A radio frequency power amplifier system and a method for linearizing output signals thereof

Abstract

The present disclosure relates to a radio frequency power amplifier system (200) comprising a first input port (114) and a second input port (121). The radio frequency power amplifier system (200) comprises a main amplifier (101) having an input (107) and an output (108), and a first auxiliary amplifier (102) and a second auxiliary amplifier (122) having respective inputs (109, 129) and outputs (110, 128). The radio frequency power amplifier system (200) comprises an internal load (103) connected to the output (110) of the first auxiliary amplifier (102), a feedback network (104) having an input (111) connected to the output (110) of the first auxiliary amplifier (102) and an output (112) connected to the input (109) of the first auxiliary amplifier (102). The radio frequency power amplifier system (200) further comprises a feedforward amplifier (123) having an input (124) and an output (130). The inputs (107, 129, 109) of the main amplifier and the auxiliary amplifier are interconnected with a first input port (114) at a common input node (113), the output (128) and the second input port (121) of the second auxiliary amplifier (122) are interconnected with an input (124) of a feedforward amplifier (123) at a common node (127), and the outputs (130, 108) of the feedforward amplifier (123) and the main amplifier (101) are interconnected at a common output node (125). The main amplifier (101) is a replica of the first auxiliary amplifier (102) with increased gain, and the second auxiliary amplifier (122) is a replica of the first auxiliary amplifier (102).

Description

Technical Field

[0001] The inventive concept relates to the field of radio frequency power amplifier systems. In particular, the inventive concept relates to a device capable of linearizing the relationship between its input and output signals, and a method for performing such linearization. Background Art

[0002] It is well known that the output signal from an RF power amplifier can be linearized using various techniques, such as predistortion, feedforward error correction, and feedback. These techniques are well described in textbooks and various scientific and white papers, such as the white paper entitled "Linearizing High-Power Amplifiers" by Allen Katz, Linear Technology Inc., and can be summarized as follows:

[0003] Predistortion techniques can be implemented as either analog or digital predistortion. In both approaches, the PA's behavior is characterized, and its response is compensated by intentionally distorting the signal driving the PA. If the distortion applied to the input signal is carefully chosen, the PA's output signal can become more linear. However, the main drawbacks of this technique are that initial calibration and training are typically required, and predistortion systems are often sensitive to drift, such as temperature.

[0004] Another known technique is a feedback method, which can be described by using so-called Cartesian feedback. In a Cartesian feedback system, the response from the power amplifier is down-converted and compared to the baseband IQ signal. This approach eliminates drift issues and detailed characteristics of the power amplifier transfer function. A major disadvantage of Cartesian feedback systems is stability issues and the limited bandwidth they can handle while still maintaining stable operation. Therefore, Cartesian feedback is not suitable for systems where signal bandwidths increase to hundreds of megahertz (for example, the wireless communication standard 802.11ac, which has a maximum bandwidth of 160 MHz). Cartesian feedback also increases circuit complexity and power consumption.

[0005] Linear feedback is also used to linearize power amplifiers. This technique involves running a feedback network from the power amplifier's output to its input. This method offers superior performance, but it can be difficult to achieve stability under all different load conditions.

[0006] Although the above techniques allow a certain degree of linearization, there is still a need for a technique that allows for improved linearization of power amplifier signals. Summary of the Invention

[0007] The object of the inventive concept is to provide a technique that addresses at least some of the above concerns. This object and other objects, which will become apparent hereinafter, are achieved by the method and apparatus defined in the independent claims. Preferred embodiments are defined in the dependent claims.

[0008] According to a first aspect of the inventive concept, there is provided a radio frequency power amplifier system comprising first and second input ports arranged to receive first and second input signals, respectively. The radio frequency power amplifier system comprises a main amplifier having an input and an output and first and second auxiliary amplifiers having respective inputs and outputs. The radio frequency power amplifier system comprises an internal load connected to the output of the first auxiliary amplifier, a feedback network arranged to linearize the first input signal and having an input connected to the output of the first auxiliary amplifier and an output connected to the input of the first auxiliary amplifier. The radio frequency power amplifier system further comprises a feedforward amplifier having an input and an output.

[0009] The inputs of the main amplifier and the auxiliary amplifier are interconnected with the first input port at a common input node, the output of the second auxiliary amplifier and the second input port are interconnected with the input of the feedforward amplifier at a common node, and the outputs of the feedforward amplifier and the main amplifier are interconnected at a common output node.

[0010] The main amplifier is a replica of the first and second auxiliary amplifiers with increased gain, and the second auxiliary amplifier is a replica of the first auxiliary amplifier.

[0011] The ratio of the second input signal to the first input signal is the same as the ratio of the gain provided by the second auxiliary amplifier to the gain provided by the first auxiliary amplifier.

