JPH04369126A - High frequency power amplifier - Google Patents

Abstract

PURPOSE:To keep an output power at a low output constant with high accuracy even when a temperature is subject to change. CONSTITUTION:Part of an output of a power amplifier circuit 1 is branched by a directional coupler 2 and boosted by a transformer 3 and the result is rectified by a rectifier circuit 4. The rectified signal is compared with an output power command signal to control a gain of the power amplifier circuit 1. Thus, a voltage in which a fluctuation width due to a temperature change in the rectifier circuit is negligible is rectified.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency power amplification device used in transmitters, broadcasters, or wire communication equipment using high frequency carrier waves.

0002

2. Description of the Related Art In recent years, wireless devices have become smaller and more solid-state. In particular, portable wireless telephone devices such as car phones and mobile phones have become smaller and lighter. The high-frequency power amplification device built into these devices, which amplifies the transmission power to the required power, can control the transmission power of the mobile station to be increased or decreased based on commands from the base station based on the received field strength at the base station. It is being said. In other words, when the electric field strength of the mobile station reaching the base station is high, reducing the transmitting power of the mobile station can improve the battery life or reduce the battery life if the mobile station is powered by a battery. It is possible to reduce weight by making it smaller, and furthermore, by using the minimum amount of power required, effective use of frequencies is achieved. Therefore, the transmitter of such a wireless device needs to maintain a fixed transmission power and also vary the transmission power. A high-frequency power amplifier device that maintains a constant transmission output is a negative feedback loop that detects a part of the transmission output with a directional coupler, rectifies it, compares it with a command value, and changes the gain of the power amplifier. It is common to have a

[0003] A conventional high frequency power amplification device will be explained below. FIG. 4 is a block diagram of a conventional high frequency power amplification device.

In FIG. 4, reference numeral 1 denotes a power amplification circuit that amplifies an input high-frequency signal to a required power, and is constructed using active elements such as bipolar transistors. 2 is a directional coupler which branches a part of the power and obtains an output from the output terminal 24, and has an electrical length of 1/4 wavelength, is arranged parallel to each other, and has an equal width to match the output impedance of the power amplifier circuit 1. A strip line 21 having a characteristic impedance equal to
22 and a terminating resistor 23. 4 is a rectifier circuit that outputs a DC signal proportional to the magnitude of the input high-frequency voltage to an output terminal 43. Reference numeral 5 denotes an error detection means for outputting an error signal corresponding to the difference between the output of the rectifier circuit 4 and the output power command signal, and is constituted by a differential amplifier. 6
is a gain control means that changes the gain of the power amplifier circuit 1 according to the output of the error detection means 5, and is realized by changing the power supply voltage of the power amplifier circuit 1 or the bias of the active element used in the circuit. ing. 7 is a connector that outputs an amplified high frequency signal, and 8 is a coaxial line that connects the connector 7 and the directional coupler 2.

[0005] The operation of the conventional high frequency power amplification device configured as described above will be explained below.

The input high frequency signal is transmitted to the power amplifier circuit 1.
The signal is amplified by the directional coupler 2, the coaxial line 8, the connector 7, and if necessary, is supplied to a load such as an antenna via other coaxial lines. At this time, a signal proportional to the traveling wave power appears at the output end of the directional coupler 2. Therefore, the output terminal 43 of the rectifier circuit 4 connected to the output terminal 24
A traveling wave power, that is, a direct current voltage proportional to the power consumed by the load is generated. The DC voltage is compared with the output power command signal by the error detection means 5, and the gain of the power amplifier circuit 1 is controlled via the gain control means 6 according to the difference between the two. If the high frequency power supplied to the load increases for some reason, the voltage at the output terminal 43 of the rectifier circuit 4 will rise, the output of the error detection means 5 will decrease, and the output will be passed through the gain control means 6 to the power amplifier circuit. 1 and lowers the output power. Conversely, when the high frequency power supplied to the load increases, the voltage at the output terminal 43 of the rectifier circuit 4 decreases, the output of the error detection means 5 increases, and the gain control means 6
The gain of the power amplifier circuit 1 is increased through the power amplifier circuit 1, and the output power is increased. In this way, a negative feedback loop is formed, and the output power can be controlled to be constant. In addition, when changing the output power, it is sufficient to change the output command signal according to the desired output power, and if the open loop gain of the same loop is large enough, the output power is terminal 43
The voltage becomes the output power that is approximately equal to the output power command signal.

