CN109818587B - Self-adaptive bias radio frequency power amplifier - Google Patents
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Abstract
The application discloses a self-adaptive bias radio frequency power amplifier, which comprises an amplifying circuit and a bias circuit. The amplifying circuit is provided with a power transistor, the biasing circuit is provided with a biasing transistor, and the emitter of the biasing transistor is connected with the base electrode of the power transistor through a resistor to provide biasing current and/or biasing voltage for the power transistor. The bias circuit is also provided with a capacitor serial branch, and at least two capacitors are connected in series; one end of the capacitor series branch is connected with the base electrode of the power transistor, and the other end is grounded. The method reduces the adverse effect of the parasitic capacitance of the base electrode and the collector electrode of the power transistor on linearity, and improves the AM-PM imbalance of the radio frequency power amplifier; the gain compression phenomenon of the radio frequency power amplifier is delayed, and the AM-AM imbalance of the radio frequency power amplifier is improved.
Description
Technical Field
The present application relates to a radio frequency power amplifier.
Background
With the development of mobile communication technology, data traffic is continuously increased, and spectrum resources become increasingly exhausted. To solve such problems, a modern mobile communication system generally employs a linear modulation technique such as QPSK (Quadrature Phase Shift Keying ), QAM (Quadrature Amplitude Modulation, quadrature amplitude modulation), HPSK (Hybrid Phase Shift Keying ), OFDM (Orthogonal Frequency Division Multiplexing, orthogonal frequency division multiplexing), and the like. The signals generated by the modulation mode are all modulation signals with non-constant envelope, the system is multi-carrier multi-channel, and the Peak-to-Average Ratio (PAR) of the signals is large.
The radio frequency power amplifier is an important component of the mobile communication system, and is used as a final amplifying unit of a transmitting channel, and the radio frequency power amplifier is used for amplifying a low-power radio frequency signal and then transmitting the low-power radio frequency signal to an antenna for transmission. Design metrics for a radio frequency power amplifier typically include output power (Pout), efficiency (PAE), gain (gain), bandwidth, linearity, and the like. For mobile communication systems employing linear modulation techniques, the linearity index of the radio frequency power amplifier is very important. Any nonlinearity of the radio frequency power amplifier tends to produce undesirable frequency components that can severely impact the performance of the mobile communication system.
Combining cost and performance factors, power transistors in radio frequency power amplifiers typically employ gallium arsenide HBT (heterojunction bipolar transistor ) processes. Please refer to fig. 1, which is a schematic diagram of the parasitic capacitance of the HBT. The HBT has a Base (Base), a Collector (Collector), and an Emitter (Emitter). There is a base-collector parasitic capacitance Cbc between the base and collector, a base-emitter parasitic capacitance Cbe between the base and emitter, and a collector-emitter parasitic capacitance ccoe between the collector and emitter. In general, a rf power amplifier is expected to have a larger output power, but the rf power amplifier cannot convert the dc power of a power supply into the rf signal output power in one hundred percent, which causes a heat dissipation problem. To facilitate heat dissipation, power transistors are typically large in area, which in turn increases parasitic capacitance. These parasitic capacitances are varied in the case of the smaller and larger output powers of the rf power amplifier, so that as the output power increases, a phase offset (AM-PM offset) is generated between the input power and the output power. In addition, in the process of amplifying a low-power signal into a high-power signal, the rf power amplifier may have a phenomenon of gain compression, which is a phenomenon of gain reduction with an increase of output power, and thus an amplitude offset (AM-AM offset) is generated.
A paper "PCS/W-CDMA Dual-Band MMIC Power Amplifier With a Newly Proposed Linearizing Bias Circuit" (hereinafter referred to as document A) is published in 9 2002, volume 37, 9 of IEEE JOURNAL OF SOLID-STATE CIRCUITS. Fig. 1 of this article shows a radio frequency power amplifier of self-biasing structure with the addition of a ground capacitance Cb at the base of the active bias transistor. As the input power increases, the impedance of the bias circuit decreases, the portion of the rf power coupled into the bias circuit increases, the bias circuit can draw more dc current, the base-emitter voltage of the active bias transistor decreases, the base bias voltage of the power transistor decreases, and finally linearity is improved. However, the parasitic capacitance of the power transistor is not reduced by the scheme, and the AM-PM imbalance still has room for improvement.
