CN100517958C - High frequency power amplifier circuit - Google Patents

Abstract

The invention discloses a high-frequency power amplifying circuit, which consists of modulator and power amplifier, wherein the modulator includes signal amplification circuit, add circuit and drive circuit; the power amplifier consists of first stage amplifying circuit and secondary amplifying circuit; the secondary amplifying circuit has high-frequency choke which adopts magnet ring with manganese- zinc or nickel- zinc material. The invention improves the envelope rise and descent rate of final export radiofrequency signal.

Description

High frequency power amplifier circuit

technical field

The invention belongs to the technical field of power amplification, and is especially used for a high-frequency power amplification system requiring high-speed switching.

Background technique

Generally, the efficiency of a high-frequency power amplifier increases as the output power of the amplifier increases in a linear range, reaching a maximum efficiency at a certain point in the amplifier's saturated operation.

In the FM communication system, due to the constant envelope nature of the signal, the amplifier can always be in a saturated state, so that higher efficiency can be achieved, but in the communication system that requires linear amplification, the signal envelope is no longer constant, so the amplifier efficiency is reduced.

In the field of laser marking, at present, the well-known manufacturers of acousto-optic Q-switch drivers for Nd:YAG laser marking machines include NEOS in the United States and Guilin Xingchen Company in China. When the operating frequency is 27MHz, their output powers are 50W, 75W, 100W three kinds. Among them, the rising time and the falling time corresponding to the laser off time and the laser on time are a very important performance index. The performance index given by the Q switch driver of NEOS company is that the rise time is less than 500ns, and the fall time is less than 100ns; The index of its falling time is far better than that of rising time. If the rising time is too long, it means that the time delay for the marking machine to turn off the laser is too long, which will affect the marking quality.

The existing acousto-optic Q-switch driver has a high-frequency power amplifier circuit inside. The disadvantage of this circuit is that the rise time of the output radio frequency signal is too long, much longer than the fall time, which affects the performance of the system.

Contents of the invention

The object of the present invention is to overcome the disadvantages of the above-mentioned prior art and provide a high-frequency power amplifier circuit. The power amplifying circuit can not only realize high-efficiency high-frequency power amplification, but also greatly increase the rising and falling speed of the envelope of the final output radio frequency signal.

