Abstract: The present invention relates to a four-way Doherty amplifier. The invention further relates to a mobile telecommunications base station. The invention proposes a new Doherty combiner topology that allows peak efficiencies to be reached at deeper back-off levels than conventional Doherty combiners.

Abstract: An apparatus has advanced amplifier Classes and low pass filter technologies for using software generated ascending or level waveforms that are effective when applying cardiac defibrillation and cardioversion waveforms which significantly reduce damage to the heart muscle. The apparatus comprises a waveform energy control system for delivering software generated waveforms comprising differentially driven Class D and Class B amplifier sections, wherein the Class D amplifier section produces Phase 1 ascending waveforms and has a programmable lowpass filter (LPF) and wherein the Class B amplifier section delivers hard-switched Phase 2 waveforms.

Abstract: To downsize a magnetic sensor by reducing the number of terminals of the magnetic sensor. A magnetic sensor to detect a magnetic field is provided, including: a drive terminal; a first output terminal; a second output terminal; and a magnetic sensing unit in which a first conduction path through which a driving current flows between the drive terminal and the first output terminal and a second conduction path through which a driving current flows between the drive terminal and the second output terminal are formed integrally. The magnetic sensing unit may have a first extending unit extending to the first output terminal and a second extending unit extending to the second output terminal.

Abstract: An operational amplifier includes an output node; an output stage, comprising a plurality of output current paths and a plurality of control nodes, wherein the plurality of control nodes are respectively coupled to the plurality of output current paths, and the plurality of output current paths are coupled to the output node and respectively coupled to a plurality of power supply sources providing different voltages; and a selecting unit, configured to couple an internal output node of the operational amplifier to one of the plurality of control nodes of the output stage.

Abstract: A digital amplifier includes a pulse-width adjustment circuit that adjusts the pulse width of a digital signal, a switching circuit that amplifies the output signal of the pulse-width adjustment circuit, and a feedback signal generator that generates a feedback signal based on the output signal of the switching circuit.

Abstract: A power tube driver of a class-D audio amplifier includes high-side and low-side fixed charge/discharge gate driving circuits, high-side and low-side power tubes, a dead time generation circuit based on gate voltage detection, high-side and low-side gate charge/discharge accelerating circuits, and high-side and low-side gate voltage detection circuits. The class-D audio amplifier with the features of low radiation interference, and high efficiency, linearity and robustness can be balanced easily.

Abstract: The present invention is in the field of programmable pulse width modulator (PWM) controller comprising filters and a mixer, such as for use in a digital audio converter and digital amplifier controller, a chip comprising said PWM controller, a device comprising said PWM controller or said chip, as well as uses thereof.

Abstract: Circuits and methods for achieving high linearity, high efficiency power amplifiers, including digital predistortion (DPD) and pulse cancellation in switched-state RF power amplifier systems are described.

Abstract: Resistor mismatch may be digitally compensated based on a known resistor mismatch, power supply information, and/or other operating parameters of the amplifier. The digital compensation may be applied to the digital input signal before conversion for processing and amplification in the analog domain. An amplifier with digital compensation for resistor mismatch may be used in a class-D amplifier with a closed loop and feedforward feedback. A class-D or other amplifier with digital compensation may be integrated with electronic devices such as mobile phones.

Abstract: A wideband, frequency agile, radio frequency digital-to-analog converter (RF-DAC) based phase modulator includes first, second, and third RF-DACs, each configured to upconvert an input I/Q digital baseband signal pair to a local oscillator (LO) frequency but with the first RF-DAC being driven by a first set of LO clocks, the second RF-DAC being driven by a second set of LO clocks that is forty-five degrees out of phase with respect to the first set of LO clocks, and the third RF-DAC being driven by a third set of LO clocks that is a further forty-five degrees out of phase with respect to the second set of LO clocks. First, second, and third upconverted analog signals produced by the first, second, and third RF-DACs are combined to reinforce the fundamental LO component while canceling 3rd-order and 5th-order LO harmonics.

Abstract: Various methods and devices that involve power converter with stable feedback are disclosed. A disclosed power converter comprises an input node on an input side of the power converter and an output node on an output side of the power converter. The power converter also comprises a switch coupled to the input node and having a control node, a feedback path between the output node and the control node, and a first circuit block on the feedback path with a multipath feedback active filter. The first circuit block is at least partly defined by a pure bandpass transfer function.

