Driving circuits for switch mode RF power amplifiers

Driving circuit of switching mode radio frequency power amplifier

<p>1. . . lead</p><p>2. . . driver</p><p>3. . . lead</p><p>5. . . Active device</p><p>6. . . Single pole single throw switch</p><p>6-1. . . Wave</p><p>6-2. . . Wave</p><p>6-3. . . Wave</p><p>7. . . DC power supply</p><p>9. . . Load network</p><p>10-1. . . Wave</p><p>10-2. . . Wave</p><p>10-3. . . Wave</p><p>10-4. . . Wave</p><p>11. . . load</p><p>201. . . RF input signal</p><p>203. . . Driver amplifier</p><p>205. . . Matching network</p><p>207. . . Field Effect Transistor</p><p>301. . . RF input signal</p><p>303. . . Drive circuit</p><p>305. . . Active device switch</p><p>307. . . Load network</p><p>309. . . Fast variable power supply</p><p>401. . . Output network</p><p>501. . . Impedance matching transmission line</p><p>901. . . Output network</p>

From the following description and referring to the accompanying drawings, the present invention will be more clear:

Figure 1 is a simplified block diagram of a known single-ended switching mode RF amplifier;

Figure 2 is a schematic diagram of a part of a known radio frequency amplifier;

Figure 3 is a block diagram of the RF switching mode amplifier of the present invention;

4 is a schematic diagram of a part of the RF switching mode amplifier in an example of the present invention;

Figure 5 is a schematic diagram of the load network used in the RF switching mode amplifier of Figure 4;

Figure 6 is a waveform diagram of the input voltage and related waveforms of the RF switching mode amplifier used in Figure 4;

FIG. 7 is a waveform diagram of switching the base and collector currents of the transistor in FIG. 4;

Fig. 8 is a waveform diagram of the output voltage of the RF switching mode amplifier of Fig. 4;

9 is a schematic diagram of a part of a radio frequency switching mode amplifier of another example of the present invention;

Figure 10 is a waveform diagram of the input voltage and related waveforms of the RF switching mode amplifier of Figure 9;

Figure 11 is a waveform diagram of the collector current of the driving transistor in Figure 9; and

Fig. 12 is a waveform diagram of the gate voltage of the switching transistor of Fig. 9;

Background of the invention 1. Field of invention

The present invention is related to a driving circuit for switching mode radio frequency power amplifiers.

2. Technical level

The battery life is the main key to radio communication devices such as mobile phones, pagers, and wireless modems. The contributing factor for the power consumption of these devices is the insufficient operating efficiency of the power amplifier. A standard RF power amplifier used for radio communications only operates with an efficiency of about 10%. Obviously, a low-cost technology that can greatly increase amplifier efficiency will meet this urgent need.

In addition, most modem digital radio communication devices operate in an encapsulated manner, that is, the transmitted information is sent out in a series of one or more short packets and the transmitter only works in the time of the cluster but at other times None of them work. Therefore, it is best to control the energy-efficient removal of clusters, so as to extend the battery life.

Power amplifiers can be divided into different types: Class A, Class B, Class AB, etc. Different types of power amplifiers usually indicate different bias or load conditions. When designing RF power amplifiers, there is usually a trade-off between linearity and efficiency. Different types of amplifier operations can give designers a way to balance these two parameters.

Generally speaking, there are two types of power amplifiers, namely linear and non-linear. Linear amplifiers (such as class A amplifiers and class B push-pull amplifiers) maintain a high degree of linearity and have faithful reproduction of the input signal at their output because the output signal is proportional to the input signal in terms of linearity. In non-linear amplifiers (such as single-ended Class B and Class C amplifiers), the output signal is not directly proportional to the input signal. As a result, the amplitude distortion caused on the output signal makes this type of amplifier most commonly used for signals without any amplitude modulation, also known as fixed envelope signals.