[0012] The second auxiliary amplifier, the second input port and the feed-forward amplifier together form a feed-forward network arranged to at least partially remove deviation from the main amplifier output.

[0013] According to a second aspect of the present inventive concept, there is provided a method for linearizing an output signal of a radio frequency power amplifier system according to the first aspect. The method comprises:

[0014] A deviation from an ideal response of the first auxiliary amplifier is obtained by means of a feedback network, the deviation is isolated by removing the second input signal from the output of the second auxiliary amplifier, the isolated deviation is amplified by means of a feedforward amplifier, and the amplified deviation is added to the output of the main amplifier.

[0015] Therefore, the radio frequency power amplifier system defined in the first aspect of the inventive concept may be used to perform the method of the second aspect.

[0016] The inventive concept allows combining (i) indirect feedback to the main amplifier with (ii) feed-forward biasing to the main amplifier output, thereby allowing an improvement in the transfer function between input and output signals of a radio frequency power amplifier system.

[0017] With regard to indirect feedback (i), the feedback network arranged around the first auxiliary amplifier is connected to an internal load for which the load conditions are known and stable. Such load conditions allow stabilization of the feedback path and, therefore, linearization of the signal processed by the first auxiliary amplifier. The stable feedback path also allows an ideal response to the signal to be obtained from the first auxiliary amplifier. Since the loop gain of the feedback loop is generally not infinite, a deviation from the ideal response is also obtained. Furthermore, the interconnection at the common input node allows the input signal of the main amplifier to be identical to the input signal of the first auxiliary amplifier. Since the main amplifier represents a replica of the first auxiliary amplifier, it allows the response of the main amplifier to the input signal to be a replica of the response of the first auxiliary amplifier to the same input signal. Thus, indirect feedback allows the output signal of the main amplifier to be linearized (i.e., less distorted), but carries an amplification deviation from the ideal response of the first auxiliary amplifier, which deviation depends on the finite loop gain of the feedback loop.

[0018] Regarding the feedforward deviation (ii), the interconnection at the common input node also allows the input signal of the second auxiliary amplifier to be the same as the input signal of the first auxiliary amplifier. Since the second auxiliary amplifier is a replica of the first auxiliary amplifier, it allows the output signal of the second auxiliary amplifier to be similar to the output signal of the first auxiliary amplifier, increasing or decreasing from the output signal of the first auxiliary amplifier, that is, due to the finite loop gain of the feedback loop, the linearized output signal includes a deviation that is similar to, increasing or decreasing from the ideal response of the first auxiliary amplifier. The feedforward network composed of the second auxiliary amplifier, the common node and the feedforward amplifier connected in parallel with the main amplifier also allows the included deviation to be isolated from the total output signal of the second auxiliary amplifier and amplified by the feedforward amplifier. The isolation of the deviation is made possible by subtracting the signal provided by the second input port from the output signal of the second auxiliary amplifier via the common node of the feedforward network. The feedforward network then allows the amplified deviation to be added to the output signal of the main amplifier, resulting in the complete or at least significant removal of the deviation from the ideal response that depends on the finite loop gain of the feedback loop.

[0019] The inventive concept thus allows an improvement in the relationship between the input signal and the output signal in a radio frequency power amplifier. This concept makes it possible to suppress the nonlinearity of said relationship over a wider operating frequency range by improving the removal of distortions generated when amplifying the input signal and by completely or at least significantly removing the deviations that depend on the finite loop gain of the feedback loop. Furthermore, the combination of indirect feedback and feedforward deviation allows the inventive concept to be less sensitive to drift than other linearization techniques mentioned in the prior art. The inventive concept allows for reduced power consumption losses and is very suitable for chip integration, both in CMOS and bipolar technologies, for which implementation examples will be further explained in the detailed description of the embodiments.

[0020] In the present application, the main amplifier and the auxiliary amplifier may be understood to mean a transconductance amplifier, a voltage amplifier, a current amplifier, a transimpedance amplifier and / or a power amplifier.

[0021] A feedforward amplifier may be understood to mean a current amplifier, a voltage amplifier, a transconductance amplifier, a transimpedance amplifier and / or a power amplifier.

[0022] The gain of an amplifier can be understood as the factor by which the signal is increased from the input to the output of the amplifier. The gain of an amplifier represents the signal or amplitude ratio of its output signal to its input signal. For example, if the gain of a main amplifier is nA, its output signal will represent the input signal increased by a factor of nA.

[0023] The loop gain can be thought of as the gain provided by the feedback network multiplied by the gain in the forward amplifier path. For example, if an amplifier (the forward amplifier) ​​provides a gain of A and a feedback path providing a gain of β is connected around it, the loop gain of the feedback loop will be Aβ.