Abstract: An amplifier includes a power amplifier that amplifies an input signal, a VI detection circuit that is connected to a rear stage of the power amplifier to detect power of an output signal of the power amplifier, and a controller that turns on the power amplifier when the input signal is inputted to the power amplifier, turns off the power amplifier when the input signal is not inputted to the power amplifier, and turns on the power amplifier when the VI detection circuit detects a voltage that exceeds a predetermined value when the power amplifier is in off state.

Abstract: Circuits and methods for achieving high linearity, high efficiency power amplifiers, including digital predistortion (DPD) and pulse cancellation in switched-state RF power amplifier systems are described.

Abstract: An envelope tracking (ET) circuit is provided. The ET circuit includes an amplifier array(s) configured to amplify a radio frequency (RF) signal(s) based on a first input voltage and a second input voltage. The ET circuit includes a pair of tracker circuits each configured to generate a modulated voltage. Control circuitry couples a selected tracker circuit among the tracker circuits to provide a selected modulated voltage (e.g., ET modulated voltage) to the amplifier array(s) as the first input voltage. Depending on usage scenarios, the control circuitry also provides an ET modulated voltage, an average power tracking (APT) modulated voltage, or a constant voltage to the amplifier array(s) as the second input voltage. As such, the ET circuit can support the RF signal(s) modulated in a wide range of modulation bandwidth without compromising efficiency and/or increasing heat dissipation of the amplifier array(s).

Abstract: A method is for reducing pulse skipping from a characteristic affecting a modulating signal input to an integrator of a pulse width modulation (PWM) modulator, together with a square wave carrier signal for generating a triangular waveform of the PWM modulator. The method may include creating a broad synchronous peak at vertexes of the triangular waveform output by the integrator.

Abstract: A standard cell architecture provides an improved immunity to power-supply voltage-drop, does not induce power-supply voltage drop on a continuous-row power rail of a standard cell, and maintains standard-cell environment compatibility. A circuit includes a first metal layer and a second metal layer that are formed different distances above a substrate. At least one first standard cell drives a first timing signal and includes at least one transistor receiving power from a first power rail in the first metal layer. At least one second standard cell drives a second timing signal and includes at least one transistor receiving power from a second power rail in the second metal layer. The second power rail has both a low peak noise level and a resistance that is lower than that of the first metal layer.

Abstract: An apparatus for providing a supply control signal for a supply unit, the supply unit being configured to provide a variable controlled power supply to the power amplifier. The apparatus includes a determination module configured to determine a deviation of a signal from at least one nominal value; and an adjustment module configured to provide the supply control signal after an adjustment based on the determined deviation.

Abstract: A digital amplifier includes a digital PWM generator, a first amplifier circuit, a first low-pass filter, a second amplifier circuit, a second low-pass filter, an attenuator, an error extractor, an adder, and a voltage supply unit. The first amplifier circuit amplifies a digital PWM signal at a second voltage. The first low-pass filter extracts a low-frequency band voltage signal from the amplified digital PWM signal, and outputs the extracted voltage signal to a load. The second amplifier circuit amplifies the generated digital PWM signal at a third voltage. The error extractor extracts an error signal. The adder adds a digital error signal whose feedback gain is adjusted to a digital audio signal. The voltage supply unit generates the third voltage that has a voltage value of a predetermined ratio to a voltage value of the second voltage, and supplies the third voltage to the second amplifier circuit.

Abstract: A receiver includes a decision circuit, a circuit to adjust an input signal of the decision circuit, a correction circuit and a control circuit. The decision circuit makes a data decision based on an input signal of the decision circuit. The circuit to adjust the input signal of the decision circuit adjusts the input signal of the decision circuit based on an input correction signal. The correction circuit combines a plurality of signals corresponding to different input correction parameters into a preliminary input correction signal. An input of the correction circuit is coupled to an output of the decision circuit. The control circuit maps the preliminary input correction signal into the input correction signal using a nonlinear code mapping.