In order to achieve the above object, the technical solution adopted by the present invention is: a high-frequency power amplifier circuit is composed of a modulator and a power amplifier, the modulator includes a signal amplifier circuit, an addition circuit and a drive circuit, and the power amplifier includes a first-stage amplifier circuit and a power amplifier. The second-stage amplifying circuit, the input of the signal amplifying circuit is an external analog modulation signal, the output terminal of the signal amplifying circuit is connected to the input end of the adding circuit, the input of the first-stage amplifying circuit is an externally input radio frequency signal, and the second-stage amplifying circuit The output V ₂ is the final RF signal output; the connection method of the drive circuit is: the input terminal of the emitter follower is connected to the output terminal of the above adding circuit, the output terminal of the emitter follower is connected to the power supply terminal of the optocoupler U ₁ , and the optocoupler The positive input terminal of U ₁ is connected to one end of resistor R ₆ , the other end B of resistor R ₆ is connected to the external selection control signal, the negative input terminal of optocoupler U ₁ is grounded, and the gate of power MOS transistor Q ₂ is connected to optocoupler U ₁ The output terminal of the output terminal, the drain is connected to the +12V power supply, the source is connected to the ground terminal of the optocoupler _U2 , the positive input terminal of the optocoupler _U2 is connected to one end of the resistor _R9 , and the other end C of the resistor _R9 is connected to the external digital modulation signal , the negative input end of optocoupler _U2 is grounded, one end of resistor _R8 is connected to +24V power supply, and the other end is connected to the power end of optocoupler _U2 through diode _D1 , and the power end of optocoupler _U2 is connected to the power end of optocoupler _U2 . The ground terminal is connected in parallel with a voltage regulator diode D ₂ , an electrolytic capacitor C ₂ and a capacitor C ₁ , the negative terminals of the two diodes D ₃ and D ₄ are connected to the ground terminal of the optocoupler U ₂ , and the two diodes D ₃ and D After the positive ends of ₄ are connected to the ground through the resistor _R10 , the gate of the power MOS transistor _Q3 is connected to the output terminal of the optocoupler _U2 , the drain is connected to the +12V power supply, the source is connected to the ground terminal of the optocoupler _U2 , and the resistor One end of R ₁₁ is connected to the ground terminal of the optocoupler _U2 , and the other end is grounded, and the ground terminal of the optocoupler _U2 is the modulation signal output _V1 of the modulator; the connection method of the second stage amplifier circuit is: the base of the transistor _Q5 Connect to the output of the first-stage amplifying circuit, the base of the transistor _Q5 is connected to the modulation signal input terminal E through the diode _D5 , and the high-frequency choke coil RFC and the capacitor _C4 are connected in parallel between the base of the transistor _Q5 and the ground , the collector of the triode _Q5 is connected to the modulation signal input terminal E through the inductance _L3 and the inductance _L6 in sequence, and the modulation signal input terminal E is connected to the modulation signal output _V1 of the driving circuit, and the emitter of the triode _Q5 is grounded. A capacitor C ₉ is connected between the signal input terminal E and the ground. One end of the capacitor C ₈ is connected between the inductor L ₃ and the inductor L ₆ , and the other end is grounded. The collector of the transistor Q ₅ passes through the inductor L ₁ , capacitor C ₁₁ , The capacitor C ₆ is grounded, and the junction point between the capacitor C ₁₁ and the capacitor C ₆ is the output V ₂ of the power amplifier; the high-frequency choke coil RFC is a magnetic ring made of manganese-zinc or nickel-zinc material.

Compared with the prior art, the present invention has the following advantages:

(1) Due to the optimization of the design of the high-frequency power amplifier and modulator, the envelope of the final output radio frequency signal rises and falls faster, so the power amplifier circuit of the present invention can realize high-speed switching.

(2) Since the drive circuit in the modulator of the present invention adopts a power MOS transistor with low on-resistance, the power consumed by the modulator in the on-state is very small, so that the present invention has higher efficiency.

(3) The present invention can be applied to the acousto-optic Q switch driver of Nd:YAG laser marking machine, because the modulator in the present invention also has the function of providing analog amplitude modulation, can control its output power by the analog quantity of external input, so It can take into account the "first pulse suppression function" required by the Q-switch driver, and can eliminate the "matchhead phenomenon" during laser marking. In addition, its extremely fast rise and fall time can also effectively improve the marking quality of the marking machine.

(4) It can be applied to communication systems using amplitude modulation, especially in amplitude keying modulation, where the amplitude keying modulation ASK signal is input from the digital modulation signal input end of the modulator, while maintaining a relatively high output power of the power amplifier, The baud rate of the ASK signal can be as high as hundreds of K.

Description of drawings

Fig. 1 is a system block diagram using the high frequency power amplifier circuit of the present invention.

FIG. 2 is a block diagram of the modulator in FIG. 1 .

FIG. 3 is a circuit diagram of a modulator in FIG. 2 .

FIG. 4 is a block diagram of the high frequency power amplifier in FIG. 1 .

FIG. 5 is a circuit diagram of a high-frequency power amplifier in FIG. 4 .

FIG. 6 is a schematic structural diagram of the magnetic ring in FIG. 5 .

Detailed ways

The invention includes a modulator and a high frequency power amplifier.

As shown in Figure 1, the modulator receives an externally input digital modulation signal or analog modulation signal, and amplifies the input digital modulation signal or analog modulation signal to a modulation signal with strong drive capability to provide the required signal for the high-frequency power amplifier. The high-frequency power amplifier amplifies the input RF signal to the level required by the load.

