Amplifier power supply circuit

Abstract

The invention relates to an amplifier power supply circuit. A circuit for setting an amplifier supply voltage of an amplifier is provided. The circuit comprises a switching circuit having: a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier; and a second transistor arranged to switchably couple a second supply voltage to the supply terminal of the amplifier, where the amplitude of the first supply voltage is greater than the amplitude of the second supply voltage. The circuit further comprises a control circuit arranged to control the switching circuit to set an amplifier supply voltage at a supply terminal of the amplifier based on an output signal of the amplifier. The control circuit is configured to set the amplifier supply voltage to be substantially equal to the second supply voltage when a magnitude of a tracking voltage is less than a magnitude of the second supply voltage, and set the amplifier supply voltage to track the amplifier output signal when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage.

Description

Technical Field

[0001] The present disclosure relates to an amplifier power supply circuit configured to control a voltage supply to an amplifier. Background Art

[0002] There are many different types or classes of power amplifier circuits, each with specific advantages and disadvantages. For example, Class A amplifiers are configured to have a 360° conduction angle, meaning they amplify all input sinusoidal signals. Advantages of Class A amplifiers include simplicity and low distortion levels. However, because Class A amplifiers are always conducting, they are relatively inefficient. Class B amplifiers are similar to Class A amplifiers, but have a 180° conduction angle, meaning they only amplify half of the input sinusoidal signal. As a result, they are more efficient than Class A amplifiers, but typically have higher distortion levels.

[0003] Some specific classes of power amplifiers are configured to vary the supply voltage based on the magnitude of the amplifier's output signal. For example, a Class G amplifier can switch between two different supply voltage levels, such as on a low voltage supply, V low and high voltage power supply V high When the amplified output signal is relatively low (for example, less than V low ), the amplifier can use a low voltage supply. When the amplified output signal is relatively high (e.g., close to or greater than V low ), the amplifier can use a high voltage supply. In this way, the amplifier can be made more efficient by using a lower voltage supply whenever possible and operating only at the high power levels associated with the higher voltage supply when necessary. However, the amplifier may have a reduced level of linearity when switching between the low supply voltage and the high supply voltage, and may suffer from glitches or noise in the output signal. Class H amplifiers are similar to Class G amplifiers, but instead of switching between discrete voltage supplies, the amplifier is configured to change the supply voltage in a manner that tracks the output voltage level. For example, the amplifier can be configured to maintain a supply voltage equal to the amplified output signal plus a predetermined headroom voltage (e.g., 2V). Therefore, Class H amplifiers may be more power efficient than Class G amplifiers and may tend to have improved linearity and glitch immunity, but tend to be more complex and expensive. Summary of the invention

[0004] In a first aspect of the present disclosure, a circuit for setting an amplifier supply voltage of an amplifier is provided, the circuit comprising: a switch circuit comprising: a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier; and a second transistor arranged to switchably couple a second supply voltage to the supply terminal of the amplifier, wherein the amplitude of the first supply voltage is greater than the amplitude of the second supply voltage; and a control circuit configured to control the switch circuit to set the supply voltage of the amplifier at the supply terminal of the amplifier based on an output signal of the amplifier, wherein the control circuit is configured to set the amplifier supply voltage to be substantially equal to the second supply voltage when the amplitude of the tracking voltage is less than the amplitude of the second supply voltage, and to set the amplifier supply voltage to track the amplifier output signal when the amplitude of the tracking voltage is greater than the amplitude of the second supply voltage, and wherein the tracking voltage is based on the output signal of the amplifier.

[0005] In a second aspect of the present disclosure, a voltage power supply circuit is provided, which is configured to set an amplifier power supply voltage for a power amplifier, and the voltage power supply circuit includes: a switching circuit for switchably coupling the power supply terminal of the power amplifier between a first power supply voltage and a second power supply voltage, wherein the amplitude of the first power supply voltage is greater than the amplitude of the second power supply voltage, and the switching circuit includes: a first transistor, including a first channel terminal coupled to the first power supply voltage and a second channel terminal coupled to the power supply terminal of the power amplifier; and a second transistor, including a first channel terminal coupled to the power supply terminal of the power amplifier and a second channel terminal coupled to the second power supply voltage, wherein the first transistor and the second transistor are arranged in an anti-series configuration; and a control circuit, which is configured to control the first transistor and the second transistor based on an output signal of the power amplifier.

[0006] In a third aspect of the present disclosure, there is provided a power supply circuit configured to set an amplifier power supply voltage for an amplifier, the power supply circuit comprising: a first transistor arranged to switchably couple a first power supply voltage to a power supply terminal of the amplifier; a second transistor arranged to switchably couple a second power supply voltage to a power supply terminal of the power amplifier, wherein the magnitude of the first power supply voltage is greater than the magnitude of the second power supply voltage; and a control circuit configured to control the first transistor and the second transistor based on an output signal of the amplifier, wherein the power supply circuit is configured such that: when the magnitude of a tracking voltage is greater than the magnitude of the second power supply voltage, the first transistor is turned on and uses the first power supply voltage to set the amplifier power supply voltage equal to the tracking voltage, and the second transistor is turned off to decouple the power supply terminal of the power amplifier from the second power supply voltage; and when the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, the first transistor is turned off to decouple the power supply terminal of the power amplifier from the first power supply voltage, and the second transistor is turned on to couple the power supply terminal of the power amplifier to the second power supply voltage, and the amplifier power supply voltage is set substantially equal to the second power supply voltage, wherein the tracking voltage depends on the output signal of the amplifier.

[0007] In a fourth aspect of the present disclosure, a voltage supply circuit for setting an amplifier supply voltage of an amplifier is provided, the voltage supply circuit being configured to have a controllable operating mode, wherein the available operating modes include a voltage tracking mode or a locking mode, wherein when the operating mode is set to the voltage tracking mode, the voltage supply circuit operates to set the amplifier supply voltage based on the magnitude of the output voltage of the amplifier, and when the operating mode is set to the locking mode, the voltage supply circuit operates to set the amplifier supply voltage to a fixed voltage.

