Doherty multi-band power amplifier

Abstract

The invention relates to a Doherty amplifier comprising: - an input port; - a pre-amplification stage; - at least one output port; characterized in that the Doherty amplifier further comprises: - a high-band amplification channel; - a low-band amplification channel; the high-band amplification channel (HAB) and the low-band amplification channel each comprising a main amplifier, an auxiliary amplifier, and an output impedance matching network; - a common network connected to the high-band amplification channel and the low-band amplification channel, the common network comprising a switch configured to selectively activate either the high-band amplification channel or the low-band amplification channel; wherein an intermediate impedance matching network is distributed between the common network, the high-band amplification channel, and the low-band amplification channel. Figure for the abstract: Fig. 1

Description

Title of invention: Multi-band Doherty power amplifier Technical field

[0001] The present invention relates to a multi-band Doherty power amplifier. The invention is particularly applicable to telecommunications equipment usable in mobile telephone networks or in WiFi networks.

[0002] Modern communication standards such as 4G / 5G / 6G and WiFi6 / 6E / 7 significantly increase the complexity of RF front-end modules, of which the power amplifier represents a critical part, in terms of size and power consumption.

[0003] Indeed, the need for reduced energy consumption with reduced size and manufacturing cost is driving research towards high-efficiency, high-integration multi-band power amplifiers with high linearity requirements.

[0004] The signals used in the 4G / 5G / 6G and Wifi6 / 6E / 7 standards have high peak-to-average power ratios (PAPR) (greater than 4 dB), due in particular to the presence of a large number of modulated subcarriers in these OFDM type communication systems.

[0005] With a high PAPR, it is all the more necessary to lower the power level of the power amplifier relative to the peak power ("back-off" according to English terminology), in order to meet strict linearity specifications.

[0006] More specifically, power back-off is a power level below the saturation point that allows the amplifier to operate in a linear region. Typically, power amplifiers operate near the saturation point because this is where efficiency is highest. To ensure that the amplifier operates in the linear region, the power level is lowered from the point of maximum efficiency. The power reduction level is called power back-off.

[0007] In state-of-the-art power amplifiers, power reduction significantly degrades the average efficiency of the power amplifier. Thus, in addition to the power amplifier having to maintain high efficiency despite power back-off, the power amplifier must also be broadband or multi-band in order to support an increased number of frequency bands.

[0008] The Doherty power amplifier represents an interesting solution for a efficient amplification of high PAPR signals. The operating principle of the Doherty amplifier is illustrated in [Fig.l], and in more detail in [1]. The input signal RF1N is pre-amplified by a pre-amplification stage 1, and the signal is separated by a power divider 5. The Doherty amplifier comprises a main amplifier 2, an auxiliary amplifier 3, an impedance matching circuit 6 at the input of the main amplifier 2 and the auxiliary amplifier 3, and an output impedance matching circuit 4 comprising a quarter-wave line acting here as an impedance inverter. It is possible to consider other types of combiners which do not necessarily use a quarter-wave line. The impedance matching circuit 6 applies a predetermined phase compensation between the main chain and the auxiliary chain.An output matching network (not shown) can optionally transform the system load impedance (typically 50 Ohm) into an optimal operating impedance.

[0009] The Doherty power amplifier uses the concept of active (or dynamic) load modulation, in which the load seen by the main amplifier 2 is modulated by injecting a current from the auxiliary amplifier 3. The main amplifier 2, conventionally operating in class AB, is always active, while the auxiliary amplifier 3, conventionally operating in class C or deep AB, contributes only in the backoff region.

[0010] Doherty power amplifiers generally have a limited optimal operating band (fractional band FBW < 10%) and require precise phase control at the impedance matching circuit 6 to maintain high performance (efficiency and linearity) over the target frequency band.

[0011] The fractional operating band is given by the following relation:

[0012] FBW=(Fmax-Fmin) / Fcentral

[0013] With Fmin the minimum frequency of the operating band, Fmax the maximum frequency of the operating band, and Fcentral the central frequency.

[0014] To overcome the performance degradation of Doherty power amplifiers over a high frequency range, tunable Doherty power amplifier architectures have recently been introduced.

[0015] In [2], a Doherty power amplifier architecture having a wide frequency band (1.55 - 2.3 GHz) comprises several tunable capacitors. The amplifier requires the use of a digital (external) pre-distortion technique, in order to maintain the required level of linearity over the entire frequency band, which is detrimental to the energy efficiency of the system.

