JPH04348618A - Transmitter - Google Patents

Abstract

PURPOSE:To protect a circuit and the deterioration in a transmitting output by prohibiting the maximizing of the gain when an input is decreased to a very low level or the input is lost. CONSTITUTION:The output of a high frequency amplifier 6 is sent from a signal output terminal 7 and detected by a detection circuit 8, a detection signal is given to an output constant control circuit 9 and a gain signal from the circuit 9 is given to an output switching device 10. On the other hand, an input transmission signal from a signal input terminal 1 is branched and inputted to an input level detection circuit 11, and a reference gain control signal from the circuit 11 is given to a time constant circuit 12. A prescribed time constant characteristic is given to the input signal in the circuit 12 and the result is fed to the output switching device 10. The switching device 10 selects a lower level in the outputs of the circuits 12, 9 and gives the selected level to a variable gain amplifier circuit 3 as a gain control signal to control the amplification factor of the circuit 3. Thus, the output from an intermediate frequency circuit 2 is amplified at a minimum gain and large level noise radiation is not caused.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmitter used in multiple radio equipment and the like.

0002

2. Description of the Related Art As shown in FIG. 3, a transmitting device used in a conventional multiplex radio device or the like amplifies a transmitted signal inputted from a signal input terminal 1 in an intermediate frequency circuit 2, and then converts the signal into a variable gain amplifier circuit. 3, and further sent to the frequency converter 4, where the carrier wave in the radio frequency band is modulated with this transmission signal, thereby converting it into a transmission signal in the radio frequency band, which is then filtered by a bandpass filter. The configuration is such that only components in a predetermined band are extracted by filtering with a filter 5, amplified with a high frequency amplifier 6, and then outputted from a signal output terminal 7.The signal outputted from this signal output terminal 7 is sent to an antenna. The configuration is such that the information is sent and transmitted wirelessly.

Further, the detection circuit 8 and the constant output control circuit 9 in the transmitting device constitute a gain control circuit of the variable gain amplifier circuit 3, and the amplified output of the high frequency amplifier 6 is detected by the detection circuit 8 and then the output is constant. The signal is sent to the control circuit 9, where the level of the detected signal is detected, a gain control signal corresponding to the detected level is generated, and this signal is used for gain control of the variable gain amplifier circuit 3.

The constant output control circuit 9 generates a gain control signal such that the amplified output of the high frequency amplifier 6 falls within a certain level range, and supplies it to the variable gain amplifier circuit 3 to control the amplification factor. The more input transmission signal will be transmitted at the optimum level.

[0005] In this way, in the conventional transmitter, the input transmission signal is amplified by the variable gain amplifier 3 which is a variable gain type amplifier, modulated into a high frequency signal, and this is amplified by the high frequency amplifier 6. After that, this high frequency transmission output is transmitted from the antenna, but the signal level of the output of the transmission stage is detected, and based on this detection level, the output constant control circuit 9 controls the high frequency transmission output to be at a constant level. A gain control signal is obtained, the gain of the variable gain amplifier 3 is controlled by this gain control signal, and the input of the high frequency amplifier 6 is adjusted so that the level of the high frequency transmission output, which is the output of the high frequency amplifier 6, is within a certain range. Since the output of the high frequency amplifier 6 decreases, since the transmission is controlled so that the
It is controlled to increase the gain of the variable gain amplifier circuit 3 and increase the output of the high frequency amplifier 6. Conversely, when the output of the high frequency amplifier 6 increases, the gain of the variable gain amplifier circuit 3 is controlled to decrease. The transmission output is controlled to be constant.

[0006]

[Problems to be Solved by the Invention] In this way, in conventional transmitting devices, an input transmission signal is amplified by a variable gain amplifier, which is a variable gain amplifier, which is then modulated into a high frequency signal, and this is converted into a high frequency signal. After being amplified by an amplifier, this high-frequency transmission output is transmitted from an antenna, but the signal level of the output in the transmission stage is detected, and based on this detection level, the high-frequency transmission output is adjusted to a constant level by an output constant control circuit. Obtain a gain control signal such that the gain is within a certain range, use this gain control signal to control the gain of the variable gain amplifier, and adjust the input of the high frequency amplifier so that the level of the high frequency transmission output, which is the output of the high frequency amplifier, falls within a certain range. I'm trying to control it and send it.