There is a paper A Compact Composite Transistor as a Novel RF Power Cell for High Linearity Power Amplifiers in IEEE Microwave and Optical Technology Letters published 6 2006. This article describes reducing AM-PM misalignment by reducing the base-collector parasitic capacitance Cbc of the power transistor. But AM-AM imbalance of this scheme still has room for improvement.
The invention patent application of China (application publication number is CN106571780A, application publication date is 2017, 4 month 19) discloses a radio frequency power amplifier (hereinafter referred to as document B) with self-adaptive bias. The power stage amplifying circuit adopts a cascode structure, the cascode transistor plays a role in signal amplification, and the cascode transistor plays a role in improving voltage resistance. As the input power increases, the turn-on voltage of the cascode transistor decreases, thereby causing the drain voltage of the cascode transistor to decrease with a delay, improving gain compression. In addition, the gate of the common-gate transistor is connected in series with a capacitance in the bias circuit, thereby reducing the gate-collector parasitic capacitance of the common-gate transistor. The disadvantage of this solution is: the technical means for improving linearity is not directly applied to the amplifying transistor, but directly applied to the voltage-withstanding transistor, and AM-AM imbalance and AM-PM imbalance are improved in an indirect manner, so that there is still room for improvement.
The invention patent application of China, with the application publication number of CN103715997A and the application publication date of 2014, 4 and 9, discloses a radio frequency power amplifier. A diode is added between the current source and the input end of the power transistor, and the working state of the diode is adjusted to enable the radio frequency input signal to generate distortion characteristics opposite to those of the power amplifier, so that the aim of linearization is achieved. Meanwhile, as the input power increases, the diode takes half of a cycle in the forward and reverse directions (the capacitance effect in the forward state is weak), so that the resistor plays a role in compensating linearity. The parasitic capacitance of the power transistor is not reduced by the scheme, and the AM-PM imbalance still has room for improvement. This scheme also does not improve gain compression, and AM-AM imbalance also has room for improvement.
Disclosure of Invention
The technical problem to be solved by the application is to provide a radio frequency power amplifier, which can improve AM-PM imbalance and AM-AM imbalance and improve linearity.
In order to solve the technical problems, the self-adaptive bias radio frequency power amplifier provided by the application comprises an amplifying circuit and a bias circuit. The amplifying circuit is provided with a power transistor, the biasing circuit is provided with a biasing transistor, and the emitter of the biasing transistor is connected with the base electrode of the power transistor through a resistor to provide biasing current and/or biasing voltage for the power transistor. The bias circuit is also provided with a capacitor serial branch, and at least two capacitors are connected in series; one end of the capacitor series branch is connected with the base electrode of the power transistor, and the other end is grounded. The parasitic capacitance of the base electrode and the collector electrode of the power transistor is grounded through the capacitor serial branch circuit, so that the adverse effect of the parasitic capacitance of the base electrode and the collector electrode of the power transistor on linearity is reduced, AM-PM imbalance of the radio frequency power amplifier is improved, and linearity is improved.
Further, at least one capacitor in the series branch of capacitors connects the base of the power transistor and the base of the bias transistor, the capacitor being configured to couple the radio frequency input signal to the base of the bias transistor. At least one other of the series-connected branches of capacitors is grounded, which reduces the impedance of the bias circuit, making it easier for the radio frequency signal to be coupled to the bias circuit. The two capacitors are used for coupling the radio frequency input signal to the base electrode of the bias transistor when the radio frequency input power is increased, so that the static voltage of the base electrode of the bias transistor is increased, the base electrode current provided by the bias transistor to the power transistor is increased, the gain compression phenomenon of the radio frequency power amplifier is delayed, the AM-AM imbalance of the radio frequency power amplifier is improved, and the linearity is improved.
Preferably, in the amplifying circuit, a base electrode of the power transistor receives a radio frequency input signal through a capacitor III; the emitter of the power transistor is grounded; the collector electrode of the power transistor outputs an amplified radio frequency signal; there is a base-collector parasitic capacitance between the base and collector of the power transistor. This is a specific implementation of the amplifying circuit.
