JPH0964774A - Received signal attenuation controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a received signal attenuation controller capable of reducing the attenuation of a received signal so as to prevent the attenuation due to thermal noise when the signal level of the received signal is small. SOLUTION: A reception field intensity detection circuit 4 detects the signal level of an amplified received signal, that is, a field intensity value. When the detected field intensity value is threshold or below, a control circuit 5 outputs voltage value of zero to an attenuation circuit 2. When the value is the threshold or above the field intensity value detected in a reception field intensity detection circuit 4 is outputted to the attenuation circuit 2 as it is. Then attenuation circuit 2 changes attenuation in accordance with the output voltage value from the control circuit 5 to attenuate the received signal.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an attenuation control device, and more particularly to an attenuation control device that attenuates a received signal in a wireless communication device.

[0001]

2. Description of the Related Art Generally, in a wireless device, an amplifier circuit is used to amplify a received signal and supply it to a demodulator. However, when a signal having a high signal level, that is, a signal having a high electric field strength is received, it is saturated due to the non-linearity of the transistor included in the amplifier circuit, and the operating point of the transistor moves. When the operating point of the transistor moves, the gain of the amplification circuit for the desired wave included in the received signal decreases, and the receiving sensitivity of the desired wave deteriorates.

Therefore, in order to prevent the reception sensitivity of the desired wave from deteriorating, an attenuator circuit for attenuating the received signal is provided in the preceding stage of the amplifier circuit. The attenuator circuit attenuates the received signal, thereby weakening the electric field strength and preventing the gain of the amplifier circuit from decreasing.

FIG. 9 is a functional block diagram showing a conventional radio device having the above-mentioned attenuation circuit.

In FIG. 9, the radio device includes an antenna 1, an attenuation circuit 2, an amplification circuit 3, a reception electric field strength detection circuit 4 and a demodulation circuit 6.

The attenuation circuit 2 attenuates the reception signal received by the antenna 1. The amount of attenuation in the attenuation circuit 2 is determined by the output voltage value from the reception electric field strength detection circuit 4. The amplification circuit 3 amplifies the attenuated reception signal from the attenuation circuit 2 and outputs the amplified reception signal to the reception electric field strength detection circuit 4 and the demodulation circuit 6. The received electric field strength detection circuit 4 detects the electric field strength value of the received signal, that is, the amplifier circuit 3.
The amplitude of the received signal from is detected and a DC voltage corresponding to the amplitude is output to the attenuation circuit 2.

FIG. 10 is a characteristic diagram showing an ideal relationship between the input voltage value to the amplifier circuit 3 and the output voltage value from the received electric field strength detection circuit 4.

As shown in FIG. 10, the input voltage value to the amplifier circuit 3, that is, the electric field strength value of the received signal and the output voltage value from the received electric field strength detection circuit 4 have a direct proportional relationship. When the electric field strength value of is strong, the output voltage value from the reception electric field strength detection / detection circuit 4 becomes large.

Since the attenuation amount of the attenuation circuit 2 is set according to the output voltage value from the reception electric field strength detection circuit 4, the electric field strength value of the reception signal becomes strong and the reception electric field strength detection circuit 4
When the value of the output voltage from is increased, the amount of attenuation in the attenuation circuit 2 is increased. Due to this increase in the amount of attenuation, the electric field of the received signal having a strong electric field strength value is weakened, and a decrease in the gain in the amplifier circuit 3 is prevented.

[0009]

However, in the above-mentioned conventional radio equipment, the relationship between the input voltage value to the amplifier circuit and the output voltage value from the detection circuit is actually the characteristic as shown in FIG. Of course, as shown in the characteristic diagram of FIG. 11, when the input voltage value to the amplifier circuit is from 0 to A,
The output voltage value from the received electric field strength detection circuit remains constant at B and does not become zero.

Even if the electric field strength of the received signal becomes small, noise due to thermal noise is input to the received electric field strength detection circuit through the amplifier circuit, and the received electric field strength detection circuit causes the electric field strength value of this noise ( (Amplitude) is converted to a DC voltage and output from the attenuation circuit. Since the attenuation amount of the attenuation circuit is set by the DC voltage value from the reception electric field strength detection circuit at this time, even if the electric field strength value of the reception signal is small, the attenuation amount in the attenuation circuit is equal to the electric field strength value. On the other hand, a large value is set, and the electric field strength value of the received signal is weakened more than necessary. Therefore, there arises a problem that the reception sensitivity is deteriorated.

