Patent ID: 12244269

DETAILED DESCRIPTION

Below, exemplary embodiments will be described in detail with reference to accompanying drawings so as to be easily realized by a person having ordinary knowledge in the art. The inventive concept may be embodied in various forms without being limited to the exemplary embodiments set forth herein. Descriptions of well-known parts are omitted for clarity, and like reference numerals refer to like elements throughout.

FIG.1is a circuit diagram of a power amplifier10according to an embodiment of the present invention. The power amplifier10comprises a bias circuit100, a compensation circuit200, and a core circuit300. The core circuit300comprises an amplifying transistor T1, a resistor RB1, and a resistor RB2. The amplifying transistor T1is configured to amplify a radio frequency (RF) signal RFin and output an amplified radio frequency signal RFa. A control end of the amplifying transistor T1receives the radio frequency signal RFin, and a first end of the amplifying transistor T1is coupled to a first system voltage end VCC for receiving a first system voltage. A second end of the amplifying transistor T1is coupled to the first reference voltage end GND, and the first reference voltage end GND is configured to provide a ground voltage or other reference voltage lower than the voltage level of the first system voltage end VCC. The first end of the amplifying transistor T1is coupled to a matching circuit so as to output the amplified radio frequency signal RFa, or the first end of the amplifying transistor T1is coupled to a next-stage amplifying circuit. A first end of the resistor RB1is coupled to the output end of the bias circuit100, a first end of the resistor RB2is coupled to the output end of the compensation circuit200, and a second end of the resistor RB1and a second end of the resistor RB2are both coupled to a control end of the amplifying transistor T1. The resistor RB1is configured to provide a first resistance, and the resistor RB2is configured to provide a second resistance. Furthermore, the bias circuit100comprises a bias transistor QB1, which would provide a bias current iB1. The compensation circuit200comprises a compensation transistor QB2, which would provide a compensation current iB2. The compensation transistor QB2of the compensation circuit200's operation region may be controlled according to the radio frequency signal RFin.

In some embodiments, the resistance between the control end of the amplifying transistor T1and the bias transistor QB1is greater than the resistance between the control end of the amplifying transistor T1and the compensation transistor QB2. As shown inFIG.1, the first resistance of the resistor RB1is greater than the second resistance of the resistor RB2. For example, the first resistance may be one or more hundred times the second resistance, but the present invention is not such limited. The ratio between the second resistance and the first resistance may be adjusted and optimized according to the specification requirements of the power amplifier10.

In some embodiments, the first system voltage end VCC may provide a direct-current (DC) voltage, and the voltage provided by the first system voltage end VCC may not change with the power of the radio frequency signal RFin.

In the embodiment shown inFIG.1, since the second end of the resistor RB1and the second end of the resistor RB2are both coupled to the control end of the amplifying transistor T1, the resistor RB1and the resistor RB2are in likewise parallel with each other, so that the equivalent resistance of the combination of the resistors RB1and RB2may approximately be a parallel resistance of the resistors RB1and RB2, and the equivalent resistance is less than the first resistance of the resistor RB1and less than the second resistance of the resistor RB2. In the absence of compensation transistor QB2and the resistor RB2, the greater the power of the RF signal RFin, the greater the current flowing through the bias transistor QB1, which will cause an increase in the cross voltage of the resistor RB1, thereby pulling down a node voltage VBTand affecting the operations of the amplifying transistor T1. In the embodiment, when the power of the radio frequency signal RFin is great enough, the bias transistor QB1and the compensation transistor QB2are both turned on, thereby providing a greater driving current. Since the equivalent resistance of the resistors RB1and RB2is less than the first resistance of the resistor RB1and less than the second resistance of the resistor RB2, a bias voltage at the control end of the power transistor T1(i.e., the node voltage VBT) would be maintained relatively stable. Therefore, the gain of the power amplifier10for the radio frequency signal RFin may not be such affected and the saturation output power of the power amplifier10may not be reduced.

In an embodiment of the present invention, when the power of the radio frequency signal RFin is a first power, the bias transistor QB1is turned on, the compensation transistor QB2is turned off, the compensation current iB2is almost zero, and the bias current iB1is greater than the compensation current iB2. When the power of the radio frequency signal RFin increases, the conduction degree of the compensation transistor QB2would be increased to provide an appropriate compensation current iB2. When the power of the radio frequency signal RFin is further increased to a second power, both the bias transistor QB1and the compensation transistor QB2are turned on. Since the first resistance of the resistor RB1is greater than the second resistance of the resistor RB2, the bias current iB1would be less than the compensation current iB2.