Abstract: A tunable amplifier includes continuous tunability for both frequency and power levels. The tunable amplifier includes a combination of a tunable series resonator and a multi-stage LC network as the output matching network. The tunable amplifier incorporates a variable diode varactor with high breakdown voltage and high tuning range into a tunable resonator. The tunable resonator is connected to a fixed output matching network to enable a wide range of operating frequencies. The tunable amplifier enables high power, high efficiency, broadband and load-modulated power amplification, which is greatly desired for next-generation wireless communication systems and other high-frequency applications.

Abstract: The present disclosure relates to Class D amplifier circuitry comprising: an input for receiving an input signal; first and second output nodes for driving a load connected between the first and second output nodes. A first driver stage is provided for switching the first node between a first supply rail and a second supply rail, and a second driver stage is provided for switching the second node between the first supply rail and the second supply rail. The Class D amplifier circuitry also includes first driver control circuitry configured to receive a first carrier wave and control the switching of the first driver stage based in part on the first carrier wave; second driver control circuitry configured to receive a second carrier wave and control the switching of the second driver stage based in part on the second carrier wave; and a carrier wave generator configured to provide the first carrier wave and the second carrier wave.

Abstract: A signal amplifying circuit and associated methods and apparatuses, the circuit comprising: a signal path extending from an input terminal to an output terminal, a gain controller arranged to control the gain applied along the signal path in response to a control signal; an output stage within the signal path for generating the output signal, the output stage having a gain that is substantially independent of its supply voltage, and a variable voltage power supply comprising a charge pump for providing positive and negative output voltages, the charge pump comprising a network of switches that is operable in a number of different states and a controller for operating the switches in a sequence of the states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage.

Abstract: A reconfigurable amplifier load includes a power supply node, a first inductor comprising a first terminal coupled to a first switch, and a second inductor comprising a first terminal coupled to a second switch. The reconfigurable amplifier load further includes a third inductor comprising a first terminal coupled to the first switch. The first switch is configured to selectively couple the first terminal of the third inductor to the power supply node. A fourth inductor comprising a first terminal coupled to the second switch. The second switch is configured to selectively couple the first terminal of the fourth inductor to the power supply node. At least one additional switch configured to selectively couple a second terminal of the first inductor or a second terminal of the second inductor or both the second terminal of the first inductor and the second terminal of the second inductor to the power supply node.

Abstract: A tracking device may produce audio signals for a variety of reasons. However, tracking devices typically have a limited power supply and contain additional components that require power, such that directing too much power to produce an audio signal may interfere with the functionality of other components. A tracking device determines an amount of power available to produce an audio signal based on a first amount of power available from a battery or power source and a second amount of power required by other components of the tracking device.

Abstract: A class D audio amplifier with an output stage is provided. The class D audio amplifier includes a plurality of power transistors coupled in cascade between a first DC supply voltage and a second DC supply voltage. The class D audio amplifier also includes a plurality of gate drivers having respective inputs coupled to a modulated audio signal and configured to generate respective modulated gate drive signals to the plurality of power transistors. A first overload protection circuit includes a model transistor possessing electric characteristics representative of a first power transistor of the output stage for determining a drain-source reference voltage of the model-transistor and this drain-source reference voltage may be utilized to indicate an overload event or condition of the first power transistor.

Abstract: Systems and methods for improving power amplifier operation are provided. A system may include a baseband signal generator communicatively coupled to a baseband signal digital-to-analog converter. The baseband signal digital-to-analog converter may be communicatively coupled to two or more power amplifiers. The system may also include an envelope signal generator communicatively coupled to an envelope signal digital-to-analog converter. The system may further include a supply modulator communicatively coupled to the envelope signal digital-to-analog converter and the two or more power amplifiers for shared envelope tracking across the two or more power amplifiers.

Abstract: Apparatus and associated methods relate to modulating the frequency of a switch signal to achieve a fast transient response while holding the average frequency constant over a predetermined number of N cycles. In an illustrative example, a quantum charge modulator may include a compensation processor configured to compensate an error signal and generate a compensation signal by performing operations to maintain an average switching frequency over the N cycles in response to the transient. The compensation signal may be a function of a real phase deviation ?TSW between a stable pulse modulated signal having a cycle period TSW before the transient and a measured pulse modulated signal having a cycle period TSW_M after the transient. A forgetting factor may be used to calculate the phase deviations. The quantum charge modulator may provide a compensation free, stable, and high performance response over power stage component changes.