Therefore, when the output of the high-frequency amplifier decreases, the gain of the variable gain amplifier circuit is increased to increase the output of the high-frequency amplifier, and conversely, when the output of the high-frequency amplifier increases, the gain of the variable gain circuit is decreased. As a result, the high frequency transmission output can be controlled to be constant.

However, according to this conventional device,
If there is no input transmission signal or the level drops, the output of the high frequency amplifier will drop, so the variable gain amplifier circuit will be controlled to the maximum gain state, and in this state the input transmission signal will not be input. , if the level becomes high, this input transmission signal will be amplified with maximum gain and applied to the high frequency amplifier, resulting in the problem of excessive input being applied to the high frequency amplifier.

[0009] This causes problems such as the transmitted signal being distorted and the high frequency amplifier being deteriorated due to excessive input. In addition, when there is no input, noise is the main component, but since this is amplified and outputted at the maximum gain, there is also the problem that the high frequency transmission signal amplifies the noise before transmitting it.

[0010] Therefore, the purpose of this invention is to
To provide a transmitting device capable of protecting a circuit and preventing deterioration of transmission output by preventing the gain from increasing to the maximum even when the input drops to an extremely low level or is lost. There is a particular thing.

[0011]

[Means for Solving the Problems] In order to achieve the above object, the present invention is constructed as follows. That is, an input transmission signal is amplified by an output amplification means and sent out as a transmission output, and the input transmission signal is amplified by a variable gain amplification means and given to the output amplification means, and the variable gain amplification means The gain control is performed by the control output of a constant output control means that generates a control output with a gain that makes the transmission signal output level of the output amplification means fall within a predetermined range according to the transmission signal output level of the output amplification means. In a transmitting device configured to adjust the output level of a transmitted signal, it detects the input level of the input transmitted signal to determine whether it is abnormal or normal, and generates a control output that minimizes the gain when it is abnormal, and when it is normal. is a detection means that generates a control output that maximizes the gain, a time constant means that changes the control output of this detection means at a predetermined time constant, and controls the output of this time constant means and the output constant control means. and switching means for comparing the outputs and selecting the output that provides a lower gain and applying it to the variable gain amplification means for gain control.

0012

[Operation] In the above configuration, the detection means detects the input level of the input transmission signal and determines whether it is abnormal or normal, and generates a control output that minimizes the gain when it is abnormal, and generates the maximum gain when it is normal. A control output is generated. and,
The control output generated by this detection means is sent to the time constant means,
The output is changed at a predetermined time constant and is applied to the switching means. The switching means is also provided with a control output of a constant output control means that generates a control output with a gain that makes the transmission signal output level fall within a predetermined range based on the output of the output amplification means,
The switching means selects the output that provides a lower gain from both of these inputs and applies it to the variable gain amplification means to control the gain.

In this device, when there is no transmission input or it is extremely low, the detection means determines that it is abnormal and outputs a control signal that minimizes the gain, and the switching means outputs a control signal that is small compared to the control signal from the constant output control means. Since the gain is selected and given to the variable gain amplification means, the variable gain amplification means is controlled to minimize the gain, but when the transmission input is input from this state, the detection means determines that it is normal and increases the gain to the maximum. Outputs a control signal that provides gain. The change in this signal has a slow rising (or falling) characteristic due to the time constant means, and is given to the switching means, so the output of the time constant means is smaller than the control signal from the constant output control means. The switching means selects the output of the time constant means and applies it to the variable gain amplification means to control the gain, since it is a signal that obtains a gain.
When the output of the time constant means exceeds the gain given by the control signal from the constant output control means, the switching means switches to the control signal from the constant output control means to control the gain of the variable gain amplification means.