[0024] The ideal response or ideal case of an amplifier to an input signal can be understood as a completely linear behavior of the amplifier. This ideal response means that there is no distortion or other nonlinearity between the input signal and the output signal of the amplifier.

[0025] A replica amplifier can be understood as defining an amplifier that responds similarly to the same input signal but provides a different gain to that signal. Thus, a replica amplifier can define the relationship between the gain provided by one amplifier and the gain provided to the input signal by another amplifier. For example, the main amplifier of the present invention concept represents an amplified replica of a first auxiliary amplifier, where the relationship between the gains of the amplifiers follows a factor of n:1. That is, if the gain of the first auxiliary amplifier is A, the gain provided by the main amplifier will be nA.

[0026] A node or common node may be understood as an interconnection between at least two of the input and output of the amplifier and may be represented by at least one of an adder, a subtractor or a general interconnection of conductors.

[0027] According to one embodiment, the main amplifier and the auxiliary amplifier can be configured to provide the same response to the input signal. Since the second auxiliary amplifier is a replica of the first auxiliary amplifier, and the main amplifier is also a replica of the first auxiliary amplifier, the responses of all amplifiers to the same input signal can be similar in terms of linearity. Since the inputs of all amplifiers are interconnected at a common input node within the feedback loop, the feedback loop can improve this linearity. Deviations from the ideal response of the first auxiliary amplifier are also carried by the second auxiliary amplifier and the main amplifier because they are all driven by the same input signal, which relies on the finite loop gain of the feedback loop. However, the gain between the main amplifier and the auxiliary amplifier is different because the main amplifier is an amplified replica of the first auxiliary amplifier and therefore provides greater gain. The second auxiliary amplifier can also provide a different gain compared to the first auxiliary amplifier.

[0028] According to an embodiment, the first input port of the RF power amplifier system and the feedback network output can be connected to a common input node via a subtractor. This subtractor allows the feedback signal to be subtracted from the signal at the first input port to suppress nonlinearity between the input signal and the output signal of the first auxiliary amplifier. This subtractor does not need to be a separate physical circuit; it can be a connection node to which the feedback signal is fed while being subtracted from the input signal at the first input port.

[0029] According to an embodiment, the common node at which the output of the second auxiliary amplifier and the second input port of the second auxiliary amplifier are interconnected with the input of the feedforward amplifier can be a subtractor. This subtractor allows the input signal of the second input port to be subtracted from the output signal of the second auxiliary amplifier. This subtraction allows deviations that are dependent on the finite loop gain of the feedback loop of the first auxiliary amplifier to be isolated from the total output signal of the second auxiliary amplifier. Thus, this subtractor allows the input signal of the feedforward amplifier to represent only the deviations to be amplified and fed forward to the output of the main amplifier.

[0030] According to an embodiment, the ratio of the input signal provided by the second input port to the input signal provided by the first input port can be the same as the ratio of the gain provided by the second auxiliary amplifier to the gain provided by the first auxiliary amplifier. This embodiment is advantageous in that it ensures that the deviation contained in the output signal of the second auxiliary amplifier can be isolated from the rest of the output signal. In fact, since the input signal of the second auxiliary amplifier is the same as the input signal of the first auxiliary amplifier, the signal provided by the second input port to be subtracted from the output signal of the second auxiliary amplifier should be scaled similarly to the signal provided by the first input port, as the second auxiliary amplifier is scaled relative to the first auxiliary amplifier. In other words, if the second auxiliary amplifier has a gain ratio of 1:m relative to the first auxiliary amplifier, the input signal provided by the second input port must have a signal ratio of 1:m relative to the input signal provided by the first input port. For example, if the second auxiliary amplifier provides a gain of 0.5 to its input signal, the input signal provided by the second input port should represent half the input signal provided by the first input port.

[0031] According to one embodiment, the feedforward amplifier can be configured to provide gain so that its output signal has the same amplitude but opposite phase as the output signal of the main amplifier. An advantage of this embodiment is that it allows the output signal of the feedforward amplifier to represent an amplification of the deviation generated by the finite loop gain of the feedback network of the first auxiliary amplifier, having the same amplitude but opposite phase as the deviation included in the output signal of the main amplifier, resulting in complete or at least significant removal of the deviation that depends on the finite loop gain. Furthermore, the gain provided by the feedforward amplifier can depend on the gain provided by the second auxiliary amplifier. For example, if the gain provided by the second auxiliary amplifier is 0.5 and the gain provided by the main amplifier is 4, the gain provided by the feedforward amplifier must be 8. It should be noted that the amplitude of the output signal from the feedforward amplifier is lower than the amplitude of the output signal of the main amplifier, which allows partial removal of the deviation included in the output signal, thus still resulting in improved linearization.

