Boost stage circuit for power amplifier

Abstract

The invention belongs to the field of booster stages for power amplifiers and external supply voltage power amplifiers comprising such booster stages, for example for amplifying electronic signals to loudspeaker systems. These amplifiers may be provided with an external supply voltage.

Description

Technical Field

[0001] The invention belongs to the field of booster stages for power amplifiers and external supply voltage power amplifiers comprising such booster stages, for example for amplifying electronic signals to loudspeaker systems (audio amplifiers). These amplifiers may be provided with an external supply voltage. Background Art

[0002] Prior art electronic amplifier circuits are often limited in the range of output voltages they can provide with the supply voltage they are provided with. For battery operated devices this can be a problem when the battery voltage is not high enough to deliver the desired output signal (in all cases). This is for example a problem in audio amplifiers which often have output signals with peak signals many times higher than the average signal power (so called high crest factor).

[0003] In order to overcome this power supply limitation, many amplifier circuit extensions have been proposed in the past which enable the available power supply voltage to be boosted instantaneously to a voltage beyond that available from an external power supply. Two approaches may be mentioned in particular: Circuits using large storage capacitors ("flying capacitors") which can instantaneously double the power supply, such as in US8212620, this document shows an amplifier device comprising an amplifier having an input for receiving an audio input signal and an output for sending an output signal to a load, wherein a boost rail circuit is connected to the power supply and has a single boost rail connected to a BTL amplifier, such as Figure 1a As shown in; and other circuits using separate switching power stages to generate local power supplies, the other circuits are typically composed of Figure 1b , with an inductor and a capacitor. Both variants of the prior art discussed above still have problems. In the case of the flying capacitor, the main problem is that it discharges during use and can only achieve a doubling of the power supply at most. In addition, when it is discharged in large quantities, recharging will produce power dissipation, for example in the existing diodes. In the case of the switching booster, the problem is that it takes time to charge the local power supply 15 to a level higher than the external power supply 5. In more detail, this second problem involves the following situation: when the boost phase is required, the inductor 10 must first be charged by connecting it to the ground 35 via the bottom transistor 30, which has the side effect that the local power supply 15 will drop before it is boosted. This initial charging produces a momentary drop in the output before it starts to rise above the power supply, and is a manifestation of a "right half plane" zero, which is generally a well-known problem in the control of switching boost stages. In applications for amplifiers this means either some headroom in the control of the power supplies (to create some margin for undesired supply variations), or some delay in the processing of the inputs to be able to "look ahead" and predict switching before a boost is actually needed. Figure 1b Another disadvantage of the switching boost in FIG. 1 is that the supply current always flows through the primary inductor 10, even when boosting is not required. The parasitic resistance of this inductor causes additional losses.

[0004] Incidentally, US2018 / 115246 A1 describes a system comprising a combination of a boost converter and a power converter, wherein the boost converter and the power converter are coupled in series so that the series combination boosts an input voltage arriving at the series combination to an output voltage greater than the input voltage, so that the boost provided by the series combination is greater than the boost provided by the boost converter alone. The system may also include an amplifier, wherein the input of the amplifier is coupled to the output of the series combination of the boost converter and the power converter. However, the system is relatively complex and not very energy efficient.

[0005] The object of the present invention is to overcome the disadvantages of prior art booster circuits and in particular the disadvantages of their electrical and audio functions without compromising functionality and advantages. Summary of the invention