FIG.2shows a relationship curve510between the bias current iB1and the output power of the power amplifier10inFIG.1and a relationship curve520between the compensation current iB2and the output power of the power amplifier10. In an embodiment of the present invention, when the power amplifier10is powered, the bias transistor QB1would be turned on to provide the bias current iB1. When the power of the radio frequency signal RFin is low, the compensation transistor QB2is turned off. When the power of the radio frequency signal RFin is high enough, the output power of the power amplifier10may be relatively high, and both the bias transistor QB1and the compensation transistor QB2would be turned on to provide the bias current iB1and the compensation current iB2respectively. The bias current iB1flows through the resistor RB1, and the compensation current iB2flows through the resistor RB2. For example, as shown inFIG.2, when the output power of the power amplifier10is less than about 23 dB, the compensation transistor QB2is turned off, and the bias transistor QB1is turned on, such that the drive current for the amplifying transistor T1is approximately equal to the bias current iB1. When the output power of the power amplifier10is approximately equal to or greater than 23 dB, both the bias transistor QB1and the compensation transistor QB2are turned on, such that the drive current for the amplifying transistor T1is approximately equal to the sum of the bias current iB1and the compensation current iB2(i.e., approximately equal to iB1+iB2). In the embodiment, the power amplifier10may operate in a back off region where the bias transistor QB1is turned on and the compensation transistor QB2is turned off. In this case, the power amplifier10may be operated as a class-B amplifier to obtain a better power added efficiency (PAE). When the output power of the power amplifier10is great enough, both the bias transistor QB1and the compensation transistor QB2are turned on. In this case, the equivalent resistance of the resistors RB1and RB2is relatively reduced, so that the saturation output power of the power amplifier10would be increased.

FIG.3is a circuit diagram of a power amplifier30according to an embodiment of the present invention. The power amplifier30comprises a bias circuit100A, a compensation circuit200A, and a core circuit300. The functions and operations of the core circuit300are similar to those of the core circuit300inFIG.1. For this part, please refer to the above description, which will not be repeated here. An example of the compensation circuit200A is further described below.

As shown inFIG.3, the compensation circuit200A comprises a detection circuit210, a voltage adjustment circuit220A, and a compensation transistor QB2. The detection circuit210is configured to generate a detection signal Sc according to the radio frequency signal RFin (e.g., according to the power of the radio frequency signal RFin). In an embodiment of the present invention, the detection circuit210comprises a diode D1. The cathode of the diode D1is coupled to the input end of the detection circuit210, and the anode is coupled to the output end of the detection circuit210. In the embodiment, the diode D1would clip the radio frequency signal RFin to generate the detection signal Sc. The detection circuit210may further comprise a capacitor C1, and the capacitor C1may be coupled between the input end of the detection circuit210and the diode D1, or coupled between the diode D1and the output end of the detection circuit210. The capacitor C1is configured to block a direct-current (DC) part of the radio frequency signal RFin.

As shown inFIG.3, in an embodiment of the present invention, the input end of the voltage adjustment circuit220A may be coupled to the output end of the detection circuit210, and the output end of the voltage adjustment circuit220A is configured to output the adjustment voltage VBto the control end of the compensation transistor QB2. Furthermore, the voltage adjustment circuit220A would adjust the adjustment voltage VBaccording to the detection signal Sc, and the compensation transistor QB2is turned on/off according to the adjustment voltage VB. For example, when the compensation transistor QB2is turned on, the compensation transistor QB2would provide the compensation current iB2flowing to the control end of the amplifying transistor T1. In other words, the compensation transistor QB2would be turned off or turned on according to the detection signal Sc, thereby selectively providing the compensation current iB2.