[0032] According to one embodiment, the common output node at which the outputs of the feedforward amplifier and the main amplifier are interconnected can be an adder. Such an adder allows the amplified deviation representing the output signal of the feedforward amplifier to be added (i.e., fed forward) to the output of the main amplifier. Thus, such summing allows the deviation that depends on the finite loop gain of the feedback loop to be completely or at least significantly removed from the output signal of the main amplifier.

[0033] According to an embodiment, each auxiliary amplifier may include a first transistor and a second transistor connected in series. The types of transistors used in the present inventive concept may include, but are not limited to, metal oxide semiconductor field effect transistors (MOSFETs) and / or bipolar junction transistors (BJTs). Such transistors allow for modulation of an input signal into an amplified output signal. Furthermore, such transistors may allow for modulation of power signals, voltage signals, and / or current signals.

[0034] According to an embodiment, the main amplifier may include a first transistor and a second transistor connected in series. Since the main amplifier represents a replica of the first auxiliary amplifier, it includes first and second transistors (e.g., MOSFETs, BJTs, etc.) similar to those of the first auxiliary amplifier, but with larger sizes to achieve greater amplification of the input signal, i.e., to provide greater gain.

[0035] According to one embodiment, the feedforward amplifier may represent an indirect feedback amplifier. Such an indirect feedback amplifier may include a feedback network that may serve the same purpose as the feedback network arranged around the first auxiliary amplifier, namely, reducing nonlinearity between the output signal and the input signal of the feedforward amplifier. This feedback may be connected to a second internal load for which the load conditions are known and stable, thereby allowing for feedback stability. Thus, the feedback network of the feedforward amplifier allows the deviation from the first auxiliary amplifier to be amplified and fed forward to the output of the main amplifier without any significant distortion that the feedforward amplifier may produce.

[0036] According to one embodiment, the RF power amplifier system can be configured to receive input signals at first and second input ports, which can be provided from a driver circuit on the front of the system. An alternative to this embodiment can be that the RF power amplifier system includes only one input port. The input signal received at the single input port from the driver circuit on the front of the system can then be equally provided to the common input node and the common node.

[0037] According to one embodiment, the output signal of an RF power amplifier system can be fed to a load. The load and its conditions can affect the load capability required by the RF power amplifier system, that is, the amplification required between the system's input and output signals to power the load. This load can be represented by any suitable electronic device, such as an antenna, filter, external power amplifier, speaker, etc. Operation requires an amplified input signal.

[0038] According to one embodiment, the feedforward amplifier, the main amplifier, and the auxiliary amplifier may be included on the same integrated circuit. The term "integrated circuit" as used herein refers to an electronic circuit formed on a significantly small piece of semiconductor material (e.g., silicon). This embodiment is advantageous in that it allows the circuitry of the RF power amplifier system to be constructed with a significantly smaller size, making it suitable for chip integration applications, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The above and additional objects, features and advantages of the present invention will be better understood through the following illustrative and non-limiting detailed description of the embodiments of the present invention. Reference will be made to the accompanying drawings, in which:

[0040] Figure 1 A block diagram of a radio frequency power amplifier system with indirect feedback is illustrated;

[0041] Figure 2 illustrates a block diagram of an embodiment of a radio frequency power amplifier system according to the present invention, wherein indirect feedback is combined with a feed-forward bias;

[0042] Figure 3 Pictured Figure 2 Example circuit of a CMOS-based implementation of an RF power amplifier;

[0043] Figure 4 Pictured Figure 3 An example circuit of a radio frequency power amplifier, wherein an example circuit of a feedforward amplifier is shown; and

[0044] Figure 5 The diagram shows Figure 1 The linear performance of the system shown in Figure 3 and Figure 4 A comparison of the present invention implementations shown in . DETAILED DESCRIPTION

[0045] Figure 1 The figure shows a block diagram of an RF power amplifier system implementing the indirect feedback linearization technique. Figure 1The block diagram of FIG. 1 shows a main amplifier 101 having an input 107 and an output 108, a first auxiliary amplifier 102 having an input 109 and an output 110, an internal load 103 connected to the output 110 of the first auxiliary amplifier, and a feedback network 104 having an input 111 connected to the output 110 of the first auxiliary amplifier 102 and an output 112 connected to the input 109 of the first auxiliary amplifier 102 via a subtractor 115. The inputs 107, 109 of the main amplifier 101 and the first auxiliary amplifier 102 are interconnected at a common input node 113. The power amplifier system 100 has a first input port 114 connected to the common input node 113 via a subtractor 115. The RF power amplifier system 100 is connected to the external load 105. Figure 1 The antenna is represented in the figure.

