JPH09312585A - If filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output only a received electric field intensity signal by a desired wave in an IF(intermediate frequency) filter used by various receivers. SOLUTION: A first automatic gain control amplifier 1 executes prescribed amplitude limit to an input signal large than a gain range. In addition, a band- pass filter 3 gives prescribed attenuation to an interference wave, connects the output it a second automatic gain control amplifier 2 with a prescribed gain range, a gain control signal adding circuit 4 adds the gain control signals of the first and second automatic gain control amplifiers 1 and 2 to generate the received electric field intensity signal, a comparator 5 compares the gain control signal of the second amplifier 2 and the detected level threshold value of a input terminal 15 with each other, and a switch circuit 6 outputs the received electric field intensity signal obtained by the adder circuit 4 only when the gain control signal of the second amplifier 2 is larger then the detected level threshold value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an IF (intermediate frequency) filter of a receiver, and more particularly to detection of received electric field strength suitable for use in mobile radio equipment and the like.

[0002]

2. Description of the Related Art At present, there is a super-heterodyne system in which a high frequency signal in a radio frequency band is converted into an intermediate frequency band and then demodulated as a receiving system of a receiver. However, only a necessary signal in the intermediate frequency band is selected. A ceramic filter is used as the IF filter.

Further, in recent years, it has been desired that the above-mentioned IF filter is made into an LSI by using a transistor, but since the transistor is used, the dynamic range is narrow due to the generation of noise and the limitation of the linear operation range. There was a flaw.

As one of the solutions to this problem, an automatic gain control amplifier is provided in front of the IF filter so as to improve the S / N ratio by amplifying when the input signal is small, and suitable for the IF filter when the input signal is large. There has been proposed a method of improving the dynamic range by controlling the gain so that the input level becomes large.

As a conventional example of the above-mentioned method, a reference (Toshi
o Adachi, Akira Ishikawa, Koji Tomioka, Susumu Har
a, Kaoru Takasuka, Hiroshi Hisajima, Allen Balow,
“ALow Noise Integrated AMPS IF Filter” IEEE CUST
OM INTEGRATED CIRCUITS CONFERENCE, pp. 8.2.
1-8.2.4, 1994).

FIG. 8 is a block diagram showing the circuit configuration of the IF filter shown in the above document. In FIG.
101, 102, 103, 104 are automatic gain control amplifiers, 105, 106,
107 is a band pass filter, 108 is a gain control signal addition circuit, 109 is a discriminator for demodulating an FM signal, 110
Is a PLL (phase locked loop) for controlling the characteristics of the bandpass filter, 111 is an input terminal of the automatic gain control amplifier 101, 112 is an output terminal of the automatic gain control amplifier 104, and 113
Is an output terminal of the discriminator 109, 114 is a PLL 110
Reference clock input terminal of 115, gain control signal adder circuit 115
It is the output terminal of 08.

A conventional method of detecting the received electric field strength is shown in FIG.
As shown in FIG.
Automatic gain control amplifiers 101 to 104 are provided before and after each filter, gain control signals of the automatic gain control amplifiers are added by a gain control signal adding circuit 108, and a reception electric field strength signal is obtained from an output terminal 115.

[0008]

However, the received electric field strength needs to be proportional to the magnitude of the desired wave in the pass band, but in the conventional IF filter described above, the desired wave level in the pass band is Even when it is so small that it is not output as a received electric field strength signal, when the interfering wave level of the adjacent channel outside the pass band is large and the gain decreases so that the output level of the automatic gain control amplifier 101 in the first stage becomes a constant value. However, there is a problem that the gain control voltage of the automatic gain control amplifier 101 is output as a received electric field strength signal.

The present invention solves the above-mentioned conventional problems, and provides an IF filter for detecting a received electric field strength capable of outputting only a received electric field strength signal of a desired wave without outputting a received electric field strength signal of an interfering wave. The purpose is to provide.