As shown in FIG. 2 , the modulator is composed of a signal amplifier circuit 1 , an addition circuit 2 and a drive circuit 3 . The signal amplifying circuit 1 and the adding circuit 2 adopt general signal amplifying circuits and adding circuits; the driving circuit 3 adopts a specially designed driving circuit.

As shown in Figure 3, a connection method of the signal amplifying circuit 1 can be: one end A of the resistor _R2 is connected to an externally input analog modulation signal, the other end of the resistor _R2 is connected to the positive phase input terminal of the operational amplifier _A1 , and the potential One end of the potentiometer _R4 is connected to the output end of the operational amplifier _A1 , and the other end is grounded, and the middle tap of the potentiometer _R4 is connected to the inverting input end of the operational amplifier _A1 .

A connection method of the addition circuit 2 can be: one end of the potentiometer _R1 is connected to the output end of the above-mentioned operational amplifier _A1 , the other end is connected to the +12V power supply, and the middle tap of the potentiometer _R1 is connected to the positive phase input of the operational amplifier _A2 The output terminal of the operational amplifier _A2 is grounded through the resistor _R3 and the resistor _R5 in turn, and the connection point of the resistor _R3 and the resistor _R5 is connected to the inverting input terminal of the operational amplifier _A2 .

The operational amplifier A ₁ and the operational amplifier A ₂ can use dual operational amplifiers NE5532 or two single operational amplifiers NE5534.

The connection method of the drive circuit 3 is: the input terminal of the emitter follower 6 is connected to the output terminal of the above adding circuit 2, the output terminal of the emitter follower 6 is connected to the power supply terminal of the optocoupler _U1 , and the positive input terminal of the optocoupler _U1 Connect one end of the resistor _R6 , the other end B of the resistor _R6 is connected to the external selection control signal, the negative input terminal of the optocoupler _U1 is grounded, the gate of the power MOS transistor _Q2 is connected to the output terminal of the optocoupler _U1 , and the drain Connect high-power +12V power supply, the source is connected to the ground terminal of optocoupler U ₂ , the positive input terminal of optocoupler U ₂ is connected to one end of resistor R ₉ , and the other end C of resistor R ₉ is connected to the external digital modulation signal, optocoupler U 2 The negative input terminal of ₂ is grounded, one end of resistor _R8 is connected to +24V power supply, and the other end is connected to the power supply terminal of optocoupler _U2 through diode _D1 , between the power supply terminal of optocoupler _U2 and the ground terminal of optocoupler _U2 The Zener diode D ₂ , electrolytic capacitor C ₂ and capacitor C ₁ are connected in parallel, the negative ends of the two diodes D ₃ and D ₄ are connected to the ground end of the optocoupler U ₂ , the positive ends of the two diodes D ₃ and D ₄ After the terminals are connected to the ground through the resistor _R10 , the gate of the power MOS transistor _Q3 is connected to the output terminal of the optocoupler _U2 , the drain is connected to the high-power +12V power supply, the source is connected to the ground terminal of the optocoupler _U2 , and the resistor _R11 One end of the optocoupler U ₂ is connected to the ground end, and the other end is grounded, and the ground end of the optocoupler U ₂ is the modulated signal output V ₁ of the modulator.

Since the output power of the power amplifier in the example of the present invention is 50W, the supply voltage is +12V, calculated by 60% efficiency, the supply current is about 7A, and the driving capability of the modulated signal output by the modulator is very high, so, in In the present invention, a power MOS tube is used. Power MOS tubes Q ₂ and Q ₃ can use IRF540N or IRF530N; optocoupler U ₁ and optocoupler U ₂ can use TLP250, optocoupler U ₁ and U ₂ both play the role of driving power MOS tubes Q ₂ and Q ₃ , And play an isolation role.

One connection method of the emitter follower 6 is: the collector of the triode _Q1 is connected to the +24V power supply, the base is connected to the output terminal of the operational amplifier _A2 , the emitter is connected to the -12V power supply through the resistor _R7 , and the emitter is connected to the light source. Coupled to the power supply terminal of _U1 .

