Nonlinear Feedforward Correction in a Multi-Level Output System

Abstract

A feedforward correction block for use in a multi-level output system may include circuitry configured to determine the occurrence of a mode transition between operating modes of the multi-level output system, capture the loop filter output of the signal path of the multi-level output system that occurs before and after the mode transition occurs, and determine a transition-specific compensation function based on the transition and a change in the loop filter output in response to the transition to apply to a feedforward input signal of the signal path combined with the loop filter output.

Description

Field of the Invention

[0001] The field of representative embodiments of the present disclosure relates to methods, apparatus, and / or implementations regarding or involving multilevel driver circuits such as may be used to drive transducers, and particularly to non-linear feedforward correction in such multilevel driver circuits. Background Art

[0002] Many electronic devices include transducer driver circuits for driving a transducer with a suitable drive signal, such as an audio output transducer for driving a host device or a connected accessory with an audio drive signal.

[0003] In some applications, the driver circuit may include a switched amplifier stage for generating the drive signal, e.g., a class-D amplifier output stage or the like. The switched amplifier stage can be relatively power efficient and can thus be advantageously used in some applications. The switched amplifier stage typically operates to switch an output node between a defined high-side switch voltage and a low-side switch voltage, having a duty cycle that provides a desired average output voltage during the duty cycle of the drive signal.

[0004] At least one of the high-side voltage and the low-side voltage for the output driver can be generated by a DC-DC converter from a suitable input voltage (e.g., a battery voltage). In some cases, the DC-DC converter can be a variable voltage converter that is operable to selectively change the switch voltage in use.

[0005] It has been found that in certain architectures of multilevel output stages, due to the discharge characteristics of the flying capacitors integrated into the multilevel power converter, non-linearity may occur in the signal path powered by the multilevel power converter. The drop in the flying capacitor voltage due to such discharge may itself manifest as a duty-cycle-dependent output resistance, where this dependence follows a different distribution for each mode of the multilevel converter. The result of this mode-dependent output resistance variation may be a discontinuity in the output impedance at each node transition. Thus, systems and methods for correcting such mode-dependent output resistance variations may be desirable. Summary of the Invention

[0006] In accordance with the teachings of the present disclosure, disadvantages and problems associated with mode transitions in multilevel power converters can be reduced or eliminated.

[0007] According to an embodiment of the present disclosure, a feedforward correction block for use in a multi-level output system may include circuitry configured to determine the occurrence of a mode transition between operation modes of the multi-level output system, capture loop filter outputs of a signal path of the multi-level output system that occur before and after the mode transition occurs, and determine a transition-specific compensation function based on the transition and a change in the loop filter output in response to the transition to apply to a feedforward input signal of the signal path combined with the loop filter output.

[0008] According to these and other embodiments of the present disclosure, a method for feedforward correction of a multi-level output system may include determining the occurrence of a mode transition between operation modes of the multi-level output system, capturing loop filter outputs of a signal path of the multi-level output system that occur before and after the mode transition occurs, and determining a transition-specific compensation function based on the transition and a change in the loop filter output in response to the transition to apply to a feedforward input signal of the signal path combined with the loop filter output.

[0009] According to these and other embodiments of the present disclosure, a multi-level output system may include an output driver subsystem for outputting an output drive signal in response to an input signal, wherein the multi-level output system is configured to operate in a selected operation mode selected from a plurality of operation modes based on the input signal, and a supply voltage for the output driver subsystem is selected based on the selected operation mode. The multi-level output system may further include a feedforward correction block that includes circuitry configured to determine the occurrence of a mode transition between operation modes of the multi-level output system, capture loop filter outputs of a signal path of the multi-level output system that occur before and after the mode transition occurs, and determine a transition-specific compensation function based on the transition and a change in the loop filter output in response to the transition to apply to a feedforward input signal of the signal path combined with the loop filter output.

[0010] The technical advantages of the present disclosure will be apparent to those of ordinary skill in the art from the accompanying drawings, description, and claims included herein. The objectives and advantages of the embodiments will be realized and attained at least by the elements, features, and combinations particularly pointed out in the claims.