Preferably, in the bias circuit, a base electrode of the bias transistor is connected with the voltage division branch, and is also connected with a base electrode of the power transistor through a capacitor and is also grounded through a capacitor II; the first capacitor and the second capacitor are connected in series to form the capacitor series branch. The collector of the bias transistor is connected with a power supply voltage; the emitter of the bias transistor is connected to the base of the power transistor through a resistor two. The voltage dividing branch is formed by sequentially connecting a first resistor, a first diode and a second diode in series between the power supply voltage and the ground; the base of the bias transistor is connected between the first resistor and the first diode in the voltage dividing branch, i.e. to the anode of the first diode. This is the first specific implementation of the bias circuit.
Further, the bias circuit also has a mirror transistor therein. The base of the bias transistor is connected to the collector of the mirror transistor. The base electrode of the bias transistor is also connected with the base electrode of the power transistor through a capacitor and grounded through a capacitor II. The first capacitor and the second capacitor are connected in series to form the capacitor series branch. The collector of the bias transistor is connected to a supply voltage. The emitter of the bias transistor is connected with the base of the power transistor through a resistor II. The base of the mirror transistor is connected to the emitter of the bias transistor through a resistor three. The collector of the mirror transistor is connected to the supply voltage via a resistor connection. The emitter of the mirror transistor is grounded. The mirror transistor and the bias transistor form a current mirror circuit. This is a second specific implementation of the bias circuit.
Alternatively, the first capacitor is replaced by a third diode, the cathode of the third diode is connected with the base electrode of the bias transistor, and the anode of the third diode is connected with the base electrode of the power transistor. The diode III is equivalent to the parallel connection of the adjustable resistor I and the adjustable capacitor I. The resistance value of the first adjustable resistor and the capacitance value of the first adjustable capacitor are changed according to the voltage difference value of the two ends of the third diode. Wherein the tunable capacitor one and the replaced capacitor together have the same function and function. The first adjustable capacitor and the second adjustable capacitor are connected in series to form the capacitor series branch. The tunable capacitance also serves as a capacitance connecting the base of the power transistor and the base of the bias transistor.
Alternatively, the second capacitor is replaced by a fourth diode, the cathode of the fourth diode is connected with the base electrode of the bias transistor, and the anode of the fourth diode is grounded. The fourth diode is equivalent to the parallel connection of the second adjustable resistor and the second adjustable capacitor. The resistance value of the second adjustable resistor and the capacitance value of the second adjustable capacitor are changed according to the voltage difference value of the two ends of the fourth reverse diode. The second adjustable capacitor and the second replaced capacitor play the same roles and functions. The first capacitor and the second adjustable capacitor are connected in series to form the capacitor series branch.
Alternatively, the first capacitor is replaced by a third diode, the cathode of the third diode is connected with the base electrode of the bias transistor, and the anode of the third diode is connected with the base electrode of the power transistor. The diode III is equivalent to the parallel connection of the adjustable resistor I and the adjustable capacitor I. And replacing the second capacitor with a fourth diode, wherein the cathode of the fourth diode is connected with the base electrode of the bias transistor, and the anode of the fourth diode is grounded. The fourth diode is equivalent to the parallel connection of the second adjustable resistor and the second adjustable capacitor. The first adjustable capacitor and the second adjustable capacitor are connected in series to form the capacitor series branch. The tunable capacitance also serves as a capacitance connecting the base of the power transistor and the base of the bias transistor.
Further, the part or all of the diodes are formed by shorting and equivalent connecting the base and the collector of the HBT, the shorted base and collector of the HBT are equivalent to the anode of the diode, and the emitter of the HBT is equivalent to the cathode of the diode. This can integrate diode fabrication into HBT fabrication, simplifying the fabrication process.
Preferably, part or all of the power transistor, bias transistor, mirror transistor is a gallium arsenide HBT. The radio frequency power amplifier is realized by gallium arsenide HBT, and has advantages in performance and cost.
The technical effect that this application obtained is: on one hand, the adverse effect of parasitic capacitance of the base electrode and the collector electrode of the power transistor on linearity is reduced, and AM-PM imbalance of the radio frequency power amplifier is improved. On the other hand, the gain compression phenomenon of the radio frequency power amplifier is delayed, and the AM-AM imbalance of the radio frequency power amplifier is improved.
Drawings
Fig. 1 is a schematic diagram of parasitic capacitance of an HBT.
Fig. 2 is a schematic circuit configuration diagram of a first embodiment of an adaptive bias rf power amplifier of the present application.