[0008] Aspects of the Disclosure

[0009] Non-limiting aspects of the present disclosure are listed in the following numbered clauses:

[0010] 1. A circuit for setting an amplifier power supply voltage of an amplifier, the circuit comprising:

[0011] Switching circuit, comprising:

[0012] a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier; and

[0013] a second transistor arranged to switchably couple a second supply voltage to a supply terminal of the amplifier, wherein the magnitude of the first supply voltage is greater than the magnitude of the second supply voltage; and

[0014] a control circuit configured to control the switch circuit to set a power supply voltage of the amplifier at a power supply terminal of the amplifier based on an output signal of the amplifier,

[0015] wherein the control circuit is configured to set the amplifier supply voltage to be substantially equal to the second supply voltage when the magnitude of the tracking voltage is less than the magnitude of the second supply voltage, and to set the amplifier supply voltage to track the amplifier output signal when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, and

[0016] Wherein the tracking voltage is based on an output signal of the amplifier.

[0017] 2. The circuit of clause 1, wherein the control circuit is configured to:

[0018] When the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, the first transistor is turned off and the second transistor is turned on, and

[0019] When the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage, the first transistor is turned on and the second transistor is turned off.

[0020] 3. The circuit of clause 2, wherein the control circuit comprises:

[0021] a first op amp coupled to the switch circuit and configured to turn on the first transistor when the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage, and to turn off the first transistor when the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage; and

[0022] A second op amp is coupled to the switch circuit and configured to turn on the second transistor when the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, and to turn off the second transistor when the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage.

[0023] 4. A circuit as described in clause 2 or clause 3, wherein the tracking voltage is equal to the output voltage of the amplifier plus a headroom voltage, or the tracking voltage is equal to the output voltage.

[0024] 5. A circuit according to any preceding clause, wherein the second transistor is arranged so that when the amplitude of the amplifier supply voltage is greater than the amplitude of the second supply voltage, the body diode of the first transistor is reverse biased to prevent current from flowing between the first supply voltage and the second supply voltage.

[0025] 6. A circuit according to any preceding clause, wherein the first transistor and the second transistor are coupled in anti-series with each other.

[0026] 7. A circuit according to any preceding clause, wherein the first transistor and the second transistor are both n-type transistors, and

[0027] wherein a drain terminal of the first transistor is coupled to the first supply voltage and a source terminal of the first transistor is coupled to a supply terminal of the amplifier, and

[0028] Wherein a drain terminal of the second transistor is coupled to a power supply terminal of the amplifier and a source terminal of the second transistor is coupled to the second power supply voltage.

[0029] 8. A circuit according to any one of clauses 1 to 6, wherein the first transistor and the second transistor are both p-type transistors, and

[0030] wherein a source terminal of the first transistor is coupled to the first supply voltage and a drain terminal of the first transistor is coupled to a power supply terminal of the amplifier, and

[0031] Wherein a source terminal of the second transistor is coupled to a power supply terminal of the amplifier, and a drain terminal of the second transistor is coupled to the second power supply voltage.

[0032] 9. A voltage supply circuit configured to set an amplifier supply voltage for a power amplifier, the voltage supply circuit comprising:

[0033] A switch circuit for switchably coupling a power supply terminal of the power amplifier between a first power supply voltage and a second power supply voltage, wherein the magnitude of the first power supply voltage is greater than the magnitude of the second power supply voltage, the switch circuit comprising:

[0034] a first transistor comprising a first channel terminal coupled to the first supply voltage and a second channel terminal coupled to a supply terminal of the power amplifier; and

[0035] a second transistor comprising a first channel terminal coupled to a power supply terminal of the power amplifier and a second channel terminal coupled to the second supply voltage,

[0036] wherein the first transistor and the second transistor are arranged in an anti-series configuration; and

[0037] The control circuit is configured to control the first transistor and the second transistor based on an output signal of the power amplifier.

[0038] 10. The circuit of clause 9, wherein the first transistor and the second transistor are both n-type transistors, and the first channel terminal is a drain terminal, and the second channel terminal is a source terminal, or

[0039] The first transistor and the second transistor are both p-type transistors, and the first channel terminal is a source terminal, and the second channel terminal is a drain terminal.

[0040] 11. A voltage supply circuit according to clause 9 or clause 10, wherein the second transistor is arranged so that when the amplitude of the amplifier supply voltage is greater than the amplitude of the second supply voltage, the body diode of the second transistor is reverse biased, thereby blocking the current flowing between the power supply terminal of the power amplifier and the second supply voltage.

[0041] 12. A voltage supply circuit according to any of clauses 9 to 11, wherein the control circuit is configured to, when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage:

[0042] turning on the first transistor so that the first transistor sets the amplifier supply voltage equal to the tracking voltage, and

[0043] turning off the second transistor to decouple a power supply terminal of the power amplifier from the second supply voltage;

[0044] The tracking voltage depends on the output signal of the power amplifier.

[0045] 13. A voltage supply circuit according to clause 12, wherein the control circuit comprises:

[0046] The first op amp includes:

[0047] a first input terminal arranged to receive said amplifier supply voltage;

[0048] a second input terminal arranged to receive the tracking voltage; and

[0049] An output terminal is coupled to a control node of the first transistor to control the first transistor.

[0050] 14. A voltage supply circuit according to claim 13, configured such that when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the first op-amp outputs a signal by an amount required to turn on the first transistor so that the amplifier supply voltage at the first input terminal is equal to the tracking voltage at the second input terminal.

[0051] 15. A voltage supply circuit according to any of clauses 9 to 14, wherein the first transistor is a p-type LDMOS transistor or an n-type LDMOS transistor.

[0052] 16. A voltage supply circuit according to any of clauses 12 to 15, wherein the control circuit is further configured to, when the magnitude of the tracking voltage is less than the magnitude of the second supply voltage:

[0053] turning off the first transistor to decouple a power supply terminal of the power amplifier from the first supply voltage, and

[0054] The second transistor is turned on to couple a power supply terminal of the power amplifier to the second supply voltage.

[0055] 17. A voltage supply circuit according to clause 16, wherein the control circuit comprises:

[0056] The second op amp includes:

[0057] a first input terminal arranged to receive said amplifier supply voltage;

[0058] a second input terminal arranged to receive the second supply voltage; and

[0059] an output terminal coupled to a control node of the second transistor so as to turn off the second transistor when the magnitude of the amplifier power supply voltage is greater than the magnitude of the second power supply voltage, and to turn on the second transistor when the magnitude of the amplifier power supply voltage is less than the magnitude of the second power supply voltage.