As shown inFIG.3, in the embodiment, the voltage adjustment circuit220A comprises a resistor R3, a transistor T3, a resistor R4, and a transistor T4. A first end of the resistor R3is coupled to a second reference voltage end VREF, a second end of the resistor R3is coupled to a first end of the transistor T3, and a second end of the transistor T3is coupled to the first reference voltage end GND. The control end of the transistor T3is coupled to the input end of the voltage adjustment circuit220A, so as to receive the detection signal Sc. As shown inFIG.3, the first end of the transistor T3may be coupled to the output end of the voltage adjustment circuit220A, so as to output the adjustment voltage VB. A first end of the resistor R4is coupled to the second reference voltage end VREF, and a second end of the resistor R4is coupled to a first end of the transistor T4. A second end of the transistor T4is coupled to the first reference voltage end GND, and a control end of the transistor T4may be coupled to the first end of the transistor T4. In other words, the second end of the resistor R4, the first end of the transistor T4, and the control end of the transistor T4are coupled to each other, and are further coupled to the input end of the voltage adjustment circuit220A. In other embodiments, the voltage adjustment circuit220A further comprises a resistor R7. A first end of the resistor R7may be coupled to the control end of the transistor T4, and a second end is coupled to the input end of the voltage adjustment circuit220A. As shown inFIG.3, the first end and the control end of the transistor T4are coupled to each other via the resistor R7.

As shown inFIG.3, in an embodiment of the present invention, the voltage adjustment circuit220A comprises a filter LP1. The filter LP1is coupled between the input end of the voltage adjustment circuit220A and the control end of the transistor T3. Furthermore, the filter LP1may comprise a resistor Ra and a capacitor Ca. One end of the resistor Ra is coupled to the input end of the voltage adjustment circuit220A, and the other end is coupled to the control end of the transistor T3. One end of the capacitor Ca is coupled to the control end of the transistor T3, and the other end is coupled to the first reference voltage end GND. The voltage adjustment circuit220A may further comprise a filter LP2, which comprises a resistor Rb and a capacitor Cb. The filter LP2is coupled between the first end of the transistor T3and the output end of the voltage adjustment circuit220A. That is, the first end of the transistor T3may be coupled to the output end of the voltage adjustment circuit220A via the filter LP2. Furthermore, one end of the resistor Rb may be coupled to the first end of the transistor T3, and the other end may be coupled to the output end of the voltage adjustment circuit220B. One end of the capacitor Cb is coupled to the above other end of the resistor Rb, and the other end of the capacitor Cb is coupled to the first reference voltage end GND. In some embodiments, the filter LP1and/or the filter LP2may be low-pass filters, which allow lower-frequency signals to pass. In the above embodiments, the capacitance of the capacitor Cb may be greater than the capacitance of the capacitor Ca. For example, the capacitance of the capacitor Ca can be 1 to 2 picofarads (1 PF to 2 PF), and the capacitance of the capacitor Cb can be 8 picofarads (8 PF), but the present invention is not such limited. The capacitance of capacitor Ca and the capacitance of the capacitor Cb may be adjusted according to the specification requirements of the voltage adjustment circuit220A.

In an embodiment of the present invention, the compensation circuit200A may further comprise a compensation capacitor Cq coupled between the first end of the compensation transistor QB2and the first reference voltage end GND.

As shown inFIG.3, in an embodiment of the present invention, as for the compensation transistor QB2, the first end of may be coupled to a device voltage end VDD, the second end may be coupled to the first end of the resistor RB2, and the control end may be coupled to the output end of the voltage adjustment circuit220A so as to receive the adjustment voltage VB. In a further embodiment, the compensation circuit200A may further comprise a compensation resistor R2, a first end of which is coupled to the device voltage end VDD, and a second end of which is coupled to the first end of the compensation transistor QB2. In other embodiments, the first end of the compensation resistor R2may also be coupled to the second reference voltage end VREF (as shown inFIG.5).

In some embodiments, when the power of the radio frequency signal RFin changes, the detection signal Sc generated by the detection circuit210changes accordingly. For example, when the power of the radio frequency signal RFin increases, the average voltage of the detection signal Sc output by the detection circuit210decreases due to the clipping effect (on the radio frequency signal RFin of the reversely connected diode D1in the detection circuit210. As shown inFIG.3, the rectification by the filter LP1reduces the node voltage VA. That is, the voltage at the control end of the transistor T3is reduced, thereby reducing the conduction degree of the transistor T3. In this case, the current flowing between the first end and the second end of the transistor T3would decrease, so that the voltage across two ends of the resistor R3decreases. Accordingly, the voltage at the first end of the transistor T3increases, and the adjustment voltage VBof the voltage adjustment circuit220A increases. When the adjustment voltage VBincreases to be greater than a predetermined value, the compensation transistor QB2is turned on. Meanwhile, the compensation transistor QB2would provide the compensation current iB2flowing to the control end of the amplifying transistor T1.