Fig. 3 is a schematic diagram of an equivalent circuit of the power transistor of fig. 2 with a parasitic base-collector capacitance in series with the added capacitance.
Fig. 4 is a schematic diagram of a first modified circuit structure of an embodiment of the adaptive bias rf power amplifier of the present application.
Fig. 5 is an equivalent circuit schematic diagram of the reverse-connected diode tri-D3 in fig. 4.
Fig. 6 is a schematic diagram of a second modified circuit structure of the first embodiment of the adaptive bias rf power amplifier of the present application.
Fig. 7 is an equivalent circuit schematic diagram of the reverse-connected diode four D4 in fig. 6.
Fig. 8 is a schematic diagram of a third modified circuit structure of the first embodiment of the adaptive bias rf power amplifier of the present application.
Fig. 9 is an equivalent circuit schematic diagram of the reverse-connected diode tri D3 and the reverse-connected diode tetra D4 in fig. 8.
Fig. 10 is a schematic circuit configuration diagram of a second embodiment of an adaptive bias rf power amplifier of the present application.
Fig. 11 is a graph showing the gain versus output power of a rf power amplifier.
Fig. 12 is a graph of phase versus output power for a rf power amplifier.
The reference numerals in the drawings illustrate: cbc is the base-collector parasitic capacitance; cbe is the base-emitter parasitic capacitance; ice is collector-emitter parasitic capacitance; RFin is a radio frequency input signal; RFout is a radio frequency output signal; HBT1 is a power transistor; HBT2 is a bias transistor; HBT3 is a mirror transistor; r is a resistor; c is a capacitor; d is a diode.
Detailed Description
Referring to fig. 2, an embodiment of an adaptive bias rf power amplifier provided in the present application mainly includes an amplifying circuit and a bias circuit.
The amplifying circuit mainly comprises a power transistor HBT1, for example a gallium arsenide HBT. The radiofrequency input signal RFin is connected to the base of the power transistor HBT1 through a capacitor tri-C3, the emitter of the power transistor HBT1 is grounded, and the collector outputs an amplified radiofrequency signal. And carrying out impedance matching on the amplified radio frequency signals through an output matching network to obtain radio frequency output signals RFout. There is a base-collector parasitic capacitance Cbc between the base and collector of the power transistor HBT1, which is one of the main factors responsible for the non-linearity of the power transistor HBT 1.
The bias circuit mainly comprises a bias transistor HBT2, for example a gallium arsenide HBT. A resistor I R1, a diode I D1 and a diode II D2 are sequentially connected in series between the power supply voltage Vcc and the ground to form a voltage division branch. The diode is formed by short-circuiting and equivalent-circuiting a base electrode and a collector electrode of the HBT, wherein the short-circuited base electrode and collector electrode of the HBT are equivalent to the anode of the diode, and the emitter of the HBT is equivalent to the cathode of the diode. The base of the biasing transistor HBT2, i.e. node a, is connected between the resistor one R1 and the diode one D1 in the voltage dividing branch, i.e. to the anode of the diode one D1. Node a is also connected to the base of the power transistor HBT1 (i.e. node B) via a capacitor C1. Node a is also connected to ground through capacitor two C2. The collector of bias transistor HBT2 is connected to supply voltage Vcc and the emitter is connected to node B, i.e. to the base of power transistor HBT1, via resistor two R2. The emitter of bias transistor HBT2 provides a bias current to the base of power transistor HBT 1.
Compared with the existing self-adaptive bias radio frequency power amplifier (for example, document A), the self-adaptive bias radio frequency power amplifier provided by the application has the following characteristics and beneficial technical effects.
First, the capacitor one C1 and the capacitor two C2 in the bias circuit are connected in series to form a capacitor serial branch, and the base-collector parasitic capacitance Cbc of the power transistor HBT1 is grounded through the capacitor serial branch, which can be equivalent to the circuit shown in fig. 3. The equivalent capacitance C12 in fig. 3 is the sum of the series capacitances of the first capacitor C1 and the second capacitor C2, c12=c1×c2/(c1+c2). The sum of the series capacitances of the series branches consisting of the base-collector parasitic capacitance Cbc, the first capacitor C1 and the second capacitor C2 is smaller than the base-collector parasitic capacitance Cbc, so that the base-collector parasitic capacitance Cbc of the power transistor HBT1 is reduced, AM-PM imbalance of the radio frequency power amplifier is improved, and linearity is improved.