The output efficiency of the amplifier is determined by the ratio between the RF output power and the input (DC) power. The main source of power amplifier efficiency is the power dissipated in the transistor. The poor efficiency of Class A amplifiers is because current continues to flow through the device regardless of whether there is an output signal. The traditional way to improve efficiency is to sacrifice linearity in exchange for increased efficiency. For example, in the class B amplifier, the selection of the bias condition is to make the output signal cut off in half a cycle unless there are quasi-two transistors (push-pull) in the opposite half of the cycle. Therefore, the linearity difference of the waveform is less. The output waveform may still need to use a tank or other filter to filter out higher or lower frequency components into a sine wave.

Class C amplifier conducts in less than half a cycle to increase efficiency: that is, if the conduction angle of the output current is less than 180 degrees, the amplifier is called Class C. This mode of operation is more efficient than Class A or Class B but also causes more distortion than Class A or Class B amplifiers. For class C amplifiers, when the input amplitude changes, the output amplitude will still change somewhat. This is because the Class C amplifier operates like a controlled current source-although only briefly closed-but not a switch.

The other types of amplifiers also have the problem of dissipating power in the transistor, and only use the transistor as a switch. The theory of this type of amplifier is that the switch will ideally not dissipate power, because neither voltage nor current flows. Because the VI product of the switch is always zero, ideally it will not consume power. Class E power amplifiers use a single transistor in contrast to Class D power amplifiers that use two transistors.

But in fact the switch is not ideal (the switch has opening and closing time and closing resistance). The associated dissipation will also reduce efficiency. Therefore, the previous technology seeks to modify the so-called "switching mode" amplifier (in which the transistor is used as a switch at the operating frequency and when the transistor is conducting, the power dissipation is minimized so that the non-zero time interval of the switching instant is The voltage of the middle switch is zero, thereby reducing power dissipation. Class E amplifiers use a reactive output network to provide a sufficient degree of freedom to make the switching voltage zero and zero slope when the switch is turned on, thereby reducing the switching loss. F Class amplifier is another switching mode amplifier that can produce a more squarer output waveform than the usual sine wave. The "more squarer" of this output waveform is because it encourages the generation of odd harmonics in the output network (ie x3, x5, x7) Etc.) while suppressing even-numbered harmonics (ie x2, x4, etc.).

Figure 1 shows an example of a known class E power amplifier described in US Patent No. 3,919,656. Here is a reference: the RF input signal is coupled to lead 1 to driver 2, which passes through the signal coupled to lead 3. Control active device 5. The active device 5 becomes a switch when it is properly driven by the driver 2. Therefore, the output port of the active device is a single-pole single-throw switch 6. The switch 6 is connected to the series combination of the DC power supply 7 and the input port of the load network 9. The output port of the load network 9 is connected to the load 11. Since the switch 6 is periodically operated at the required AC output frequency, the DC power of the power supply 7 is converted into the AC power of the switching frequency (along with its harmonics). Although the arrangement in Figure 1 can achieve high conversion efficiency, it has the disadvantage of a large voltage swing at the output of the active device due to ringing. This large voltage swing exceeding three times the supply voltage makes it impossible to use Class E circuits for some active devices with low breakdown voltage.

Furthermore, the driving circuit in the radio frequency amplifier includes a matching network including a tuning (resonant) circuit. Referring to the arrangement in FIG. 2, the RF input signal 201 is coupled to the driver amplifier 203, which is a standard type A operation. The output signal of the driver amplifier is coupled to the control connector of the switching transistor 207 (shown as a field effect transistor in FIG. 2) through the matching network 205. Just like the design of the load network in Figure 1, it is not easy to overdesign and match the road.

Brief description of the invention

The present invention generally provides a radio frequency amplifier circuit that can achieve high efficiency and avoid complicated matching networks and load networks. The active device can be bipolar transistor type or field effect transistor type. Each type of active device is equipped with a simple driving circuit. According to an example of the present invention, a single-ended switching mode radio frequency amplifier includes a radio frequency input signal, an active device with a control connector, and a non-resonant drive circuit for receiving the radio frequency signal and controlling the signal applied to the control connector to switch Mode to operate the active device.