As a result, when there is no transmission input or it is extremely low, the gain is set to the minimum, and when the transmission input of a normal level is input from this state, the control signal that provides the maximum gain is changed slowly using the time constant means. The gain of the variable gain amplification means is controlled by the control signal that changes the level and gives the maximum gain, and then the gain is varied by the control signal from the constant output control means, which is a normal gain control circuit. Since the gain of the gain amplification means is controlled, even if a normal level of transmission input is input from a state where there is no transmission input or is extremely low, the variable gain amplification means will gradually increase the gain and return to the normal state. Since the input to the output amplification means will not become excessive, the circuit can be protected, and if there is no transmission input or it is extremely low, the gain will be the lowest, so the noise will be reduced to a large level. This also makes it possible to avoid having to amplify and output the signal.

Therefore, according to the present invention, when the input drops to an extremely low level or is lost, the gain is prevented from increasing to its maximum level, thereby protecting the circuit and reducing the deterioration of the transmission output. It is possible to provide a transmitting device that can prevent this.

[0016]

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 showing one embodiment of the present invention. In FIG. 1, 1 is a signal input terminal, 2 is an intermediate frequency circuit, 3 is a variable gain amplifier circuit, 4 is a frequency converter, 5 is a filter, 6 is a high frequency amplifier, 7 is a signal output terminal, 8 is a detection circuit, 9 is a constant output control circuit, 10 is an output switch, 1
1 is an input level detection circuit, and 12 is a time constant circuit. The intermediate frequency circuit 2 is a circuit that amplifies the transmission signal (transmission signal in the intermediate frequency band) inputted from the signal input terminal 1, and the variable gain amplifier circuit 3 amplifies and outputs the transmission signal from the intermediate frequency circuit 2. This circuit amplifies the transmitted signal. The variable gain amplifier circuit 3 is gain controlled by a gain control signal from a gain control system, which will be described later, and the controlled gain (
The transmitting signal is amplified by the amplification factor (amplification factor) and output.

Furthermore, the frequency converter 4 is a circuit that converts an input transmission signal into a transmission signal in the radio frequency band by modulating the carrier wave in the radio frequency band with the transmission signal output from the variable gain amplifier circuit 3. The filter 5 is a bandpass filter that filters the transmitted signal in the radio frequency band and extracts only the components in a predetermined band.

Furthermore, the high frequency amplifier 6 amplifies the output of the filter 5 and outputs it from the signal output terminal 7.
The configuration is such that the signal output from the signal output terminal 7 is sent to an antenna and transmitted wirelessly.

The detection circuit 8 is a circuit for detecting the amplified output of the high frequency amplifier 6, and the output constant control circuit 9 detects the level of this detected signal and generates a gain control signal according to the level to control this. It is output as a gain control signal for the variable gain amplifier circuit 3, and the constant output control circuit 9 generates a gain control signal such that the amplified output of the high frequency amplifier 6 falls within a certain level range.

In addition, the input level detection circuit 11 detects the transmission signal inputted from the signal input terminal 1 and determines whether the input level is "normal" or "abnormal". Outputs a normal reference gain control signal at a normal level value (for example, the level at which the maximum allowable gain is obtained in a normal case), and suppresses the gain to a low level when the input level is abnormal. The time constant circuit 12 outputs the reference gain control signal output from the input level detection circuit 11 with a transient characteristic of a predetermined time constant.

Further, the output switch 10 receives as input the reference gain control signal outputted through the time constant circuit 12 and the gain control signal outputted from the constant output control circuit 9, and inputs the reference gain control signal and the gain control signal. The signal that provides a lower gain is selected from the two signals and is applied to the variable gain amplifier circuit 3 as a gain control signal.

These detection circuit 8, output constant control circuit 9,
The output switch 10, the input level detection circuit 11, and the time constant circuit 12 constitute a gain control system. The variable gain amplifier circuit 3 is controlled to have a gain according to the gain control signal output from the output switch 10, and operates to amplify and output the input transmission signal.