Second, a capacitor C1 in the series branch couples the radiofrequency input signal RFin to the base of the bias transistor HBT2. The capacitance C2 in the capacitive series branch reduces the impedance of the biasing circuit so that the radio frequency input signal RFin is more easily coupled to the biasing transistor HBT2. As the input power of the rf input signal RFin increases, the average base voltage of the bias transistor HBT2 increases, so that the base current provided by the bias transistor HBT2 to the power transistor HBT1 increases, which delays the gain compression phenomenon of the rf power amplifier, improves the AM-AM offset of the rf power amplifier, and improves the linearity.
Compared with the existing self-adaptive bias radio frequency power amplifier (for example, document B), the self-adaptive bias radio frequency power amplifier provided by the application directly improves AM-PM imbalance and AM-AM imbalance of the power transistor responsible for signal amplification, the improvement effect is more obvious than an indirect mode, and the circuit design is more reasonable and ingenious.
Referring to fig. 4, this is a first modification of the first embodiment. The first modification circuit differs from the first embodiment only in that: capacitor one C1 in embodiment one is replaced with a reverse-connected diode three D3. In the first variant, a reverse connection is made with a diode tri-D3 between the base of the bias transistor HBT2 (i.e. node a) and the base of the power transistor HBT1 (i.e. node B). Reverse connection refers to the cathode connection node a and the anode connection node B of the diode tri-D3. The diode tri-D3 is formed by shorting and equivalent connecting the base and collector of the HBT, the shorted base and collector of the HBT are equivalent to the anode of the diode, and the emitter of the HBT is equivalent to the cathode of the diode.
Referring to fig. 5, this is an equivalent circuit of the reverse-connected diode tri D3 of fig. 4. Since the static voltage of node a is higher than that of node B in fig. 4, the reverse-connected diode tri-D3 is equivalent to a parallel network of an adjustable resistor Ra1 and an adjustable capacitor Ca 1. The resistance value of the adjustable resistor Ra1 and the capacitance value of the adjustable capacitor Ca1 are all changed along with the voltage difference between the node a and the node B. Similarly to the embodiment, the adjustable capacitor Ca1 and the capacitor C2 which are equivalent by the reversely connected diode tri-D3 in the bias circuit are connected in series to form a capacitor serial branch, and the base-collector parasitic capacitor Cbc of the power transistor HBT1 is grounded through the capacitor serial branch, so that the base-collector parasitic capacitor Cbc of the power transistor HBT1 is reduced, the AM-PM imbalance of the radio frequency power amplifier is improved, and the linearity is improved. The adjustable capacitor Ca1 equivalent to the diode tri-D3 connected reversely couples the radio frequency input signal RFin to the base electrode of the bias transistor HBT2, and the capacitor C2 reduces the impedance of the bias circuit so that the radio frequency input signal RFin is more easily coupled to the bias transistor HBT2, thereby delaying the gain compression phenomenon of the radio frequency power amplifier, improving the AM-AM imbalance of the radio frequency power amplifier and improving the linearity.
Referring to fig. 6, this is a second modification of the first embodiment. The second modification circuit differs from the first embodiment only in that: the capacitor two C2 in the first embodiment is replaced with the diode four D4 connected in reverse. In the second variant, a reverse connection is made with a diode four D4 between the base of the biasing transistor HBT2 (i.e. node a) and ground. The reverse connection means that the cathode of the diode four D4 is connected with the node A, and the anode is grounded. The diode four D4 is formed by shorting and equivalently connecting a base and a collector of the HBT, wherein the shorted base and collector of the HBT are equivalently used as an anode of the diode, and the emitter of the HBT is equivalently used as a cathode of the diode.