Schematic description

From the following description and referring to the accompanying drawings, the present invention will be more clear:

Figure 1 is a simplified block diagram of a known single-ended switching mode RF amplifier;

Figure 2 is a schematic diagram of a part of a known radio frequency amplifier;

Figure 3 is a block diagram of the RF switching mode amplifier of the present invention;

4 is a schematic diagram of a part of the RF switching mode amplifier in an example of the present invention;

Figure 5 is a schematic diagram of the load network used in the RF switching mode amplifier of Figure 4;

Figure 6 is a waveform diagram of the input voltage and related waveforms of the RF switching mode amplifier used in Figure 4;

FIG. 7 is a waveform diagram of switching the base and collector currents of the transistor in FIG. 4;

Fig. 8 is a waveform diagram of the output voltage of the RF switching mode amplifier of Fig. 4;

9 is a schematic diagram of a part of a radio frequency switching mode amplifier of another example of the present invention;

Figure 10 is a waveform diagram of the input voltage and related waveforms of the RF switching mode amplifier of Figure 9;

Figure 11 is a waveform diagram of the collector current of the driving transistor in Figure 9; and

Fig. 12 is a waveform diagram of the gate voltage of the switching transistor of Fig. 9;

Detailed description of the preferred example

Refer to FIG. 3, which shows a block diagram of a preferred example of the RF switching mode amplifier of the present invention. The radio frequency input signal 301 is applied to the driving circuit 303, which can be a non-reactive driving circuit. The driving circuit is coupled to an active device switch 305 to drive the active device switch. The active device switch is coupled to the load network 307. The network generates a radio frequency output signal to be applied to a load such as an antenna (not shown). The power supply is preferably a fast variable power supply 309 which is a series combination of a switching mode power supply and a linear regulator so that the operating voltage of the active device switch can be changed. The above-mentioned power control, short-bus control and modulation can be achieved by changing the operating voltage in a control mode.

The active device can be a bipolar transistor or a field effect transistor. Refer to the schematic diagram of a part of the RF switching mode amplifier in FIG. 4, where the active device switch is a bipolar transistor N1, which has collector, emitter and base connections. The collector of the bipolar transistor N1 is connected to the operating voltage V through a radio frequency choke L _PA And connected to the output network 401. The emitter of the bipolar transistor N1 is connected to the ground of the circuit (AC).

The base of bipolar transistor N1 is connected to the emitter of another bipolar transistor N2 (driver transistor) in Darlington way. The collector of the driver transistor N2 is connected to the operating voltage V _DRIVER And connect to the bypass capacitor. Related to the driver transistor N2 is a bias network consisting of three resistors R1, R2, and R3. The resistor R1 is connected from the emitter of the driver transistor to the ground of the circuit. The resistor R2 is connected from the base of the driver transistor to ground. The resistor R3 is connected from the base of the driver transistor N2 to V _DRIVER . The RF input signal passes through the DC isolation capacitor C _in Add to the base of the driver transistor.

Referring to Figure 5, the output network can be an impedance matching transmission line 501 and a capacitor C _out The form.

The RF input voltage signal is a sine wave as shown in waveform 6-1 in Figure 6. The input voltage is shifted upward as shown in waveform 6-2 and a voltage is generated at the base of the driver transistor N2. The emitter voltage of the driver transistor N2 drops by one V as shown in the waveform 6-3 _be It is added to the base of the switching transistor N1. At the beginning of the positive half cycle, the driver transistor N2 operates like an emitter follower, and its output (emitter) voltage is lower than the switch-on voltage of the switching transistor N1 so that the switching transistor N1 is cut off. As shown in Figure 7, when the signal increases, the driver transistor N2 turns on the switching transistor N1 and drives it to saturation. As shown in Figure 8, the current flows through the radio frequency choke coil L and the switching transistor N1, and in the capacitor C _out The output voltage drops after discharging. At the end of the positive half cycle, the output voltage of the driver transistor N2 drops below the turn-on voltage of the switching transistor N1 and N1 is turned off. The value of the resistor R1 is selected so that the switching transistor N1 is turned off quickly. The current continues to flow through the choke coil L and the capacitor C _out Charge and make the output voltage rise.