FIG. 2 is a block diagram showing an embodiment of the output switch 10 of the present invention. In the figure, 101 and 102 are output switch input terminals, and the output switch input terminal 101 has a time constant. The output from the circuit 12 and the output from the constant output control circuit 9 are input to the output switch input terminal 102, respectively. 103 is a comparator, which compares both gain control signals inputted from the output switch input terminals 101 and 102 and selects a predetermined comparison signal (for example, the level of the reference gain control signal is higher than that of the gain control signal) depending on which one is lower. When the level of the reference gain control signal is low, it outputs "H", and when the level of the reference gain control signal is higher than that of the gain control signal, it outputs "L", or vice versa). 104 and 107 are control circuits, and the control circuit 104 is connected to the comparator 103.
It outputs a switching control signal in response to a comparison signal from.

Reference numerals 105 and 106 are switching devices whose opening and closing are controlled by a switching control signal output from the control circuit 104, and the switching device 105 receives the output from the time constant circuit 12 which is input from the output switching device input terminal 101. , switch 1
06, the output from the constant output control circuit 9 is input to the output switch input terminal 102, and the output from the constant output control circuit 9 is inputted to the output switching device input terminal 102.
According to the switching control signal from 4, when one switch is "closed", the other switch is controlled to be "open". 108 is an output terminal of the output switch.

Further, the control circuit 107 receives the output from the time constant circuit 12 or the output from the constant output control circuit 9, which is input via the switch 105 or the switch 106.
Generates a gain control signal output corresponding to the signal level,
It is applied to the variable gain amplifier circuit 3 to perform gain control.

Next, the operation of the apparatus having the above structure will be explained. In this device, an intermediate frequency input transmission signal input to a signal input terminal 1 is amplified by an intermediate frequency circuit 2, further amplified by a variable gain amplifier circuit 3 with an amplification factor corresponding to the signal level, and then sent to a frequency converter 4. The signal is converted into microwaves, filtered to remove components other than those in a predetermined band, passed through a high-frequency amplifier 6, amplified to a sufficient transmission output level, and outputted from a signal output terminal 7. The output from this signal output terminal 7 is transmitted from an antenna (not shown).

On the other hand, the output of the high frequency amplifier 6 is sent to the detection circuit 8.
It is detected here to produce a detection signal corresponding to the output level, which is then applied to the output constant control circuit 9, which outputs the high frequency signal from the high frequency amplifier 6 according to the level of the detected signal. Obtain a gain control signal that keeps the transmission output within a certain level. If the level of the input transmission signal is normal, the gain of the variable gain amplifier 3 is controlled by this gain control signal from the constant output control circuit 9, and the level of the high frequency transmission output, which is the output of the high frequency amplifier 6, is kept constant. Control the transmission so that it stays within the range.

However, when the level of the input transmission signal becomes abnormally low or is cut off, if the gain control of the variable gain amplifier 3 is continued using the gain control signal from the constant output control circuit 9, When the gain of the variable gain amplifier 3 reaches its maximum, noise components are amplified to a large level before being transmitted, or when the gain of the variable gain amplifier 3 reaches its maximum, the level of the input transmission signal suddenly recovers. , when the application of the input transmission signal is started, the input transmission signal amplified to a large level is input to the high frequency amplifier 6, and the input to the high frequency amplifier 6 becomes excessive.

Therefore, in this device, the gain control signal from the constant output control circuit 9 is applied to the variable gain amplifier 3 via the output switch 10. A reference gain control signal that changes gradually according to the level change of the input transmission signal is input to the output switch 10, and the output switch 10 selects the lower level of the gain control signal and the reference gain control signal. (the one giving a lower gain) is selected and applied to the variable gain amplifier 3, and used for gain control of the variable gain amplifier 3.

That is, the input transmission signal from the signal input terminal 1 is also branched and input to the input level detection circuit 11, and the input level detection circuit 11 determines whether the input level is "normal" or not.
Determine whether the input level is “normal.”
level, the input level detection circuit 11 outputs a normal reference gain control signal (a gain control signal that provides the maximum allowable gain) at a predetermined normal level; When input level detection circuit 1
1 outputs an abnormal reference gain control signal (for example, a gain control signal that provides the minimum gain) at a predetermined abnormal level.