[0060] 18. A voltage supply circuit according to clause 16 or clause 17, wherein the second transistor is a p-type LDMOS transistor or an n-type LDMOS transistor.

[0061] 19. A voltage supply circuit as described in any of clauses 12 to 18, wherein the tracking voltage is the sum of an output voltage of the power amplifier and a predetermined headroom voltage.

[0062] 20. A power supply circuit configured to set an amplifier supply voltage for an amplifier, the power supply circuit comprising:

[0063] a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier;

[0064] a second transistor arranged to switchably couple a second supply voltage to a supply terminal of the power amplifier, wherein the magnitude of the first supply voltage is greater than the magnitude of the second supply voltage; and

[0065] a control circuit configured to control the first transistor and the second transistor based on an output signal of the amplifier,

[0066] The power supply circuit is configured such that:

[0067] When the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the first transistor is turned on and uses the first supply voltage to set the amplifier supply voltage equal to the tracking voltage, and the second transistor is turned off to decouple the power supply terminal of the power amplifier from the second supply voltage; and

[0068] When the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, the first transistor is turned off to decouple the power supply terminal of the power amplifier from the first power supply voltage, and the second transistor is turned on to couple the power supply terminal of the power amplifier to the second power supply voltage and set the amplifier power supply voltage substantially equal to the second power supply voltage,

[0069] The tracking voltage depends on the output signal of the amplifier.

[0070] 21. The voltage supply circuit of clause 20, wherein when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the control circuit is configured to turn on the first transistor by an amount required to set the amplifier supply voltage equal to the tracking voltage.

[0071] 22. A voltage supply circuit as described in clause 20 or clause 21, wherein the tracking voltage is the output voltage of the amplifier plus a predetermined headroom voltage.

[0072] 23. A voltage supply circuit for setting an amplifier supply voltage of an amplifier, the voltage supply circuit being configured to have a controllable mode of operation, wherein the available modes of operation include a voltage tracking mode or a locking mode, wherein

[0073] When the operating mode is set to the voltage tracking mode, the voltage supply circuit operates to set the amplifier supply voltage based on the magnitude of the output voltage of the amplifier, and

[0074] When the operation mode is set to the lock mode, the voltage supply circuit operates to set the amplifier power supply voltage to a fixed voltage.

[0075] 24. A voltage supply circuit according to clause 23, wherein the voltage supply circuit is to be coupled to a first supply voltage and a second supply voltage, wherein the magnitude of the first supply voltage is greater than the magnitude of the second supply voltage, and

[0076] When the operation mode is set to the voltage tracking mode, the voltage supply circuit operates to set the amplifier supply voltage to a voltage between the first supply voltage and the second supply voltage based on the magnitude of the output voltage of the amplifier.

[0077] 25. A voltage supply circuit according to clause 24, wherein the lock mode comprises a lock low mode, and when the operating mode is set to the lock low mode, the fixed voltage to which the amplifier supply voltage is set is the second supply voltage.

[0078] 26. A voltage supply circuit according to clause 24 or clause 25, wherein the lock mode comprises a lock high mode, and when the operating mode is set to the lock high mode, the fixed voltage to which the amplifier supply voltage is set is the first supply voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] By way of example only, various aspects of the present disclosure are described with reference to the following drawings, in which:

[0080] Figure 1 An example of a typical Class G amplifier is shown;

[0081] Figure 2 An example of a typical class H amplifier is shown;

[0082] Figure 3A An example schematic diagram of a voltage supply circuit according to one aspect of the present disclosure is shown;

[0083] Figure 3B Shows the representation Figure 3A An example diagram of the operation of a voltage supply circuit;

[0084] Figure 4 Shows Figure 3A A schematic diagram of an example implementation of a switching circuit for a voltage supply circuit;

[0085] Figure 5 Shows Figure 3A An example schematic diagram of an example alternative implementation of a switching circuit for a voltage supply circuit;

[0086] Figure 6 Shows Figure 3A A schematic diagram of an example of a portion of a control circuit of a voltage supply circuit;

[0087] Figure 7 Shows Figure 6 An example implementation of the control circuit portion shown;

[0088] Figure 8 Shows Figure 3Aa schematic diagram of an example of another portion of a control circuit of a voltage supply circuit;

[0089] Fig. 9 Shows Figure 8 An example implementation of the control circuit portion shown;

[0090] Fig.10 Shows Figure 3A a schematic diagram of an example implementation of a control circuit for a voltage supply circuit;

[0091] Fig.11 Shows Fig.10 An example implementation of the control circuit shown;

[0092] Fig.12 Shows Figure 3A A schematic diagram of an alternative example of a voltage supply circuit; and

[0093] Fig.13 Shows Figure 3A An example schematic diagram of a further example implementation of a control circuit for a voltage supply circuit. DETAILED DESCRIPTION

[0094] The present disclosure relates to a voltage supply circuit, which is configured to set a voltage supplied to an amplifier based on an output voltage of the amplifier. In particular, the voltage supply circuit is configured to use two fixed voltage levels V low and V high When the output voltage of the amplifier is relatively low, the voltage supply circuit is configured to set the amplifier supply voltage to V low When the amplifier output voltage is relatively high (for example, greater than V low ), the voltage supply circuit is configured to set the amplifier supply voltage to track the output pressure of the amplifier.

[0095] This behavior improves power efficiency because the power supplied to the amplifier is kept at a reasonable level for the amplifier's amplification requirements, thereby minimizing excess power usage by the amplifier. Furthermore, the voltage supply circuit is decoupled from the amplifier in that it simply sets the amplifier's supply voltage but does not affect or interact with the amplifier in any other way. As a result, considerable design freedom is achieved for the amplifier, and the voltage supply circuit can also be used to improve the power efficiency of existing amplifiers.

[0096] Figure 1 shows that at low voltage supply V DD and high voltage power supply V DD2 An example of a typical class G voltage amplifier 100 switching between. The amplifier 100 is configured to receive an input voltage V inand amplifies it to produce an amplified output voltage V out When the output voltage V out Relatively small, for example, less than V DD When the amplifier 100 is configured to be powered by a low voltage supply V DD When the output voltage V out Relatively large, for example, larger than V DD When the amplifier 100 is configured to be powered by a high voltage supply V DD2 powered by.