[0006] The present invention relates in a first aspect to a boost stage circuit for a power amplifier circuit for amplifying an input signal and producing an output signal, the boost stage circuit comprising circuitry for producing a supply rail voltage to the power amplifier. When the output signal exceeds the voltage available from an external power source (e.g. a battery), the supply voltage for the power amplifier is boosted by a flying capacitor. The flying capacitor is efficiently automatically recharged after each boost cycle through the inductor, thereby also increasing the voltage across the flying capacitor to above the external power supply. When a boost is required, the capacitor 240 is then boosted and placed in series with the power supply by means of a switching transistor 230. Thus, an instantaneous doubling of the power supply is available without Figure 1b 230 . When the switching transistor 230 is closed, current will also begin to accumulate in the primary inductor 210. When the circuit returns to the normal power supply by opening 230 and closing 220, this inductor current will recharge the capacitor 240. By alternating quickly enough between the normal power supply 220 closed, 230 opened and the boost power supply 220 opened and 230 closed, a relatively small capacitance value 240 can be used while avoiding significant discharge, which is a significant advantage over conventional flying capacitor power multipliers. In addition to the above functionality, there is also an increase in the average voltage across the flying capacitor depending on the duty cycle of the two switching phases. In addition, as the capacitor is connected through the inductor 35 rather than through the boost power supply 220, the average voltage across the flying capacitor increases. Figure 1a The prior art dissipation diode 50 is efficiently recharged without providing a degradation in power efficiency. As with other boost circuits, switching between modes can occur with variable, ie limited or full, energy transferred from the inductor to the capacitor.

[0007] Therefore, the present boost stage circuit is particularly suitable for a power amplifier and comprises an electrical connector 5 for an external power supply, at least one capacitor 240, the capacitor having a first side and a second side, the capacitor being electrically connected to at least one first switch (220) at its first side and electrically connected to at least one second switch (230) at its second side, typically a single first switch 220 and / or a single second switch 230, wherein each individual switch is adapted to operate at a switching frequency of >20kHz, wherein each individual switch and the other side are adapted to be electrically connected to the electrical connector 5, it should be noted that the "switch side" may be on the capacitor side and on the electrical connector side, and wherein in the boost mode, the at least one first switch 220 at one side of the capacitor is in an open state and the at least one first switch 220 at the other side of the capacitor is in an open state. The at least one second switch 230 is in a closed state, or wherein in the base mode, the at least one first switch 220 at one side of the capacitor is in a closed state and the at least one second switch 230 at the other side of the capacitor is in an open state, at least one inductor 210, which is electrically connected at one side to (i) one side of the capacitor 240 and (ii) to at least one of the first switches 220, and at the other side (iii) to ground, inputs 261 and 262 are respectively adapted to receive control inputs from a controller for operating the at least one first switch 220 and the at least one second switch 230, and optionally, a controller for operating the at least one first switch 220 and the at least one second switch 230. If reference is made to "ground", it may also be referenced to a lower input voltage of the power supply. Between the boost mode and the base mode, the switches 220, 230 may both be open, which may be referred to as a dead zone mode, in order to prevent short circuits.

[0008] In a second aspect, the invention relates to an external supply voltage power amplifier 60 comprising at least one boost stage circuit, wherein the power amplifier is selected from an audio amplifier, a hearing aid amplifier, a motor control amplifier, a variable power supply unit, a time-varying power supply, and combinations thereof.

[0009] Applications are especially those amplifiers with a fixed supply voltage, either because they are battery powered (including car amplifiers) or because the power supply unit is fixed. The main application is audio amplifiers. However, the concept can easily be extended to other areas, such as motor control, variable power supply units or any other area where a time-varying power signal is required.

[0010] Thus, the present invention provides a solution to one or more of the above-mentioned problems.

[0011] Advantages of the present specification are detailed throughout the description.

[0012] Detailed description of the invention

[0013] The invention in a first aspect relates to a boost stage circuit.

[0014] In an exemplary embodiment of the boost stage circuit, the at least one first switch 220 and the at least one second switch 230 may each be individually selected from transistors such as NMOS transistors, PMOS transistors, bipolar transistors, FETs such as GaN FETs, IGBTs, and combinations thereof.

[0015] In an exemplary embodiment of the present boost stage circuit, at least one capacitor 240 may be individually selected from a ceramic capacitor, a filled capacitor, an electrolytic capacitor, a non-polarized capacitor, a multilayer capacitor, and a capacitance of 10 pF to 10000 μF, preferably 50 pF to 100 μF, more preferably 100 pF to 50 μF, even more preferably 1 nF to 5 μF, such as 100 nF to 1 μF, and combinations thereof. For high power applications, larger capacitance is preferred.

[0016] In an exemplary embodiment of the present boost stage circuit, at least one inductor 210 may be individually selected from an air core inductor, a ferromagnetic core inductor, a variable inductor, a choke, a solenoid, and its inductance is 10nH to 20H, preferably 0.1μH to 10H, more preferably 1μH to 1H, for example 100μH to 0.01H, and combinations thereof.