[0016] In [3], an alternative Doherty power amplifier architecture has linear behavior over the 1.9 GHz - 2.7 GHz band without requiring a digital pre-distortion. The amplifier includes integrated SOLCMOS tunable capacitors, which improves frequency linearity. However, the FBW operating bandwidth remains below 25%.

[0017] There is therefore a need to provide a linear Doherty power amplifier having an improved fractional FBW operating bandwidth, and not using a digital pre-distortion technique. Summary of the invention

[0018] An object of the invention is therefore a Doherty amplifier comprising: - an input port, configured to receive an input RF signal to be amplified; - a pre-amplification stage configured to partially amplify the input RF signal; - at least one output port for the amplified RF signal; characterized in that the Doherty amplifier further comprises: - a high-band amplification channel, adapted to amplify the input RF signal whose operating frequency band is in a so-called upper frequency band; - a low-band amplification channel, adapted to amplify the input RF signal whose operating frequency band is in a so-called lower frequency band; the high band amplifier path and the low band amplifier path each comprising a main amplifier, an auxiliary amplifier, and an output impedance matching network connected to the main amplifier, the auxiliary amplifier, and the output port; - a common network connected to the high band amplification path and to the low band amplification path, the common network comprising a switch configured to selectively activate the high band amplification path or the low band amplification path; in which an intermediate impedance matching network, connected between the pre-amplification stage and each of the main and auxiliary amplifiers, is distributed between the common network, the high band amplification path and the low band amplification path.

[0019] Advantageously, in each of the high band and low band amplification paths, the intermediate impedance matching network comprises a first tunable resonant network connected to the grid of the main amplifier and configured to introduce a first predefined phase shift, and a second tunable resonant network connected to the grid of the auxiliary amplifier and configured to introduce a second predefined phase shift, the value of the first phase shift and the value of the second phase shift being determined so that their difference has a predefined value in the back-off region of the Doherty amplifier, the second tunable resonant network of the high band amplification path comprising an additional inductance compared to the second tunable resonant network of the low band amplification path.

[0020] Advantageously, the difference is optimized to maximize the efficiency and overall linearity of the amplifier.

[0021] Advantageously the difference is equal to 90°.

[0022] Advantageously, the first tunable resonant network and the second tunable resonant network comprise variable capacitors.

[0023] Advantageously, each variable capacitor comprises a fixed-capacitance capacitor, a set of coarse-adjustment capacitors and a set of fine-adjustment capacitors, the set of coarse-adjustment capacitors and the set of fine-adjustment capacitors being made up of several branches of capacitors, each capacitor being connected to a stack of transistors in order to weight the value of the coarse adjustment or the fine adjustment respectively.

[0024] Advantageously, the intermediate impedance matching network comprises a power divider composed of a first resonant circuit arranged in the common network, a second resonant circuit arranged in the high band amplification path, and a third resonant circuit arranged in the low band amplification path.

[0025] Advantageously, the third resonant circuit comprises a variable resistor.

[0026] Advantageously, the pre-amplification stage comprises: - a first floor; - an input impedance matching network configured to match the input impedance of the first stage to a predefined value; - a second stage connected directly to the intermediate impedance matching network; - a second input impedance matching network connected between the first stage and the second stage.

[0027] Advantageously, the second input impedance matching network comprises a second harmonic filter.

[0028] Advantageously, the first stage and / or the second stage comprise a common grid assembly and a common source assembly, according to a cascode type assembly.

[0029] Advantageously, a feedback circuit, comprising a capacitor and a variable resistor, is connected between the drain of the transistor mounted as a common gate and the gate of the transistor mounted as a common source in the first stage, the value of the variable resistance being adjusted according to the activated amplification channel.

[0030] Advantageously, the main amplifier and the auxiliary amplifier of the high band amplification channel and of the low band amplification channel comprise LDMOS type transistors.

[0031] Advantageously, the output matching network of the high band amplification channel and the output matching network of the low band amplification channel each comprise an output combiner, connected directly to the main amplifier and to the auxiliary amplifier.

[0032] Advantageously, the output combiner comprises an impedance inverter. Description of figures

[0033] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended drawings given by way of example.

[0034] [Fig. 1], already described, illustrates the operating principle of a Doherty power amplifier.