[0011] It should be understood that the foregoing general description and the following detailed description are both exemplary and explanatory and are not restrictive of the claims set forth in the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] To better understand the examples of the present disclosure and to more clearly show how these examples may be effective, reference will now be made, by way of example only, to the following drawings, in which:

[0013] Figure 1Shows an example drive circuit for driving a load according to an embodiment of the present disclosure, where such a drive circuit includes a multi-stage power converter;

[0014] Figure 2 Shows an example functional block diagram of a signal path according to an embodiment of the present disclosure; and

[0015] Figure 3 Shows an example functional block diagram of a feedforward correction block according to an embodiment of the present disclosure. Detailed Description

[0016] Figure 1 Shows an example drive circuit 100 for driving a load transducer 101 with an output voltage VOUT according to an embodiment of the present disclosure. In some embodiments, the drive circuit 100 may be implemented in accordance with U.S. Patent Application No. 17 / 678,527, filed on February 23, 2022, which is hereby incorporated by reference in its entirety.

[0017] The load transducer 101 may include an audio output transducer (e.g., a speaker), a haptic transducer, a piezoelectric transducer, a ceramic transducer, or any other suitable transducer.

[0018] As Figure 1 shown, the output node 102a can be selectively coupled to any one of three supply voltages V1, V2, or V3 at corresponding switched voltage nodes via switch paths S1a, S2a, and S3a. Also as Figure 1 shown, the supply voltages V1 and V2 can be system voltages, where a system voltage as used herein can refer to any generally continuous voltage maintained or generated by other components and received / available to the driver device. For example, V1 and V2 can be ground and a received input supply voltage +VDD (or -VDD). The input supply voltage V2 can be obtained from a system battery voltage (where some voltage regulation and / or boosting may be applied by some other upstream circuitry) and / or the input supply voltage can be provided from a system power supply such as a switched-mode power supply. The switch path S1a can selectively couple the output node 102a to the received voltage V1, and the switch path S2a can selectively couple the output node 102a to the received voltage V2.

[0019] As Figure 1 depicted, a third different supply voltage V3 can be generated by a DC-DC converter 103, which can include a charge pump, an inductive converter, or the like. In the embodiment represented by Figure 1 , the DC-DC converter 103 can use the received system voltages V1 and V2 to generate the supply voltage V3. The switch path S3a can selectively couple the output node 102a to the supply voltage V3.

[0020] In use, each of the voltages V1, V2, and V3 can be maintained in a substantially continuous manner, i.e., the associated voltage can be held at a substantially constant level and the voltage at the associated switch node can remain substantially unchanged over the entire switching cycle of the drive circuit 100. In embodiments where the DC-DC converter 103 includes a switched-mode converter such as a charge pump, the DC-DC converter 103 is operable to maintain the supply voltage over the entire switching cycle of the DC-DC converter 103. Accordingly, the voltage at the associated switch node can be substantially independent of the input signal to the drive circuit 100. Of course, it will be understood that the output voltage of a DC-DC converter such as a charge pump or an inductor boost converter or the like may exhibit some voltage ripple due to the operation of the DC-DC converter, but the degree of such ripple is relatively small and a switched DC-DC converter such as a charge pump typically includes an energy storage element such as a storage capacitor to maintain the output voltage over the entire switching cycle of the DC-DC converter.

[0021] In some embodiments, when the DC-DC converter 103 is activated, the supply voltage V3 generated by the DC-DC converter 103 can be generated in a substantially continuous manner. However, this continuous voltage generation does not mean that the DC-DC converter 103 needs to be continuously activated. For example, if the supply voltage V3 generated by the DC-DC converter 103 is only used to switch a relatively high-amplitude output signal, then in some cases, if the signal amplitude is relatively low, the DC-DC converter 103 can be controlled to be deactivated. However, when activated, the DC-DC converter 103 can operate to maintain its output supply voltage V3 in a continuous manner.

[0022] The supply voltages V1, V2, and V3 provide a first set of switching voltages, and in use, the output node 102a can be switched between selected pairs of these switching voltages at a controlled duty cycle in order to provide a desired output signal. The output node 102a can be switched between these voltages by controlling the associated switching paths S1a, S2a, and S3a to couple the output node 102b to the associated supply voltage at a controlled duty cycle. This operation can be regarded as a direct-coupled switch, or a direct charge transfer mode of operation, since the output node 102a can be switched to be directly coupled to the associated DC voltage source. For example, the DC supply voltage can be obtained from a battery, an inductive switched-mode power supply, or a switched-capacitor power supply, and the voltage is maintained in a substantially continuous manner, i.e., generally capable of supplying current over an extended period of time, e.g., greater than the period of the output drive signal at the lowest required frequency. The terms "direct coupling" and "DC coupling" are used herein to refer to such switching of the output node between such supply voltages.