Abstract: A power amplifier includes an output signal generator constructed to generate, on the basis of an input AC signal, an output signal including, in cycles, a first pulse being width higher in voltage than a first reference voltage and a second pulse being width lower in voltage than the first reference voltage and a feedback circuit constructed to generate a first bias signal corresponding to the output signal and feed back the first bias signal to an input side of the output signal generator to equalize a width of the first pulse and a width of the second pulse in the cycles of the output signal.

Abstract: A class-D amplifier that amplifies an input audio signal includes: a push-pull circuit that has at least two switching transistors; an electric current suppressor that is disposed between the push-pull circuit and a power source that supplies electric power to the push-pull circuit; a switch that is connected in parallel with the electric current suppressor; a determiner that determines whether or not the class-D amplifier is in a state where sound is not emitted; and a controller. When the determiner determines that the class-D amplifier is in a state where sound is not emitted, the controller turns off the switch such that a path for electric current flowing from the power source to the push-pull circuit runs through the electric current suppressor. When the determiner determines that the class-D amplifier is in a state where sound is emitted, the controller turns on the switch such that the path for electric current bypasses the electric current suppressor.

Abstract: A class D audio amplifier includes a modulator for receipt of an audio signal and converting the audio signal into a modulated audio signal having a predetermined carrier frequency. The class D audio amplifier additionally includes an output stage having a plurality of power transistors coupled in cascade between a first DC supply voltage and a second DC supply voltage, and a plurality of gate drivers configured to generate respective modulated gate drive signals to the plurality of power transistors. A controller is configured to adjust a level of a first modulated gate drive signal applied to a first power transistor of the output stage based on a level of the audio signal.

Abstract: A class D amplifier includes an output stage that performs a switching operation, a feedback circuit that generates a feedback signal based on the output signal output from the output stage, an integration amplifier that outputs an integrated value signal in response to an input signal and the feedback signal, a comparator that compares the integrated value signal with a standard signal, a driver that controls the output stage based on a signal output from the comparator, a carrier signal generator that generates a carrier signal, a reference signal generator that outputs a reference signal indicating a driving amount for a load at the output stage, and a standard signal switch that switches the standard signal to the carrier signal or a standard potential based on whether a level of the reference signal is smaller than a threshold value.

Abstract: An AC capable power amplifier arrangement is realized that includes a buck converter with a power inductor, two buck switches, and alternately a buck-boost converter using four switches, each driving an output polarity steering set of four switches. The polarity steering switches convey the converter output current to output terminals that connect to a load with a capacitor connected in parallel. A differential receiver is connected to the output terminals to provide negative feedback. A mixer receives an input voltage signal, an output of the differential receiver, and output from a triangle wave generator. A set of two comparators for buck amplifier conversion, or four comparators for buck-boost amplifier conversion, each receives an output of the mixer. Each of the comparators produces a respective output for driving the converter switches through simple steering logic interfaces between the comparators, the converter components and a polarity steering output stage.

Abstract: It is provided a method for providing feedback to pre-distorters in branches of a MISO system such that the pre-distortion cancels distortions caused by the signal path and the combiner combining the signals from the branches into which input signals are input. The method includes generating uncorrelated noises and mixing them with the input signals, evaluating the output of the combiner based on the input signals and the noises in order to determine a respective contribution of each input signal to the output of the combiner, and accordingly determining an appropriate pre-distortion. The signal path may apply a non-linear and/or dynamic function on the signal.

Abstract: A microphone assembly includes a transducer and a processing circuit. The processing circuit includes an analog-to-digital converter (ADC) configured to receive, sample and quantize an electrical signal generated by the transducer to generate a corresponding digital signal. The processing circuit includes a feedback path including a digital loop filter configured to receive and filter the digital signal to provide a first digital feedback signal and a digital-to-analog converter (DAC) configured to convert the first digital feedback signal into a corresponding analog feedback signal. The processing circuit additionally includes a summing node configured to combine the electrical signal and the analog feedback signal.

Abstract: In some examples, an amplifier comprises a first integrator to receive a differential input signal, a second integrator coupled to the first integrator, a third integrator coupled to the second integrator, and a comparator to receive outputs of the second and third integrators, to compare each of the outputs to a reference signal that is below a power supply rail voltage supplied to the amplifier, and to produce an error current based on the comparison. The amplifier also comprises a feedback connection between the comparator and inputs to the second integrator. The feedback connection injects the inputs to the second integrator with a current that is determined at least in part by the error current.