These reference gain control signals are supplied to the time constant circuit 1.
2, and the time constant circuit 12 gives a predetermined time constant characteristic to the input reference gain control signal, outputs it, and adds it to the output switch 10. Output switch 10
Then, of the two inputs of the time constant circuit 12 and the output of the constant output control circuit 9, the one with the lower level is selected and applied to the variable gain amplifier circuit 3 as a gain control signal to control the amplification factor of the variable gain amplifier circuit 3. do.

Therefore, in normal operation, the input level detection circuit 11 indicates "normal" and outputs the reference gain control signal in the normal state, and the constant output control circuit 9 also outputs the gain control signal in the normal state. Since the output switch 10 selects the input on the constant output control circuit 9 side by the comparator 103 and controls the variable gain amplifier circuit 3, the output is controlled to be constant.

When the level of the input transmission signal decreases or is cut off, the input level detection circuit 11 indicates "abnormality", so it outputs an abnormality reference gain control signal, and this abnormality reference gain control signal has a time constant. The circuit 12 sends the signal to the output switch 10 with a characteristic of a predetermined time constant. At this time, since the level of the detected signal sent from the detection circuit 8 has become small due to the level abnormality of the input transmission signal, the constant output control circuit 9 sends a gain control signal necessary to return it to a constant level. will be output. Therefore, output switch 1
0, the comparator 103 compares the abnormal reference gain control signal and the gain control signal and outputs a predetermined comparison signal depending on which one is lower.

In the above example, since the level of the input transmission signal is lowered or cut off, the abnormal reference gain control signal with the minimum gain is generated, and since it is lower than the gain control signal from the constant output control circuit 9, the "H" ” Outputs a comparison signal. This comparison signal is sent to the control circuit 104, and the control circuit 104 controls the switch 105 to be selected based on this comparison signal. Therefore, the reference gain control signal is sent to the control circuit 107 via the switch 105. Then, the control circuit 107 outputs a gain control signal that provides a minimum gain in response to this reference gain control signal, and outputs a gain control signal that provides a minimum gain to the variable gain amplifier circuit 3.
Therefore, the input from the intermediate frequency circuit 2 is amplified with this minimum gain, converted into a microwave by the frequency converter 4, and then passed through the filter 5 and input to the high frequency amplifier 6. Therefore, the input to the high frequency amplifier 6 is suppressed to a low level, and no large level noise is emitted.

In this manner, when the level of the input transmission signal significantly decreases or is interrupted, the input level detection circuit 11 outputs a predetermined low-level abnormality reference gain control signal,
As a result of comparing this with the gain control signal from the output constant control circuit 9 based on the amplified output of the high frequency amplifier 6 and selecting the one with the lower level, control is performed so that the abnormality reference gain control signal is selected, and the variable gain The gain of the amplifier circuit 3 becomes minimum.

Next, when an input transmission signal of a normal level is added from the above state, the input level detector 11 changes from "abnormal" to "normal". Therefore, the input level detector 1
The output from 1 is switched from the conventional abnormal reference gain control signal to the normal reference gain control signal, and this normal reference gain control signal is given transient characteristics corresponding to the time constant by the time constant circuit 12 and then sent to the output switcher. 10 is input.

The abnormal reference gain control signal is a control signal for providing the minimum gain, and the normal reference gain control signal is a control signal for providing the maximum allowable gain.
Although the level difference between the two is large, a time constant circuit 12 is provided to suppress such rapid level changes. That is, the level change from the abnormal reference gain control signal to the normal reference gain control signal gradually increases due to the time constant of the time constant circuit 12. In this way, you can make the slope gentler and gradually raise the level.

In the output switch 10, a comparator 103 compares the abnormal reference gain control signal and the gain control signal, and outputs a predetermined comparison signal depending on which one is lower. In this case, the normal reference gain control signal provides the maximum allowable gain, but due to the time constant of the time constant circuit 12, it gradually increases from the abnormal reference gain control signal level. The gain control signal from the output constant control circuit 9 that outputs a gain control signal that maintains the output of the high frequency amplifier 6 at a constant level based on the output of the high frequency amplifier 6 changes as the level of the input transmission signal increases. At the time of signal application, a gain control signal that maximizes the gain is output. Therefore, for a while from this point on, the normal state reference gain control signal that gradually changes and is obtained via the time constant circuit 12 is selected.