[0023] Additionally, output node 102a can be selectively coupled to the output voltage node 104 of the flying capacitor driver 106 via a switching path S0a. The output voltage node 104 can be coupled to the first terminal of capacitor 105. The second terminal of capacitor 105 can be configured to selectively switch between two different voltages Vac1 and Vac2 via switches Sac1 and Sac2. The first terminal of capacitor 105 can also be selectively coupled to voltage Vac3 via switch Sac3. In use, capacitor 105 can be cyclically charged and then coupled to provide a boost (positive or negative) of one of voltages Vac1 and Vac2 to generate a boosted voltage at the switching voltage node, and thus capacitor 105 can be used as a flying capacitor. In some embodiments, voltages Vac1, Vac2, and Vac3 can be selected such that the boosted voltage generated at output voltage node 104 is different from any of voltages V1, V2, and V3. Voltage Vac1 can be different from voltage Vac2, and if switches Sac1 and Sac3 operate in phase with each other, Vac1 and Vac3 can also be different from each other such that when both switches Sac1 and Sac3 are closed, capacitor 105 can be charged by the voltage difference between Vac1 and Vac3. Voltages Vac2 and Vac3 can be the same as or different from each other. It should be understood that Vac1 can be more or less positive than Vac2 and / or Vac3. Conveniently, at least one, and possibly all, of voltages Vac1, Vac2, and Vac3 can be provided by one of power supply voltages V1, V2, and V3, but any other system voltage can be used to provide one or more of these voltages.

[0024] For example, consider that the supply voltage V2 is used for the voltage Vac1, and the supply voltage V1 is used for both the voltages Vac2 and Vac3, where the supply voltage V2 is more positive than V1. In use, in a state where the second terminal of the capacitor 105 is coupled to Vac1 = V2 and the first terminal of the capacitor 105 is coupled to Vac3 = V1, the capacitor can be charged to the voltage +(V2 – V1), where the positive plate is at the second terminal. In this state, the output voltage node 104 can be at the voltage Vac3 = V1. In a second state, the second terminal of the capacitor 105 can instead be coupled to Vac2 = V1, and the first terminal of the capacitor 105 can be decoupled from Vac3. In this state, the capacitor 105 can provide a negative boost of the supply voltage Vac2, thereby generating a negatively boosted voltage V0 at the output voltage node, where V0 = -(V2 – V1). In this example, the output voltage node 104 can thus switch between the voltages V1 and V0, where the duty cycle is controlled by the switching of the switches Sac1, Sac2, and Sac3. The capacitor 105 together with the switches Sac1, Sac2, and Sac3 can thus be regarded as a flying-capacitor-based auxiliary driver or charge pump 106 for driving the output node.

[0025] The capacitor 105 can thus be selectively switched to provide a selective boost to provide the voltage V0, which can be different from the voltages V1, V2, and V3. This operation can be regarded as an indirect coupling switch, or an indirect charge transfer operation mode, since in the operation of generating the voltage V0, the output voltage node 104 can be indirectly coupled to the supply voltage Vac2 via the capacitor 105. The voltage V0 may not be continuously maintained throughout the switching cycle of the drive circuit 100. As used herein, the term "indirect coupling" or "indirect switching" will be used to refer to this operation, and the term "AC coupling" will also be used to refer to this operation.

[0026] Thus, the drive circuit 100 can be operable in a direct coupling operation mode and can switch the output between selected supply voltages among the supply voltages V1, V2, V3, and can also be operable in an indirect coupling operation mode to generate at least one additional voltage V0. Thus, the drive circuit 100 can be a hybrid direct coupling and indirect coupling switch driver. Depending on the desired output signal, energy can be transferred to the load transducer 101 via a mixture of "DC coupling" and "AC coupling" paths.