[0046] The main amplifier 101 forms a replica of the first auxiliary amplifier 102. In many applications, the scaling factor between the main amplifier 101 and the first auxiliary amplifier 102 can be approximately in the range of 2:1 up to 8:1, although other relationships are also possible. This scaling factor defines the relationship between the gain between the input and output signals of the main amplifier 101 and the corresponding gain of the first auxiliary amplifier 102. Thus, for example, with a scaling factor of 4:1, the gain of the main amplifier 101 is equivalent to four times the gain of the first auxiliary amplifier 102.

[0047] Figure 1 The RF power amplifier system 100 operates as follows: an input signal is provided to the system at a first input port 114, from which a feedback signal, namely the output of the feedback network 104, is subtracted at a subtractor 115. Since the feedback network 104 is connected around the first auxiliary amplifier 102, it linearizes the first auxiliary amplifier 102 and reduces distortion of the output signal at its output 106. Since the internal load 103 is known and inaccessible from the outside, the operation of the feedback network 104 around the first auxiliary amplifier 102 can be stabilized. In other words, the load conditions are known and do not change. Therefore, due to the feedback network 104, nonlinearities in the first auxiliary amplifier 102 are suppressed. The main amplifier 101 is then driven by the same input signal as the first auxiliary amplifier 102, as their two inputs are interconnected at a common input node 113. Since the main amplifier 101 is a replica of the first auxiliary amplifier 102, it will respond to the same input signal in the same manner as the first auxiliary amplifier 102, resulting in nonlinearities between the input and output signals of the main amplifier 101 being suppressed. The output signal of the main amplifier 101 is then provided to the load 105 with increased linearity.

[0048] However, the limited loop gain provided by the feedback loop including the first auxiliary amplifier 102 and the feedback network 104 may cause the signal to deviate from the ideal response of the first auxiliary amplifier, which may not be compensated in this embodiment. Such deviations may be carried by the main amplifier 101 and thus amplified with the rest of the linearized signal.

[0049] Figure 2 A block diagram of a radio frequency power amplifier system 200 is shown, which includes Figure 1 The RF power amplifier system 100 and the feedforward network 120 are added. Therefore, Figure 1 The components and their functions are described in Figure 2 are represented identically. Figure 2 The feedforward network 120 includes a second auxiliary amplifier 122 having an input 129 and an output 128. The second auxiliary amplifier 122 is a replica of the first auxiliary amplifier 102. Therefore, the two auxiliary amplifiers 102 and 122 respond to the input signal in the same way. The feedforward network 120 also includes a feedforward amplifier 123 having an input 124 and an output 130. The input 129 of the second auxiliary amplifier 122 is interconnected with the inputs (107, 109) of the main amplifier 101 and the first auxiliary amplifier 102 at a common input node 113. The output 128 and the second input port 121 of the second auxiliary amplifier 122 are interconnected with the input 124 of the feedforward amplifier 123 at a subtractor, and the output 130 of the feedforward amplifier 123 and the output 108 of the main amplifier 101 are interconnected at a common output node represented by an adder. The feedforward network 120 is therefore connected in parallel with the main amplifier 101.

[0050] The indirect feedback provided to the main amplifier 101 by the feedback network 104 arranged around the first auxiliary amplifier 102 is based on the above reference Figure 1The RF power amplifier system 100 described above operates in accordance with the operation of the RF power amplifier system 100 described above. In addition to indirect feedback, the feedforward network 120 of the RF power amplifier system 200 operates as follows: the input signal to the second auxiliary amplifier 122 is identical to the input signal to the first auxiliary amplifier 102, which represents a linearized signal including deviations resulting from the finite loop gain of the feedback loop. Because the second auxiliary amplifier 122 is a replica of the first auxiliary amplifier 102, the output signal of the second auxiliary amplifier 122 is similar to the output signal of the first auxiliary amplifier 102, either increased or decreased from the output signal of the first auxiliary amplifier 102. Furthermore, the input signal provided at the second input port 121 is scaled relative to the input signal provided at the first input port 114 by the same ratio as the ratio of the gain of the second auxiliary amplifier 122 to the gain of the first auxiliary amplifier 102. At a subtractor, the input signal at the second input port 121 is subtracted from the output signal of the second auxiliary amplifier 122, thereby isolating deviations from the ideal response of the first auxiliary amplifier 102 from the remaining output signal of the output 128. Thus, the input signal 124 of the feedforward amplifier 123 represents only the deviation, which is then amplified by the feedforward amplifier 123 in such a way that it comprises the same amplitude as the deviation carried by the output 108 of the main amplifier, with a 180° phase shift, i.e., an opposite phase. The adder then adds the amplified deviation to the output 108 of the main amplifier 101, resulting in a linearized output signal 126, from which the deviation from the ideal response of the power amplifier is completely or at least significantly removed. The output signal 126 is then supplied to the load 105.

