JPH08316745A - Amplifier circuit - Google Patents

Abstract

PURPOSE: To provide the amplifier circuit in which a signal level is attenuated without causing a distortion in the characteristic and without destroying post- stage circuits when a signal with an excess level is received. CONSTITUTION: A 1st switch 3 and an attenuator 4 are provided between a 1st RF amplifier 2 and a 2nd RF amplifier 5. A diode switch 7 to detect excess of a prescribed level by a signal level is connected to an input of the 1st RF amplifier 2, and a 2nd switch 8 and a high resistance resistor 9 are provided between the diode switch 7 and a photocoupler 10. A level monitor 15 to detect that the signal level restores a usual level or a very weak level is provided to an output side of the 2nd RF amplifier 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an amplifier circuit having a signal attenuator.

[0002]

2. Description of the Related Art FIG. 2 is a schematic diagram of a general receiver for receiving a high frequency signal. This receiving device receives a high frequency signal higher than, for example, about 1 GHz.

In FIG. 2, a weak signal received by an antenna 21 is a first high frequency amplifier (hereinafter referred to as a first RF amplifier) 22 and a second high frequency amplifier (hereinafter referred to as a second RF amplifier). It is subjected to high-frequency amplification by a filter 23 and supplied to the mixer 24. The mixer 24 has a second R
The high frequency signal supplied from the F amplifier 23 is mixed with the local oscillation signal output from the local oscillator 25 and frequency-converted into an intermediate frequency signal. The intermediate frequency signal is amplified by an intermediate frequency amplifier (hereinafter referred to as an IF amplifier) 26 and then demodulated in a signal processing unit 27.

The first RF amplifier 22 carries out low noise amplification so as to prevent deterioration of signal quality such as image quality, sound quality, and error rate of data signal as much as possible, and the second RF amplifier 23
It is necessary to perform high gain amplification to make the signal power the required magnitude after the mixer 24. Thereby, a good reception state can be obtained.

However, when the power of the input signal exceeds a certain value, the higher the power, the more the characteristic distortion occurs in each part of the receiving device. As a result, the intermodulation characteristic, which is one of the important characteristics of the receiving device, deteriorates. Therefore, when it is desired to widen the power range of the received signal, in the first and second RF amplifiers 22 and 23,
It is necessary to realize two reception modes, in which high gain amplification is performed from a case where the power of the input signal is weak to a normal magnitude and low gain amplification is performed when the input signal has a large power.

In order to realize such two reception modes, the gain of the amplifier circuit (with respect to the input power of the first RF amplifier 22 is determined according to the magnitude (power level) of the input signal input from the antenna 21. It is necessary to change the ratio (output power ratio) of the second RF amplifier 23, and for that purpose, it is necessary to detect the power level of the signal. Therefore, 2
A level monitor and an attenuator are used to realize the one reception mode.

To which part of the receiving device the level monitor is added is determined from the viewpoint of low noise amplification. Loss occurs in the signal on the main transmission line due to the addition of the level monitor, but when calculating the total noise characteristic, the further the level monitor is inserted behind the amplifier circuit, the lower the deterioration of the noise characteristic is suppressed. be able to.

FIG. 3 is a circuit diagram showing a conventional amplifier circuit having an attenuator. In the amplifier circuit of FIG. 3, the first R
A switch 31 and an attenuator 32 are provided between the F amplifier 22 and the second RF amplifier 23, and the second RF amplifier 2
A level monitor 33 is provided between 3 and the output terminal O1.

When the power level of the output signal of the second RF amplifier 23 is equal to or lower than a predetermined value, the switch 31 has the terminal e.
, And the output signal of the first RF amplifier 22 is directly applied to the second RF amplifier 23.

When the power level of the output signal of the second RF amplifier 23 becomes higher than a predetermined value, the control signal CNT output from the level monitor 33 causes the switch 31 to switch the terminal f.
, And the output signal of the first RF amplifier 22 is given to the attenuator 32. As a result, the power level of the output signal of the first RF amplifier 22 is attenuated by the attenuator 32 and input to the second RF amplifier 23. as a result,
The characteristic distortion does not occur in the second RF amplifier 23,
Even in the mixer 24 (see FIG. 2) connected to the output terminal O1, characteristic distortion does not occur.

[0011]

In the above conventional amplifier circuit, the second RF amplifier 2 is considered in consideration of low noise amplification.
The power level of the signal is detected behind 3. Therefore, the switch 31 is switched to the attenuator 32 side only when a high level signal is output from the second RF amplifier 23 and input to the mixer 24.