Abstract: Disclosed is the audio amplifier comprising an input for an audio signal to be amplified and an output for powering a load on the basis of the amplified audio signal; a generator of reference voltage of very high linearity and low output impedance, able to receive, as input, the audio signal to be amplified; a power current generator comprising a power voltage generator whose output is connected to the output of the reference voltage generator through a coupling impedance. The coupling impedance comprises two coupling inductances mounted in series between the output of the reference generator and the output of the power voltage generator and an attenuation impedance linking a mid-point between the two coupling inductances and a reference potential, wherein the attenuation impedance includes an attenuation inductance.

Abstract: A system is provided for combining frames in a plurality of ways to provide as output a new frame comprising a function of the combined frames. A system is also provided for combining a plurality of frames to provide as output a new frame that generates a specified average period as a function of the periods of the combined frames.

Abstract: The present disclosure relates to a modulator for a digital amplifier and a device comprising such a modulator and a digital amplifier. The modulator includes a pulse shaper and a control unit for controlling the pulse shaper to convert an input signal into a bit stream configured for a digital amplifier which encodes an amplitude value per clock of a carrier signal. The pulse shaper can represent a respective amplitude value of the input signal with different bit patterns. The control unit includes an assignment of the control commands to associated amplitude values resulting from amplification of the associated bit patterns with the digital amplifier is stored or at least is provided in that the control unit selects a control command per clock by means of the assignment and the amplitude value of the input signal and drives the pulse shaper accordingly.

Abstract: An acoustic transducer includes a controller configured to receive an input audio signal and to generate a first reference signal indicative of an envelope of the input audio signal. The controller is further configured to provide a stationary coil signal to a stationary coil of an acoustic transducer based on the first reference signal and to measure a current through the stationary coil after providing the stationary coil signal to the stationary coil. The controller is further configured to generate a first output indicative of the current through the stationary coil and to determine a magnetic flux in an air gap of magnetic material based on the first output. The controller is further configured to generate a voltage output for a moving coil that is inversely proportional to the magnetic flux in the air gap. The voltage output provides an undistorted output that corresponds to the input audio signal.

Abstract: This application relates to Class D amplifier circuits (200). A modulator (201) controls a Class D output stage (202) based on a modulator input signal (Dm) to generate an output signal (Vout) which is representative of an input signal (Din). An error block (205), which may comprise an ADC (207), generates an error signal (?) from the output signal and the input signal. In various embodiments the extent to which the error signal (?) contributes to the modulator input signal (Dm) is variable based on an indication of the amplitude of the input signal (Din). The error signal may be received at a first input (204) of a signal selector block (203). The input signal may be received at a second input (206) of the signal selector block (203).

Abstract: An input protection circuit (110) for an optocoupler (20) is provided. The input protection circuit (110) includes a first voltage limiter (D1) with a first terminal that is electrically coupled to an input terminal of an amplifier circuit (120), wherein the input terminal of the amplifier circuit (120) is configured to receive a PWM signal and the amplifier circuit (120) is configured to provide a voltage to the optocoupler (20).

Abstract: A Galvanically Isolated Amplifier (GIA) includes an isolation barrier to galvanically isolate high voltage circuitry from low voltage circuitry. The high voltage circuitry has at least two voltage supply rails, with the voltage supply rail closest to ground potential at a first potential relative to the ground potential. The low voltage circuitry has at least two voltage supply rails, with the voltage supply rail closest to the ground potential at a second potential, the second potential being smaller than the first potential. A Radio Frequency (RF) carrier is digitally Phase Shift Keying (PSK) modulated for transmission across the isolation barrier. The unmodulated RF carrier could also be transmitted across the isolation barrier. PSK modulation could be applied to the RF carrier based on a test waveform to generate a PSK-modulated test signal for transmission while a voltage transient is applied between the high voltage circuitry and the low voltage circuitry.

Abstract: A quaternary/ternary modulation selecting circuit of an amplifier includes: a signal generating circuit, a detecting circuit, and a selecting circuit. The signal generating circuit is arranged to generate a ternary signal and a quaternary signal. The detecting circuit coupled to the signal generating circuit is arranged to generate a mode selecting signal according to at least the ternary signal. The selecting circuit coupled to the signal generating circuit and the detecting circuit is arranged to select and output one of the ternary signal and the quaternary signal to an output stage of the amplifier according to the mode selecting signal.