As shown inFIG.3, in an embodiment of the present invention, the bias circuit100A is similar to the bias circuit100inFIG.1with the difference that, in addition to the bias voltage transistor QB1, the circuit100A may further comprise a reference current source110, a reference resistor Rf, at least one diode Df (e.g., two diodes Df as shown inFIG.3), and a capacitor Cf. The reference current source110is configured to provide a reference current IREF. A first end of the reference resistor Rf is coupled to the reference current source IREF, and a second end of the reference resistor Rf is coupled to the control end of the bias transistor QB1. In the embodiment, the number of diodes Df is two, but the invention is not such limited. The bias circuit100A may comprise three or more diodes Df connected in series. The diodes Df of the bias circuit100A are coupled between the second end of the reference resistor Rf and the first reference voltage end GND, so as to control the bias voltage at the control end of the bias voltage transistor QB1, so that an output end O1of the bias circuit100A mat provide the bias current iB1. The capacitor Cf may be coupled between the control end of the bias transistor QB1and the first reference voltage end GND.

FIG.4is a circuit diagram of a bias circuit100B of a power amplifier according to another embodiment of the present invention. The bias circuit100B is configured to replace the bias circuit100A inFIG.3. The bias circuit100B comprises a bias transistor QB1, a reference current source110, and a transistor Q3. The reference current source110is configured to provide the reference current IREF, and the output end of the reference current source110is coupled to a control end of the bias transistor QB1. As for the transistor Q3, a first end of is coupled to the output end of the reference current source110, a second end is coupled to the first reference voltage end GND, and a control end is coupled to the second end of the bias transistor QB1and coupled to the output end O1of the bias circuit100B. In the embodiment, the first end of the bias transistor QB1may be coupled to a battery voltage end VBATT, and the battery voltage end VBATT is configured to receive a voltage provided by an external battery. In other embodiments, the first end of the bias transistor QB1may also be coupled to the device voltage end VDD (as shown inFIG.3). In a further embodiment, the bias circuit100B may further comprise a resistor Rx, a first end of the resistor Rx is coupled to the control end of the transistor Q3, and a second end of the resistor Rx is coupled to the second end of the bias transistor QB1. In the embodiment, the output end O1of the bias circuit100B may be coupled to the first end of the resistor RB1(as shown inFIG.3).

FIG.5is a circuit diagram of a power amplifier20according to another embodiment of the present invention. The power amplifier20comprises the bias circuit100A, a compensation circuit200B, and the core circuit300. The compensation circuit200B comprises a detection circuit210, a voltage adjustment circuit220B, and a compensation transistor QB2. In the embodiment, the bias circuit100A, the core circuit300, the detection circuit210of the compensation circuit200B, and the compensation transistor QB2of the compensation circuit200B are similar to those inFIG.3, which will not be repeated here. Hereinafter, an example of the voltage adjustment circuit220B of the compensation circuit200B is further described.

As shown inFIG.5, in an embodiment of the present invention, the voltage adjustment circuit220B comprises a resistor R5, a transistor T5, and a resistor R6. As for the resistor R5, a first end of is coupled to the second reference voltage end VREF, and a second end is coupled to a first end of the transistor T5. As for the transistor T5, a second end of is coupled to the first reference voltage end GND, and a control end is coupled to the input end of the voltage adjustment circuit220B so as to receive the detection signal Sc. As shown inFIG.5, the first end of the transistor T5may be coupled to the output end of the voltage adjustment circuit220B to output the adjustment voltage VB. A first end of the resistor R6is coupled to the bias circuit100A, specifically, to the second end of the bias transistor QB1of the bias circuit100A. A second end of the resistor R6is coupled to the input end of the voltage adjustment circuit220B.

As shown inFIG.5, in an embodiment of the present invention, the voltage adjustment circuit220B comprises a filter LP1and/or a filter LP2. The filter LP1is coupled between the input end of the voltage adjustment circuit220A and the control end of the transistor T5, and/or the filter LP2is coupled between the first end of the transistor T5and the output end of the voltage adjustment circuit220B. The filter LP1and/or the filter LP2may be similar to those shown inFIG.3, which will not be repeated here.