[0007]

[Problems to be Solved by the Invention] However, in the conventional high-frequency power amplifier device described above, the forward voltage drop characteristics of the semiconductor diodes normally used in the rectifier circuit change depending on the temperature, so the output power varies depending on the temperature and temperature. will change. For example, when using a Schottky barrier diode, the amount of change in voltage drop characteristics due to temperature change is -
It is generally about 0.1 V with a temperature change of about 30°C to 30°C. Therefore, there is no problem when the output is relatively large and the amount of change can be ignored, but when the output of the rectifier circuit is small, the error due to temperature changes becomes large. For example, according to IS-3-D, a standard for cellular telephone systems established by the Electronic Industries Association (EIA), the minimum nominal output power of a mobile station is:
When using an antenna with an absolute gain of 0 dB, it is 6.3 mW, and if the coupling degree of the directional coupler is -15 dB and the input/output impedance of the coupler is 50 Ω, the input voltage of the rectifier circuit is the peak value. It becomes 0.14V. If the voltage drop of the rectifier circuit decreases by, for example, 0.05V due to a temperature change, an error of 3.9 dB will occur in the output, which may deviate from the transmission power error of +2 dB and -4 dB specified in the same standard.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a high-frequency power amplification device that can supply constant output power even with small power and over a wide range of temperature changes.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides boosting means for boosting the signal branched by the branching means.

0010

[Operation] With the above-described structure, the present invention can perform rectification at a voltage sufficiently higher than the fluctuation due to temperature change in the forward voltage drop characteristic of the rectifier.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a high frequency power amplifier according to an embodiment of the present invention. In FIG. 1, 1 is a power amplifier circuit, 2 is a directional coupler, 5 is an error detection means, 6 is a gain control means for changing the gain of the power amplifier circuit 1 according to the output of the error detection means 5, and 7 is an amplified circuit. The connector 8 for outputting a high frequency signal is a coaxial line, which is the same as the conventional technology, so a description thereof will be omitted. 3 is a transformer that boosts the output power signal branched by the directional coupler 2; 4 is a rectifier circuit that outputs a DC signal proportional to the magnitude of the input high-frequency voltage to an output terminal 43, and is composed of a diode 41 and a capacitor 42. Reference numeral 9 denotes a voltage dividing circuit, which divides the output voltage of the rectifier circuit 4 into appropriate values using resistors 91 and 92 connected in series.

The operation of the high frequency power amplification device configured as described above will be explained below.

The input high frequency signal is transmitted to the power amplifier circuit 1.
The signal is amplified and supplied to a load such as an antenna via the directional coupler 2, the coaxial line 8, the connector 7, and, if necessary, other coaxial lines. At this time, regardless of the impedance matching with the load, the output terminal of the directional coupler 2 has a power proportional to the traveling wave power and a magnitude of the directional coupler 2.
An output power signal appears that is attenuated by the degree of coupling. Note that the degree of coupling of the directional coupler 2 is approximately -15 dB to -30 dB, which is an appropriate and common value.

The signal output from the directional coupler 2 is
After being boosted by the transformer 3, the voltage is rectified by the rectifier circuit 4. The rectified signal is divided by the voltage dividing circuit 9, and then compared with the output power command signal by the error detection means 5.
The gain of the power amplifier circuit 1 is controlled via the gain control means 6 according to the difference between the two. If the high frequency power supplied to the load increases for some reason, the rectifier circuit 4
The voltage at the output terminal 43 of the circuit increases, the output of the error detection means 5 decreases, and the gain of the power amplifier circuit 1 is lowered via the gain control means 6, thereby lowering the output power. Conversely, when the high frequency power supplied to the load decreases, the voltage at the output terminal 43 of the rectifier circuit 4 decreases, the output of the error detection means 5 increases, and the output of the power amplifier circuit 1 increases via the gain control means 6. Increase gain and increase output power. When changing the output power, the output command signal input to the error detection means 5 is changed according to the desired output power, and if the open loop gain of the loop is large enough, the output power is changed to the rectifier circuit 4. The voltage at the output terminal 43 becomes an output power that is approximately equal to the output power command signal. Note that the voltage dividing ratio of the voltage dividing circuit 9 is set so that when the power amplifier circuit 1 generates the maximum output, the input voltage of the error detection means 5 is equal to or lower than the allowable input voltage.