The object of the present invention is to solve the above-mentioned problems,
It is an object of the present invention to provide a received signal attenuation control device that improves the minimum operation sensitivity with respect to the signal level of a received signal.

[0012]

In order to achieve the above-mentioned object, a received signal attenuation control device according to the present invention detects an electric field strength value of a received signal and outputs an electric field strength signal indicating the detected electric field strength value. An electric field strength detecting means for outputting, an attenuating means for attenuating the received signal based on the amount of attenuation set by the magnitude of the electric field strength value indicated by the electric field strength signal, and a predetermined value for the electric field strength value indicated by the electric field strength signal Control means for controlling the attenuating means so as to give a smaller attenuation amount than the set attenuation amount at the following time.

Further, the attenuation amount smaller than the set attenuation amount may be set to almost zero, and when the electric field strength value is larger than a predetermined value, a high level signal is output to the control means, and the electrolytic strength value is When the value is equal to or less than the predetermined value, a Schmitt trigger circuit that outputs a low-level signal, a switch that operates on when a high-level signal is input, and an off operation when a low-level signal is input, and one end is a switch. A resistor connected to the other end and grounded at the other end may be provided.

The control means supplies the electric field strength signal to the attenuating means when the electric field strength value is less than or equal to a predetermined value, and when the electric field strength value is greater than the predetermined value, the predetermined means is set. The resulting signal is supplied to the attenuating means.

In the present invention, by adopting the above-mentioned configuration,
When the electric field strength value indicated by the electric field detection signal is equal to or lower than a predetermined value by the control means, the electric field strength signal showing the electric field strength value of zero is output. The amount of attenuation is reduced, and the electric field strength value of the received signal is not weakened more than necessary. Therefore, the minimum operation sensitivity with respect to the received signal level, that is, the electric field strength value of the received signal can be improved.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a functional block diagram of a received signal attenuation controller according to an embodiment of the present invention.

In FIG. 1, the present invention comprises an antenna 1, an amplifier circuit 3, a received electric field strength detection circuit 4, a control circuit 5 and a demodulation circuit 6.

The received signal received via the antenna 1 is attenuated by the attenuation circuit 2 and output to the amplification circuit 3.
The attenuation amount of the attenuation circuit 2 is set according to the output voltage value from the reception electric field strength detection circuit 4.

The reception signal attenuated by the attenuation circuit 2 is amplified by the amplification circuit 3 and output to the reception electric field strength detection circuit 4 and the demodulation circuit 6. The electric field strength value of the amplified received signal, that is, the amplitude of the received signal from the amplifier circuit 3 is converted into a DC voltage by the received electric field strength detection circuit 4, and this DC voltage value is output to the control circuit 5.

A threshold value VTH is set in the control circuit 5, and when the voltage value from the reception electric field strength detection circuit 4 is less than or equal to the threshold value VTH, the output voltage value zero to the attenuation circuit 2 is output. When the threshold value is VTH or more, the voltage value from the reception electric field strength detection circuit 4 is output as it is.

FIG. 2 is a circuit diagram of the attenuation circuit shown in FIG.

In FIG. 2, the attenuation circuit 2 includes a diode 21 whose anode is connected to a constant power supply terminal and a diode 21.
A diode 22 whose anode is connected to the cathode of, and a resistor 23 whose one end is connected to the cathode of this diode 21,
Is provided. In the attenuation circuit 2, a transistor 24 having a collector terminal connected to the other end of the resistor 23, a base terminal connected to one end of the resistor 25, and an emitter terminal grounded.
And a resistor 2 having the other end connected to the received electric field strength detection circuit 4.
5 is provided.

In this attenuation circuit 2, the impedance of the transistor 24 changes in proportion to the magnitude of the DC voltage value from the reception electric field strength detection circuit 4, and the diode 21
And the value of the current flowing through 22 changes. Since the impedances of the diodes 21 and 22 change due to the change of the current value, the impedance of the attenuation circuit 2 changes.