Refer to the schematic diagram of part of the RF switching mode amplifier shown in Figure 9, where the active device switch is a field-effect transistor M1 (metal semiconductor field-effect transistor, junction field-effect transistor, etc.) with sink, source and gate connections . The suction pole of the field effect transistor M1 is connected to the operating voltage V through the RF choke L1 _PA It is also connected to the output network 901. The source of the field effect transistor is connected to the circuit (AC) ground.

The gate of the field-effect transistor is biased through a large-value resistor R1 to obtain a voltage from the power supply -V _B It is connected to a pair of bipolar transistors (driver transistors) in a push-pull arrangement via the DC blocking capacitor C1. The driver transistor includes an NPN transistor N1 and a PNP transistor P1. The collector of NPN driver transistor N1 is connected to the operating voltage V _CC Also connected to a bypass capacitor. The collector of PNP driver transistor P1 is connected to the negative reference voltage -V _B Also connected to a bypass capacitor. The bases of the driver transistors are connected together. Large value resistors R2 and R3 connect the common node to each power supply rail.

Another NPN bipolar transistor N2 is connected in a common base configuration. The emitter of the other bipolar transistor is connected to -V through resistor R4 _B And connected to the RF input signal through the capacitor C3. The collector of the other bipolar transistor is connected to V through the inductor L2 _CC And connected to a bypass capacitor.

Refer to the input voltage waveforms 10-1~10-4 of the circuit of Figure 9 shown in Figure 10. Input voltage 1 is shifted downward by one V _be And add to the emitter of the bipolar transistor N2. The inductor L2 generates a large voltage swing 3 at the collector of the bipolar transistor N2. This voltage swing shifts downward to generate a voltage 4 applied to the base of the driving transistor at node N. In operation, when the other bipolar transistor N2 is turned off at the beginning of the positive half cycle. When current flows through the inductor L2 and enters the capacitor C2 coupled to the base of the pair of transistors, the NPN transistor N1 is turned on and the PNP transistor P1 is turned off (Figure 11). DC blocking capacitor C1 from power supply V _CC Charge the potential of the high field-effect transistor M1 and make it turn on (Figure 12). In the negative half cycle, the bipolar transistor N2 is turned on. Current flows through inductor L2 and transistor N2 to V _B rail. The current also flows out of the base of the PNP transistor P1 and turns it on. The DC blocking capacitor C1 discharges to reduce the potential between the field effect capacitors M1 and turn it off. The operation of the output network is the same as the aforementioned method.

Those who have general knowledge of this technology will know that there are other forms of examples without departing from the essential spirit of the present invention. Therefore, the examples given here are only for illustration and not for limitation. The scope of the present invention should be subject to the scope of the attached patent application instead of the above description. Changes in the same meaning and scope are still considered to be included in this specification.

Symbol description of main components

1. . . lead

2. . . driver

3. . . lead

5. . . Active device

6. . . Single pole single throw switch

6-1. . . Wave

6-2. . . Wave

6-3. . . Wave

7. . . DC power supply

9. . . Load network

10-1. . . Wave

10-2. . . Wave

10-3. . . Wave

10-4. . . Wave

11. . . load

201. . . RF input signal

203. . . Driver amplifier

205. . . Matching network

207. . . Field Effect Transistor

301. . . RF input signal

303. . . Drive circuit

305. . . Active device switch

307. . . Load network

309. . . Fast variable power supply

401. . . Output network

501. . . Impedance matching transmission line

901. . . Output network