When the voltage of the detection signal Sc increases, the conduction degree of the transistor T5increases, and the current flowing between the first end and the second end of the transistor T5increases, resulting in an increase in voltage across the two ends of the resistor R5. Therefore, the voltage level at the first end of the transistor T5decreases, so that the adjustment voltage VBprovided by the voltage adjustment circuit220B decreases. When the adjustment voltage VBdrops below a predetermined value, the compensation transistor QB2is turned off, where the compensation transistor QB2stop providing the compensation current iB2flowing to the control end of the amplifying transistor T1. Similar to the related description inFIG.3, when the voltage level of the detection signal Sc decreases, the conduction degree of the transistor T5decreases, which in turn causes the adjustment voltage VBto increase. It may be noted that the detection signal Sc is generated according to the radio frequency signal RFin clipped by the diode D1. The diode D1may cut off the upper swing of the radio frequency signal RFin. Therefore, the higher the power of the radio frequency signal RFin is, the larger the swing of the radio frequency signal RFin is, and the more of the swing of the radio frequency signal RFin may be clipped off by the diode D1. However, since the lower swing of the radio frequency signal RFin may also be larger, an average voltage of the detection signal Sc is reduced and the node voltage VAis therefore reduced. When the node voltage VAdecreases, the conduction degree of the transistor T5will decrease, and the current flowing through the resistor R5will decrease. When the current flowing through the resistor R5decreases, the voltage across the two ends of the resistor R5will also decrease, so that the adjustment voltage VBincreases and the compensation transistor QB2is turned on to provide the compensation current iB2. In addition, the reference voltage provided by the second reference voltage end VREF may be adjusted according to the characteristics (e.g., resistance) of the components of the voltage adjustment circuit220B, so that the compensation transistor QB2of the voltage adjustment circuit220B would be turned on to provide the compensation current iB2when the node voltage VAdrops to a predetermined voltage (correspondingly, when the adjustment voltage VBincreases to be greater than a predetermined value).

In the above embodiments, it is noted that the input end of the detection circuit210is coupled to the input end of the core circuit300which belongs to the same-stage power amplifier (e.g., the power amplifier30inFIG.3), to receive the radio frequency signal RFin. However, the present invention is not such limited. In other embodiments, the input end of the detection circuit210may also be coupled to an input end of a pre-stage or post-stage power amplifier, so as to receive the input radio frequency signal of the pre-stage or post-stage power amplifier. Similarly, in other further embodiments, the input end of the detection circuit210may also be coupled to an output end of a power amplifier (e.g., an output end of a same-stage, pre-stage, and/or post-stage power amplifier) so as to receive an output frequency signal of the same-stage, pre-stage, or post-stage power amplifier (e.g., the amplified radio frequency signal RFa of the power amplifier30inFIG.3). In this case, since the input and output RF signals of the pre-stage, same-stage, and post-stage power amplifiers may be correlated with each other (e.g., positively correlated), the detection signal Sc generated by the detection circuit210would be transmitted to the voltage adjustment circuit to control the operations of the compensation transistor QB2.

In an embodiment of the present invention, the core circuit300also comprises a blocking capacitor C, which is coupled between the input end of the power amplifier and the control end of the amplifying transistor T1to block a direct current (DC) signal in the radio frequency signal RFin. In an embodiment of the present invention, the core circuit300may further comprise a resistor RE coupled between the second end of the amplifying transistor T1and the first reference voltage end GND.

In other embodiments of the present invention, the aforementioned resistor RB2may be omitted, and the second end of the compensation transistor QB2may be coupled to the control end of the amplifying transistor T1. For example, a conducting wire between the second end of the compensation transistor QB2and the control end of the amplifying transistor T1may be used to replace the resistor RB2.

According to the above embodiments of the present invention, when the output power of the power amplifier is low, the bias transistor is turned on, and the compensation transistor is turned off. When the output power of the power amplifier is large enough, both the bias transistor and the compensation transistor are turned on, thereby providing a larger driving current. Since the equivalent resistance of the combination of the two resistors is less than the resistance of any one of the two resistors, where the two resistors are respectively coupled to the bias transistor and the compensation transistor, the bias voltage at the control end of the amplifying transistor would be maintained relatively stable. Therefore, even if the power amplifier outputs a large power, gain of the power amplifier may be still maintained, and power of the amplified RF signal output by the power amplifier may be maintained stable. Accordingly, the embodiments of the present invention would provide good power added efficiency (PAE).

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.