Therefore, characteristic distortion occurs in the second RF amplifier 23 and the mixer 24 immediately before the switch 31 is switched. In addition, the second RF amplifier 23
If the level of the signal output from is extremely high,
The mixer 24 may be damaged.

An object of the present invention is to provide an amplifier circuit capable of attenuating a signal level without causing characteristic distortion when a signal of an excessive level is input and without damaging a subsequent circuit. It is to be.

[0014]

An amplifier circuit according to the present invention comprises an amplifier means, a first detecting means, an attenuating means, a first switching means, a resistance means, a second switching means, a second detecting means, and A control means is provided.

The amplification means amplifies the signal. The first detection means has a first level with which the level of the signal input to the amplification means is predetermined.
It is detected whether the value of is exceeded. The attenuator is provided on the output side of the amplifier and attenuates the level of the signal. First
The switching means can switch between a first state in which the output signal of the amplifying means is output via the attenuating means and a second state in which the output signal of the amplifying means is output without passing through the attenuating means.

The resistance means is provided in the signal path of the first detection means and divides the voltage. The second switching means is a third switching means for allowing the signal of the signal path of the first detecting means to pass through the resistance means.
And the signal of the signal path of the first detection means can be switched to the fourth state in which the resistance means is not passed. Second
The detecting means is provided on the output side of the first switching means and detects whether or not the signal level is lower than a predetermined second value.

The control means sets the first detecting means when the first detecting means detects that the level of the signal exceeds the first value.
The switching means and the second switching means are switched to the first state and the third state, respectively, and when the second detection means detects that the level of the signal is lower than the second value, The switching means and the second switching means are respectively the second
And the fourth state.

In particular, the first detection means may be a switching element which is turned on / off according to the voltage of the signal input to the amplification means. The amplification means may include a first amplifier that performs low noise amplification, and may further include a second amplifier that performs high gain amplification between the first switching means and the second detection means.

[0019]

In the amplifying circuit according to the present invention, when the level of the signal input to the amplifying means is equal to or lower than the first value, the first switching means is set to the second state and the second switching means is set. The means is set to the fourth state. As a result, the output signal of the amplification means is output without being attenuated by the attenuation means, and the signal voltage of the signal path of the first detection means is not divided by the resistance means.

When the level of the signal input to the amplifying means becomes high and the first detecting means detects that the signal level exceeds the first value, the first switching means sets the first state to the first state. And the second switching means is switched to the third state. As a result, the output signal of the amplification means is attenuated and output by the attenuation means, and the signal voltage of the signal path of the first detection means is divided by the resistance means.

When the level of the signal input to the amplifying means becomes low and the second detecting means detects that the signal level becomes lower than the second value, the first switching means makes the second switching means. The second switching means is returned to the fourth state. As a result, the output signal of the amplification means is output without being attenuated by the attenuation means, and the signal voltage of the signal path of the first detection means is not divided by the resistance means.

As described above, the detection when the signal level becomes high is performed at the input side of the amplification means, and the detection when the signal level becomes low is performed at the subsequent stage side of the amplification means.
Therefore, an excessive level signal is not input to the amplifying means, and an excessive level signal is not output from the amplifying means. Therefore, the characteristic distortion does not occur in the amplifying means and the circuit in the subsequent stage, and the circuit in the subsequent stage is not damaged.

Further, when the level of the signal inputted to the amplifying means becomes high, the first detecting means is connected to the resistance means immediately after detecting that the signal level exceeds the first value. Signal leakage to the detection means is suppressed.

That is, when the first detecting means is composed of the switching element, the switching element is turned on when the voltage of the signal inputted to the amplifying means becomes high. As a result, a current flows in the signal path of the switching element, but when the signal voltage is divided by the resistance means, the voltage across the switching element becomes smaller than the threshold value, and the switching element is turned off. Therefore, almost no current flows through the switching element, and the signal does not leak to the first detecting means.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of an amplifier circuit according to an embodiment of the present invention.