Referring to fig. 7, this is an equivalent circuit of the reverse-connected diode four D4 in fig. 6. Since the static voltage at node a in fig. 6 is higher than ground, the reverse-connected diode four D4 is equivalent to a parallel network of the adjustable resistor two Ra2 and the adjustable capacitor two Ca 2. The resistance value of the adjustable resistor two Ra2 and the capacitance value of the adjustable capacitor two Ca2 are changed along with the voltage of the node A. Similar to the embodiment, the capacitance C1 in the bias circuit and the adjustable capacitance Ca2 equivalent by the diode D4 in the reverse connection form a capacitance series branch, and the base-collector parasitic capacitance Cbc of the power transistor HBT1 is grounded through the capacitance series branch, so that the base-collector parasitic capacitance Cbc of the power transistor HBT1 is reduced, the AM-PM imbalance of the radio frequency power amplifier is improved, and the linearity is improved. The capacitance C1 couples the radio frequency input signal RFin to the base electrode of the bias transistor HBT2, and the adjustable capacitance Ca2 equivalent by the reversely connected diode four D4 reduces the impedance of the bias circuit, so that the radio frequency input signal RFin is more easily coupled to the bias transistor HBT2, the gain compression phenomenon of the radio frequency power amplifier is delayed, the AM-AM imbalance of the radio frequency power amplifier is improved, and the linearity is also improved.
Referring to fig. 8, this is a third modification of the first embodiment. The third modification circuit differs from the first embodiment only in that: the capacitor one C1 in the first embodiment is replaced with the diode three D3 connected in reverse, and the capacitor two C2 is replaced with the diode four D4 connected in reverse. In the third variant, a reverse connection is made with a diode tri-D3 between the base of the bias transistor HBT2 (i.e. node a) and the base of the power transistor HBT1 (i.e. node B). Reverse connection refers to the cathode connection node a and the anode connection node B of the diode tri-D3. There is a diode four D4 reverse connection between the base of the bias transistor HBT2 (i.e. node a) and ground. The reverse connection means that the cathode of the diode four D4 is connected with the node A, and the anode is grounded. The three D3 and four D4 diodes are formed by shorting and equivalent connecting the base and collector of the HBT, the shorted base and collector of the HBT are equivalent to the anode of the diode, and the emitter of the HBT is equivalent to the cathode of the diode.
Referring to fig. 9, this is an equivalent circuit of the reverse-connected diode tri D3 and the reverse-connected diode tetra D4 in fig. 8. Since the static voltage of node a is higher than that of node B in fig. 8, the reverse-connected diode tri-D3 is equivalent to a parallel network of an adjustable resistor Ra1 and an adjustable capacitor Ca 1. The resistance value of the adjustable resistor Ra1 and the capacitance value of the adjustable capacitor Ca1 are all changed along with the voltage difference between the node a and the node B. Since the static voltage at node a in fig. 8 is higher than ground, the reverse-connected diode four D4 is equivalent to a parallel network of the adjustable resistor two Ra2 and the adjustable capacitor two Ca 2. The resistance value of the adjustable resistor two Ra2 and the capacitance value of the adjustable capacitor two Ca2 are changed along with the voltage of the node A. Similar to the embodiment, the first adjustable capacitor Ca1 equivalent to the third diode D3 and the second adjustable capacitor Ca2 equivalent to the fourth diode D4 in the reverse connection in the bias circuit are connected in series to form a capacitor serial branch, and the parasitic base-collector capacitor Cbc of the power transistor HBT1 is grounded through the capacitor serial branch, so that the parasitic base-collector capacitor Cbc of the power transistor HBT1 is reduced, the AM-PM offset of the radio frequency power amplifier is improved, and the linearity is improved. The adjustable capacitor one Ca1 equivalent to the diode three D3 connected in the reverse direction couples the radio frequency input signal RFin to the base electrode of the bias transistor HBT2, and the adjustable capacitor two Ca2 equivalent to the diode four D4 connected in the reverse direction reduces the impedance of the bias circuit so that the radio frequency input signal RFin is easier to couple to the bias transistor HBT2, thereby delaying the gain compression phenomenon of the radio frequency power amplifier, improving the AM-AM imbalance of the radio frequency power amplifier and improving the linearity.
