JPH08149020A - Sending power control circuit - Google Patents

Abstract

PURPOSE: To provide a sending power control circuit which can prevent the emission of undesired radio waves and also can protect an ALC amplifier circuit despite the frequency abnormality of a transmitting signal. CONSTITUTION: An ALC amplifier circuit consists of an amplifier part 12, a detection part 13 and an ALC circuit 14 and performs the automatic level control amplification to the high frequency signal received from an amplifier part 11 to produce a transmitting signal of constant power. A signal switching part 21 transmits the transmitting signal through a detection part 22 when no switch signal is received from a comparator 25 and cuts off the transmission of the transmitting signal when the switch signal is received. A filter part 23 transmits the transmitting signal received from the part 21 via the part 22 according to the signal damping characteristic that defines a prescribed frequency band as a pass band. The part 22 detects the reflection level of the transmitting signal reflected from the input terminal of the part 23. When this detected level is higher than a prescribed level, the comparator 25 produces a switch signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency signal transmission power control circuit, and more particularly, to the prevention of emission of unnecessary radio waves even when the transmission frequency becomes abnormal in a base station transmitter of an automobile telephone system, and the like. The present invention relates to a transmission power control circuit capable of protecting and detecting the transmission frequency abnormality.

[0002]

2. Description of the Related Art Conventionally, in a radio communication device or the like, a large number of transmission power control circuits for amplifying the transmission power of a high frequency signal using an automatic level control (ALC) circuit and keeping the transmission power constant have been realized. One of them is published patent gazette, Showa 64
No.-7718 (Title of Invention: Transmission power control circuit of wireless communication device). The transmission power control circuit amplifies the high-frequency input, keeps the transmission output at a predetermined power, and detects the reflected power from the high-frequency output terminal in the transmission power control circuit that outputs the transmission output from the high-frequency output terminal. The power of the transmission output is controlled in response to the detection output.

[0003]

In a transmitting apparatus such as a radio base station of an automobile telephone system, the frequency of a high-frequency signal (that is, a transmission signal) input to the ALC circuit may be erroneous. At times, there is a demand for prevention of emission of unnecessary radio waves and protection of the ALC (amplification) circuit. However, in such a transmission device, it is often required to insert a filter circuit for limiting the band of a transmission signal between the ALC circuit and the high frequency output terminal. In this case, even if the reflected power detection circuit is inserted between the filter circuit and the high-frequency output terminal as in the disclosed transmission power control circuit, the high-frequency output is output in the case of a transmission signal having an abnormal frequency. The reflected power from the terminal is attenuated by the filter circuit. For this reason, if there is a frequency abnormality, the detection circuit cannot detect that there is a reflection after the ALC circuit. Therefore, in the conventional example, the ALC amplifier circuit cannot be deactivated, and unnecessary radio waves There is a drawback that it is not possible to achieve emission prevention and protection of the ALC (amplification) circuit.

A voltage standing wave ratio (VSWR) or a return loss R of the high-frequency output terminal of a general wireless communication device is described.
It is often difficult to accurately determine that L is abnormal because it is difficult to predict or grasp the frequency characteristics of the circuit connected to the high-frequency output terminal. For example, for an antenna for a wireless communication device, the VSWR is usually specified to be about 2.0 (return loss RL ≒ 9.5 dB) in the used band, and the disclosed transmission power control circuit
Judgment VSW for abnormality such as opening of the high-frequency output terminal
There is a problem that it is necessary to give a large margin value to the R value.

[0005]

A transmission power control circuit according to the present invention includes an ALC amplifier circuit for automatically level-amplifying a first high-frequency signal to generate a transmission signal of constant power, and an ALC amplifier circuit for receiving a switching signal. A signal switching unit that passes a transmission signal and blocks the transmission signal when the switching signal is received, and a filter that passes the transmission signal from the signal switching unit according to a signal attenuation characteristic having a predetermined frequency band as a pass band. A detection unit that detects a reflection level of the transmission signal reflected from an input terminal of the filter unit, and a comparison circuit that generates the switching signal when the reflection level is equal to or higher than a predetermined level.

In one of the transmission power control circuits, the comparison circuit generates a frequency abnormality signal indicating that the transmission signal is not in the predetermined frequency band when the reflection level is equal to or higher than a predetermined level. Can be taken.