[0010]

In order to solve the above problems and achieve the object, the present invention discriminates whether a received electric field strength signal is due to a desired wave or an interfering wave, and receives the electric field strength signal due to the interfering wave. Is provided so as to output only the received electric field intensity signal by the desired wave.

Thus, there is an effect that only the reception field strength signal of the desired wave can be output without outputting the reception field strength signal of the interference wave.

[0012]

An embodiment of the present invention according to claim 1 of the present invention discriminates whether the received electric field strength signal is due to a desired wave or an interference wave, and outputs the received electric field strength signal due to the interference wave. Is an IF filter configured to output only the reception field strength signal of the desired wave by providing a means that does not output the reception field strength signal of the interference wave without outputting the reception field strength signal of the interference wave. Only signals can be output.

According to another aspect of the present invention, there is provided an automatic gain control amplifier which has a predetermined gain range for an input signal and applies a predetermined amplitude limit to an input signal larger than the gain range. Means, the output signal of the automatic gain control amplification means, and at least one circuit including a bandpass filter having a predetermined attenuation amount with respect to an interference wave, and the bandpass filter means. The final stage automatic gain control amplifying means having a predetermined gain range with respect to the output signal of the final stage band pass filter means, and the gain control signals of all the automatic gain control amplifying means are added to obtain a received electric field strength signal. Gain control signal adding means to obtain, means for comparing the gain control signal of the final stage automatic gain control amplifying means and the detection level threshold,
An IF for performing reception electric field strength detection having switch means for outputting the reception electric field strength signal obtained from the gain control signal adding means only when the gain control signal of the automatic gain control amplifying means at the final stage is larger than the detection level threshold value. The filter is capable of outputting only the received electric field strength signal of the desired wave without outputting the received electric field strength signal of the interference wave.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment) FIG. 1 is a block diagram showing a configuration of an IF filter according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is a first automatic gain control amplifier, and 2 is a second automatic gain control amplifier.
2 is an automatic gain control amplifier of FIG. Reference numeral 3 is a bandpass filter, and a continuous time filter composed of transistors, an active filter, a switched capacitor filter or the like is used. FIG. 3 shows a frequency characteristic diagram of the bandpass filter 3. Reference numeral 4 is a gain control signal addition circuit, 5 is a comparator, and 6 is a switch circuit.

Here, the first automatic gain control amplifier 1 is used.
Amplifies a small input signal to improve the S / N ratio of the bandpass filter 3, and keeps the output level of the input signal of a predetermined magnitude or more constant by the first automatic gain control amplifier 1. Prevent an excessive signal from being input to the pass filter 3.

The input and output terminals of each block will be described. Reference numeral 7 is an input terminal of the first automatic gain control amplifier 1, 8 is an output terminal of the first automatic gain control amplifier 1,
Reference numeral 9 is an output terminal of the bandpass filter 3, and 10 is an output terminal of the second automatic gain control amplifier 2. Further, 11 is a gain control signal output terminal of the first automatic gain control amplifier 1, 12 is a gain control signal output terminal of the second automatic gain control amplifier 2, and 13
Is an output terminal of the gain control signal adding circuit 4, adds gain control signals from the gain control signal output terminals 11 and 12, and outputs the output terminal.
The received electric field strength signal is obtained from 13. 14 is an output terminal of the switch circuit 6, 15 is a detection level threshold value input terminal of the comparator 5, 16 is a control terminal of the switch circuit 6, 17 is a ground terminal of the switch circuit 6, and the gain control signal output terminal 12 The output is compared with the input of the detection level threshold input terminal 15 by the comparator 5, and if the output of the gain control signal output terminal 12 is larger, a Hi signal is output to the control terminal 16 and the gain control signal output terminal is output. When the output of 12 is smaller, the Lo signal is output to the control terminal 16. The switch circuit 6 connects the switch to the output terminal 13 when the control terminal 16 is Hi, and the control terminal 16 is L level.
When o, the switch is connected to the ground terminal 17.