[0017] In an exemplary embodiment of the present boost stage circuit, each individual switch may be adapted to operate at a switching frequency of 50 kHz to 2.4 GHz, preferably 100 kHz to 1.2 GHz, such as 250 kHz to 30 MHz.

[0018] In an exemplary embodiment, the boost stage circuit may further include details of its feedback loop, preferably wherein the feedback loop includes a feedback filter.

[0019] In an exemplary embodiment, the boost stage circuit may further comprise a clock, wherein the clock is adapted to provide a clock frequency >50 kHz, preferably 100 kHz to 10 GHz, more preferably 300 kHz to 2.4 GHz, such as 500 kHz to 1.2 GHz.

[0020] In an exemplary embodiment, the boost stage circuit may further include a rectifier, such as a diode, connected in parallel to at least one switch 220, 230, or a second capacitor connected in parallel to the first capacitor and a third switch between the first capacitor and the second capacitor, and combinations thereof.

[0021] While described in the context of a detailed explanation, the invention is best understood in conjunction with the accompanying examples and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figures 1a to 1b , 2 to 3, 3a to 3c and 4 to 11 show the details of the boost circuit. DETAILED DESCRIPTION

[0023] The drawings are of an exemplary nature. Elements of the drawings may be combined.

[0024] In the attached picture:

[0025] 100a, 100b boost circuit

[0026] 5 Electrical connector to the power supply

[0027] 10 Inductor

[0028] 15 Electrical connector

[0029] 20 First switch

[0030] 25 Electrical connector

[0031] 30 Second switch

[0032] 35 Electrical connector for return power or ground

[0033] 40 Capacitor

[0034] 50 Rectifier, e.g. diode

[0035] 60 Audio Amplifier

[0036] 70 Third switch

[0037] 75 Electrical connector

[0038] 80 Fourth switch

[0039] 90 Inductor

[0040] 105 Electrical connector

[0041] 115 Electrical connector

[0042] 110 Speakers

[0043] 120 Capacitor

[0044] 121 Capacitor

[0045] 130 Inductor

[0046] 140 Fifth Switch

[0047] 145 Electrical connector

[0048] 150 Sixth Switch

[0049] 210 Inductor

[0050] 215 Electrical connector

[0051] 215a Electrical Connector

[0052] 215b Electrical Connector

[0053] 220 First switch

[0054] 225 Electrical connector

[0055] 230 Second switch

[0056] 240 Capacitor

[0057] 250 Control Circuit

[0058] 255 Inductor Current Sense Connector

[0059] 260 Gate Driver Circuit

[0060] 261 Electrical connector

[0061] 262 Electrical connector

[0062] 266 Electrical connector

[0063] 267 Electrical connector

[0064] 268 Electrical connector

[0065] 269 ​​Electrical connector

[0066] Figure 1a Shows a prior art circuit that uses a large storage capacitor ("flying capacitor") that can instantaneously double the power supply, such as Figure 1a As shown in (with various conceivable embodiments).

[0067] Figure 1b A prior art circuit is shown which uses a separate switching power stage to generate a local power supply, typically consisting of a boost circuit with an inductor 10 and a capacitor 40. Controls and transistors for such an amplifier exist, for example, in the Texas Instruments TAS2563.

[0068] Figure 2The circuit of the present invention is shown, which can be viewed as a combination of a flying capacitor power multiplier (using the voltage stored on the capacitor to increase the power supply) and a switching booster, thereby overcoming the above disadvantages. During normal operation, in the basic mode, for example when boosting is not required, the local power supply 215 is directly connected to the external power supply 5, with only the switching transistor 220 in between, so there is no additional dissipation in the power supply inductor. During this operation, the voltage across the flying capacitor 240 becomes equal to the power supply 5 because its bottom plate is discharged to ground 35 via the inductor 210.