[0007] Another one of the transmission power control circuits includes an amplifier for amplifying a second high frequency signal to generate the first high frequency signal only when receiving a control signal, and a transmission ON signal. It is possible to further include a switching circuit that generates the control signal when receiving the switching signal and not receiving the switching signal.

In the transmission power control circuit, the detection unit derives the transmission signal inserted between the signal switching unit and the filter unit and reflected from the filter unit to a signal coupling end of the reflected signal. A configuration including a directional coupler and a detector that is connected to the signal coupling end and detects the transmission signal reflected by the envelope and averages the envelope to generate the DC reflection level can be adopted.

[0009]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of a transmission power control circuit according to the present invention. FIG. 2 is a diagram illustrating an example of a frequency characteristic of the filter unit 23 used in the present embodiment.

Referring to FIGS. 1 and 2, this transmission power control circuit is applied to a transmission section of a base station device of a car telephone system, and has a transmission device 1 mainly having a function of ALC amplifying a high frequency signal. A transmission shared device 2 which mainly has a function of synthesizing transmission signals of the same kind as those described above, although the transmission signal from the transmission device 1 and the frequency are different, and an antenna 3 for transmitting a synthesized transmission signal from the transmission shared device 2 to a mobile station. Including. The car telephone system, for example,
"IS-54 Analog MTS, EIA standard, T
ELECOMMUNICATIONS INDUSTR
Y ASSOCIATION established ". If the car telephone system is based on this analog MTS, the high frequency signal will be 869.04 MHz-89.
Δf = 30 KH in a frequency band of 3.97 MHz
can be selected at z frequency intervals. However, in this system, the minimum frequency interval Δf that can be selected in the same base station is 600 KHz. This high frequency signal generally uses a frequency synthesizer capable of obtaining high frequency stability as an original signal source.

The transmitting apparatus 1 transmits a high-frequency signal of a predetermined frequency f0 in the frequency band to a transmission input terminal 101 from a device (not shown) of the base station apparatus.
03, the transmission on / off signal is received, and the reference voltage terminal 105 receives the reference voltage V1 having a predetermined value. The high frequency signal is amplified by the amplifier 11. The high frequency signal amplified by the amplifier 11 is supplied to the amplifier 12. Here, the amplifier 11 uses, for example, a bipolar transistor as an amplifying element, and when the supply of the control signal from the switching circuit 14 is stopped, the power is turned off to stop the amplifying operation.

The amplifier 12, the detector 13, and the ALC circuit 15
These constitute an ALC amplifier circuit for the high frequency signal. That is, the amplifier 12 amplifies the high frequency signal to generate a transmission signal. The detection unit 13 outputs most of the power of the transmission signal to the transmission output terminal 102, and also detects and averages a part of the transmission signal by performing envelope detection and averaging to generate a detection voltage. The ALC circuit 15 compares and controls the detection voltage and the reference voltage V1 to generate an ALC voltage for controlling the power of the transmission signal output from the amplification unit 12 to be constant, and supplies the ALC voltage to the amplification unit 12. The amplifying unit 12 uses, for example, a bipolar transistor as an amplifying element, adds the ALC voltage to the base of the bipolar transistor, and changes the amplification degree according to the ALC voltage. The detection unit 13 can use a known circuit including a strip line type directional coupler and a diode detector connected to a signal coupling terminal of the directional coupler. By the operation as described above, the ALC amplifier circuit forms a feedback loop and generates a transmission signal with constant power. The power value of the transmission signal is maintained at a substantially constant value even by a slight frequency change of the high frequency signal, for example, a change of 600 kHz or more.

The transmission device 1 can also stop the transmission of the transmission signal to the output terminal of the amplification unit 11, that is, the transmission output terminal 102, by the control of the amplification unit 11 by the switching circuit 14. That is, the switching circuit 14 generates a control signal when it receives the transmission ON signal of the transmission ON / OFF control signals from the transmission control terminal 103 and does not receive the transmission of the switching signal from the switching signal terminal 106. Activate 11 On the other hand, when receiving the transmission off signal of the transmission on / off signals or when receiving the switching signal, the switching circuit 14 does not generate the control signal for activating the amplifying unit 11. Note that the transmission ON signal is H
When the level signal and the transmission off signal are an L level signal and no switching signal is transmitted, an H level signal is used. When the switching circuit 14 is configured by an AND circuit, the control signal is amplified when the output of the switching circuit 14 is at an H level. It will be added to the unit 11.