[0035] [Fig.2a] and [Fig.2b] illustrate detailed views of an amplifier circuit of Doherty power according to the invention, and [Fig.2c] illustrates a variant of [Fig.2b].

[0036] [Fig.3] illustrates different performances obtained with the Doherty power amplifier circuit according to the invention.

[0037] The Doherty amplifier according to the invention is illustrated by Figures 2a, 2b and 2c.

[0038] The input port PE receives the input RF signal RF^ to be amplified. A pre-amplifier stage PRA amplification is used to amplify the RF input signal to increase the overall gain of the Doherty amplifier.

[0039] A common network RCO, which includes a switch SW, is connected to the output of the pre-amplification stage PRA. The common network RCO is also connected to a high-band amplification path VAHb and to a low-band amplification path VAlb. The switch SW can selectively activate the high-band amplification path VAHb or the low-band amplification path VALB depending on the carrier frequency of the input RF signal. The Doherty amplifier also includes external means for adjusting the bias signals for the transistors depending on whether the high-band amplification path VAHb or the low-band amplification path VALB is selected.

[0040] For this purpose, the switch SW comprises an input terminal BE, connected to the pre-amplification stage PRA, and two output terminals. An output terminal BS1 is connected to the high band amplification channel VAHB, and an output terminal BS2 is connected to the low band amplification channel VALB. An example of a usable switch is an SPDT (for "Single Pole Double Throw") type switch with one input and two outputs.

[0041] The selection of one or other of the amplification channels of the Doherty amplifier is carried out automatically based on knowledge of the carrier frequency of the signal to be amplified.

[0042] For example, switching between the amplification paths can be performed dynamically, i.e. while the Doherty amplifier is in use. According to another embodiment, the Doherty amplifier, integrated in telecommunications equipment (for example a base station or a user terminal), can control switching between the amplification paths depending on the movement of the user and / or the change of cell of the user.

[0043] Switching from one amplification channel to another can be controlled by a control device (not shown in the figures).

[0044] The high-band amplification channel VAHB is adapted to amplify the input RF signal RF1N whose operating frequency band is in a so-called upper frequency band. According to the operating principle of the Doherty amplifier recalled previously, the high-band amplification channel VAHb comprises a main amplifier APHB operating in class AB, and an auxiliary amplifier AAHB operating in class C or deep AB. Furthermore, the high-band amplification channel VAHb comprises an output impedance matching network OMNhb connected to the main amplifier APHb, to the auxiliary amplifier AAHb, and to the output port PSI at which the amplified signal is taken. The recombination of the signals from the main and auxiliary amplifiers takes place at node A.

[0045] The main / auxiliary amplifier can consist of a transistor (LDMOS type transistor in figures 2a and 2b but another type of transistor can be used), a stack of transistors (case of driver stages, but this could also be the case for the output stage), or a combination of transistors.

[0046] Advantageously, the main amplifier and the auxiliary amplifier of each channel comprise LDMOS (laterally-diffused metal-oxide semiconductor) type transistors, which offer a high breakdown voltage (greater than 10 Volts), which is necessary for applications requiring high output powers (> 1W) such as mobile phones or telecommunications base stations. Other technologies can be considered for the transistors of the power stage, in particular stacked transistors of the MOS+MOS or MOS+LDMOS type, BiCMOS or GaAs, GaN or InP transistors.

[0047] According to one embodiment, the output of the main amplifier APHb (transistor drain) is connected to the output of the auxiliary amplifier AAHB (transistor drain) via a lumped element pi-network type impedance inverter equivalent to a quarter-wave line. The impedance inverter is composed of a capacitor Cinvmi connected between the output of the main amplifier APHB and ground, of a capacitor Cinvai connected between the output of the auxiliary amplifier AAhb and ground, and of a coil Linvi connecting the two outputs of the main amplifier APHB and the auxiliary amplifier AAHB.

[0048] The output combiner may adopt a different topology, such as a topology described in [4].

[0049] The capacitors Cinvmi and Cinvai, and the coil Linvi are dimensioned so that the characteristic impedance Zc of the impedance inverter is equal to Zc = 2 x Zopt, with Zopt the optimal load impedance at node A which corresponds to the output of the auxiliary amplifier AAHB.

[0050] The output network OMNHB comprises a coil LSUpmi connected between the external supply voltage source Vdd of the main amplifier APHB and the output of the main amplifier APHB. Similarly, a coil LSUpai is connected between the external supply voltage source Vdd2 of the auxiliary amplifier AAHB and the node A.