Therefore, as the electric field strength value of the received signal increases, the impedance of the attenuation circuit 2 increases,
When the electric field strength value of the received signal becomes small, the impedance of the attenuation circuit 2 becomes small. Therefore, when the electric field strength value of the received signal which is the input voltage to the amplifier circuit 3 becomes large, the attenuation amount in the attenuation circuit 4 becomes large, The electric field strength value of the received signal is weakened.

FIG. 3 is a circuit diagram of the control circuit 5 shown in FIG.

In FIG. 3, the control circuit 5 includes an attenuation circuit 2
And a switch 51 connected in series to the received electric field strength detection circuit 4, a Schmitt trigger circuit 52 for controlling ON / OFF of the switch 51 according to a DC voltage value from the received electric field strength detection circuit 4, an attenuator circuit 2 and a switch 51. And a resistor 53 connected to one end and grounded at the other end.

As shown in the characteristic diagram of FIG. 4, the Schmitt trigger circuit 52 has a low-level voltage value VL when the input voltage, that is, the voltage value from the reception electric field strength detection circuit 4 is from zero to the threshold value VTH. Is output and the input voltage is higher than the threshold value VTH, the high-level voltage value VH
Is output. The threshold value VTH is set to the voltage B shown in FIG. 12, for example.

Next, the operation of the control circuit 5 will be described with reference to the characteristic diagram showing the relationship between the input voltage and the output voltage in the control circuit 5 of FIG.

The input voltage from the received electric field strength detection circuit 4 is supplied to the switch 51 and the Schmitt trigger circuit 52. As shown in FIG. 4, the Schmitt trigger circuit 52 outputs a low level voltage value VL when the input voltage is equal to or lower than the threshold value VTH, and outputs a high level voltage value VH when the input voltage is higher than VTH. To do.

Then, when the output of the Schmitt trigger circuit 52 is VH, the switch 51 is turned on, and when it is VL, it is turned off. Therefore, the Schmitt trigger circuit 5
When the input voltage value to 2 is higher than VTH, switch 5
1 is turned on, and the input voltage value is directly output to the attenuation circuit 2. The input voltage value at this time becomes a voltage value equal to the input voltage value to the control circuit 5, as shown in FIG.

On the other hand, when the voltage value from the received electric field strength detection circuit 4 is VTH or less, the switch 51 is turned off,
Since the attenuation circuit 2 and the ground are grounded via the resistor 53, the voltage value output to the attenuation circuit 2 becomes zero as shown in FIG.

FIG. 6 is a characteristic diagram showing the amount of attenuation with respect to the input voltage from the antenna 1 to the attenuation circuit 2.

In FIG. 6, the antenna 1 to the attenuation circuit 2
When the input voltage from is small, that is, when the voltage value is D or less, the attenuation amount becomes a value close to zero, and the attenuation circuit 2
When the input voltage from the antenna 1 to the
The amount of attenuation increases rapidly. The input voltage value D is a voltage level that is not affected by thermal noise.

Next, another embodiment of the present invention will be described with reference to FIGS. 7 and 8. 7 is a characteristic diagram showing the relationship between the input voltage of the Schmitt trigger circuit 52 and the output voltage, and FIG. 8 is a characteristic diagram showing the relationship of the output voltage with respect to the input voltage of the control circuit 5.

In the present embodiment, the threshold value is set to VTHH when the input voltage is increasing, and the threshold value is set to VTHL when the input voltage is decreasing.

The input / output characteristics of the control circuit 9 at this time are shown in FIG.
When the input voltage is in the process of increasing, the output voltage value is set to zero when the input voltage is equal to or lower than the threshold value VTHH, and the output voltage value is input when the input voltage is higher than the threshold value VTHH. Make it equal to the voltage value.

On the other hand, when the input voltage is in the process of decreasing, the output voltage value is made equal to the input voltage value when the input voltage is above the threshold value VTHL, and when the input voltage value is below the threshold value VTHL, The output voltage value is set to zero.