[0097] Figure 2 An example of a typical class H amplifier 200 is shown. In this example, the amplifier 200 receives an input current I in and amplifies it to generate an amplified output current I out The voltage V at the output of amplifier 200 is out depends on the impedance of any load at the output of amplifier 200 and I out (eg, according to Ohm's law for an ohmic load at the output of amplifier 200). Figure 2 The graph in Figure 2 shows the V out In this example, the load at the output of amplifier 200 is kept constant so that as I out The increase (between time = 100us and time = 800us) of V out The power controller 210 is configured to adjust the power supply voltage V DD To set the power supply voltage V used by the amplifier 200 DPC+ , so that it always tracks the output voltage V of amplifier 200 out (For example, by out The voltage V DD In the example shown in the figure, the power controller 210 is configured to use a fixed power supply voltage V DD To set V DPC+ To track above V out A predetermined amount (in this particular example, approximately above 2V) is applied to maintain the headroom voltage (i.e., V DPC+ Set to V out +predetermined headroom voltage).

[0098] Figure 3A FIG. 2 shows an example schematic diagram of a voltage supply circuit 300 according to one aspect of the present disclosure. The voltage supply circuit 300 is configured to output a voltage V out The amplifier supply voltage V is set at the power supply terminal 335 of the amplifier 330. supplyThe amplifier 330 can be a current amplifier or a voltage amplifier, so that the input signal Sig in It can be a current signal or a voltage signal, that is, I in or V in , and the output signal is the corresponding amplified current signal or pressure signal I out or V out In the case of a current amplifier, the output voltage V out will depend on the I of any load at the output of amplifier 330 (not shown in FIG. 3 ). out and impedance. For example, for a pure ohmic load R, the voltage V out will be equal to I out *R.

[0099] The voltage supply circuit 300 includes a switch circuit 310, which is arranged to use two supply voltages V high and V low To set the power supply voltage 335. For example, two power supply voltages V high and V low It can be a fixed supply voltage, such as a voltage rail, to which the circuit 300 can be connected. The first supply voltage V high Greater than the second power supply voltage V low As a non-limiting example, the first power supply voltage V high Can be set to 28V, the second power supply voltage V low Can be set to 12V, or the first power supply voltage V high can be set to 20V, the second supply voltage V low Can be set to 10V, or the first supply voltage V high can be set to 12V, the second supply voltage V low It can also be set to 5V, etc.

[0100] The voltage supply circuit 300 further includes a control circuit 320 configured to use the amplifier output voltage V out To control the switch circuit 310 to set the amplifier supply voltage V supply In this way, the control circuit 320 can control the switch circuit 310 to out The amplifier supply voltage V supply Set to V low and V high (including V low and V high ) between the voltages.

[0101] Figure 3B shows how the voltage supply circuit 300 is configured according to V outSet the amplifier supply voltage V supply In this example, amplifier 330 is a current amplifier, so the x-axis represents the output current I in mA. out Assume that the amplifier output load is fixed to 1kΩ, so that when I out When increasing from 0mA to 22mA, V out The voltage supply circuit 300 is configured to maintain V out With V supply At least a predetermined headroom voltage V headroom , in this example the predetermined headroom voltage is 3V (although V headroom can be any desired voltage, or in some instances can be eliminated entirely, such as V headroom =0V). In this example, V low is 12V, V high are 24V, although they can be any other suitable supply voltage.

[0102] It can be seen from the figure that when V out +V headroom Less than V low When the voltage supply circuit 300 is configured to supply Set to be essentially equal to V low (For example, 12V). When V out +V headroom Greater than V low When the voltage supply circuit 300 is configured to supply Set to track V out In this particular example, because the voltage supply circuit 300 is configured to maintain at least a predetermined headroom voltage V headroom , so V supply is set to track V out +V headloom (i.e., V supply is set equal to V out +V headroom ). In an alternative approach, where headroom voltage is not required, when V out Greater than V low When the voltage supply circuit 300 is configured to supply Set equal to V out Throughout this disclosure, the term “tracking voltage” is used when a headroom voltage is desired, which is V out +V headroom , or when headroom pressure is not desired, it is simply equal to V out .

[0103] By using V out Setting V supply , the voltage supply circuit 300 and the amplifier 330 can be implemented more directly than typical class G and class H amplifiers, and are therefore more cost-effective (as will be understood from the details later in this disclosure). In particular, because the voltage supply circuit 300 is separated or decoupled from the amplifier 330 and is configured to simply set the supply voltage provided to the amplifier 330, more design freedom is provided to the amplifier 330 compared to some class G amplifiers that perform control of the power supply level within the amplifier circuit itself. This implementation of a class G amplifier tends to increase the design complexity of the amplifier gain stage and reduce the design freedom. This also means that the voltage supply circuit 300 can be used in combination with existing amplifiers, enabling these amplifiers to achieve efficiency improvements without any redesign. In addition, because the implementation may be relatively simple, the voltage supply circuit 300 and the amplifier 330 can be integrated into a small area of ​​silicon.

[0104] In addition, the amplifier glitch immunity can be improved compared to Class G amplifiers. This is because when the tracking voltage increases to a value greater than V low , the supply voltage does not hard switch between two different levels, but instead switches from V low Smoothly transitions to track V out (like Figure 3B Similarly, when the tracking voltage drops below V low When it tracks V out Smoothly transition to a fixed level V low (like Figure 3B For example, if V out +V headroom In V low The level may even be around V low Slight oscillation above and below, then V out There should not be any significant glitches or distortion caused by changes in the amplifier supply voltage, since the V supply This is most apparent when operating the amplifier in HART mode, where a varying signal, such as a 1.2kHz / 2.2kHz frequency-shift keyed (FSK) signal, is applied to the DC V in signal. Depending on the DC bias point, the supply voltage V low and V high In a conventional Class G amplifier, this regular voltage source switching may occur at V out However, for the voltage source circuit 300 of the present disclosure, Vout Any glitches in the signal are small enough to be acceptable.

[0105] Finally, amplifier linearity can be improved compared to some Class G designs. In particular, in some Class G designs, when the supply voltage changes, the bias of key devices within the gain stage of the amplifier changes. This bias change tends to promote amplifier nonlinearity. In contrast, due to the operation of the voltage supply circuit 300 of the present disclosure, when V supply When changing, the bias conditions of key components within amplifier 330 can remain substantially unchanged. As a result, the linearity of the amplifier can be improved.