[0051] An adjustable resonant network, composed of a coil LH2Oi and a variable capacitor CH2oi, is connected between node A and ground. This resonant network constitutes an adjustable harmonic termination which is used to improve the rejection of the second harmonic with respect to the fundamental frequency.

[0052] The LC filter composed of a coil LSoi, a capacitor CSoi, the capacitor C pol and the coil Lpoi, is part of the output adaptation network at the fundamental frequency.

[0053] The low-band amplification channel VALB is adapted to amplify the input RF signal RF1N whose operating frequency band is in a so-called lower frequency band. It comprises an output impedance matching network of the low-band amplification channel 0MNLB which may be identical (but not necessarily) to the output impedance matching network of the high-band amplification channel 0MNHB, the dimensioning of the components possibly being different from one channel to another.

[0054] The Doherty amplifier includes a PSI output port for the high band amplification path VAHB and a PS2 output port for the low band amplification path VAlb. The PSI output port of the high band amplification path VAHB can be connected to an antenna or an antenna selection switch, and the PS2 output port of the low band amplification path VALB can be connected to a different antenna or an antenna selection switch.

[0055] The upper frequency band and the lower frequency band are preferably disjoint. For example, the components of the high band amplification path VAhb can be sized to amplify the input signal in the band 2.1-2.7 GHz operating band, while the components of the VALB low band amplifier path can be sized to amplify the input signal in the 1.7-2.1 GHz operating band.

[0056] The Doherty amplifier according to the invention comprises an intermediate impedance matching network ISMN2, connected between the pre-amplification stage PRA and each of the main (APHB, APLB) and auxiliary (AAHB, AALB) amplifiers. The intermediate impedance matching network ISMN2 makes it possible to present an optimal source impedance to each of the amplifiers. It is advantageously distributed between the common network RCO, the high-band amplification path VAHB and the low-band amplification path VALB. Thus, some of the components of the intermediate impedance matching network ISMN2 are part of the common network RCO, while other components of the intermediate impedance matching network ISMN2 are part of the high-band amplification path VAHB and the low-band amplification path VALB.

[0057] The design of the intermediate impedance matching network ISMN2 represents a critical aspect in order to obtain good RF performance for the Doherty amplifier. Indeed, it must present both an optimal source impedance for the output stages and an optimal load impedance for the pre-amplification stage.

[0058] The fact that part of the components of the intermediate impedance matching network ISMN2 is part of the common network RCO, between the preamplification stage PRA and the switch SW, makes it possible to reduce the size of the chip on which the Doherty amplifier is etched.

[0059] Thus, the power divider stage, which makes it possible to distribute the signal power between the main amplifier APHB and the auxiliary amplifier AAHB, comprises a first resonant circuit LC1 arranged in the common network RCO, a second resonant circuit RC2 arranged in the high band amplification path VAHB, and a third resonant circuit RC3 arranged in the low band amplification path VALB.

[0060] The first resonant circuit LC1 comprises a capacitor CCd connected between the output of the pre-amplification stage PRA and the input terminal of the switch SW, and an inductor Ldiv connected between the input terminal of the switch SW and ground.

[0061] The second resonant circuit RC2 comprises two capacitors (Cdivn, Cdivi2) connected in parallel across the resistor Rdivi. Both capacitors are connected to the output terminal of the switch SW which activates the high band amplification path VAHB. The capacitor Cdivn is on the main amplifier branch APHB, and the capacitor Cdivi2 is on the auxiliary amplifier branch AAhb. An inductor Lpai is connected between the capacitor Cdivi2 and ground. The resistor Rdivi connects the capacitors (Cdivn, Cdivi2) connected in parallel. The resistor Rdivi can be a variable resistor, in order to adjust the amplitude and phase on the path VAHB high band amplification.

[0062] The shared inductance Ldiv thus forms a modified Wilkinson divider with the capacitors Cdivn and Cdivi2 and the resistor Rdivi when the high band amplification channel VAhb is activated and with the capacitors Cdiv2i and Cdiv22, and the resistor Rdiv2 when the low band amplification channel VALB is activated.