Transistor Q ₁ can use NPN transistor 2SD669 or 2SD880.

The emitter follower 6 can also adopt an integrated chip, and the model can be LM1875.

The analog modulation signal input from terminal A is amplified and shifted by the signal amplification circuit 1 and the addition circuit 2, and then output to the optocoupler U ₁ by the voltage follower 6 . When the selection control signal input from terminal B to optocoupler U ₁ is TTL high level, the analog modulation mode is selected, and the analog modulation signal is input from terminal A. When the selection control signal input from terminal B to optocoupler U ₁ is TTL low When the level is selected, the digital modulation method is selected, and the digital modulation signal is input from the C terminal.

The core device for realizing the analog modulation is the power MOS transistor Q ₂ , and the source voltage V ₁ of the power MOS transistor Q ₂ is controlled by controlling the gate voltage of the power MOS transistor Q 2 . When the analog modulation mode is selected, the power MOS transistor _Q3 is in the off state, and at this time the output of the optocoupler _U1 is amplified and shifted by the signal amplifier circuit 1 and the addition circuit 2, and then the analog modulation signal of the voltage follower 6, this The voltage controls the gate of the power MOS transistor _Q2 to realize analog modulation; when the digital modulation mode is selected, the power MOS transistor _Q2 is in an off state. The power MOS transistor _Q3 works in a switch state, either on or off. Since the output voltage _V1 returns to the pin ground of the optocoupler _U2 , when the power MOS transistor _Q3 is turned off or on, the optocoupler _U2 actually controls the gate-source voltage difference of the power MOS transistor _Q3 , this method is superior to the method of only controlling the gate voltage of the power MOS transistor, and because the driving current of the optocoupler _U2 is as high as plus or minus 1.5A, it reduces the turn-on time and turn-off time of the power MOS transistor _Q3 , Make it as close as possible to the value given in the device manual of the power MOS transistor _Q3 . Experiments have shown that the rise and fall times are all controlled at around 60ns.

As shown in Figure 4, this is the block diagram of the power amplifier in Figure 1. The power amplifier is composed of a first-stage amplifying circuit 4 and a second-stage amplifying circuit 5. The input radio frequency signal is amplified by the first-stage amplifying circuit 4 and then together with the modulation signal It is input to the second stage, and the second stage amplifying circuit 5 amplifies and modulates the radio frequency signal again and outputs it.

As shown in Fig. 5, a connection method of the first-stage amplifying circuit 4 can be: the primary a terminal of the transformer T is connected to the externally input radio frequency signal at the D terminal, and a capacitor C is connected between the secondary c terminal and the d terminal of the transformer T. _5. The primary b terminal of the transformer T is connected to the secondary d terminal and grounded, the secondary c terminal of the transformer T is connected to the base of the transistor _Q4 , the emitter of the transistor _Q4 is grounded, the collector is connected to one end of the inductor _L4 , and the inductor The other end of L ₄ is grounded through the capacitor C ₇ , and the other end of the inductor L ₄ is connected to the +12V power supply through the inductor L ₅ , the collector of the transistor Q ₄ is connected to the ground through the capacitor C ₃ , and the collector of the transistor Q ₄ passes through the capacitor in turn C ₁₀ and inductance L ₂ are connected to the input end of the second stage amplifier circuit 5 .

Transistor Q ₄ is a high-frequency power amplifier tube, which can be a high-frequency power amplifier tube of model 2SC2539 or 2SC1972; the turns ratio of the transformer T can be changed according to the impedance of the radio frequency signal input to the D terminal.