Referring to fig. 10, a second embodiment of an adaptive bias rf power amplifier is provided. The second embodiment also mainly includes an amplifying circuit and a bias circuit, wherein the amplifying circuit is the same as the first embodiment, and the bias circuit is different from the first embodiment. The bias circuit in the second embodiment mainly includes a bias transistor HBT2 and a mirror transistor HBT3, which are, for example, gallium arsenide HBTs. A resistor R1 and a mirror transistor HBT3 are connected in series in sequence between the supply voltage Vcc and ground. The collector of the mirror transistor HBT3 is connected to resistor R1 and the emitter is grounded. The base of biasing transistor HBT2 (i.e. node a) is connected to the collector of mirror transistor HBT3. Node a is also connected to the base of the power transistor HBT1 (i.e. node B) via a capacitor C1. Node a is also connected to ground through capacitor two C2. The collector of bias transistor HBT2 is connected to supply voltage Vcc and the emitter is connected to node B, i.e. to the base of power transistor HBT1, via resistor two R2. The base of the mirror transistor HBT3 is connected to the emitter of the bias transistor HBT2 via a resistor tri R3. The emitter of bias transistor HBT2 provides a bias current to the base of power transistor HBT 1.
In the bias circuit of the second embodiment, the bias transistor HBT2 and the mirror transistor HBT3 constitute a current mirror. The working principle of the second embodiment is similar to that of the embodiment. On the one hand, the parasitic capacitance Cbc of the base-collector of the power transistor HBT1 is grounded through a capacitor serial branch composed of a capacitor one C1 and a capacitor two C2 in the bias circuit, which improves AM-PM imbalance of the radio frequency power amplifier and improves linearity. On the other hand, the first capacitor C1 couples the radio frequency input signal RFin to the base of the bias transistor HBT2, and the second capacitor C2 reduces the impedance of the bias circuit so that the radio frequency input signal RFin is more easily coupled to the bias transistor HBT2, thereby improving the AM-AM offset of the radio frequency power amplifier and improving the linearity. The second embodiment directly aims at the AM-PM imbalance and AM-AM imbalance of the power transistor responsible for signal amplification, the improvement effect is more obvious than that of an indirect mode, and the circuit design is more reasonable and ingenious.
Similarly to the first embodiment having three modified circuits, the first capacitor C1 in the second embodiment may be replaced with the third diode D3 connected in the reverse direction, the second capacitor C2 may be replaced with the fourth diode D4 connected in the reverse direction, and the two alternatives may be replaced separately or simultaneously.
Referring to fig. 11, a graph of gain versus output power of a rf power amplifier is shown. Where curve a represents a conventional adaptive biased radio frequency power amplifier and curve B represents an adaptive biased radio frequency power amplifier of the present application. Experiments have shown that as the output power increases (and also as the input power increases), curve a enters the gain compression stage earlier; curve B enters the gain expansion stage and then the gain compression stage. Curve B enters the gain compression stage later than curve a. This indicates that the present application ameliorates AM-AM imbalance.
Referring to fig. 12, a schematic diagram of the phase versus output power of the rf power amplifier is shown. Where curve a represents a conventional adaptive biased radio frequency power amplifier and curve B represents an adaptive biased radio frequency power amplifier of the present application. Experiments have shown that as the output power increases (and also as the input power increases), curve a exhibits phase imbalance earlier and curve B exhibits phase imbalance later. This suggests that the present application improves AM-PM imbalance.
The foregoing is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.
Claims (9)
1. An adaptive bias radio frequency power amplifier comprises an amplifying circuit and a bias circuit; the amplifying circuit is provided with a power transistor, the biasing circuit is provided with a biasing transistor, and an emitter of the biasing transistor is connected with a base electrode of the power transistor through a resistor to provide biasing current and/or biasing voltage for the power transistor; the bias circuit is characterized in that the bias circuit is also provided with a capacitor serial branch circuit, and the bias circuit is formed by connecting at least two capacitors in series; one end of the capacitor serial branch is connected with the base electrode of the power transistor, the other end of the capacitor serial branch is grounded, at least one capacitor in the capacitor serial branch is connected with the base electrode of the power transistor and the base electrode of the bias transistor, and at least one other capacitor in the capacitor serial branch is grounded.
2. The adaptively biased rf power amplifier of claim 1, wherein in said amplifying circuit, the base of the power transistor receives the rf input signal through a capacitor three; the emitter of the power transistor is grounded; the collector electrode of the power transistor outputs an amplified radio frequency signal; there is a base-collector parasitic capacitance between the base and collector of the power transistor.