In FIG. 1, the input signal received by the antenna 1 is input to the first RF amplifier 2 via the input terminal I1.
Given to. The first RF amplifier 2 low-noise amplifies the input signal and outputs it. The first switch 3 is connected to the output terminal of the second RF amplifier 5. The terminal a of the first switch 3 is connected to the input terminal of the second RF amplifier 5 by a through line, and the terminal b is connected to the input terminal of the attenuator 4. The output terminal of the attenuator 4 is the second RF amplifier 5
Is connected to the input terminal of

The first switch 3 gives the output signal of the first RF amplifier 2 directly to the second RF amplifier 5 when switched to the terminal a side, and when switched to the terminal b side. The output signal of the first RF amplifier 2 is given to the attenuator 4. The attenuator 4 attenuates the voltage level of the signal input from the terminal b by a predetermined amount of attenuation.

The second RF amplifier 5 is connected to the first switch 3
The signal output from the output terminal or the signal output from the attenuator 4 is amplified with high gain and output to the output terminal O1. Output terminal O
The mixer 24 shown in FIG. 3 is connected to 1.

On the other hand, a resistor 6, a diode switch 7 and a second switch 8 are connected in series to the input terminal I1. As a result, a part of the signal from the input terminal I1 is given to the diode switch 7 via the resistor 6.

The terminal c of the second switch 8 is connected to the anode of the light emitting diode 10a in the photocoupler 10 by a through line, and the terminal d is connected to the anode of the light emitting diode 10a via the high resistance body 9. The cathode of the light emitting diode 10a is grounded. The anode of the photodiode 10b in the photocoupler 10 is grounded, and the cathode is connected to one input terminal of the OR circuit 13 in the control circuit 12 via the buffer 11.

The second switch 8 gives the output signal of the diode switch 7 directly to the light emitting diode 10a when switched to the terminal c side, and outputs the output signal of the diode switch 7 when switched to the terminal d side. Is given to the high resistance body 9. The high resistance body 9 has a large resistance value and transmits the signal voltage input to the input terminal I1 to the diode switch 7
At the same time, the voltage is divided to reduce the voltage applied across the diode switch 7.

The resistance value of the high resistor 9 is 100 kΩ or more, for example, about 1 MΩ. The current when the diode switch 7 is off is 0.1 nA or more, and is 0.1 μA, for example.
It is about A. The current when the diode switch 7 is turned on is 0.1 mA to 10 mA, for example, 1 mA. The ON voltage of the diode switch 7 is around 0.6V.

On the output side of the second RF amplifier 5,
A level monitor 15 is provided. Level monitor 15
Is connected to one input terminal of the AND circuit 14 in the control circuit 12, and the output terminal of the AND circuit 14 is OR.
It is connected to the other input terminal of the circuit 13. The output terminal of the OR circuit 13 is connected to the other input terminal of the AND circuit 14. The output signal of the OR circuit 13 is the control signal CN
It is given as T to the first switch 3 and the second switch 8.

In the amplifier circuit of FIG. 1, the first RF amplifier 2, the first switch 3, the attenuator 4 and the second RF amplifier 5 constitute the main transmission line, and the resistor 6, the diode switch 7, and the second RF amplifier 2 are provided. The switch 8, the high resistance body 9 and the light emitting diode 10a constitute a detection line.

Next, the operation of the amplifier circuit of FIG. 1 will be described.
When a signal of a normal power level or a minute power level is input from the antenna 1 to the first RF amplifier 2, the first switch 3 is set to the side of the terminal a and the second switch 8 is set to the terminal. It is set on the c side. As a result, the output signal of the first RF amplifier 2 is directly given to the second RF amplifier 5, and in the main transmission line, the signal of the normal power level or the minute power level is not attenuated and the low noise amplification and the high gain are achieved. It is amplified.

At this time, the detection signal D2 output from the level monitor 15 is "1". On the other hand, the diode switch 7 is off, and the detection line has a high resistance. Therefore, no current flows through the light emitting diode 10a of the photocoupler 10, and the photodiode 10b is in the off state. In this case, the detection signal D1 output from the buffer 11 is "0".

When the voltage level of the signal input from the antenna 1 to the first RF amplifier 2 exceeds the threshold value of the diode switch 7, the diode switch 7 is turned on. As a result, a current flows from the input terminal I1 to the light emitting diode 10a of the photocoupler 10 via the resistor 6, the diode switch 7 and the second switch 8, and the light emitting diode 10a emits light. As a result, the photodiode 10b is turned on, and the detection signal D1 output from the buffer 11 becomes "1".