Further, as in this embodiment, if the signal branched by the directional coupler 2 is boosted by the transformer 3, V
Even if the line length of the directional coupler 2 is 1/4 wavelength or less and a sufficient degree of coupling cannot be obtained in order to miniaturize a transmitter for a frequency band below the HF band, the rectifier circuit 4 has the required size, That is, it is possible to supply a voltage that is sufficiently higher than the change in forward voltage drop of the diode due to temperature change.

The input impedance of the rectifier circuit 4 generally exhibits capacitance due to the junction capacitance of the diode and the high frequency bypass on the output side, that is, the smoothing capacitor. At frequencies above the UHF band, even if the resistance values of the resistors 91 and 92 of the voltage divider circuit 9 are set high, the absolute value of the input impedance of the rectifier circuit 4 does not increase, and a sufficient rectified output may not be obtained. In such a case, as shown in FIG. 3, an inductance may be connected in parallel with the input of the rectifier circuit 4 to achieve matching. This inductance may be a general wire-type air-core coil, or when constructed on a printed wiring board, may be a printed coil formed by meandering printed wiring. According to experiments by the inventors, a frequency of 800
Matching can be achieved with an inductance of 10 nH to 20 nH at MHz. Further, in the case where the output power is relatively small, if the output voltage of the rectifier circuit 4 when the power amplifier circuit 1 generates the maximum output is below the allowable input voltage of the error detection means 5, the voltage divider circuit 9 may be omitted.

As described above, according to this embodiment, the voltage input to the rectifier circuit 4 becomes high, and the change in forward voltage drop of the diode due to temperature change becomes relatively small.

For example, if the step-up ratio of the transformer 3 is set to 4, the same conditions as described in the problem of the prior art are met, namely, the minimum nominal output power is 6.3 mW, and the degree of coupling of the directional coupler 2 is -15 dB. (power ratio), the input voltage of the rectifier circuit 4 is 0.56V at the peak value. Therefore, it can be seen that if the voltage drop of the rectifier circuit 4 decreases by, for example, 0.05 V due to a temperature change, only an error of 0.7 dB occurs in the output, which does not deviate from the transmission power errors of +2 dB and -4 dB specified by the same standard.

Furthermore, in this embodiment, a single-turn type transformer in which the primary winding and the secondary winding are shared is used as the transformer 3;
For this purpose, a conventional one in which the primary and secondary windings are insulated from each other may be used. Further, in this embodiment, the output power signal obtained by branching a part of the output power is boosted by the transformer 3, but the electrical length is 1/4 wavelength, and the output from the output terminal 24 of the directional coupler 2 is The voltage may be boosted by a transmission line having a characteristic impedance higher than the impedance. In this case, if the output impedance of the output terminal 24 of the directional coupler 2 is Zo and the characteristic impedance of the transmission line is Zc, the impedance looking into the transmission line from the input of the rectifier circuit 4 is expressed by the following formula. .

[0021]

[Math 1]

Therefore, since the boost ratio is the square root of the impedance ratio,

[0023]

[Math 2]

For example, if the output impedance of the branched output of the directional coupler 2 is 50Ω and the characteristic impedance of the transmission line is 200Ω, the voltage can be increased four times. Boosting using this distributed constant circuit is extremely effective in a frequency band of 1 GHz or higher, where it is difficult to construct an efficient transformer. In addition, a booster circuit using a lumped constant resonant circuit such as a series resonant circuit may be applied.