[0106] Figure 4 FIG. 4 shows an example implementation of the switch circuit 310. In this example, the switch circuit includes a first transistor 410 configured to switchably connect a first power supply voltage V high is coupled to the power supply terminal 335 of the amplifier 330, and the second transistor 420, which is configured to switchably connect the second power supply voltage V low A power supply terminal 335 is coupled to the amplifier 330 . Figure 4 The diodes shown in are the body diodes of the two transistors, rather than discrete diode components. In this example, the transistors are n-type MOSFETs, such as n-type LDMOS transistors.

[0107] Figure 5 An alternative embodiment of the switch circuit 310 is shown. In this example, the switch circuit includes a first transistor 510 and a second transistor 520. The arrangement of the two transistors is similar to Figure 4 The voltage supply circuit 300 of the present disclosure may be used in the embodiment of FIG. 1 and perform the same function, but they are p-type MOSFETs, such as p-type LDMOS transistors. Figure 4 and Figure 5 The switch circuit 310 can be implemented with either of the illustrated switch circuits 310. Both implementations of the switch circuit 310 are beneficial designs because they each include only two transistors, which minimizes cost, complexity, and space. Figure 4 The n-type implementation is particularly space-saving and can be Figure 5 However, both designs are very efficient and the choice of which to use depends on the design requirements.

[0108] In these examples, as explained in more detail later, control circuit 320 is configured to provide a voltage control circuit when the tracking voltage is less than V low When the first transistor 410, 510 is turned off and the second transistor 420, 520 is turned on, V supply Set to be essentially equal to V lowThe control circuit 320 is further configured to, when the tracking voltage is greater than V low When the second transistor 420, 520 is turned off and the first transistor 410, 510 is turned on for a certain amount, so that V supply is set equal to the tracking voltage. In both examples, the first transistor 410, 510 and the second transistor 420, 520 are coupled in anti-series with each other. In particular, Figure 4 In the example of FIG. 4 , the source of the first transistor 410 is coupled to the drain of the second transistor 420, and Figure 5 In the example of FIG. 5 , the drain of the first transistor 510 is coupled to the source of the second transistor 520. As a result, when V supply Greater than V low When the target voltage is greater than V low In this case, the body diode of the second transistor 420, 520 is reverse biased, thereby blocking the current from V supply Flow to V low As a result, V high and V low between them, thus preventing the current from V high Flow to V low .

[0109] Figures 6 to 11 Shows the Figure 4 The n-type switch circuit combines different details of the control circuit 320. Figure 6 Example details of a portion of the control circuit 320 are shown, which is arranged to control the second transistor 420 so that when the tracking voltage is less than V low When the tracking voltage is greater than V low To this end, the control circuit 320 includes a second operational amplifier (op-amp) 610 (the "first" operational amplifier will be described later). The second operational amplifier 610 is arranged to receive an amplifier supply voltage V supply And receives V at the second input low The output of the second operational amplifier 610 is coupled to the control terminal (i.e., the gate) of the second transistor 420. low Greater than V supply , the output of the second operational amplifier 610 goes high (eg, it is equal to the high-side supply voltage of the second operational amplifier 610—for simplicity, Figure 6 When V low Less than V supply , the output of the second operational amplifier 610 goes low (eg, it is equal to the low-side supply voltage of the second operational amplifier 610, such as ground—for simplicity, Figure 6 Therefore, when V supplyLess than V low When V suppy Greater than V low When the tracking voltage is greater than V low When V supply is set equal to the tracking voltage. When the tracking voltage is less than V low When the first transistor 410 is completely turned off, due to the on-state resistance of the second transistor 420, V supply In fact, it should be slightly smaller than V low As a result, when the tracking voltage is less than V low At all times, the second transistor should be kept in a fully conductive state by the second operational amplifier 610. Therefore, it should be understood that throughout this disclosure, it is said that when the tracking voltage is less than V low When V supply is set to be substantially equal to V low , which should be interpreted as meaning that V supply Set equal to V low subtract the voltage V coupled to the amplifier power supply terminal 335 and low Therefore, it can be seen that when the input of the second operational amplifier 610 is V supply and V low When the second operational amplifier 610 effectively operates to track the voltage less than V low The second transistor 420 is turned on when the tracking voltage is greater than V low The second transistor 420 is turned off.

[0110] Figure 7 An example implementation of the second operational amplifier 610 is shown. It can be seen that the second operational amplifier in this example embodiment includes four transistors 710, 720, 730 and 740, such as four MOSFETs, such as LDMOS transistors, and two current sources 750 and 760, which can be of any suitable design known to those skilled in the art. Alternatively, any other suitable operational amplifier implementation can be used.

[0111] Figure 8 4 is shown in Figure 3. This portion of the control circuit 320 is arranged to control the first transistor 410 so that when the tracking voltage is less than V low When the tracking voltage is greater than V low , turning it on is enough to turn V supplyTo this end, the control circuit 320 includes a first operational amplifier (op-amp) 810, which is arranged to receive an amplifier supply voltage V at a first input. supply and receives a tracking voltage (V out +V headroom The control circuit 320 further includes a dynamic headroom voltage generator 820, which is configured to generate a predetermined dynamic headroom voltage V headroom (e.g. 1V, 2V, 3V, etc.) added to V out , so as to set the tracking voltage at the input of the second operational amplifier 810. The headroom voltage generator 820 may be implemented in any suitable manner, examples of which will be given later in this disclosure. As previously mentioned, the headroom voltage generator 820 is optional, and if omitted, the control circuit 320 may be arranged such that the first input of the first operational amplifier 810 receives the voltage V out , so that the tracking voltage is V out .

[0112] The output of the first operational amplifier 810 is coupled to the control terminal (i.e., the gate) of the first transistor 410. supply , the output of the first operational amplifier 810 goes low (eg, it is equal to the low-side supply voltage of the first operational amplifier 810, such as ground—for simplicity, Figure 8 As previously mentioned, Figure 6 As explained, when the tracking voltage is less than V low , the second transistor 420 is controlled to be fully turned on to turn V supply Set to be essentially equal to V low Therefore, it can be seen that when the tracking voltage is less than V low When V supply Should be essentially equal to V low , causing the output of the first operational amplifier 810 to be low, and the first transistor 410 is therefore turned off. When the tracking voltage is equal to or greater than V supply The arrangement of the first op amp 810 effectively forms a servo loop with the first transistor 410 when V is equal to V. As will be well understood by those skilled in the art, an op amp is configured to set its output voltage to any voltage between the op amp supply rails in an effort to make the two input voltages equal. Therefore, when the tracking voltage increases to a value equal to or greater than V low When the second transistor 420 is turned off, the first operational amplifier 810 will set an output voltage, which causes the first transistor 410 to turn on and turn V supply Set to the amount necessary to track the voltage (until it equals V high Therefore, it can be seen that when the tracking voltage is greater than Vlow (but less than or equal to V high ), the voltage supply circuit 300 is set to V supply Set to track V out V low and V hig The voltage between h, such as Figure 3B As shown in the curve graph.