Abstract: A bridge output stage is coupled to an electroacoustic conversion element via an inductor L. Driving circuits drive the output stage according to pulse signals S2H and S2L that correspond to an audio signal S1. An overcurrent detection circuit asserts an overcurrent detection signal S3L (i) when a current IML that flows through a transistor ML to be monitored that forms the output stage is continuously larger than a first threshold value for a first period of time or (ii) when the current IML that flows through the transistor ML to be monitored is larger than a second threshold value that is higher than the first threshold value after a predetermined second period of time elapses after the transistor ML to be monitored turns on.

Abstract: A signal amplifier includes a pulse width modulator, a level shifter, and a power amplifier. The pulse width modulator is driven by a positive power supply and a negative power supply, and a reference voltage of the pulse width modulator is set to a GND. The power amplifier is driven by a positive power supply, and a reference voltage of the power amplifier is set to a middle value between the positive power supply and the GND. The level shifter shifts a voltage level of a first PWM signal whose high level corresponds to the positive power supply of the pulse width modulator and whose low level corresponds to the negative power supply of the pulse width modulator, to a voltage level of a second PWM signal whose high level corresponds to the positive power supply of the power amplifier and whose low level corresponds to the GND.

Abstract: An amplifier circuit comprising: a delta-PWM-modulator, a three-level-DAC, a loop-integrator, and a comparator. The delta-PWM-modulator receives a digital-input-signal; and processes the digital-input-signal and a modulator-triangular-signal to generate a delta-pulse-width-modulation-signal. The delta-pulse-width-modulation-signal is representative of the difference between a square-wave-carrier-signal and a digital-pulse-width-modulation of the digital-input-signal. The three-level-DAC receives the delta-pulse-width-modulation-signal from the delta-PWM-modulator and provides a three-level-analog-signal. The loop-integrator comprises: a virtual-ground-node-terminal configured to receive: (i) the three-level-analog-signal from the three-level DAC; and (ii) a feedback-signal from an output stage of the amplifier circuit via a feedback loop; and an integrator-output-terminal configured to provide a loop-integrator-output-signal.

Abstract: A method can be used to measure a load driven by a switching amplifier having a differential input, an LC output demodulator filter and a feedback network between the amplifier output and the differential input. The amplifier is AC driven in a differential and in a common mode by applying a common. The feedback network provides feedback towards the differential input from downstream the LC demodulator filter by computing the impedance of the load as a function of the differential mode output current and the common mode output current. The feedback network provides feedback towards the differential input from upstream the LC demodulator filter by measuring the impedance value of the inductor of the LC demodulator filter, and computing the impedance of the load as a function of the differential mode output current, the common mode output current and the impedance value of the inductor of the LC demodulator filter.

Abstract: An amplifier system includes a Class-D power amplifier integrated circuit (IC) that is nested inside a feedback loop of a low noise differential operational amplifier (op-amp).

Abstract: A new and improved self-oscillating amplifier system is presented, suitable for use in high fidelity audio applications. The self-oscillating amplifier system comprises a feedback path and a forward path including a pulse modulator, a switching power amplification stage and a demodulation filter. The forward path further includes a pair of parallel forward filters preceding the pulse modulators, a differentiating forward filter and an integrating forward filter. The differentiating forward filter is utilized for controlling a switching frequency of the system while the integrating forward filter is utilized for controlling the behavior of the amplifier system within an operating frequency band (e.g. audio band). The self-oscillating amplifier system exhibits improved performance in terms of open loop gain, reduced phase turn and improved robustness as compared to other previously known self-oscillating amplifier systems.

Abstract: Systems and methods are provided for dynamically biasing power amplifiers. A power amplifier (PA) that amplifies an input signal may be controlled based on processing of the input signal. The controlling may include adjusting biasing applied to the power amplifier (PA). The processing of the input signal may include applying clipping to the input signal and determining one or more parameters of the input signal. The biasing applied to the power amplifier (PA) may be adjusted based on the one or more parameters of the input signal. The clipping may be configured such that signals applied to positive and negative sides of the power amplifier (PA) are not differential.