-current to direct-current converter including one or more low-frequency components of the envelope tracked by the envelope detector. Related systems, apparatuses, and computer program products are also disclosed.

Abstract: A composite amplifier providing digitally selectable amplification includes a plurality of channels and a combiner. Each of the channels includes a digitally controllable selector, a Class-S power amplifier, and bandpass filter. The digitally controllable selector selectively couples a digital bitstream to the amplifier. The amplifier receives the digital bitstream and provides an amplified signal. The bandpass filter generates a filtered signal as a function of the amplified signal. The combiner couples filtered signals provided by the channels to form a composite output signal.

Abstract: An RF PA system that generates its own local characterization information. The RF PA system includes a PA to generate a RF output signal from a RF input signal, the PA powered by a supply voltage. A characterization block generates characterization information corresponding to a relationship between the supply voltage and performance (e.g., gain, power efficiency, distortion, receive band noise) of the RF PA system for a plurality of levels of one or more operating conditions (e.g., temperature, operating frequency, modulation format, antennae mismatch, etc.) of the RF PA system. An amplitude estimator block estimates an amplitude of the RF input signal. A supply control block generates a supply voltage control signal for controlling the supply voltage based on the characterization information and the amplitude of the RF input signal.

Abstract: There is provided an amplification stage including an envelope tracking modulated supply for tracking a reference signal, comprising a low frequency path for tracking low frequency variations in the reference signal and for providing a first output voltage, and a high frequency path for tracking high frequency variations in the reference signal and for providing a second output voltage, and a combiner for combining the first and second output voltages to provide a third output voltage, the amplification stage further comprising a first amplifier arranged to receive the first output voltage as a supply voltage, and a second amplifier arranged to receive the third output voltage as a supply voltage, wherein the first and second amplifiers are enabled in different modes of operation.

Abstract: The present disclosure includes circuits and methods for power amplifiers. In one embodiment, a main and peaking amplifier receive dynamic power supply voltages to operate an RF power amplifier in a high efficiency range for a particular output voltage. The power supply voltages may be changed based on an output voltage so that the power amplifier operates within a high efficiency plateau. In one embodiment, different discrete power supply voltage levels are used for different output voltage ranges. In another embodiment, a continuous time varying power supply voltage is provided as the power supply voltage. A dynamic supply voltage may be generated having a lower frequency than a signal path of the power amplifier.

Abstract: The output of a Radio Frequency (RF) Power Amplifier (PA) is sampled and down-converted, and the amplitude envelope of the baseband feedback signal is extracted. This is compared to the envelope of a transmission signal, and the envelope tracking modulation of the RF PA supply voltage VCC is adaptively pre-distorted to achieve a constant ISO-Gain (and phase) in the RF PA. In particular, a nonlinear function is interpolated from a finite number gain values calculated from the feedback and transmission signals. This nonlinear function is then used to pre-distort the transmission signal envelope, resulting in a constant gain at the RF PA over a wide range of supply voltage VCC values. Since the gains are calculated from a feedback signal, the pre-distortion may be recalculated at event triggers, such as an RF frequency change. Furthermore, the method improves nonlinearity in the entire transmitter chain, not just the RF PA.

Abstract: An amplification stage comprising: an input scaling block for scaling an input signal in dependence on an input scaling factor to generate a scaled version of the input signal; a power amplifier for generating an amplified version of the scaled input signal; an envelope detector for generating a signal representing the envelope of the input signal; an envelope scaling block for scaling the envelope signal in dependence on an envelope scaling factor to generate a scaled version of the envelope signal; a non-linear mapping block for generating a voltage representative of the supply voltage in dependence on the scaled envelope signal; a modulator for generating a power supply voltage for the amplifier in dependence on the voltage generated by the non-linear mapping block; and a power control block for maintaining a linear relationship between the envelope scaling factor and the input scaling factor.

Abstract: An envelope-tracking (ET) power supply may include a boost control pin. The boost control pin receives a boost enable signal that activates or enables a supplemental power supply in the ET power supply. The supplemental power supply facilitates the generation of a power supply signal for a selected processing stage, e.g., a power amplifier. The supplemental power supply helps the processing stage meet the demands on it caused by the signal that the processing stage needs to handle.

Abstract: Optimization methods via various circuital arrangements for amplifier with variable supply power are presented. In one embodiment, a switch can be controlled to include or exclude a feedback network in a feedback path to the amplifier to adjust a response of the amplifier dependent on a region of operation of the amplifier arrangement (e.g. linear region or compression region).

Abstract: An apparatus and method for sensing load current of an envelope tracking (ET) modulator enables load impedance of a power amplifier to be measured. Impairments associated with the load impedance characteristic can be suppressed by calibration and predistortion instead of by feedback (as done in the prior art). The ET modulator provides a switching regulator that can be reconfigured as a linear regulator for the purpose of sensing the load current. This allows the ET modulator to be operated open-loop, thereby eliminating the power consumption overhead resulting from utilization of a loop filter and error amplifier (used in the prior art) and achieving a higher overall efficiency.