[0051] It should be understood that another example of the RF power amplifier system 200 may be one in which the amplification of the isolated deviation by the feedforward amplifier 123 has the same phase as the deviation carried by the output 108 of the main amplifier 101, but the common output node is represented by a subtractor. It should also be understood that another example of the RF power amplifier 200 may be one in which the input signal at the second input port 121 includes a 180° phase shift compared to the input signal at the first input port 114, but the common node is represented by an adder.

[0052] Figure 2 The operation of the RF power amplifier 200 described in FIG. 1 can be further explained using mathematical representation. Considering that the gains provided by the first and second auxiliary amplifiers 102, 122 are the same and equal to A, the gain provided by the main amplifier 101 is nA (i.e., n times the gain of the auxiliary amplifiers 102, 122), the gain provided by the feedforward amplifier 123 is -n (i.e., a gain of n with a 180° phase shift), and the gain provided by the feedback network 104 is β, the signal S after the subtractor 115 is 113It can be expressed as follows:

[0053] S 113 =S in -S 113 Aβ (1)

[0054]

[0055] S in represents the input signal of the first input port 114, and Aβ represents the finite loop gain of the feedback loop, which produces a deviation from the ideal response of the first auxiliary amplifier 102, where the term Similarly, the output signal of the main amplifier 101 and the output signal of the second auxiliary amplifier 122 can be expressed as:

[0056]

[0057] And the output signal from the subtractor can be expressed as:

[0058]

[0059] The output signal S of the subtractor 124 It is then amplified by the feedforward amplifier 123 and added to the output signal S of the main amplifier 101. 108 , resulting in an output signal 126 as shown in the following equation.

[0060]

[0061] The above equation shows that the dependency of the loop gain Aβ, ie the deviation from the ideal response of the amplifier in the relationship between the output and input of the RF power amplifier system 200, is removed.

[0062] Thus, in contrast to prior art linearization techniques, the signal processing performed with the added feed-forward network 120 results in a more defined relationship between the output signal and the input signal, thereby resulting in improved linearity.

[0063] Figure 3 An example of a CMOS-based implementation of the inventive concept is shown. Figure 3 The diagram shows a differential implementation consisting of an upper half 301 and a lower half 302, where the two halves are identical. Each half 301, 302 is driven by an input signal connected to a corresponding first and second input port, IN1+ and IN2+ for the upper half 301 and IN1- and IN2 for the lower half 302. The two input ports are driven by the same but opposite phase current i s304, 305 are fed, and the current is generated by the driving circuit before the RF power amplifier system. The differential output ports OUT+ and OUT- are connected to the transformer 306 respectively, and the transformer 306 converts the differential output signal into a single-ended output signal OUT provided to the load 307. The following describes the upper half 301 based on CMOS implementation. Figure 2 The different blocks of the RF power amplifier system 200 are shown in FIG.

[0064] The main amplifier can include a capacitor C2 and two transistor devices, which are n-channel MOSFETs or NMOS, N3 and N4. The first auxiliary amplifier is implemented with a capacitor C1 and two transistor devices, which are NMOS, N1 and N2, which are connected to an internal load consisting of a parallel resonant circuit 308. The first auxiliary amplifier is implemented in a similar manner to the main amplifier, that is, the two amplifiers provide the same response to the input signal. The feedback network can include a short circuit 309 from the drain of transistor N1 to the input port IN1+. The two capacitors C1 and C2 can be considered as short circuits at the operating frequency and are not necessary for the behavior of the RF power amplifier system. The second auxiliary amplifier is implemented by a capacitor C3 and two transistor devices (NMOS) N5 and N6.

[0065] The second auxiliary amplifier is connected in parallel with the main amplifier, but is not scaled to provide gain in this implementation, i.e., the gain provided by the second auxiliary amplifier is the same as the gain in the first auxiliary amplifier. Since the auxiliary amplifiers are identical copies in this implementation, the sizes of transistor devices N5 and N6 should be equal to the sizes of transistor devices N1 and N2, respectively. Thus, due to indirect feedback, the current i d2 becomes equal to the current i in transistor devices N1 and N2 d1 Furthermore, the feedforward amplifier 303 may be represented by a current amplifier and provide gain so that its output signal may have the same amplitude as the output signal of the main amplifier but an opposite phase.