FIG. 2 is a block diagram of a high frequency power amplifier according to another embodiment of the present invention, in which the primary and secondary windings are insulated from each other as described above. In FIG. 2, 1 is a power amplifier circuit, 4 is a rectifier circuit, 9 is a voltage divider circuit, 5 is an error detection means, 6 is a gain control means, 7 is a connector, and 8 is a coaxial line, which was explained in the first embodiment. Since it is the same as , the explanation will be omitted. Reference numeral 2 designates a directional coupler, for example, as shown in the figure, it is composed of strip lines 21 and 22 of different widths arranged in parallel with each other, each having an electrical length of 1/4 wavelength, and a terminating resistor 23. A branched part of the passing power transmitted from the left side to the right side, that is, a high frequency output proportional to the traveling wave power is obtained at the output terminal 24. By configuring the width of the strip line 22 to be narrower than the width of the strip line 21, the output impedance of the output terminal 24 can be made higher than the output impedance of the power amplifier circuit 1.

The operation of the embodiment of the high frequency power amplifier according to the present invention constructed as described above will be described below.

The input high frequency signal is transmitted to the power amplifier circuit 1.
The signal is amplified and supplied to a load such as an antenna via the directional coupler 2, the coaxial line 8, the connector 7, and, if necessary, other coaxial lines. At this time, an output power signal proportional to the traveling wave power appears at the output terminal 24 of the directional coupler 2. Since the output impedance of the output terminal 24 is higher than that of the conventional example, the output impedance of the output terminal 24 in FIG. 2 is Zo', and the output impedance of the output terminal 24 in the conventional example shown in FIG.
o, the output power signal will be

0028
]

[Math 3]

The voltage becomes higher by . Therefore, at the output terminal 43 of the rectifier circuit 4, a traveling wave power, that is, a DC voltage corresponding to the power consumed by the load appears, and is higher than the output voltage of the rectifier circuit 4 of the conventional example. Next, the DC voltage is divided by a voltage dividing circuit 9. The divided DC voltage is compared with the output power command signal by the error detection means 5,
The gain of the power amplifier circuit 1 is controlled via the gain control means 6 according to the difference between the two. If the high frequency power supplied to the load changes for some reason, a negative feedback loop is formed just like the embodiment shown in Figure 1, so the output power is controlled to be constant and the desired output power is maintained. Can be changed. Note that the voltage dividing ratio of the voltage dividing circuit 9 is set in exactly the same manner as described in the embodiment of FIG.

In the case of this embodiment, the circuit can be constructed with fewer parts than the first embodiment, and the circuit can be made smaller. Furthermore, since no transformer is used, it is extremely effective in frequency bands of 1 GHz or higher, where it is difficult to construct an efficient transformer.

Furthermore, when the output power is relatively small and the power amplifier circuit 1 generates the maximum output, the rectifier circuit 4
If the output voltage is below the allowable input voltage of the error detection means 5, the voltage dividing circuit 9 may be omitted.

[0032]

As described above, according to the present invention, since the boosting means is provided which is connected to the output of the power amplifier circuit and boosts the signal branched by the branching means, the forward voltage drop characteristic of the rectifying means can be improved. Since rectification can be performed in a state that is sufficiently higher than fluctuations caused by temperature changes, the change in forward voltage drop of the diode due to temperature changes is relatively small, and the output high frequency can be maintained over a wide temperature range without temperature compensation. Power can be maintained constant and accurately.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a high-frequency power amplifier according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a high frequency power amplifier according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a rectifier circuit of a high frequency power amplifier according to an embodiment of the present invention.

[Figure 4] Configuration diagram of a conventional high-frequency power amplification device

[Explanation of symbols]

1 Power amplifier circuit 2 Directional coupler 3 Transformer 4 Rectifier circuit 5 Error detection means 6 Gain control means

Claims (1)

[Claims] 1. High frequency power amplifying means for amplifying a signal and sending it to the antenna, branching means for branching a part of the signal sent from the high frequency power amplifying means to the antenna, and boosting the signal branched by the branching means. A high-frequency power amplifying device comprising: a boosting means for boosting the voltage, a rectifying means for rectifying the signal boosted by the boosting means, and a control means for controlling the amplification gain of the high-frequency power amplifying means according to the output of the rectifying means.