Abstract: A power supply circuit includes: a direct current to direct current converter; a linear amplifier; and a first capacitance, one terminal of the first capacitance being coupled an output of the linear amplifier, another terminal of the first capacitance being coupled to an output terminal, wherein the linear amplifier configured to operate in a variable voltage mode and the linear amplifier configured to stop operating and couples an output of the linear amplifier to a ground in a fixed voltage mode.

Abstract: A radio frequency amplification stage comprising: an amplifier for receiving an input signal to be amplified and a power supply voltage; and a power supply voltage stage for supplying said power supply voltage, comprising: means for providing a reference signal representing the envelope of the input signal; means for selecting one of a plurality of supply voltage levels in dependence on the reference signal; and means for generating an adjusted selected power supply voltage, comprising an ac amplifier for amplifying a difference between the reference signal and one of the selected supply voltage level or the adjusted selected supply voltage level, and a summer for summing the amplified difference with the selected supply voltage to thereby generate the adjusted supply voltage.

Abstract: A power management system includes a power system. A powered component is coupled to the power system. A power detect circuit is coupled to the power system. A power system controller is coupled to the power system, the powered component, and the power detect circuit. The power system controller is operable, for each of at least one workload run using the powered component, to program the power detect circuit with a first threshold for a first system operation setting and determine that the first threshold was not exceeded while the workload was running. The power system controller is then operable to program the power detect circuit with a second threshold for the first system operation setting, determine that the second threshold was exceeded while the workload was running and, in response, use the second threshold to allocate power from the power system.

Abstract: There is described a method of controlling signal alignment in a power amplifier, comprising: receiving an input signal to be amplified; receiving a supply voltage for the power amplifier, the supply voltage being derived in dependence on the signal to be amplified; amplifying the input signal to produce an output signal; comparing the output signal with a plurality of distorted versions of the input signal, each distorted version of the input signal being associated with a different time delay value; and adjusting the timing of either the input signal or the supply voltage by an amount in dependence on a time delay value determined to be associated with a distorted version of the input signal which most closely matches the output signal.

Abstract: An apparatus for providing envelope tracking (ET), comprising: a power amplifier (PA) load variation pre-distortion, and an open loop ET modulator operatively coupled to the PA load variation pre-distortion, wherein the PA load variation pre-distortion is configured to determine a load variation at a PA supply voltage path based on an input signal received by a PA, and generate a pre-distortion compensation signal using the load variation, and wherein the open loop ET modulator is configured to generate a PA supply voltage on the PA supply voltage path using the pre-distortion compensation signal.

Abstract: A power supply circuit includes: a push-pull amplifier unit which amplifies an input signal with a push-pull amplification protocol; a variable power supply unit which varies, with a control signal, the voltage level of a power supply voltage which is supplied to the push-pull amplifier; a switch control unit which, on the basis of the input signal, outputs the control signal which controls the voltage level of the power supply voltage; and a timing control unit which applies a specified time delay to the input signal. When the control signal rises, the switch control unit causes the control signal to rise at a faster timing, according to the voltage level switch transition timing, than a delay time upon the timing control unit, and when the control signal falls, the switch control unit causes the control signal to fall at the timing of the delay time.

Abstract: There are provided a bias circuit and an amplifier controlling a bias voltage, the bias circuit and the amplifier including a control voltage generating unit generating a control voltage using a reference voltage, a bias voltage generating unit generating a bias voltage according to the control voltage, and a voltage drop unit dropping the bias voltage from the bias voltage generating unit to a base voltage so as to provide the base voltage to an amplifying unit, wherein the control voltage generating unit controls the control voltage according to an amplitude of a high-frequency signal input to the amplifying unit.

Abstract: An amplifier is capable of reducing the quantization error caused by conversion accuracy in an A/D converter circuit and, particularly, capable of improving the S/N ratio and distortion rate when an input audio signal is small. In an amplifier (1) using a voltage variable power supply (73) as a power supply to follow an input audio signal level (S1) to the amplifier (1) in order to increase or decrease the level of supply voltage supplied to a power amplifier stage (4), when the level of source power of the power amplifier stage (4) is changed, the voltage level of a reference voltage supplied to an A/D converter (62) of a negative feedback circuit is controlled.

Abstract: There are provided a high-frequency amplifier and a high-frequency module having a high efficiency for an extensive input modulated signal power, and base station/mobile wireless machines using the amplifier or the module. The high-frequency amplifier includes a circuit that detects an envelope of an input modulated signal; a control signal generator circuit (a voltage controlled circuit or a current controlled circuit) that can change a voltage or a current according to a given function on the basis of a magnitude of the detected envelope signal; and a diode clamped variable power circuit that connects a plurality of diode clamped circuits each including a diode, a transistor, and a DC power supply to one another.

Abstract: An amplifier circuit includes: a first filter that receives input of amplitude information of an input signal, and performs filtering so that a gain of a frequency component higher than a first cutoff frequency becomes greater than a gain of a frequency component lower than the first cutoff frequency; a power supply circuit that has a low-pass filter characteristic, and receives input of amplitude information outputted from the first filter and generates a power supply voltage corresponding to the amplitude information outputted from the first filter; an amplifier that receives supply of the power supply voltage, and amplifies a signal based on the input signal; and a phase difference detector that detects a phase difference between the amplitude information of the input signal and the power supply voltage, wherein the first filter changes the first cutoff frequency in a direction in which the phase difference decreases.