[0113] Fig. 9 An example implementation of the first operational amplifier 810 is shown. It can be seen that the first operational amplifier 810 in this example embodiment includes four transistors 910, 920, 930 and 940, such as four MOSFETs, such as LDMOS transistors, and two current sources 950 and 960, which can be of any suitable design known to those skilled in the art. Alternatively, any other suitable operational amplifier implementation can be used.

[0114] Fig.10 A representation of the control circuit 320 is shown, including a first operational amplifier 810 and a second operational amplifier 610, which are configured to operate as described above. Fig.10 As shown, when the tracking voltage is less than V low When V supply is set to be substantially equal to V low If V out Increase so that the tracking voltage is greater than V low , the first operational amplifier 410 will turn on the first transistor 410 by a certain amount, so that the first transistor 410 uses V high Come and V supply is set equal to the tracking voltage. Since the tracking voltage (and therefore V supply ) is greater than V low , so the output of the second operational amplifier 610 will completely turn off the second transistor 420 to connect the amplifier power supply terminal 335 to V low decoupling. There may be a period of time, such as when the tracking voltage is equal to V low When V is increased, both the first transistor 810 and the second transistor 610 are turned on. However, this is not a problem because due to the arrangement of the voltage supply circuit 300, the first transistor 410 increases V when the tracking voltage increases. supply With a value greater than V low , the second transistor 420 is turned off to decouple V low , and the body diode of the second transistor 420 is reverse biased to prevent current from flowing to V lowTherefore, when the current may flow from V high Flow to V low Therefore, in this case, the current of the amplifier 330 is at V high and V low shared between them, but no current is drawn from V high To V low Likewise, when the tracking voltage drops below V low When the first transistor 410 is turned off, the power supply voltage V supply is set to a stable voltage V by the second transistor 420 low Again, during a period of time, both the first transistor 410 and the second transistor 420 may be turned on, but during this period, V high and V low can share the current supply to amplifier 330, where the current from V high Flow to V low Before the condition of V exists, the second transistor 420 is turned off. Therefore, the voltage supply circuit 300 is configured to out A low value of V supply Set to be essentially equal to V low , then when the tracking voltage increases to greater than V low smoothly transitions to track V out , and similarly when V out When decreasing from a high value to a low value, it smoothly follows V out converted to be essentially equal to V low Optionally, a finite amount of hysteresis may also be employed in the control circuit 320 to help account for any offsets associated with transistor mismatches and the like.

[0115] Fig.11 An example implementation of the first operational amplifier 810 and the second operational amplifier 610 is shown. It can be seen that due to the symmetry of the two operational amplifiers, some components can perform functions within the first operational amplifier 810 and the second operational amplifier 610 (in particular, transistors 730 and 740 and current source 760 perform the same functions as transistors 930 and 940 and current source 960), so that the two operational amplifiers can be conceptually constructed by a combination of a total of six transistors and three current sources. This further improves the space efficiency of the voltage supply circuit 300 and also reduces cost and power consumption, especially for high voltage designs (i.e., at V high The amplitude is relatively large in order to handle the relatively large amplitude V out In the case, for example, at V highThe headroom voltage generator 820 in this example is implemented by a resistor between two transistors of the first operational amplifier 810 .

[0116] It should be understood that in order for the first transistor 410 to supply Set to V high The first operational amplifier 810 will need to be able to drive the gate of the first transistor 410 to a value greater than V high To achieve this, one or more current sources (and optionally Fig.11 The high-side voltage source for all current sources shown in the figure can be greater than V high This can be achieved in a number of different ways, such as using a voltage greater than V high (available) three voltage rails, or by using one or more charge pumps that can obtain the voltage V high and increases it by an amount greater than or equal to the on-threshold of the first transistor 410, for example 4V, to power the current source, etc. This arrangement is optional, and the current source may alternatively be directly from V high power supply, although this means that the maximum possible amplifier supply voltage V supply Will be V high minus the on-state voltage of the first transistor 410. This may limit the voltage supply circuit 300 to be able to operate to track V out The output voltage V out range.

[0117] Fig.12 FIG. 3 shows an example implementation of the control circuit 320 when the switch circuit includes a p-type transistor. Fig.10 The example is very similar, except that the input polarity of the first operational amplifier 810 and the second operational amplifier 610 has been reversed. In addition, optionally, the capacitor C comp can be used to couple the control terminal of the first transistor 510 to V high , so as to help compensate the servo loop formed by the first transistor 510 and the first operational amplifier 810 given the higher effective gain of the first transistor 510. As mentioned above, the state of the first transistor 510 can be controlled by the first operational amplifier 810. For simplicity and efficiency, the transistor level diagram of the control circuit 320 (equivalent to Fig.11 ), but those skilled in the art will Figure 7 , Fig. 9 and Fig.11 It is easy to understand how to implement Fig.12The first operational amplifier 810 and the second operational amplifier 610 are shown in FIG.

[0118] Optionally, the control circuit 320 can be further configured to enable setting of the locked amplifier supply voltage. This function can enable the user to set V supply locked to be essentially equal to V low (by completely turning off the first transistor 410, 510 and completely turning on the second transistor 420, 520) or V high (by fully turning on the first transistor 410, 510 and fully turning off the second transistor 420, 520), and V out For example, this may be achieved by including additional switches within the control circuit 320 that may be arranged to connect at least some of the inputs of the operational amplifiers 610, 810 to V supply and / or V out decoupled, and conversely, if the user chooses to lock to V low , couple these inputs to a fixed low voltage (such as ground or V low , or from V low Exported and less than V low voltage, such as using a voltage divider), or if the user has selected to lock to V high , couple them to a fixed high voltage (such as V high or greater than V high , such as the voltage used to supply the current sources of the operational amplifiers 610 and 810). Therefore, it can be seen that the voltage supply circuit 300 can be configured to be controllably set to operate in any of the following modes: Figure 3B The setting V supply Tracking mode; Lock low mode, where V supply is set to be substantially equal to V low ; or V supply is set to be substantially equal to V high The locked high mode can increase the versatility of the voltage supply circuit 300.