[0063] The third resonant circuit RC3 comprises two capacitors (Cdiv2i, Cdiv22) connected in parallel across the resistor Rdiv2. The two capacitors are connected to the output terminal of the switch SW which activates the low band amplification path VALB. The resistor Rdiv2 connects the capacitors (Cdiv2i, Cdiv22) connected in parallel.

[0064] According to one embodiment of the invention, in the high band amplification path VAhb, a first tunable resonant network RRA1HB is connected to the grid of the main amplifier APHB and configured to introduce a first predefined phase shift <e>m. For this purpose, the first tunable resonant network RRA1Hb comprises an inductor Lpmi, connected between the second resonant circuit RC2 and ground, and a variable capacitor Csmi connected between the second resonant circuit RLC2 and the grid of the main amplifier APHB.

[0065] Similarly, in the high band amplification path VAHB, a second tunable resonant network RRA2HB is connected to the grid of the auxiliary amplifier AAHB and configured to introduce a second predefined phase shift <e>a. For this purpose, the second tunable resonant network RRA2LB comprises an inductor Lpai, connected between a node B1 and ground. Node B1 connects the second resonant circuit RC2 to the gate of the auxiliary amplifier AAHB via a variable capacitor Csa[ connected in series with an inductor Lsai. A capacitor Cpai is connected between an intermediate point located between the variable capacitor Csa[ and the inductor Lsai, and ground.

[0066] The first tunable resonant network RRA1HB is sized and adjusted so that it presents the optimal source impedance to the main amplifier APHB while introducing the first predefined phase shift <e>m. Similarly, the second tunable resonant network RRA2HB is sized and adjusted so that it presents the optimal source impedance to the auxiliary amplifier APLB while introducing the second predefined phase shift <e>has.

[0067] In the low-band amplification path VALB, a first tunable resonant network RRA1lb is identical to the first resonant network RRA1Hb of the high-band amplification path VAHb. The first tunable resonant network RRA1LB introduces a first predefined phase shift <e>m.

[0068] In the low band amplification path VALB, a second tunable resonant network RRA2lb is connected to the grid of the auxiliary amplifier AALB and configured to introduce a second predefined phase shift df, to the RF signal. For this purpose, the second tunable resonant network RRA2LB comprises a variable capacitor Csa2 connected in series with an inductor Lsa2. A capacitor Cpa2 is connected between an intermediate point located between the variable capacitor Csa2 and the inductor Lsa2, and ground.

[0069] According to a particularly advantageous embodiment, the second tunable resonant network RRA2LB of the low-band amplification channel VALB does not comprise an inductance connected between the node B2 and the ground. The second tunable resonant network RRA2LB of the low-band amplification channel VALB thus comprises one less inductance (or coil) than the second tunable resonant network RRA2HB of the high-band amplification channel VAHB.

[0070] Indeed, the switch SW does not provide perfect isolation between the high band amplification path VAHB and the low band amplification path VALB. When the low band amplification path VALB is activated, the intermediate impedance matching network ISMN2 is capable of forming the required impedance and phase level taking into account the parasitics of the inactive path (i.e. the high band amplification path VAHB). The variable capacitors of the amplification paths and the bias voltages of the transistors can also be adjusted so that the performances are optimized according to the target frequency. The resistor Rdiv2 of the third resonant circuit RC3 can be a variable resistor, which makes it possible to adjust the required amplitude and phase levels taking into account the parasitics of the inactive path.

[0071] Thus, the parasitic impedance of the high band amplification channel VAHB makes it possible to do without an additional bulky inductance in the second tunable resonant network RRA2LB of the low band amplification channel VALB.

[0072] This is particularly advantageous for use of the Doherty amplifier in size-constrained applications such as mobile phones, connected objects or small access points (“small cells”).

[0073] In the high band amplification channel VAHB and in the low band amplification channel VALB, the value of the first phase shift <e>m and the value of the second phase shift <e>a are determined so that their difference has a predefined value in the back-off region of the main amplifier (APHB, APLB) and the auxiliary amplifier (AAHB, AALB).

[0074] The phase difference = <e> m - <e>a is optimized to ensure optimal load modulation and power combination, at node A, in the back-off region (0diff approximately equal to 90° in theory). At a given frequency, the difference depends on the power due to the non-linearity of the input impedances of the main amplifier and the auxiliary amplifier. These impedances input, as well as the transfer function of the intermediate impedance matching networks, vary with frequency. These effects induce a variation in Odiff and degrade the performance of the Doherty amplifier. To avoid such degradation, Odiff is optimized and readjusted in the back-off region (typical back-off value of 4 to 8 dB for mobile applications).