[0069] When a voltage boost is required, capacitor 240 is then raised and placed in series with the power supply via switching transistor 230. Thus, an instantaneous doubling of the power supply is available without Figure 1b The charging delay present in prior art boosters in FIG. 2 is reduced by 0.1% compared to the charging delay present in prior art boosters in FIG. 2. When the switching transistor 230 is closed, current will also begin to accumulate in the primary inductor 210. When the circuit returns to the normal power supply by opening 230 and closing 220, this inductor current will recharge the capacitor 240. By alternating between the normal power supply (220 closed, 230 open) and the boost power supply (220 open and 230 closed) quickly enough, a relatively small capacitance value 240 can be used while avoiding significant discharge, which is different from conventional flying capacitor power multipliers ( Figure 1a This is a significant advantage compared to the prior art.

[0070] In addition to the above functionality, there is also an increase in the average voltage on the flying capacitor depending on the duty cycle of the two switching phases, following a similar relationship as other switching converters. Examples of the voltage and current waveforms involved are shown in Figures 3a to 3c middle.

[0071] Various extensions of this concept are possible. First, the boost stage can be loaded with multiple amplifiers in parallel, an example with two amplifiers (60a and 60b) is shown in FIG. Figure 4 Similar techniques can be used with Figure 1b However, in the case of a conventional booster, all amplifiers will automatically use the higher supply, even if their outputs do not require the higher supply, resulting in more power consumption. Figure 4 In the proposed topology, the rail voltage on 215 is at normal supply during part of the cycle, and at boosted voltage during another cycle. The switching scheme can be arranged so that any amplifier that only needs to produce a smaller output voltage can switch its transistor to rail 215 when it is at normal supply, while those amplifiers that need a higher output voltage use rail 215 when it is boosted.

[0072] Boost stage control

[0073] The signals controlling the switching behavior in boosters 220 and 230 may be derived based on the input signal by pulse width modulation techniques, possibly by compensating for nonlinear pulse width to voltage relationships, similar to what is done, for example, for conventional boost circuits. As is customary in switching power converters, in order to better control the output signal, the output voltage 215 and / or the current in inductor 255 may be sensed and fed back to controller 250, such as Fig. 9 . For voltage and / or current sensing, any of a variety of methods known in the art of power conversion may be applied. The controller 250 itself may be an analog circuit or a digital controller. A digital controller, such as that described in [WO2017 / 179974], first digitizes the sensed signal with an analog-to-digital converter, and then uses a digital control algorithm to generate a pulse width modulated (PWM) signal. Regardless of the method of control, once the PWM signal is generated, it needs to be converted into the appropriate voltage level to control the switch, which is usually done in a so-called gate driver circuit 260.

[0074] Another option is to cascade multiple boost stages, such as Figure 5 . In this cascade, the output (215a) of the first boost stage (100a) is connected to the power input of the second boost stage (100b), which in turn generates a local power supply (215b) for the amplifier. With such a cascade, a higher boost factor is more easily achieved than with a single boost stage. When the boost mode of both stages is in progress simultaneously, then the external power supply can be tripled at the beginning of the boost mode, where once the capacitors are charged to a higher value, a higher boost factor is possible. Alternatively, when the boost mode and base mode of both stages are alternating, the amplifier power supply (215b) can obtain a boosted power supply for a longer time.

[0075] Another embodiment of the boost stage is shown in Figure 6 In this embodiment (101) is the inverting negative side equivalent of the power booster (100). Instead of boosting the power supply, the flying capacitor (241) is now used to boost the low side of the amplifier power supply (226). In basic mode, the switch (231) connects the low side of the amplifier (226) to the ground (35). In boost mode, the switch (231) is opened and the switch (221) is closed, pushing the low side (226) below the ground with a voltage equal to the stored voltage on the capacitor (241), while charging the capacitor (241) via the inductor (211) connected to the external power supply (5).

[0076] The combination of the high-side booster (100) and the low-side booster (101) produces Figure 7. This embodiment enables boosting of both sides of the power supply of the amplifier (60), which not only enables a larger boost factor, but also enables a more balanced behavior because the voltages at both ends of the load (110) can also change in opposite directions during the boost mode. Such balanced or differential behavior can reduce electromagnetic interference (EMI) generated by the amplifier.