[0066] The operation of the CMOS implementation of the radio frequency power amplifier of the present invention can be explained by the following mathematical representation: the input signal (current i s 304) generates a voltage at the first input port IN1+ and thereby generates a voltage at the gate of the transistor device N2. The voltage at the gate of the transistor device N2 generates a current i through the transistor devices N1 and N2. d1 . Similar to Figure 2 Equation (2), the current i d1 and input current i s The relationship between 304 can be expressed by the following equation:

[0067]

[0068] In a typical high frequency implementation, the loop gain Aβ may be approximately -10, resulting in a current i d1 Only the input current i s 304. Therefore, the current generated by the voltage across the load impedance of the first auxiliary amplifier represents a deviation from the ideal response of the first auxiliary amplifier. Δ1 , assuming infinite loop gain Aβ, for an ideal response, the current i d1 Equal to the input current i s 304. This relationship can be expressed as:

[0069] i d1 =i s -i Δ1 (8)

[0070] Since the second auxiliary amplifier of this implementation is an identical replica of the first auxiliary amplifier, and both amplifiers have the same input signal, the deviation generated by the finite feedback loop can be carried by the second auxiliary amplifier, resulting in the current of the transistor devices N5, N6 being expressed as:

[0071] i d2 =i s -i Δ2 (9)

[0072] According to the above equation, the deviation can be expressed as:

[0073] i Δ2 =i s -i d2 (10)

[0074] Since the second auxiliary amplifier does not provide gain in this implementation (i d1 =i d2 ), and since the input currents of the input ports IN1+ and IN2+ are the same, the deviation from the ideal response of the second auxiliary amplifier is equal to the deviation from the ideal response of the first auxiliary amplifier:

[0075] i Δ2 =i Δ1 (11)

[0076] The deviation i is then added to the output of the main amplifier before being added to the output of the main amplifier. Δ2 is amplified by the feedforward amplifier 303 with a gain of -n. Therefore, the expression of the output signal at the output port OUT- can be written as:

[0077] i o =i d3 +ni Δ2 (12)

[0078] where i d3 represents the current at transistor devices N3 and N4 of the main amplifier. Since the main amplifier is a replica of the first auxiliary amplifier and the current gain of the main amplifier is the same as the current gain of one of the feedforward amplifiers, the current i d3 It can be expressed as:

[0079] i d3 =ni d1 (13)

[0080] Therefore, the output signal at the output port OUT- can be rewritten as:

[0081] i o =ni Δ2 +i d3 =ni Δ2 +ni d1 =n(i Δ2 +i d1 )=n(i Δ1 +i d1 ) (14)

[0082] i o =n(i Δ1 +i s -i Δ1 )=ni s (15)

[0083] Thus, the inventive concept implemented in CMOS based applications removes the deviation from the ideal response of the amplifier caused by finite loop gain.

[0084] Figure 4 Shown Figure 3 An example circuit of a CMOS implementation of an RF power amplifier is shown in FIG. 3 , in which details of the circuit of the feedforward amplifier 303 are added. Figure 4In FIG, the feedforward amplifier 303 can be represented by a current amplifier and can include a capacitor C11 and transistor devices (NMOS) N11 and N12, respectively, which are connected to an internal load consisting of a parallel resonant circuit 310. The feedforward amplifier 303 therefore has a feedback network that includes a short circuit 311 from the drain of transistor N11 to the input of the current amplifier 303. The feedforward amplifier 303 also includes a second capacitor C12 and a second pair of transistor devices (NMOS) N13 and N14, respectively. The example circuit of the amplifier 303 operates using an indirect feedback technique to linearize the relationship between the input signal and the output signal of the feedforward amplifier 303. The feedback loop presented here also produces deviations from the ideal situation due to its finite loop gain. However, since the input signal level to the feedforward amplifier is small compared to the maximum signal that the feedforward amplifier can process, this deviation will not be too significant. In this implementation, the input signal to the feedforward amplifier can represent a much weaker signal than the input signal to the main amplifier 101. Therefore, its deviation is negligible.

[0085] Figure 5 Shown Figure 1 The linear performance of the system shown in Figure 3 and Figure 4 According to an example, the linear performance was simulated with an 80 MHz 802.11ac input signal. The output power level in both simulations was +20 dBm, and Figure 1 The response of the RF power amplifier is shown in output spectrum 501, and the response of the implemented invention is shown in output spectrum 502. As can be seen from these results, the EVM (error vector magnitude) performance of the implemented invention is improved by approximately 15 dB compared to the prior art, which represents a typical deviation resulting from a loop gain of -10. In addition to the improved EVM, the present invention increases the gain by approximately 0.7 dB compared to the prior art.