[0075] In each of the amplification paths, the baseband impedances at the gate and drain of the main amplifier and the auxiliary amplifier introduce a memory effect and cause a degradation of the linearity performance. To mitigate this effect, the main amplifier and the auxiliary amplifier are biased via a parallel LC resonator (Ltankll-Ctanku, Ltankl2-Ctanki2, Ltank21-Ctank2j, L tank22-Ctank22,) connected to the gate of the transistors.

[0076] According to one embodiment, the pre-amplification stage PRA (or "driver" according to English terminology) comprises two stages connected in cascade, with a first amplifier stage DRV1 and a second amplifier stage DRV2 (connected to an external power source via an inductance L supd), in order to maintain a high power gain (typically of the order of 30 dB) for all operating frequencies in high and low bands (a power gain of 30 dB or higher can be obtained with two pre-amplification stages, compared to less than 30 dB with a single pre-amplification stage). Indeed, when the high band amplification path VAHb is activated, the power gain can be reduced, due to the intrinsic gain characteristics of the transistors (for a given output power and therefore a given transistor size).

[0077] The second amplifier DRV2 is connected directly to the intermediate impedance matching network ISMN2, in particular to the capacitor CCd of the common network RCO.

[0078] The first amplifier DRV 1 and / or the second amplifier DRV2 advantageously comprise a common gate transistor (T1 1, T12) and a common source transistor (T21, T22), according to a cascode type assembly. This topology makes it possible to maximize the overall gain of the Doherty amplifier.

[0079] In the first stage DRV 1 and in the second stage DRV2, a MOS transistor (for example of the body-contact BC-MOS type in SOI technology) can be used for the common source transistor (T21 and T22), and an LDMOS transistor can be used for the common gate transistor (T1 1 and T12). This embodiment is however not exclusive, and it can be envisaged to use the LDMOS transistor for all the transistors of the pre-amplification stage PRA.

[0080] It is also possible to consider other types of transistors or combinations of transistors.

[0081] The PRA pre-amplification stage also includes a matching network input impedance IMN configured to adapt the input impedance of the first stage DRV1 to a predefined source impedance value (typically 50 Ohm). For this, a capacitor CIO, connected to the input port PE, is connected to the gate of the common source T21 via a capacitor C15. An inductor L11 is connected between an intermediate point located between the two capacitors, and ground. The gate of the common source T21 is biased via a resistor R14. The common gate T11 is biased via a resistor R12. A capacitor C13 is connected between resistor R12 and ground.

[0082] Similarly, the pre-amplification stage PRA comprises a second impedance matching network ISMN1 connected between the first stage DRV1 and the second stage DRV2 (inductors L16 and Lp2, resistor R19, and capacitors C17 and C18, connected in a similar manner to the components of the input impedance matching network IMN).

[0083] The second impedance matching network ISMN1 may comprise a second harmonic filter PSH, connected between the gate of the common source T22 and ground. The second harmonic filter PSH comprises an inductor LH2i in series with a capacitor CH2i, which may be adjustable in order to control the second harmonic impedance with respect to the carrier frequency.

[0084] Connecting the first amplifier DRV 1 and the second amplifier DRV2 in cascade can cause instabilities. In order to ensure stability of the first stage DRV1, a feedback circuit CRE comprising a capacitor C21 and a variable resistor R20 in series is connected between the drain of the common gate transistor T1 1 and the gate of the common source transistor T21.

[0085] The adjustment of the value of the variable resistor R20 is carried out according to the selected amplification channel.

[0086] According to one embodiment of the invention, it is also possible to use only one DRV amplifier stage, as illustrated in [Fig.2c].

[0087] According to one embodiment (in SOI technology), each of the variable capacitors used in the Doherty amplifier is composed of a fixed-value capacitor, a set of coarse-tuning capacitors and a set of fine-tuning capacitors, connected in parallel. The set of coarse-tuning capacitors and the set of fine-tuning capacitors is made up of several branches of variable capacitors, each capacitor being connected to a stack of transistors in order to weight the value of the coarse adjustment or the fine adjustment.