In this embodiment, since the input / output characteristic of the control circuit has a hysteresis characteristic, when the input voltage to the control circuit 5 is near the threshold value, the output voltage suddenly changes from zero to the input voltage value. It is possible to suppress a sudden change in the output voltage value that becomes a value equal to, and to stabilize the characteristics of the loop circuit including the reception electric field intensity detection circuit and the control circuit 5.

[0040]

As described above, in the received signal attenuation control device according to the present invention, when the signal level of the received signal, that is, the electric field strength value is equal to or less than a predetermined value, for example, a value affected by thermal noise, Since the voltage value that controls the attenuation amount of the attenuator circuit is set to zero, it is possible to solve the problem of excessively attenuating the received signal due to thermal noise etc. when the received signal level is low, and the receiver's minimum The operation sensitivity can be improved.

[Brief description of drawings]

FIG. 1 is a mechanism block diagram of a reception signal attenuation control device for a wireless device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of the attenuation circuit shown in FIG.

FIG. 3 is a block diagram of the control circuit shown in FIG.

FIG. 4 is a characteristic diagram showing input / output characteristics of the Schmitt trigger circuit shown in FIG.

5 is a characteristic diagram showing input / output characteristics of the control circuit shown in FIG.

6 is a characteristic diagram showing the relationship between the amount of attenuation and the input voltage value from the antenna 1 to the attenuation circuit shown in FIG.

FIG. 7 is a characteristic diagram showing input / output characteristics of a Schmitt trigger circuit according to another embodiment of the present invention.

FIG. 8 is a characteristic diagram showing input / output characteristics of a control circuit according to another embodiment of the present invention.

FIG. 9 is a mechanism block diagram showing an example of a conventional received signal attenuation control device.

FIG. 10 is a characteristic diagram showing an ideal relationship between an input voltage value to a conventional amplifier circuit and an output voltage value from a received electric field strength detection circuit.

FIG. 11 is a characteristic diagram showing the actual relationship between the input voltage value to the conventional amplifier circuit and the output voltage value from the received electric field strength detection circuit.

[Explanation of Codes] 1 ... Antenna 2 ... Attenuation circuit 3 ... Amplification circuit 4 ... Reception electric field strength detection circuit 5 ... Control circuit 6 ... Demodulation circuit

Claims (6)

[Claims] 1. An electric field strength detecting means for detecting an electric field strength value of a received signal and outputting an electric field strength signal indicating the detected electric field strength value, and an electric field strength value set by the magnitude of the electric field strength value indicated by the electric field strength signal. An attenuating means for attenuating the received signal based on an attenuating amount, and an attenuating means for giving an attenuation amount smaller than the set attenuation amount when an electric field intensity value indicated by the electric field intensity signal is equal to or less than a predetermined value. And a control means for controlling the received signal attenuation control device. 2. The received signal attenuation controller according to claim 1, wherein an attenuation amount smaller than the set attenuation amount is substantially zero. 3. The control means outputs a high level signal when the electric field strength value is larger than the predetermined value, and outputs a low level signal when the electrolytic strength value is equal to or lower than the predetermined value. A Schmitt trigger circuit that outputs a signal, a switch that is turned on when the high level signal is input, and turned off when the low level signal is input, and a resistor whose one end is connected to the switch and the other end is grounded. And, when the electric field strength value is equal to or less than the predetermined value, the electric field strength signal is supplied to the attenuating means, and when the electric field strength value is larger than the predetermined value, a predetermined value is set. 3. The received signal attenuation control device for a radio device according to claim 2, wherein the received signal is supplied to said attenuation means. 4. The received signal attenuation control apparatus for a radio device according to claim 3, wherein the input / output characteristic of the Schmitt trigger circuit has a hysteresis. 5. The attenuator includes a first diode whose cathode is connected to a power source, a second diode whose cathode is connected to an anode of the first diode, and an anode of the second diode. A first resistor having one end connected to it, a transistor having a collector terminal connected to the other end of the resistor and an emitter terminal grounded; A second resistor supplied to the base of the transistor.
A received signal attenuation control device for a wireless device as described. 6. The received signal attenuation control device according to claim 1, wherein the electric field strength detection means outputs the electric field strength signal by converting the amplitude of the received signal into a direct current.