[0027] The DC power supply voltages V1, V2, and V3, and at least one additional boost voltage V0 can be selected to provide a desired output voltage range for the single-ended drive signal at output node 102a. The difference between the highest voltage level (i.e., the most positive / least negative) and the lowest voltage level (i.e., the most non-positive / most negative) among the voltages V1, V2, V3, and V0 can be selected to provide a desired output range for the output drive signal. Other voltages are selected to provide intermediate voltage levels. In use, the drive circuit 100 can be controlled to switch the output node only between adjacent voltage levels.

[0028] For example, if V3 > V2 > V1 > V0 (in terms of more positive), the output node can be switched between voltages V2 and V3 at a controlled duty cycle to provide an (average) output voltage in the range between V2 and V3 at output node 102a. To provide a lower (average) output voltage, the output node can be switched between V1 and V2 to provide an (average) output voltage in the range between V1 and V2 or switched between V0 and V1 to provide an average voltage in that range.

[0029] The drive circuit 100 can further include switch paths S1b, S2b, and S3b for selectively coupling output node 102b, which is coupled to the opposite terminal of the load transducer 101, to the power supply voltages V1, V2, and V3, respectively. The drive circuit 100 can also have a switch path S0b for selectively coupling output node 102b to a switching voltage node for indirectly coupling the switch. In some cases, the switch path S0b can couple output node 102b to output voltage node 104, but in some cases, there can be an additional charge pump for providing an indirectly coupled switch for output node 102b. Each of output nodes 202a and 202b can be selectively switched between appropriate switching voltages to provide a desired differential voltage across load transducer 101.

[0030] Figure 2 An example functional block diagram of a signal path 200 in accordance with an embodiment of the present disclosure is shown. As Figure 2 shown, the digital PWM block 202 can receive an input signal VIN and generate a PWM equivalent of the input signal VIN. The combiner 204 can subtract the output voltage VOUT feedback from the output of the digital PWM block 202 to generate an error signal. The analog loop filter 206 can low-pass filter the error signal, and the analog-to-digital converter (ADC) 208 can convert the filtered error signal to a digital equivalent signal. The digital loop filter 210 can further low-pass filter the digital signal to generate a loop output signal LOOP.

[0031] The feed - forward correction block 212 can receive the input signal VIN, the loop output signal LOOP, and an indication MODE of the operating mode of the drive circuit 100 (e.g., a mode indicating the switch states of switches S0a, S1a, S2a, S3a, S0b, S1b, S2b, and S3b), and generate a corrected feed - forward signal based thereon, as described in more detail below. The combiner 214 can combine the corrected feed - forward signal with the output of the digital loop filter 210. The quantizer 216 (e.g., which can be implemented using a digital PWM block) can quantize the resulting signal to produce a PWM signal VPWM and transmit the PWM signal VPWM to the switch control circuit 218. Based on the PWM signal VPWM, the switch control circuit can generate control switch signals S0a, S1a, S2a, S3a, S0b, S1b, S2b, and S3b to produce an output voltage VOUT that is a function of the input signal VIN.

[0032] Figure 3 An example functional block diagram of the feed - forward correction block 212 according to an embodiment of the present disclosure is shown. As Figure 3 shown, the differential and threshold detection block 302 can receive the high - side switch voltage VH (or its digitized representation) representing the voltage present at the output node 102a, and detect whether such high - side switching voltage VH has crossed a threshold voltage level for disabling adaptation and / or whether the change in the high - side switching voltage VH (e.g., between successive samples or over a period of time) has exceeded a threshold change in the voltage level for disabling adaptation. The logical OR (OR) gate 304 can perform a logical OR of the output of the differential and threshold detection block 302 and a signal indicating whether the system including the switch drive circuit 100 is in startup, and set the variable ADAPT_DIS to "true" if the high - side switch voltage VH has crossed the threshold voltage level for disabling adaptation, the change in the high - side switch voltage VH has exceeded the threshold change in the voltage level for disabling adaptation, and / or the system including the switch drive circuit 100 is in startup. Otherwise, the logical OR gate 304 can set the variable ADAPT_DIS to "false". If the variable ADAPT_DIS is set to true, the error capture block 306 will be disabled.