[0088] The quality factor (Q) of the variable capacitor defines the adjustment range TR (ratio between maximum and minimum capacitance value), and the voltage value across the capacitor determines the number of stacked transistors (N) as well as the gate width of the transistors (Wg). Several transistors are stacked to support

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[0098] the maximum voltage level in the OFF state. There are other ways to make variable capacitors depending on the integration technology considered (RF-MEMS or BST technologies for example) [Fig. 3] illustrates the simulated performance of the Doherty amplifier according to the invention, for different operating frequencies. The left column represents the input-output transmission parameter S21 (power gain, in dB) and input matching SI 1 as a function of the operating frequency. The middle column represents the power added efficiency PAE (for "Power Added Efficiency"), in percent, as a function of the output power Pout (in dBm). The right column represents the AM / AM (amplitude modulation to amplitude modulation) and AM / PM (amplitude modulation to phase modulation) linearity characteristics. According to the PAE simulations, the Doherty amplifier maintains high efficiency, and according to the AM / AM and AM / PM characteristic curves, very good linearity is achieved over the 1.7-2.7 GHz frequency range. The performance of the Doherty amplifier according to the invention can also be characterized using a figure of merit FOM defined by the following relationship: FOM = PAE + IACLRI ACLR (for "Adjacent Channel Leakage power Ratio") is defined as the ratio of the average filtered power centered on the assigned channel frequency to the average filtered power centered on an adjacent channel frequency. The added power efficiency PAE allows to characterize energy efficiency well, while the filtered average power ratio ACLR allows to characterize linearity well in the presence of an amplitude and phase modulated transmission signal. The following table also illustrates the very good efficiency and linearity performance of the Doherty amplifier according to the invention (ACLR measured for the LTE wireless communication standard, E-UTRA for “Evolved Universal Terrestrial Radio Access”): Parameterized Low band High band Unit Freq. 1.7 1.8 2.0 23 2.5 2.7 GHz Pout 28 dBm PAE 40 42.1 42.8 42.8 42.7 41.2 ACER -37.7 -36.6 -34.8 -35.7 -38 -33.8 d®c FOM 77.7 78.7 77.6 78.5 80.6 75 Thus, the Doherty amplifier makes it possible to obtain a FOM figure of merit greater than 75 over the entire 1.7-2.7 GHz band by providing an output power Pout equal to 28 dBm, without using digital predistortion.

[0099] References cited:

[0100] [1] RF Power Amplifiers for Wireless Communications, Second Edition, Steve C. Cripps, Artech House, p. 290-298

[0101] [2] P. Draxler and J. Hur, « A multi-band CMOS Doherty PA with tunable matching network », 2017 IEEE MTT-S International Microwave Symposium (IMS), Honololu, HI, USA, Jun. 2017, pp. 944 -946. doi: 10.1109 / MWSYM.2017.8058742

[0102] [3] A. Serhan et al., « A Reconfigurable SOI CMOS Doherty Power Amplifier Module for Broadband LTE High -Power User Equipment Applications », 2020 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), Los Angeles, CA, USA, Aug. 2020, pp. 79-82. doi: 10.1109 / RFIC49505.2020.9218305

[0103] [4] J. Bachi et al., « A Novel Approach for Doherty PA Design Using a Compact L- C Combiner », in IEEE Transactions on Circuits and Systems IL Express Briefs, vol. 69, no. 10, pp. 4023-4027, Oct. 2022, doi: 10.1109 / TCSII.2022.3185174< / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e> < / e>

Claims

Claims

1. Doherty amplifier comprising: - an input port (PE), configured to receive an input RF signal (RF!n) to be amplified; - a pre-amplification stage (PRA) configured to partially amplify the input RF signal (RFIX); - at least one output port (PSI, PS2) of the amplified RF signal; characterized in that the Doherty amplifier further comprises: - a high band amplification channel (VAHB), adapted to amplify the input RF signal (RF^) whose operating frequency band is in a so-called upper frequency band; - a low band amplification channel (VALB), adapted to amplify the input RF signal (RF1N) whose operating frequency band is in a so-called lower frequency band; the high band amplifier path (VAHB) and the low band amplifier path (VALB) each comprising a main amplifier (AP HB, APlb), an auxiliary amplifier (AAHB, AALB), and an output impedance matching network (OMNHB, OMNLB) connected to the main amplifier (APHB, APLB), to the auxiliary amplifier (AA HB, AAlb), and to the output port (PSI, PS2); - a common network (RCO) connected to the high band amplification path (VAhb) and to the low band amplification path (VALB), the common network (RCO) comprising a switch (SW) configured to selectively activate the high band amplification path (VAHB) or the low band amplification path (VALB); in which an intermediate impedance matching network (ISMN2), connected between the pre-amplification stage (PRA) and each of the main (APHB, APLB) and auxiliary (AAHB, AALB) amplifiers, is distributed between the common network (RCO), the high band amplification path (VAhb) and the low band amplification path (VALB).