Abstract: A multi-mode, dynamic, DC-DC converter supplies a dynamically varying voltage, as required, from a battery to an RF power amplifier (PA). In envelope tracking mode, a fast DC-DC converter generates a dynamic voltage that varies based on the amplitude envelope of an RF signal, and regulates the voltage at the PA. A slow DC-DC converter generates a steady voltage and regulates the voltage across a link capacitor. The fast and slow converters are in parallel from the view of the PA, and the link capacitor is between the fast converter and the PA. Because different nodes are regulated, no current sharing is possible between the converters. The link capacitor boosts the dynamic voltage level, allowing a maximum dynamic voltage at the load to exceed the battery voltage. In power level tracking mode, the fast converter is disabled and the link capacitor is configured to be in parallel with the load.

Abstract: An integrated circuit includes: a digitally-controlled power generation stage for converting an input signal to a radio frequency (RF) carrier, the digitally-controlled power generation stage including a plurality of selectable switching devices capable of adjusting an envelope of the RF carrier; and a pulse width modulator (PWM) generator arranged to generate a PWM control signal according to a fractional word and operably coupleable to the plurality of selectable switching devices of the digitally-controlled power generation stage; wherein the PWM generator inputs the PWM control signal to a subset of the plurality of the selectable switching devices such that a PWM signal adjusts the envelope of the RF carrier output from the digitally-controlled power generation stage.

Abstract: A power amplifier amplifies a radio signal. Negative feedback is applied to a linear amplifier and the linear amplifier receives an envelope signal. A pulse current modulator is connected to a power supply terminal of a power amplifier and an output terminal of the linear amplifier via an inductor, and outputs a pulse current according to a control signal generated from the envelope signal. A diode has an anode connected to an output terminal of a direct current source and a cathode connected to an output terminal of the pulse current modulator. A switching element is disposed between the output terminal of the direct current source and a ground potential, and is controlled by the control signal.

Abstract: There is disclosed a technique for controlling at least one amplification stage, comprising: selecting a linearity objective for the amplification stage; in dependence on an input signal to said amplification stage, determining a combination of supply input and bias input for the amplification stage in order to meet said linearity objective; and in dependence on there being more than one combination of supply input and bias input for meeting the linearity objective, selecting the combination that optimizes a further system performance objective for the amplification stage. The further system performance objective may be one or more of: an efficiency objective; an envelope signal bandwidth objective; or a robustness to production tolerance objective.

Abstract: Apparatus and methods for envelope tracking are disclosed herein. In certain implementations, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system can include a buck converter and an error amplifier configured to operate in parallel to control the voltage level of the power amplifier supply voltage based on an envelope of an RF signal amplified by the power amplifier. The buck converter can convert a battery voltage into a buck voltage that is based on an error current, and the error amplifier can generate the power amplifier supply voltage by adjusting the magnitude of the buck voltage using an output current that is based on the RF input signal's envelope. The error amplifier can control the buck converter by changing a magnitude of the error current in relation to a magnitude of the output current.

Abstract: Circuitry, which includes data memory and processing circuitry, is disclosed. The data memory is used to store look-up table (LUT)-based radio frequency (RF) power amplifier (PA) calibration data. The processing circuitry converts at least a portion of the LUT-based RF PA calibration data to provide monotonic response curve-based data. As such, a magnitude of an envelope power supply control signal is determined based on a magnitude of an RF input signal using the monotonic response curve-based data.

Abstract: An integrated circuit comprises a radio frequency (RF) power amplifier (PA) output stage; at least one amplifier stage prior to the RF PA output stage; a linear amplifier comprising a voltage feedback wherein the linear amplifier is operably coupled to a low frequency supply module such that the linear amplifier and low frequency supply module provide a combined first power supply to the RF PA output stage; and a switched mode power supply module arranged to provide a second power supply to the linear amplifier and to the at least one amplifier stage prior to the RF PA output stage.

Abstract: Techniques for monitoring and controlling bias current of amplifiers are described. In an exemplary design, an apparatus may include an amplifier and a bias circuit. The amplifier may include at least one transistor coupled to an inductor. The bias circuit may generate at least one bias voltage for the at least one transistor in the amplifier to obtain a target bias current for the amplifier. The bias circuit may generate the at least one bias voltage based on a voltage across the inductor in the amplifier, or a current through a current mirror formed with one of the at least one transistor in the amplifier, or a gate-to-source voltage of one of the at least one transistor in the amplifier, or a voltage in a replica circuit replicating the amplifier, or a current applied to the amplifier with a switched mode power supply disabled.

Abstract: An audio playback loop circuit including an audio amplifier for amplifying an analog audio signal based on digitally controlled power supplies, and a digitally controlled power supply selection circuit for generating and selecting the digitally controlled power supplies based on a digital signal.