That is, in the output switch 10, the comparator 103 compares the gradually changing normal state reference gain control signal with the gain control signal, and selects the switch 105 until the normal state reference gain control signal exceeds the gain control signal. Outputs a comparison signal. Therefore, for a while, the time constant circuit 12
A gradually changing normal-time reference gain control signal obtained through the normal-time reference gain control signal is given to the control circuit 107, and the variable gain amplifier 3 is gain-controlled by the gain control signal based on this normal-time reference gain control signal, and the input transmission signal is is amplified at a gradually increasing amplification factor and input to the high frequency amplifier 6.

When the normal reference gain control signal exceeds the gain control signal, the output of the comparator 103 becomes a comparison signal for selecting the switch 106, so at this point the output is switched to the gain control signal from the constant output control circuit 9, and the output Switcher 10
A gain control signal from the constant output control circuit 9 is applied to the variable gain amplifier 3, and gain control is performed using this gain control signal.

In this way, when the input transmission signal is cut off or at an extremely low level, the gain is controlled to be kept at a minimum, thereby preventing noise radiation and preventing the signal from suddenly reaching the normal level. When an input transmission signal is applied, the gain of the variable gain amplifier circuit 3 is gradually increased in response to this input level change. At this time, the output of the high frequency amplifier 6 also gradually increases, so the detection output of the detection circuit 8 and the output constant control circuit 9 gradually change, and at this time, the two inputs of the output switch 10 operate in reverse to each other, and when the two inputs become the same, the input on the constant output control circuit 9 side is selected and the normal state is achieved.

As described above, this device controls the variable gain circuit using the input level detection circuit when the input level of the input transmission signal is cut off or the input level significantly decreases, and when the input level returns to the normal state, Since the configuration is such that the gain is gradually increased to the variable gain circuit and switched to the constant output circuit, it is possible to prevent excessive input from being applied to the high frequency amplifier. That is, it is possible to prevent excessive input to the high frequency amplifier 6 due to the application of an input transmission signal of a normal level from a state where the input level is off. In addition, by changing the rise and fall time constants of the time constant circuit 12, it is possible to change the switching time of the input level from "abnormal" to "normal" and from "normal" to "abnormal". , when the output level becomes abnormal, the gain is immediately set to the minimum gain, and noise radiation can be suppressed.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications without changing the gist of the invention. Although the gain amplifier circuit was provided separately from the high-frequency amplifier, a variable gain amplifier circuit was provided inside the high-frequency amplifier and placed at the first stage of its input, and the input level of the high-frequency amplifier was detected and a similar switching operation was performed. It is also possible to adopt a configuration that performs gain control, thereby making it possible to control the input of the high frequency amplifier to prevent excessive input to the high frequency amplifier. Furthermore, the present invention can be used not only in wireless devices but also in transmission stages such as optical communications and other wired communications.

As explained above, this device converts the input transmission signal into microwave and amplifies it by the output amplification means.
The input transmission signal is amplified by a variable gain amplification means and is applied to the output amplification means, and the gain control of the variable gain amplification means is performed based on the transmission signal output level of the output amplification means. In a transmitting device configured to adjust the transmitting signal output level of the output amplifying means by using a control output of a constant output control means that generates a control output with a gain that makes the transmitting signal output level of the output amplifying means fall within a predetermined range. , detects the input level of the input transmission signal and determines abnormality/normality,
a detection means that generates a control output with a minimum gain when there is an abnormality, and generates a control output with a maximum gain when it is normal;
A time constant means changes the control output of the detection means at a predetermined time constant, and compares the output of the time constant means with the control output of the constant output control means, and selects the output that gives a lower gain. and a switching means for selectively applying the gain to the variable gain amplification means and controlling the gain.