3. The adaptive bias radio frequency power amplifier according to claim 1, wherein in the bias circuit, a base electrode of the bias transistor is connected to the voltage dividing branch, and is further connected to a base electrode of the power transistor through a capacitor connection, and is further grounded through a capacitor II; the capacitor I and the capacitor II are connected in series to form the capacitor serial branch circuit; the collector of the bias transistor is connected with a power supply voltage; the emitter of the bias transistor is connected to the base of the power transistor through a resistor II; the voltage dividing branch is formed by sequentially connecting a first resistor, a first diode and a second diode in series between the power supply voltage and the ground; the base of the bias transistor is connected between the first resistor and the first diode in the voltage dividing branch, i.e. to the anode of the first diode.
4. The adaptively biased rf power amplifier of claim 1, wherein said biasing circuit further comprises a mirror transistor; the base of the bias transistor is connected to the collector of the mirror transistor; the base electrode of the bias transistor is also connected with the base electrode of the power transistor through a capacitor connection and is grounded through a capacitor II; the capacitor I and the capacitor II are connected in series to form the capacitor serial branch circuit; the collector of the bias transistor is connected with a power supply voltage; the emitter of the bias transistor is connected with the base electrode of the power transistor through a resistor II; the base electrode of the mirror image transistor is connected with the emitter electrode of the bias transistor through a resistor III; the collector of the mirror image transistor is connected with the power supply voltage through a resistor I; the emitter of the mirror transistor is grounded; the mirror transistor and the bias transistor form a current mirror circuit.
5. The adaptively biased rf power amplifier of claim 3 or 4, wherein the first capacitor is replaced by a third diode, a cathode of the third diode is connected to a base of the bias transistor, and an anode of the third diode is connected to a base of the power transistor; the diode III is equivalent to the parallel connection of an adjustable resistor I and an adjustable capacitor I; the adjustable capacitor I and the capacitor II are connected in series to form the capacitor serial branch circuit; the tunable capacitance also serves as a capacitance connecting the base of the power transistor and the base of the bias transistor.
6. The adaptively biased rf power amplifier of claim 3 or 4, wherein the second capacitor is replaced by a fourth diode, a cathode of the fourth diode is connected to a base of the bias transistor, and an anode of the fourth diode is grounded; the fourth diode is equivalent to the parallel connection of the second adjustable resistor and the second adjustable capacitor; the first capacitor and the second adjustable capacitor are connected in series to form the capacitor series branch.
7. The adaptively biased rf power amplifier of claim 3 or 4, wherein the first capacitor is replaced by a third diode, a cathode of the third diode is connected to a base of the bias transistor, and an anode of the third diode is connected to a base of the power transistor; the diode III is equivalent to the parallel connection of an adjustable resistor I and an adjustable capacitor I; the second capacitor is replaced by a fourth diode, the cathode of the fourth diode is connected with the base electrode of the bias transistor, and the anode of the fourth diode is grounded; the fourth diode is equivalent to the parallel connection of the second adjustable resistor and the second adjustable capacitor; the first adjustable capacitor and the second adjustable capacitor are connected in series to form the capacitor series branch; the tunable capacitance also serves as a capacitance connecting the base of the power transistor and the base of the bias transistor.
8. The adaptively biased radio frequency power amplifier of claim 4, wherein part or all of said power transistor, bias transistor, mirror transistor is a gallium arsenide HBT.
9. The adaptively biased rf power amplifier of claim 5, wherein some or all of the diodes are formed by shorting and equalizing the base and collector of the HBT, the shorted base and collector of the HBT being equalizing the anode of the diode and the emitter of the HBT being equalizing the cathode of the diode.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110190824B (en) * | 2019-05-30 | 2023-02-07 | 广东工业大学 | Active bias network and radio frequency power amplifier |
| CN110719077B (en) * | 2019-10-23 | 2022-08-16 | 广州慧智微电子股份有限公司 | Power amplifier and electronic equipment |
| CN111147033A (en) * | 2020-01-02 | 2020-05-12 | 尚睿微电子（上海）有限公司 | Power amplifier and electronic equipment based on HBT circuit structure |
| CN111404501B (en) * | 2020-03-26 | 2023-08-29 | 芯朴科技(上海)有限公司 | Bias circuit of thermal tracking compensation power amplifier |
| CN113783540B (en) * | 2021-08-17 | 2022-09-23 | 深圳飞骧科技股份有限公司 | Power amplifier circuit and bias circuit thereof |
| CN114553151B (en) * | 2022-02-25 | 2022-12-20 | 优镓科技(苏州)有限公司 | Doherty power amplifier based on self-adaptive bias |
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