[0077] Through from Figure 7 Another amplifier embodiment implemented by combining a high-side boost and a low-side boost is a single-ended amplifier, such as Figure 8 . A single-ended amplifier (61) typically requires a positive supply voltage and a negative supply voltage to be able to generate a positive output voltage and a negative output voltage. By means of a low-side boost stage (101), a negative supply voltage (226) can be generated as required. The high-side boost stage (100) also achieves a positive output voltage that is higher than the external power supply (5). It is also possible to omit the high-side boost stage (100) and connect the amplifier power supply (215) directly to the external power supply (5), but the highest positive voltage on the load will be limited by the power supply.

[0078] Other combinations of the various embodiments are of course possible, for example in a symmetrical configuration (such as Figure 7 or Figure 8 cascade of boosters (such as Figure 5 ), or using multiple amplifiers in a symmetrical configuration (such as Figure 4 middle).

[0079] Another option is to sense Fig.10 , and use those signals 105 and 115 as indirect indications of the rail voltages.

[0080] like Fig.11 , even better results can be achieved when the same controller controls both the boost stage and the amplifier signal itself, because this controller knows when the boost stage is active and how much it can adapt the pulse width sent to the switching amplifier at this duty cycle. To further enhance its behavior, this controller may sense not only the output voltages 105 and 115, but also the rail voltage 215 and / or the current through the inductor ( Fig. 9 signal 255 in ).

Claims

1. A boost stage circuit (100) for a power amplifier, comprising: an electrical connector (5) for an external power supply, at least one capacitor (240) having a first side and a second side, the capacitor being electrically connected at its first side to a first side of at least one first switch (220) and being electrically connected at its second side to a first side of at least one second switch (230), wherein each of the at least one first switch (220) and each of the at least one second switch (230) are adapted to operate at a switching frequency of >20 kHz, wherein each individual of the at least one first switch (220) and the at least one second switch (230) and the second side of the respective switch are adapted to be electrically connected to the electrical connector (5), and wherein in a boost mode, the at least one first switch (220) is in an open state and the at least one second switch (230) is in a closed state, and wherein in a base mode, the at least one first switch (220) is in a closed state and the at least one second switch (230) is in an open state, at least one inductor (210) electrically connected at one side to (i) the second side of the capacitor (240) and (ii) to the first side of the at least one of the second switches (230), and at another side to (iii) ground, wherein the at least one inductor (210) has an inductance of 1 µH to 20 H, The inputs (261, 262) are adapted to receive control inputs from a controller for operating the at least one first switch (220) and the at least one second switch (230), respectively, and A controller for operating the at least one first switch and the at least one second switch (220, 230).

2. The boost stage circuit according to claim 1, wherein the at least one first switch and the at least one second switch (220, 230) are each individually selected from transistors, the transistors comprising: NMOS transistor, PMOS transistor, bipolar transistor, IGBT.

3. The boost stage circuit of claim 1, wherein the at least one capacitor (240) is each individually selected from a ceramic capacitor, a filled capacitor, an electrolytic capacitor, a non-polarized capacitor, a multilayer capacitor having a capacitance of 10 pF to 10000 µF, and combinations thereof.

4. The boost stage circuit of claim 1, wherein the at least one inductor (210) is each individually selected from an air core inductor, a ferromagnetic core inductor, a variable inductor, a choke, a solenoid, and combinations thereof.

5. The boost stage circuit according to claim 1, wherein each individual one of the at least one first switch (220) and the at least one second switch (230) is adapted to operate at a switching frequency of 50 kHz to 2.4 GHz. 6 . The boost stage circuit of claim 1 , further comprising a feedback loop, wherein the feedback loop comprises a feedback filter.

7. The boost stage circuit of claim 1, further comprising a clock, wherein the clock is adapted to provide a clock frequency >50 kHz.

8. The boost stage circuit according to claim 1, further comprising a rectifier connected in parallel to the at least one first switch (220) or the at least one second switch (230).

9. An external supply voltage power amplifier (60) comprising at least one boost stage circuit according to any one of claims 1 to 8, wherein the power amplifier is selected from an audio amplifier, a hearing aid amplifier, a motor control amplifier, a variable power supply unit and a time-varying power supply.

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