As a result, the OR circuit 1 in the control circuit 10
The control signal CNT output from 3 becomes "1", and the first
The switch 3 is switched to the terminal b side, and the second switch 8 is switched to the terminal d side. Therefore, the output signal voltage level of the first RF amplifier 2 is reduced by the attenuation amount by the attenuator 4 and applied to the second RF amplifier 5. That is, in the main transmission line, a signal having a large power level is attenuated and amplified with low noise and high gain.

At the same time, the voltage level of the signal applied to both ends of the diode switch 7 is reduced by being divided by the high resistance element 9. As a result, the diode switch 7
The voltage across the voltage drops below the threshold, the diode switch 7 turns off, and the light emitting diode 10 of the photocoupler 10
a goes out. As a result, the photodiode 10b is turned off, and the detection signal D1 output from the buffer 11 returns to "0". At this time, since the detection signal D2 is "1", the control signal CNT is held at "1" regardless of the state of the detection signal D1.

When the signal input from the antenna 1 to the first RF amplifier 2 drops to the normal power level or the minute power level, the voltage level of the output signal of the second RF amplifier 5 becomes lower than a predetermined value. The detection signal D2 output from the level monitor 15 becomes "0". As a result, the output signal of the AND circuit 14 in the control circuit 12 becomes "0" and the control signal CNT becomes "0". Therefore, the first
Switch 3 returns to the side of terminal a, and second switch 8
Returns to the terminal c side.

As described above, the detection of the increase of the signal level is performed at the input side of the first RF amplifier 2, and the detection of the decrease of the signal level is performed by the second RF amplifier 5.
On the output side of. Therefore, even if a large level signal is input from the antenna 1, an excessive level signal is not input to the first RF amplifier 2 and the second RF amplifier 5, and an excessive level signal is input from the second RF amplifier 5. Is not output.

Therefore, the characteristic distortion is not generated in the second RF amplifier 5 and the circuit connected to the subsequent stage, and the circuit connected to the subsequent stage is not damaged. After the first switch 3 and the second switch 8 are switched to the terminals b and d, respectively,
Since the voltage is divided by the high resistance element 9 to reduce the voltage level of the signal and the diode switch 7 is turned off, the leakage of the signal to the detection line on the input side is suppressed.

[0043]

As described above, according to the present invention, the detection when the signal level becomes high is performed at the input side of the amplifying means, and the detection when the signal level becomes low is performed at the subsequent stage of the amplifying means. As a result, the signal of excessive level is not input to the amplifying means, and the signal of excessive level is not output from the amplifying means. Therefore, even if an excessively high level signal is input, characteristic distortion does not occur in the amplifying means and the circuit at the subsequent stage, and the circuit at the subsequent stage is not damaged.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an amplifier circuit according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a general receiving device.

FIG. 3 is a diagram showing a configuration of a conventional amplifier circuit with an attenuator.

[Explanation of symbols]

 2 1st high frequency amplifier 3 1st switch 4 Attenuator 5 2nd high frequency amplifier 6 Resistance 7 Diode switch 8 2nd switch 9 High resistance body 10 Photocoupler 12 Control circuit 15 Level monitor

Claims (3)

[Claims] 1. An amplifying means for amplifying a signal, a first detecting means for detecting whether or not a level of a signal inputted to the amplifying means exceeds a predetermined first value, and an output of the amplifying means. Attenuating means provided on the side for attenuating the level of the signal, a first state in which the output signal of the amplifying means is output via the attenuating means, and an output signal of the amplifying means without passing through the attenuating means A first switching means capable of switching to a second state for outputting to the first detecting means; a resistance means provided in a signal path of the first detecting means for dividing a voltage; and a signal path of the first detecting means. A third state in which a signal is passed through the resistance means and a fourth state in which a signal in the signal path of the first detection means is not passed through the resistance means
Second switching means capable of switching to the above state, and second detection means provided on the output side of the first switching means for detecting whether or not the signal level is lower than a predetermined second value. And when the first detection means detects that the signal level exceeds the first value, the first switching means and the second switching means are respectively activated to the first state and the first state. When the second detection means detects that the signal level is lower than the second value, the first switching means and the second switching means are respectively switched to the third state. An amplifier circuit comprising: a control means for switching between a second state and a fourth state. 2. The amplifier circuit according to claim 1, wherein the first detecting means is a switching element which is turned on / off according to a voltage of a signal input to the amplifying means. 3. The amplifying means includes a first amplifier which performs low noise amplification, and further comprises a second amplifier which performs high gain amplification between the first switching means and the second detecting means. The amplifier circuit according to claim 1 or 2, characterized in that.