[0086] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

[0087] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A radio frequency power amplifier system (200), comprising: A first input port (114) and a second input port (121) arranged to receive first and second input signals, respectively; a main amplifier (101) having an input (107) and an output (108); A first auxiliary amplifier (102) and a second auxiliary amplifier (122) having respective inputs (109, 129) and outputs (110, 128), wherein the ratio of the input signal provided by the second input port (121) to the input signal provided by the first input port (114) is the same as the ratio of the gain provided by the second auxiliary amplifier (122) to the gain provided by the first auxiliary amplifier (102); an internal load (103) connected to the output (110) of the first auxiliary amplifier (102); a feedback network (104) arranged to linearize the first input signal and having an input (111) connected to the output (110) of the first auxiliary amplifier (102) and an output (112) connected to the input (109) of the first auxiliary amplifier (102); and a feedforward amplifier (123) having an input (124) and an output (130), wherein the feedforward amplifier (123) is configured to provide gain such that its output signal (130) has the same amplitude but opposite phase as the output signal (108) of the main amplifier (101); in; The inputs (107, 109, 129) of the main amplifier (101) and the auxiliary amplifier (102, 122) are interconnected to a first input port (114) at a common input node (113); The output (128) and the second input port (121) of the second auxiliary amplifier (122) are interconnected with the input (124) of the feedforward amplifier (123) at a common node (127), wherein the common node (127) is a subtractor and wherein the input signal provided by the second input port (121) is subtracted from the output signal of the second auxiliary amplifier (122) at the subtractor; The outputs (130, 108) of the feedforward amplifier (123) and the main amplifier (101) are interconnected at a common output node (125), wherein the common output node is an adder (125) that adds the outputs (130, 108) of the feedforward amplifier (123) and the main amplifier (101) to thereby generate an output signal (126) of the radio frequency power amplifier system (200), which is linearized; And among them; The main amplifier (101) is a replica of the first and second auxiliary amplifiers (102, 122) with increased gain; The second auxiliary amplifier (122) is a replica of the first auxiliary amplifier (102); And among them; The ratio of the second input signal to the first input signal is the same as the ratio of the gain provided by the second auxiliary amplifier (122) to the gain provided by the first auxiliary amplifier (102); and The second auxiliary amplifier (122), the second input port (121) and the feedforward amplifier (123) together form a feedforward network (120) arranged to at least partially remove a deviation from the output (108) of the main amplifier (101). 2 . The RF power amplifier system of claim 1 , wherein the main amplifier and the auxiliary amplifier are configured to provide the same response to an input signal.

3. The radio frequency power amplifier system according to claim 1 or 2, wherein the first input port and the feedback network output are connected to a common input node via a subtractor (115).

4. The radio frequency power amplifier system according to claim 1, wherein each auxiliary amplifier comprises a first transistor (N1, N5) and a second transistor (N2, N6) connected in series.

5. The radio frequency power amplifier system according to claim 1, wherein the main amplifier comprises a first transistor (N3) and a second transistor (N4) connected in series.

6. The radio frequency power amplifier system of claim 1, wherein the feedforward amplifier represents an indirect feedback amplifier. 7 . The RF power amplifier system according to claim 2 , configured to receive input signals at the first and second input ports from a driving circuit preceding the RF power amplifier system.

8. The radio frequency power amplifier system according to claim 1, configured to feed an output signal of the system to a load (105).

9. The radio frequency power amplifier system of claim 1, wherein the feedforward amplifier, the main amplifier, and the auxiliary amplifier are included on the same integrated circuit.

10. A method for linearizing an output signal of a radio frequency power amplifier system, comprising: first and second input ports arranged to receive first and second input signals, respectively; a main amplifier with inputs and outputs; first and second auxiliary amplifiers having respective inputs and outputs, wherein a ratio of an input signal provided at the second input port to an input signal provided at the first input port is the same as a ratio of a gain provided by the second auxiliary amplifier to a gain provided by the first auxiliary amplifier; an internal load connected to the output of the first auxiliary amplifier; a feedback network arranged to linearize the first input signal and having an input connected to the output of the first auxiliary amplifier and an output connected to the input of the first auxiliary amplifier; as well as a feedforward amplifier having an input and an output, wherein the feedforward amplifier is configured to provide gain such that its output signal has the same amplitude but opposite phase as an output signal of the main amplifier; in; The inputs of the main amplifier and the auxiliary amplifier are interconnected to a first input port at a first common input node; the output and the second input port of the second auxiliary amplifier being interconnected with the input of the feedforward amplifier at a second common node, wherein the second common node is a subtractor and wherein the input signal provided at the second input port is subtracted from the output signal of the second auxiliary amplifier at the subtractor; The outputs of the feedforward amplifier and the main amplifier are interconnected at a third common output node, wherein the third common output node is an adder that adds the outputs of the feedforward amplifier and the main amplifier to thereby generate an output signal of the RF power amplifier system, the output signal being linearized; And among them; The main amplifier is a replica of the first and second auxiliary amplifiers with increased gain; as well as The second auxiliary amplifier is a replica of the first auxiliary amplifier; The ratio of the second input signal to the first input signal is the same as the ratio of the gain provided by the second auxiliary amplifier (122) to the gain provided by the first auxiliary amplifier (102); The method includes: obtaining a deviation from an ideal response at the first auxiliary amplifier by means of a feedback network; isolating the deviation by removing the second input signal from the output of the second auxiliary amplifier; amplifying the isolated deviation by means of a feedforward amplifier; and The amplified deviation is added to the output of the main amplifier.

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