FIG. 2 is a block diagram showing a configuration example of the first and second automatic gain control amplifiers 1 and 2 shown in FIG.
In FIG. 2, 201 is a variable gain amplifier, 202 is a limiter circuit, 203 is an envelope detector, 204 is a low-pass filter, and 205.
Is an input terminal of the variable gain amplifier 201, and 206 is a limiter circuit 20.
2 is an output terminal, 207 is a detection level lower limit input terminal of the envelope detector 203, and 208 is a gain control terminal of the variable gain amplifier 201. The variable gain amplifier 201 is an amplifier whose gain changes exponentially with respect to the input of the gain control terminal 208.

The envelope detector 203 obtains a linear envelope output with respect to the signal at the output terminal 206 of the limiter circuit 202, and determines the frequency characteristic of the gain control operation by the cutoff frequency of the low pass filter 204. The output of the low-pass filter 204 is input to the gain control terminal 208 to form a feedback loop, so that the envelope level of the output signal of the output terminal 206 approaches the detection level lower limit value input to the detection level lower limit value input terminal 207. Feedback works, and the output level of the output terminal 206 becomes constant. The limiter circuit 202 operates so as to limit the amplitude so that the output level of the output terminal 206 does not exceed a predetermined level when a signal large enough to prevent the gain control operation is input to the input terminal 205.

The operation of the IF filter configured as above will be described below. First, a level diagram when a signal having a center frequency fo (see FIG. 3) within the band of the bandpass filter 3 is input to the input terminal 7 of the first automatic gain control amplifier 1 shown in FIG. Is shown in FIG.
4, the vertical axis represents the signal level (dB), and the horizontal axis represents the position of each terminal 7 to 10 of each block in FIG. Also, 21
Is an input level range in which the gain of the first automatic gain control amplifier 1 is controlled, 22 is an output level of the first automatic gain control amplifier 1 when the gain is controlled, and 23 is a gain control of the second automatic gain control amplifier 2. Input level range, 24 is the output level of the second automatic gain control amplifier 2 during gain control, 29 is the limiter output level of the first automatic gain control amplifier 1, and 30 is the limiter of the second automatic gain control amplifier 2. This is the output level.

Reference numeral 25 is a level diagram when the signal level A is input to the input terminal 7 of the first automatic gain control amplifier 1, and 26 is a signal level B to the input terminal 7.
Is a level diagram when the input signal is input, and since the signal levels A to B are equal to or lower than the lower limit value of the input level range 21 to be gain controlled, the signal is amplified by the maximum gain of the first automatic gain control amplifier 1. In the bandpass filter 3, the gain of the signal at the center frequency fo is 0 dB, so the level does not change and the signal passes as it is. Further, the input of the signal level A becomes the level of the lower limit value of the gain-controlled input level range 23 of the second automatic gain control amplifier 2 and is amplified by the maximum gain of the second automatic gain control amplifier 2 to obtain the signal level. The input of B becomes the level of the upper limit value of the input level range 23 of the gain control of the second automatic gain control amplifier 2, and is amplified by the minimum gain of the second automatic gain control amplifier 2.

27 is a level diagram when the signal level C is input to the input terminal 7 of the first automatic gain control amplifier 1, and is the upper limit value of the input level range 21 for gain control. 1 is attenuated by the minimum gain of the automatic gain control amplifier 1 and the gain of the signal of the center frequency fo in the band pass filter 3 is 0 dB, so the level passes without any change and the input of the signal level C is the gain controlled input level. It becomes the level of the upper limit value of the range 23, and is amplified by the minimum gain of the second automatic gain control amplifier 2.

Reference numeral 28 is a level diagram when the signal level D is input to the input terminal 7 of the first automatic gain control amplifier 1, and is higher than the upper limit value of the input level range 21 for gain control. It is attenuated by the minimum gain of the first automatic gain control amplifier 1 and reaches the limiter output level 29. Since the gain of the signal at the center frequency fo in the bandpass filter 3 is 0 dB, it passes through without any change in the level, and the signal level D is input. Is equal to or higher than the upper limit value of the input level range 23 to be gain controlled, and is amplified by the minimum gain of the second automatic gain control amplifier 2 to become the limiter output level 30.