In such a configuration, the detection means detects the input level of the input transmission signal to determine whether it is abnormal or normal, and generates a control output that minimizes the gain when the signal is abnormal, and generates a control output that minimizes the gain when the signal is normal. generates a control output that maximizes the gain, so the control output generated by the detection means is sent to the time constant means, changed at a predetermined time constant, outputted, and given to the switching means. The switching means is also provided with the control output of a constant output control means that generates a control output with a gain that keeps the transmitted signal output level within a predetermined range based on the output of the output amplification means, and the switching means receives both of these inputs. Among them, the output that provides a lower gain is selected and applied to the variable gain amplification means for gain control.

As described above, in this device, when there is no transmission input or the transmission input is extremely low, the detection means determines that there is an abnormality and outputs a control signal to minimize the gain, and the switching means outputs a control signal from the constant output control means. Compare and choose the one that gives you a smaller gain,
Since the signal is applied to the variable gain amplification means, the variable gain amplification means is controlled to minimize the gain, but when the transmission input is input from this state, the detection means determines that it is normal and outputs a control signal that gives the maximum gain. . The change in this signal has a slow rising (or falling) characteristic due to the time constant means, and is given to the switching means, so the output of the time constant means is smaller than the control signal from the constant output control means. Since this is the signal from which the gain is obtained, the switching means selects the output of the time constant means and applies it to the variable gain amplification means for gain control. At the stage where the gain exceeds the gain given by the variable gain amplification means, the switching means switches to the control signal from the constant output control means to control the gain of the variable gain amplification means.

As a result, when there is no transmission input or it is extremely low, the gain is set to the minimum, and when the transmission input at a normal level is input from this state, the control signal that provides the maximum gain is changed slowly using the time constant means. The gain of the variable gain amplification means is controlled by the control signal that changes the level and gives the maximum gain, and then the gain is varied by the control signal from the constant output control means, which is a normal gain control circuit. Since the gain of the gain amplifying means is controlled, even if a normal level of transmitting input is input from a state where there is no transmitting input or is extremely low, the variable gain amplifying means will gradually increase the gain and return to the normal state. Since the input to the output amplification means will not become excessive, the circuit can be protected, and the gain will be at its lowest when there is no transmission input or it is extremely low, so it will not cause a large amount of noise. It is also possible to avoid the problem of amplifying the signal to a high level and outputting it.

Therefore, according to the present invention, even when the input drops to an extremely low level or when there is no input, the gain is not increased to the maximum level, thereby protecting the circuit and reducing the deterioration of the transmission output. A transmitting device that can prevent this can be obtained.

[0050]

[Effects of the Invention] As detailed above, according to the present invention, even when the input drops to an extremely low level or disappears, the gain is prevented from increasing to the maximum, and the circuit It is possible to provide a transmitting device that protects the transmitter and prevents deterioration of the transmitting output.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an embodiment of the output switching device of the present invention.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

1... Signal input terminal, 2... Intermediate frequency circuit, 3... Variable gain amplifier circuit, 4... Frequency converter, 5... Filter, 6... High frequency amplifier, 7... Signal output terminal, 8... Detection circuit, 9... Constant output Control circuit, 10... Output switch, 11... Input level detection circuit, 12... Time constant circuit, 101, 102... Output switch input terminal, 103... Comparator, 104, 107... Control circuit, 105, 106... Switch, 108...Output switch output terminal.

Claims (1)

[Claims] 1. An input transmission signal is amplified by an output amplification means and sent as a transmission output, wherein the input transmission signal is amplified by a variable gain amplification means and given to the output amplification means, The gain control of the gain amplifying means is carried out by the control output of the constant output control means which generates a control output that makes the transmitting signal output level of the output amplifying means a gain that is within a predetermined range according to the transmitting signal output level of the output amplifying means. In a transmitting device configured to adjust the transmitting signal output level of the output amplifying means, detecting the input level of the input transmitting signal to determine abnormality/normality, and generating a control output that minimizes the gain in the case of abnormality, a detection means that generates a control output with a maximum gain when normal; a time constant means that changes the control output of the detection means at a predetermined time constant and outputs the output; and an output of the time constant means and the output constant control. comparing the control output of the means and selecting the output that gives a lower gain and applying it to the variable gain amplifying means;
1. A transmitting device comprising: switching means for controlling gain.