[0119] Fig.13 A schematic diagram of such an example is shown, where the signal Lock_lo can be used to lock V supply Locked to V low , or use the signal Lock_hi to lock V supply Locked to V highIn this example, the control circuit 320 further includes a NOR gate 1310, a first switch 1320, a second switch 1330, and a third switch 1340. The switches may be implemented using any suitable technology, such as transistors such as MOSFETs. The control circuit 320 is configured such that when Lock_lo is a high signal (e.g., a digital "1" such as 5V or 12V) and Lock_hi is a low signal (e.g., a digital "0", such as 0V), the NOR gate 1310 outputs a low signal to disconnect the first switch 1320 and turn V out Decoupled from the first operational amplifier 810. At the same time, the second switch 1330 is closed by the Lock_lo signal, so that the input to the first operational amplifier 810 is coupled to the ground via the dynamic headroom generator 820, so that the input to the first operational amplifier 810 is maintained at the dynamic headroom voltage V headroom (Or keep it at ground and omit the dynamic headroom generator 820). Therefore, because the headroom voltage is less than V low , so V supply will be locked at V low .

[0120] When Lock_hi is a high signal (e.g., a digital “1” such as 5V or 12V) and Lock_lo is a low signal (e.g., a digital “0” such as 0V), the NOR gate 1310 outputs a low signal to turn off the first switch 1320 and turn V out Decoupled from the first operational amplifier 810. At the same time, the third switch 1340 is closed by the Lock_hi signal, so that the input of the first operational amplifier 810 is coupled to V high Therefore, V supply will be locked at V high .

[0121] When Lock_lo and Lock_hi are both low signals (eg, digital “0”, such as 0V), the NOR gate 1310 outputs a high signal to close the first switch 1320, thereby switching V out The second and third switches are both kept open, and the control circuit 320 will be as described above with reference to FIG. Fig.12 Perform the operation as described.

[0122] In an alternative, control circuit 320 may be configured so that locking to just V low or V high is possible. For example, locking only to V high is possible, in which case the NOR gate 1310 can be omitted along with the second switch 1330, and the first switch 1320 can be controlled directly by Lock_hi. Alternatively, only locking to V lowIt is possible, in which case the NOR gate 1310 may be omitted together with the third switch 1340, and the first switch 1320 may be directly controlled by Lock_lo.

[0123] It should be appreciated that this is merely one example of how the control circuit 320 may be configured so that it can be set to a voltage tracking mode of operation, in which case it operates as previously described, or to a locked mode of operation in which V supply can be locked to V low or V high In one example, GND and V high At least one of the switches 130 and 131 may be coupled to a point between the headroom generator 820 and the input of the first operational amplifier 810 , rather than a point between the headroom generator 820 and the output of the amplifier 330 , via respective second and third switches 1330 , 1340 .

[0124] It will be easily understood by those skilled in the art that various changes or modifications may be made to the above-mentioned aspects of the present disclosure without departing from the scope of the present disclosure.

[0125] For example, although the voltage supply circuit is configured to use two supply voltages V low and V high To set the amplifier supply voltage V supply , but in an alternative arrangement three or more supply voltages may be used, for example to enable a supply of more fixed voltage levels and / or tracking between more voltage ranges.

[0126] The above example shows how the positive / high supply voltage of amplifier 330 can be controlled by voltage supply circuit 300. Additionally or alternatively, voltage supply circuit 300 can be used to control the negative / low supply voltage of amplifier 330. In one example, the positive / high supply voltage of amplifier 330 can be controlled by voltage supply circuit 300 as described above, and the negative / low supply voltage of amplifier 330 can be maintained at a fixed level, such as ground (e.g., if Sig in In an alternative example, the positive / high supply voltage of amplifier 330 may be maintained at a fixed level, such as ground, and the negative / low supply voltage of amplifier 330 may be controlled by a voltage supply circuit (e.g., if Sig in will be negative signals only). In this case, V high The amplitude can be greater than V low The magnitude (for example, V high Can be -24V, V low Can be -12V, or V highCan be -15V, V low The voltage supply circuit 300 can be configured similarly to the above example (but with appropriate polarity and device type changes to the switch circuit 310 and the control circuit 320) to provide a voltage supply when the magnitude of the tracking voltage is less than V low The magnitude of the negative / low supply voltage V supply Keep at V low , and can be configured to track voltages greater than V low When the negative / high supply voltage V supply set equal to the tracking voltage, as described above with reference to Figure 3 to Fig.12 For example, you can use Fig.11 , but the switch circuit 310 uses p-type transistors, and the transistors constituting the first operational amplifier 810 and the second operational amplifier 810 use p-type to n-type and n-type to p-type interchanges. In another alternative example, two voltage supply circuits 300 can be used, each having the same basic design and operation as the example given above, one for controlling the negative / low supply voltage of the amplifier 330 and the other for controlling the positive / high supply voltage of the amplifier 330 (for example, if Sig in can be a positive or negative signal).

Claims

1. A circuit for setting an amplifier supply voltage of an amplifier, the circuit comprising: A switching circuit, comprising: a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier; and a second transistor arranged to switchably couple a second supply voltage to a supply terminal of the amplifier, wherein the magnitude of the first supply voltage is greater than the magnitude of the second supply voltage; and a control circuit configured to control the switch circuit to set a power supply voltage of the amplifier at a power supply terminal of the amplifier based on an output signal of the amplifier, wherein the control circuit is configured to set the amplifier supply voltage to be substantially equal to the second supply voltage when the magnitude of the tracking voltage is less than the magnitude of the second supply voltage, and to set the amplifier supply voltage to track the amplifier output signal when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, and Wherein the tracking voltage is based on an output signal of the amplifier.

2. The circuit according to claim 1, wherein the control circuit is configured to: When the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, the first transistor is turned off and the second transistor is turned on, and When the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage, the first transistor is turned on and the second transistor is turned off.