Inputs below the signal level A are the first and the first.
Since it is equal to or lower than the lower limit value of the input level range in which the gain of the second automatic gain control amplifiers 1 and 2 is controlled, it is amplified with the maximum gain of the first and second automatic gain control amplifiers 1 and 2. Inputs above the signal level C are the first and second automatic gain control amplifiers 1,
2 is equal to or higher than the upper limit value of the input level range to be gain-controlled, the minimum gain of the first and second automatic gain control amplifiers 1 and 2 is reached. The amplitude is limited to the limiter output levels 29 and 30 by 202 (see FIG. 2).

Next, a signal having a center frequency fo ± Δf (see FIG. 3) outside the band of the bandpass filter 3 is input to the input terminal 7 of the first automatic gain control amplifier 1 shown in FIG. FIG. 5 shows a level diagram in the case of being performed. FIG.
1, the vertical axis represents the signal level (dB) and the horizontal axis represents the positions of the terminals 7 to 10 of each block in FIG. 35 is a signal level A for the input terminal 7 of the first automatic gain control amplifier 1.
Is a level diagram when a signal level B is input to the input terminal 7, and signal levels A to B are maximum levels of the first automatic gain control amplifier 1. Amplified with gain. In the bandpass filter 3, the center frequency fo ± out of the pass band
Since the attenuation amount of the signal of Δf is X dB, the level obtained by subtracting the attenuation amount X dB from the output level 22 is set to be less than the lower limit value of the input level range 23 of the gain control of the second automatic gain control amplifier 2. , The gain control operation of the second automatic gain control amplifier 2 is disabled by the signal having the center frequency fo ± Δf.

On the other hand, 37 is a level diagram when the signal level C is input to the input terminal 7 of the first automatic gain control amplifier 1, and the first automatic gain control amplifier 1
Is attenuated to the output level 22 with the minimum gain of, and the bandpass filter 3 has a center frequency fo + Δf outside the pass band.
The signal is attenuated by the amount XdB of the signal, and becomes less than the lower limit value of the input level range 23 for gain control, and the gain control operation of the second automatic gain control amplifier 2 does not work.

Reference numeral 38 is a level diagram when the signal level D is inputted to the input terminal 7 of the first automatic gain control amplifier 1, and is attenuated by the minimum gain of the first automatic gain control amplifier 1 to be a limiter. Since it is limited by the output level 29, it is attenuated by the attenuation amount XdB of the signal of the center frequency fo + Δf outside the pass band in the band pass filter 3 and becomes less than the lower limit value of the input level range 23 in which the gain is controlled.

Inputs of signal level A or lower are the first and the first.
Since the input level range of the second automatic gain control amplifiers 1 and 2 to be gain controlled is equal to or lower than the lower limit value, the maximum gain of the first and second automatic gain control amplifiers 1 and 2 is amplified. The input of the signal level C or higher is equal to or higher than the upper limit value of the input level range in which the gain control of the first automatic gain control amplifier 1 is performed.
It becomes the minimum gain of the first automatic gain control amplifier 1 and is less than the lower limit value of the input level range 23 to be gain controlled after passing through the bandpass filter 3. Therefore, the maximum gain of the second automatic gain control amplifier 2 is set. Is amplified. Furthermore, the signal level D
The above signals are the limiter circuit 202 of the bandpass filter 3.
This limits the amplitude to the limiter output level 29.

The output characteristic of the received electric field strength signal with respect to the input of the input terminal 7 of the first automatic gain control amplifier 1 shown in FIG. 1 is shown in FIG. 6, and the gain control signal output characteristic is shown in FIG. 6 and 7, the vertical axis represents the signal level (linear) and the horizontal axis represents the input terminal 7 of the first automatic gain control amplifier 1.
Is the signal level (dB) of. Reference numeral 41 in FIG. 6 is the characteristic of the output terminal 13 of the gain control signal adder circuit 4 when a signal of the center frequency fo is input, and reference numeral 51 in FIG. 7 is the second automatic gain control amplifier 2
Is a characteristic of the gain control signal output terminal 12 and 52 is a characteristic of the gain control signal output terminal 11 of the first automatic gain control amplifier 1.