[0033] If the error capture block 306 is enabled, it can determine whether a transition between the modes of the charge pump 103 has occurred, and if such a transition has occurred, it can capture the change in the error signal in the signal path 200, as indicated by the loop output signal LOOP just before and just after the transition occurs. The error capture block 306 can further determine a mode-transition specific gain relationship (e.g., a linear gain as a function of the input signal VIN) for such a transition based on the change in the error signal, and can convey such a gain relationship to the gain calculator 308, as indicated by GAIN_PER_TRANS[N:0]. Such a gain relationship can, when applied to the feedforward input signal VIN, produce a corrected feedforward signal to minimize the change in the error signal, as indicated by the change in the loop output signal LOOP in response to the mode change. Thus, the error capture block 306 can compute a corresponding gain relationship for each of the N possible transitions between the modes of the drive circuit 100, including transitions from each mode to each other mode, and vice versa. Additionally, the error capture 306 can be configured to continuously adjust its computation of the corresponding gain relationships for each of the N possible transitions between the modes of the charge pump 103 in order to further minimize the change in the error signal in response to a transition of the charge pump 103, as indicated by the loop output signal LOOP.

[0034] The gain calculator 308 can receive from the error capture block 306 the various corresponding gain relationships for each of the N possible transitions between the modes of the charge pump 103, and based on such gains, the input signal VIN, and the current transition state (if any) of the charge pump 103 as indicated by a change in the mode indication MODE, apply a gain function (e.g., gain = f(VIN)) that is a function of the input signal VIN to compute a gain value GAIN that will be applied by the combiner 310 to the input signal VIN in order to generate a corrected feedforward signal. In some embodiments, the gain function can be a piecewise-linear gain function based on the various gain relationships.

[0035] Although the foregoing contemplates applying a transition-specific gain function to the feedforward input signal of the signal path combined with the loop filter output based on the transition and the change in the loop filter output in response to the transition, it should be understood that other compensations can be applied in addition to or instead of the gain. For example, in some embodiments, an additive compensation function (e.g., as opposed to a multiplicative gain function) can be used.

[0036] Embodiments of the present disclosure may be implemented as integrated circuits. Embodiments may be implemented in a host device, particularly a portable and / or battery-powered host device, such as a mobile computing device, e.g., a laptop computer, notebook computer, or tablet computer, or a mobile communication device, such as a mobile phone, e.g., a smart phone. The device may be a wearable device such as a smart watch. The host device may be a game console, remote control device, home automation controller, or household appliance, toy, machine, such as a robot, audio player, or video player. It will be understood that embodiments may be implemented as part of a system provided in a household appliance or in a vehicle or an interactive display. A host device incorporating the above embodiments is further provided.

[0037] Those skilled in the art will recognize that some aspects of the above-described apparatus and methods, such as aspects of controlling a switch control signal to implement different modes, may be embodied as processor control code, e.g., on a non-volatile carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or on a data carrier such as an optical or electrical signal carrier. For some applications, embodiments may be implemented on a DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit), or FPGA (Field Programmable Gate Array). Thus, the code may include conventional program code or microcode, or, e.g., code for configuring an ASIC or FPGA. The code may also include code for dynamically configuring reconfigurable devices such as re-programmable logic gate arrays. Similarly, the code may include code for a hardware description language such as Verilog TM or VHDL (Very High Speed Integrated Circuit Hardware Description Language). As those skilled in the art will understand, the code may be distributed among multiple coupled components that communicate with each other. In appropriate cases, code running on a field programmable (re)programmable analog array or similar device may also be used to implement embodiments in order to configure analog hardware.

[0038] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in the claims, "a" or "an" does not exclude a plurality, and a single feature or other unit may implement the functions of several units recited in the claims. Any reference numerals or labels in the claims should not be construed as limiting their scope.

[0039] As used herein, when two or more elements are referred to as being "coupled" to each other, the term indicates that the two or more elements are in electrical communication or mechanical communication, as the case may be, whether indirectly or directly connected, with or without intervening elements.

[0040] This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that would be understood by a person of ordinary skill in the art. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the exemplary embodiments herein that would be understood by a person of ordinary skill in the art. Additionally, in the appended claims, a reference to a device or system or a component of a device or system that is adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that device, system, or component, whether or not the particular function is activated, turned on, or unlocked, so long as the device, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Accordingly, modifications, additions, or omissions may be made to the systems, devices, and methods described herein without departing from the scope of this disclosure. For example, components of the systems and devices may be integrated or separated. Additionally, the operations of the systems and devices disclosed herein may be performed by more, fewer, or other components, and the methods described may include more, fewer, or other steps. Further, the steps may be performed in any suitable order. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

[0041] Although the exemplary embodiments are shown in the drawings and described below, the principles of this disclosure may be implemented using any number of techniques, whether currently known or not. This disclosure should not in any way be limited to the exemplary embodiments and techniques shown in the drawings and described above.