The connection method of the second-stage amplifying circuit 5 is: the base of the triode _Q5 is connected to the modulation signal input terminal E through the diode _D5 , and the high-frequency choke coil RFC and the capacitor are connected in parallel between the base of the triode _Q5 and the ground C ₄ , the collector of the transistor Q ₅ is connected to the modulation signal input terminal E through the inductor L ₃ and the inductor L ₆ in turn, the emitter of the transistor Q ₅ is grounded, and a capacitor C ₉ is connected between the modulation signal input terminal E and the ground. One end of C ₈ is connected between inductor L ₃ and inductor L ₆ , the other end is grounded, the collector of transistor Q ₅ is grounded sequentially through inductor L ₁ , capacitor C ₁₁ , and capacitor C ₆ , and the connection between capacitor C ₁₁ and capacitor C ₆ The point is the output V ₂ of the power amplifier. The high-frequency choke coil RFC provides the base DC bias of the transistor _Q5 .

The modulation signal input terminal E is connected to the modulation signal output terminal V ₁ of the modulator to provide a high-power modulation signal for the transistor Q ₅ .

Transistor Q ₅ is a high-frequency power amplifier tube with higher power than triode Q ₄ , which can be model 2SC2694 or 2SC2630.

Diode _D5 is used to increase the turn-off and turn-on speed of the RF signal, that is, to reduce the rise and fall time. Experiments have proved that when there is no diode _D5 , the fall time is about 300ns. After adding diode _D5 , the fall time is reduced to 120ns. The reason is: _the modulating signal input terminal E will have a strong downward overshoot at the moment of falling, and the base of the transistor _Q5 can be pulled to the A lower level, thereby accelerating the cut-off of the transistor _Q5 , and accelerating the falling process of the output signal.

During the experiment, it was found that the high-frequency choke coil RFC also has a great influence on the rise time of the radio frequency envelope.

The reasons why the high-frequency choke coil RFC increases the rising speed of the output signal are as follows:

Through computer simulation and actual measurement, it is found that: during normal operation, the current on the high-frequency choke coil RFC at the base of the triode _Q4 is about 1A. The existence of ₅ makes the current on the RFC become larger, around 2A. At the moment when the modulating signal at terminal E rises, the diode _D5 is disconnected, and the current flowing through the diode _D5 decreases accordingly. Since the high-frequency choke coil RFC has a certain constant current effect, the base current of the triode _Q5 increases. Large, the base voltage has a boost in a short time. At the same time, the existence of the inductance L ₃ and L ₆ on the collector of the transistor Q5 makes the current of the collector of the transistor _Q5 have a slow rising process, and the collector voltage _of the transistor _Q5 is very low during this period. Transistor _Q5 is in a saturated state, and there will be no radio frequency output. But once this period of time has passed, when leaving the saturation state, since the collector of the transistor Q ₅ already has a large current, it is equivalent to giving a very large current to the LC resonant circuit composed of the inductance L ₁ , capacitor C ₁₁ , and capacitor C ₆ . Strong excitation, the rise of the RF signal will be very fast at this time.

We have tested high-frequency choke coils made of various materials, including ordinary inductors, small magnetic beads, and wound magnetic rings. Comparing the high-frequency choke coil RFC made of different materials and parameters, when the high-frequency choke coil RFC adopts the magnetic ring made of manganese-zinc or nickel-zinc material as shown in Figure 6, the process of the envelope rise of the output radio frequency signal The period of slow rise in the middle is cut off and replaced by a sharp rise in the envelope. When the high-frequency choke coil RFC uses NXO-200 or NXO-100 enameled wire, the diameter of the enameled wire is 0.3-1.5mm, the number of turns on the magnetic ring is 3-7, the thickness d ₃ of the magnetic ring is 3-6mm, and the outer diameter The effect is better when d ₁ is 12-20 mm and the inner diameter d ₂ is 5-10 mm.