3. The circuit according to claim 2, wherein the control circuit comprises: a first operational amplifier coupled to the switch circuit and configured to turn on the first transistor when the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage, and to turn off the first transistor when the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage; and A second operational amplifier is coupled to the switch circuit and is configured to turn on the second transistor when the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, and to turn off the second transistor when the magnitude of the tracking voltage is greater than the magnitude of the second power supply voltage.

4. The circuit of claim 2, wherein the tracking voltage is equal to the output voltage of the amplifier plus a headroom voltage, or the tracking voltage is equal to the output voltage.

5. The circuit of claim 1 , wherein the second transistor is arranged such that when the magnitude of the amplifier supply voltage is greater than the magnitude of the second supply voltage, the body diode of the first transistor is reverse biased to prevent current from flowing between the first supply voltage and the second supply voltage.

6. The circuit of claim 1 , wherein the first transistor and the second transistor are both n-type transistors, and wherein a drain terminal of the first transistor is coupled to the first supply voltage and a source terminal of the first transistor is coupled to a supply terminal of the amplifier, and Wherein a drain terminal of the second transistor is coupled to a power supply terminal of the amplifier and a source terminal of the second transistor is coupled to the second power supply voltage.

7. The circuit of claim 1 , wherein the first transistor and the second transistor are both p-type transistors, and wherein a source terminal of the first transistor is coupled to the first supply voltage and a drain terminal of the first transistor is coupled to a power supply terminal of the amplifier, and Wherein a source terminal of the second transistor is coupled to a power supply terminal of the amplifier, and a drain terminal of the second transistor is coupled to the second power supply voltage.

8. A voltage supply circuit configured to set an amplifier supply voltage for a power amplifier, the voltage supply circuit comprising: A switch circuit for switchably coupling a power supply terminal of the power amplifier between a first power supply voltage and a second power supply voltage, wherein the magnitude of the first power supply voltage is greater than the magnitude of the second power supply voltage, the switch circuit comprising: a first transistor comprising a first channel terminal coupled to the first supply voltage and a second channel terminal coupled to a supply terminal of the power amplifier; and a second transistor comprising a first channel terminal coupled to a power supply terminal of the power amplifier and a second channel terminal coupled to the second supply voltage, wherein the first transistor and the second transistor are arranged in an anti-series configuration; and The control circuit is configured to control the first transistor and the second transistor based on an output signal of the power amplifier.

9. The voltage power supply circuit according to claim 8, wherein the first transistor and the second transistor are both n-type transistors, and the first channel terminal is a drain terminal, and the second channel terminal is a source terminal, or The first transistor and the second transistor are both p-type transistors, and the first channel terminal is a source terminal, and the second channel terminal is a drain terminal.

10. A voltage supply circuit according to claim 8, wherein the second transistor is arranged so that when the amplitude of the amplifier power supply voltage is greater than the amplitude of the second power supply voltage, the body diode of the second transistor is reverse biased, thereby blocking the current flowing between the power supply terminal of the power amplifier and the second power supply voltage.

11. The voltage supply circuit of claim 8, wherein the control circuit is configured to: when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage: turning on the first transistor so that the first transistor sets the amplifier supply voltage equal to the tracking voltage, and turning off the second transistor to decouple a power supply terminal of the power amplifier from the second supply voltage; The tracking voltage depends on the output signal of the power amplifier.

12. The voltage supply circuit according to claim 11, wherein the control circuit comprises: A first operational amplifier comprising: a first input terminal arranged to receive said amplifier supply voltage; a second input terminal arranged to receive the tracking voltage; and An output terminal is coupled to a control node of the first transistor to control the first transistor.

13. The voltage supply circuit of claim 12 , configured such that when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the first operational amplifier outputs a signal to turn on the first transistor by an amount required so that the amplifier supply voltage at the first input terminal is equal to the tracking voltage at the second input terminal.

14. The voltage supply circuit of claim 11 , wherein the control circuit is further configured to: when the magnitude of the tracking voltage is less than the magnitude of the second supply voltage: turning off the first transistor to decouple a power supply terminal of the power amplifier from the first supply voltage, and The second transistor is turned on to couple a power supply terminal of the power amplifier to the second supply voltage.

15. The voltage supply circuit according to claim 14, wherein the control circuit comprises: The second operational amplifier comprises: a first input terminal arranged to receive said amplifier supply voltage; a second input terminal arranged to receive the second supply voltage; and an output terminal coupled to a control node of the second transistor so as to turn off the second transistor when the magnitude of the amplifier power supply voltage is greater than the magnitude of the second power supply voltage, and to turn on the second transistor when the magnitude of the amplifier power supply voltage is less than the magnitude of the second power supply voltage. 16 . The voltage supply circuit according to claim 15 , wherein the second transistor is a p-type LDMOS transistor or an n-type LDMOS transistor.

17. The voltage supply circuit of claim 11, wherein the tracking voltage is a sum of an output voltage of the power amplifier and a predetermined headroom voltage.

18. A power supply circuit configured to set an amplifier supply voltage for an amplifier, the power supply circuit comprising: a first transistor arranged to switchably couple a first supply voltage to a supply terminal of the amplifier; a second transistor arranged to switchably couple a second supply voltage to a supply terminal of the power amplifier, wherein the magnitude of the first supply voltage is greater than the magnitude of the second supply voltage; and a control circuit configured to control the first transistor and the second transistor based on an output signal of the amplifier, The power supply circuit is configured such that: when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the first transistor is turned on and uses the first supply voltage to set the amplifier supply voltage substantially equal to the tracking voltage, and the second transistor is turned off to decouple the power supply terminal of the power amplifier from the second supply voltage; and When the magnitude of the tracking voltage is less than the magnitude of the second power supply voltage, the first transistor is turned off to decouple the power supply terminal of the power amplifier from the first power supply voltage, and the second transistor is turned on to couple the power supply terminal of the power amplifier to the second power supply voltage and set the amplifier power supply voltage substantially equal to the second power supply voltage, The tracking voltage depends on the output signal of the amplifier.

19. The voltage supply circuit of claim 18, wherein when the magnitude of the tracking voltage is greater than the magnitude of the second supply voltage, the control circuit is configured to turn on the first transistor by an amount required to set the amplifier supply voltage equal to the tracking voltage.

20. The voltage supply circuit of claim 18, wherein the tracking voltage is the output voltage of the amplifier plus a predetermined headroom voltage.

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