[0042] Unless otherwise specifically noted, the items depicted in the drawings are not necessarily drawn to scale.

[0043] All of the examples and conditional language recited herein are intended for pedagogical purposes to assist the reader in understanding the disclosure and the concepts contributed by the inventor to further the art, and are to be construed as not being limited to such specifically recited examples and conditions. Although the embodiments of this disclosure have been described in detail, it should be understood that various changes, substitutions, and alterations can be made thereto without departing from the spirit and scope of this disclosure.

[0044] Although specific advantages have been listed above, various embodiments may include some, none, or all of the listed advantages. Additionally, other technical advantages may become apparent to a person of ordinary skill in the art after reviewing the foregoing drawings and description.

[0045] To assist the Patent Office and any reader of any patent issued under this application in interpreting the claims appended hereto, the applicant wishes to note that unless the words "means for" or "step for" are expressly used in a particular claim, they are not intended to invoke 35 U.S.C. § 112(f) for any of the appended claims or claim elements.

Claims

1. A feedforward correction block for use in a multi-stage output system, the multi-stage output system having an output driver subsystem for outputting an output drive signal in response to an input signal, the feedforward correction block comprising: A circuit configured to: Determine the occurrence of a mode transition between the operating modes of the multi - level output system; Capture the loop filter output of the signal path of the multi - level output system that occurs before and after the mode transition occurs; and Determine a transition - specific compensation function based on the transition and the change in the loop filter output in response to the transition, to be applied to the feed - forward input signal of the signal path combined with the loop - filtered output; Wherein: The multi - level output system is configured to operate in a selected operating mode selected from multiple operating modes based on the input signal; And The power supply voltage for the output driver subsystem is selected based on the selected operating mode.

2. The feedforward correction block according to claim 1, wherein, The transition - specific compensation function defines the gain value as a function of the feed - forward input signal.

3. The feedforward correction block according to claim 2, wherein, The transition - specific compensation function defines the gain value as a piece - wise linear function of the feed - forward input signal.

4. A method for feedforward correction in a multi-stage output system, the multi-stage output system having an output driver subsystem for outputting an output drive signal in response to an input signal, the method comprising: Determine the occurrence of a mode transition between the operating modes of the multi - level output system; Capture the loop filter output of the signal path of the multi - level output system that occurs before and after the mode transition occurs; and Determine a transition - specific compensation function based on the transition and the change in the loop filter output in response to the transition, to be applied to the feed - forward input signal of the signal path combined with the loop - filtered output; Wherein: The multi - level output system is configured to operate in a selected operating mode selected from multiple operating modes based on the input signal; And The power supply voltage for the output driver subsystem is selected based on the selected operating mode.

5. The method according to claim 4, wherein, The transition - specific compensation function defines the gain value as a function of the feed - forward input signal.

6. The method according to claim 5, wherein, The transition - specific compensation function defines the gain value as a piece - wise linear function of the feed - forward input signal.

7. A multi-stage output system, comprising: An output driver subsystem for outputting an output drive signal in response to an input signal, wherein: The multi - level output system is configured to operate in a selected operating mode selected from multiple operating modes based on the input signal; and The power supply voltage for the output driver subsystem is selected based on the selected operating mode; and A feed - forward correction block, which includes a circuit configured to: Determine the occurrence of a mode transition between the operating modes of the multi - level output system; Capture the loop filter output of the signal path of the multi - level output system that occurs before and after the mode transition occurs; and Determine a transition - specific compensation function based on the transition and the change in the loop filter output in response to the transition, to be applied to the feed - forward input signal of the signal path combined with the loop - filtered output.

8. The multi-stage output system according to claim 7, wherein, The transition - specific compensation function defines the gain value as a function of the feed - forward input signal.

9. The multi-stage output system according to claim 8, wherein,The transition - specific compensation function defines the gain value as a piece - wise linear function of the feed - forward input signal.

Images