The transmission sharing device 2 sends a transmission signal having a frequency separated from the frequency f0 within the frequency band by Δf or more to the RF input terminal 205 from a device (not shown) of the base station device and a reference voltage V2 to the reference voltage terminal 204. In response, the input terminal 201 receives the transmission signal output from the transmission output terminal 102 of the transmitter 1. In addition, the transmission sharing device 2 connects the antenna 3 to the ANT terminal 202 for transmitting the combined transmission signal, and supplies the switching signal to the switching signal terminal 106 of the transmitting device 1 through the switching signal terminal 203.

The transmission sharing apparatus 2 receives a transmission signal from the input terminal 201 by the signal switching section 21. The signal switching unit 21
When the switching signal has not been received from the comparison circuit 25, the transmission signal is output to the detection unit 22 as it is. On the other hand, when the switching signal has been received, the signal switching unit 21 blocks the transmission of the received transmission signal to the detection unit 22. The signal switching unit 21 preferably uses a coaxial relay that can transmit a UHF frequency transmission signal with good characteristics, and more preferably uses a relay that can terminate a blocked transmission signal with a resistor. When a relay is used for the signal switching unit 21, the switching signal is applied to the control coil of the relay.

The detection unit 22 outputs most of the power of the transmission signal from the signal switching unit 21 to the filter unit 23, and also performs envelope detection on the transmission signal reflected at the input terminal of the filter unit 23 and averages the detected signal. A detection voltage Vx is generated.
This detection unit 23 can use the same circuit as the detection unit 13, but unlike the detection unit 13 that detects the power corresponding to the traveling wave component of the transmission signal, the signal coupling terminal for the reflected signal from the filter unit 23. To produce a detected voltage Vx corresponding to the power derived from

The filter unit 23 limits the band of the transmission signal received from the detection unit 22 according to the frequency characteristics shown in FIG. The filter unit 23 illustrated in FIG.
And f0 ± 30 KHz, the insertion loss IL is 1 dB or less, and the passage loss LΔf at Δf = 600 KHz away from the center frequency f0 is about 6 dB. The reflection characteristics of the filter section 23 are such that the return loss RL within f0 ± 30 KHz is 20 dB or more (VSWR is 1.2 or less), and the return loss RL at Δf = 600 KHz away from the center frequency f0 is about 1.2 dB ( VSWR is about 15). This filter unit 23 can be realized by a dielectric filter,
The frequency characteristics of the above-mentioned passage and reflection are stable with very little fluctuation due to temperature fluctuation or the like.

If the center frequency of the transmission signal supplied to the transmission sharing apparatus 2 is the predetermined frequency f0, the detection unit 22
Since the detection voltage Vx0 depends on the reflection characteristics of the filter unit 23, the detection voltage Vx0 is a voltage corresponding to the power value attenuated by 20 dB or more from the transmission signal and the amount of decoupling of the directional coupler of the detection unit 22. On the other hand, as in the present embodiment, the predetermined frequency f0
When the transmission device 1 erroneously receives a transmission signal having a frequency that is more than Δf away from the detection voltage Vx1 detected by the detection unit 22.
Is a voltage corresponding to the power value attenuated by about 1.2 dB or less from the transmission signal and the amount of decoupling of the directional coupler of the detector 22. Therefore, it is apparent that the detection voltage Vx1 / Vx0 has a large and stable level ratio (18 dB or more, a level ratio of about 10 dB or more is obtained when the detection voltage Vx0 is obtained from the reflection of the VSWR 2 by the antenna 3). It is.

The detected voltage Vx is compared with the reference voltage V2 from the reference voltage terminal 204 by the comparison circuit 25 using a differential circuit or the like. This reference voltage V2 is the detection voltage Vx1.
And Vx2. When the detection voltage Vx is Vx2 smaller than the reference voltage V2, that is, when the center frequency of the transmission signal is the predetermined frequency f0,
For example, an H level signal which does not indicate the transmission of the switching signal is transmitted. Therefore, in this case, the amplification unit 11 of the transmission device 1 is in the active state, and the transmission signal signal switching unit 2 to the detection unit 22.
Transmission to is continued.