Claims (4)

1. A high-frequency power amplifier circuit is characterized in that: it is made up of a modulator and a power amplifier, and the modulator includes a signal amplifier circuit (1), an addition circuit (2) and a drive circuit (3), and the power amplifier includes a first stage The amplifying circuit (4) and the second-stage amplifying circuit (5), the input of the signal amplifying circuit (1) is an external analog modulation signal, the output terminal of the signal amplifying circuit (1) is connected to the input terminal of the adding circuit (2), the second The input of the primary amplifier circuit (4) is an externally input radio frequency signal, and the output _V of the second stage amplifier circuit (5) is the final radio frequency signal output; The connection method of the drive circuit (3) is: the input terminal of the emitter follower (6) is connected to the output terminal of the above-mentioned adding circuit (2), and the output terminal of the emitter follower (6) is connected to the power supply terminal of the optocoupler _U1 , The positive input terminal of the optocoupler _U1 is connected to one end of the resistor _R6 , the other end B of the resistor _R6 is connected to the external selection control signal, the negative input terminal of the optocoupler _U1 is grounded, and the gate of the power MOS transistor _Q2 is connected to the optocoupler The output terminal of U ₁ , the drain is connected to the +12V power supply, the source is connected to the ground terminal of the optocoupler _U2 , the positive input terminal of the optocoupler _U2 is connected to one end of the resistor _R9 , and the other end C of the resistor _R9 is connected to the external digital Modulation signal, the negative input terminal of optocoupler U ₂ is grounded, one end of resistor R ₈ is connected to +24V power supply, the other end is connected to the power supply terminal of optocoupler U ₂ through diode D ₁ , and the power terminal of optocoupler U ₂ is connected to optocoupler U The ground terminal of ₂ is connected in parallel with Zener diode D ₂ , electrolytic capacitor C ₂ and capacitor C ₁ , the negative terminals of two diodes D ₃ and D ₄ are connected to the ground terminal of optocoupler U ₂ , and the two diodes D ₃ , _D4 ’s positive side is connected to ground through resistor _R10 , the gate of power MOS transistor _Q3 is connected to the output terminal of optocoupler _U2 , the drain is connected to +12V power supply, and the source is connected to the ground terminal of optocoupler _U2 , one end of the resistor R ₁₁ is connected to the ground end of the optocoupler U ₂ , and the other end is grounded, and the ground end of the optocoupler U ₂ is the modulation signal output V ₁ of the modulator; The connection method of the second-stage amplifying circuit (5) is: the base of the triode _Q5 is connected to the output of the first-stage amplifying circuit (4), and the base of the triode _Q5 is connected to the modulation signal input terminal E through the diode _D5 . The base of the triode _Q5 and the ground are connected in parallel with the high-frequency choke coil RFC and the capacitor _C4 , the collector of the triode _Q5 is connected to the modulation signal input terminal E through the inductance _L3 and the inductance _L6 in turn, and the modulation signal input Terminal E is connected to the modulation signal output V ₁ of the drive circuit (3), the emitter of the triode Q ₅ is grounded, a capacitor C ₉ is connected between the modulation signal input terminal E and the ground, and one end of the capacitor C ₈ is connected to the inductance L ₃ and the inductance Between L ₆ , the other end is grounded, the collector of transistor Q ₅ is grounded sequentially through inductor L ₁ , capacitor C ₁₁ , and capacitor C ₆ , and the junction point between capacitor C ₁₁ and capacitor C ₆ is the output V ₂ of the power amplifier; The high frequency choke coil RFC uses a magnetic ring made of manganese zinc or nickel zinc material. 2. The high-frequency power amplifying circuit according to claim 1, characterized in that: the number of turns on the magnetic ring is 3-7, the thickness _d3 of the magnetic ring is 3-6mm, and the outer diameter _d1 is 12-20mm , The inner diameter _d2 is 5-10mm. 3. The high-frequency power amplifying circuit according to claim 1 or 2, characterized in that: the connection of the emitter follower (6) is: the collector of the triode _Q1 is connected to the +24V power supply, and the base is connected to the operational amplifier A ₂ , the emitter is connected to the -12V power supply through the resistor _R7 , and the emitter of the triode _Q1 is connected to the power supply end of the optocoupler _U1 . 4. The high-frequency power amplifying circuit according to claim 1 or 2, characterized in that: the emitter follower (6) is an integrated chip.

Images