2. Amplifier according to claim 1, wherein, in each of the high band (VAHB) and low band (VALB) amplification paths, the intermediate impedance matching network (ISMN2) comprises a first tunable resonant network (RRA1HB, RRA1LB) connected to the grid of the main amplifier (APHB, APLB) and configured to introduce a first predefined phase shift ( <bm), et un deuxième réseau résonant accordable (RRA2HB, RRA2LB) connecté à la grille de the auxiliary amplifier (AAHB, AALB) and configured to introduce a second predefined phase shift ( <e>a), the value of the first phase shift and the value of the second phase shift being determined so that their difference ( <f>diff) has a predefined value in the back-off region of the Doherty amplifier, the second tunable resonant network (RRA2hb) of the high band amplification path (VAHB) comprising an additional inductance (Lpai) compared to the second tunable resonant network (RRA2LB) of the low band amplification path (VAlb).

3. An amplifier according to claim 2, wherein the difference (Odiff) is optimized to maximize the efficiency and overall linearity of the amplifier.

4. Amplifier according to claim 3, wherein the difference (Odiff) is equal to 90°.

5. Amplifier according to one of claims 2 to 4, wherein the first tunable resonant network (RRA1Hb, RRA1lb) and the second tunable resonant network (RRA2HB, RRA2LB) comprise variable capacitors.

6. An amplifier according to claim 5, wherein each variable capacitor comprises a fixed capacitance capacitor, a set of coarse adjustment capacitors and a set of fine adjustment capacitors, the set of coarse adjustment capacitors and the set of fine adjustment capacitors being made up of several branches of capacitors, each capacitor being connected to a stack of transistors in order to weight the value of the coarse adjustment or the fine adjustment respectively.

7. Amplifier according to one of the preceding claims, in which the intermediate impedance matching network (ISMN2) comprises a power divider composed of a first resonant circuit (LC1) arranged in the common network (RCO), a second resonant circuit (RC2) arranged in the high band amplification path (VAHB), and a third resonant circuit (RC3) arranged in the low band amplification path (VALB).

8. An amplifier according to claim 7, wherein the third resonant circuit (RC3) comprises a variable resistor (Rd;V2)-

9. Amplifier according to one of the preceding claims, in which the pre-amplification stage (PRA) comprises: - a first stage (DRV1); - an input impedance matching network (IMN) configured to match the input impedance of the first stage (DRV1) to a predefined value; - a second stage (DRV2) connected directly to the intermediate impedance matching network (ISMN2); - a second input impedance matching network (ISMN1) connected between the first stage (DRV1) and the second stage (DRV2).

10. Amplifier according to claim 9, wherein the second input impedance matching network (ISMN1) comprises a second harmonic filter (PSH).

11. Amplifier according to one of claims 9 or 10, in which the first stage (DRV1) and / or the second stage (DRV2) comprise a common grid assembly (T11, T12) and a common source assembly (T21, T22), according to a cascode type assembly.

12. An amplifier according to claim 11, wherein a feedback circuit (CRE), comprising a capacitor (C21) and a variable resistor (R20), is connected between the drain of the common-gate transistor (T11) and the gate of the common-source transistor (T21) in the first stage (DRV1), the value of the variable resistor (R20) being adjusted depending on the activated amplification path.

13. Amplifier according to one of the preceding claims, in which the main amplifier (APHB, APLB) and the auxiliary amplifier (AA HB, AAlb) of the high band amplification path (VAHB) and of the low band amplification path (VALB) comprise LDMOS type transistors.

14. Amplifier according to one of the preceding claims, in which the output matching network of the high band amplification path (0MNhb) and the output matching network of the low band amplification path (0MNLB) each comprise an output combiner, connected directly to the main amplifier (APHB, APLB) and to the auxiliary amplifier (AAHB, AALB).

15. An amplifier according to claim 14, wherein the output combiner comprises an impedance inverter.< / f> < / e>

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