On the other hand, when the detection voltage Vx is Vx1 which is higher than the reference voltage V2, that is, when the center frequency of the transmission signal is apart from the predetermined frequency f0 (it is satisfactory that the center frequency is more than Δf), the comparison circuit 25 For example, an L level signal indicating transmission of the switching signal is output. Therefore, in this case, the amplification unit 11 of the transmission device 1 is switched to the inactive state, and the transmission signal from the signal switching unit 2 to the detection unit 22 is cut off. As a result, even when the center frequency of the transmission signal is not f0, unnecessary waves that violate the Radio Law are not emitted from the transmission sharing device 2, and the reflected signal from the filter unit 23 is No damage is caused.

The frequency abnormal signal terminal 1 of the transmitting device 1
The output terminal of the comparison circuit 25 is connected to the output terminal 04. The output terminal of the comparison circuit 25 changes the L level state indicating the transmission of the switching signal to the fact that a high frequency signal having a frequency different from the predetermined frequency f0 is supplied to the transmission device 1. The signal is output from the terminal 104 as the frequency abnormal signal shown. This frequency abnormal signal is used as an alarm signal of the frequency synthesizer or the like.

The transmission sharing device 24 of the transmission sharing device 2 combines the transmission signal from the filter unit 23 and the same type of transmission signal as described above input from the RF input terminal 205 although the center frequency is different from the predetermined frequency f0. To produce a composite transmission signal. This combined transmission signal is sent to the mobile station via the ANT terminal 202 and the antenna 3. Since an isolator is generally connected to the input terminal of the transmission duplexer 24, the reflection of the transmission signal at the ANT terminal 202 due to the disconnection of the ANT terminal 202 or the like causes the detection unit 22 to reflect the transmission signal of the predetermined frequency f0. Does not propagate to.

[0024]

As described above, the present invention provides a signal switching section for passing a transmission signal from an ALC amplifier circuit when a switching signal is not received and blocking the transmission signal when receiving the switching signal. A filter unit that passes the transmission signal from the signal switching unit in accordance with a signal attenuation characteristic having a predetermined frequency band as a pass band, and a detection unit that detects a reflection level of the transmission signal reflected from an input terminal of the filter unit And a comparison circuit that generates the switching signal when the reflection level is equal to or higher than a predetermined level. Therefore, even if the transmission signal has a frequency abnormality, the frequency abnormality can be detected, and unnecessary radio waves caused by the frequency abnormality can be detected. And the protection of the ALC amplifier circuit can be achieved.

Further, the present invention can increase the ratio of the reflection level between the case where the transmission signal has a predetermined frequency and the case where the transmission signal has an abnormal frequency, so that there is an effect that the detection accuracy of the frequency abnormality can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram of one embodiment of a transmission power control circuit according to the present invention.

FIG. 2 is a diagram illustrating an example of a frequency characteristic of a filter unit 23 used in the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission device 2 transmission sharing device 3 antenna 11, 12 amplifying unit 13, 22 detection unit 14 switching circuit 15 ALC circuit 21 signal switching unit 23 filter unit 24 transmission sharing device 25 comparison circuit 101 to 106, 201 to 205 terminals

Claims (4)

[Claims] 1. An ALC amplifier circuit for automatically level-controlling and amplifying a first high-frequency signal to generate a constant power transmission signal; and transmitting the transmission signal when the switching signal is not received and receiving the switching signal when the switching signal is received. A signal switching unit that blocks passage of a signal, a filter unit that passes the transmission signal from the signal switching unit according to signal attenuation characteristics having a predetermined frequency band as a pass band, and a filter unit that is reflected from an input end of the filter unit A detection unit that detects the reflection level of the transmission signal,
A transmission power control circuit, comprising: a comparison circuit that generates the switching signal when the reflection level is equal to or higher than a predetermined level. 2. The apparatus according to claim 1, wherein the comparing circuit generates an abnormal frequency signal indicating that the transmission signal is not in the predetermined frequency band when the reflection level is equal to or higher than a predetermined level. Transmission power control circuit. 3. An amplifying unit for amplifying a second high-frequency signal to generate the first high-frequency signal only when receiving a control signal, and receiving a transmission-on signal and not receiving the switching signal. The transmission power control circuit according to claim 1, further comprising a switching circuit that generates the control signal. 4. A directional coupler, wherein the detection unit is inserted between the signal switching unit and the filter unit and guides the transmission signal reflected from the filter unit to a signal coupling end of the reflected signal. 4. The transmission power control circuit according to claim 3, further comprising: a detector connected to said signal coupling end, said detector detecting an envelope of said reflected transmission signal and averaging said transmission signal to generate said DC reflection level.