When the input to the input terminal 7 of the first automatic gain control amplifier 1 is less than the signal level A, neither the first automatic gain control amplifier 1 nor the second automatic gain control amplifier 1 performs gain control operation.
From the gain control signal output terminals 11 and 12, the gain control signal (characteristic 5
2, 51) is not output. Second at signal levels A to B
The gain control operation of the automatic gain control amplifier 2 is performed, and the gain control signal is output from the gain control signal output terminal 12 as indicated by the characteristic 51 in FIG. When the signal level is higher than the signal level B, the gain control operation of the second automatic gain control amplifier 2 is not performed and the gain control signal at the gain control signal output terminal 12 becomes constant. At the signal levels B to C, the gain control operation of the first automatic gain control amplifier 1 is performed, and the gain control signal output terminal
The gain control signal is output from 11 to as indicated by the characteristic 52 in FIG. When it is higher than the signal level C, the gain control operation of the first automatic gain control amplifier 1 is not performed, and the gain control signal at the gain control signal output terminal 11 becomes constant.

Then, the signals of the gain control signal output terminals 11 and 12 are added by the gain control signal addition circuit 4, and the output terminal 13
Is output to Reference numeral 42 in FIG. 6 is a characteristic of the output terminal 14 of the switch circuit 6 when a signal of the center frequency fo is input. The output of the gain control signal output terminal 12 is equal to or higher than the detection level threshold E. From the signal level F of the input terminal 7 of the gain control amplifier 1, the output of the output terminal 13 of the gain control signal addition circuit 4 is output to the output terminal 14 through the switch circuit 6. When the output of the gain control signal output terminal 12 is less than the detection level threshold value E, the switch circuit 6 is connected to the ground terminal 17, so that the signal of the output terminal 13 is not output from the output terminal 14.

Reference numeral 43 in FIG. 6 shows the characteristic of the output terminal 13 of the gain control signal adder circuit 4 when a signal having the center frequency fo ± Δf is input. The signal of the center frequency fo ± Δf is the input level range in which the gain of the second automatic gain control amplifier 2 is controlled.
Since it is less than the lower limit of 23 (see FIGS. 4 and 5), the gain control operation of the second automatic gain control amplifier 2 is not performed, and only the first automatic gain control amplifier 1 gains up to the signal levels B to C. The control operation is performed, and only the signal of the gain control signal output terminal 11 is added by the gain control signal addition circuit 4 and output to the output terminal 13. Reference numeral 44 in FIG. 6 is a characteristic of the output terminal 14 of the switch circuit 6 when a signal having a center frequency fo ± Δf is input, and the gain control operation of the second automatic gain control amplifier 2 is not performed. Since the output of the signal output terminal 12 is less than the detection level threshold value E, the switch circuit 6 remains connected to the ground terminal 17, so that the signal of the output terminal 13 is not output.

As is clear from the fact that the characteristic of the received electric field strength signal of the conventional IF filter is equivalent to the characteristic of the output terminal 13 in front of the switch circuit 6, the IF for carrying out the received electric field strength detection according to the embodiment of the present invention. The filter has an excellent effect in that it can output only the received electric field strength signal of the desired wave without outputting the received electric field strength signal of the interference wave.

As described above, according to the embodiment of the present invention, the output level of the first automatic gain control amplifier 1 during the gain control operation is made constant, and the gain control range of the first automatic gain control amplifier 1 is further increased. Limiter circuit for input exceeding
The amplitude is limited by 202, and after passing through the bandpass filter 3, the interference wave having the center frequency fo ± Δf is set to be less than the lower limit value of the gain control operation range of the second automatic gain control amplifier 2, so that The gain control operation of the second automatic gain control amplifier 2 is prevented from being performed on the interfering wave of the frequency fo ± Δf, and the gain control signal of the second automatic gain control amplifier 2 is compared with the detection level threshold value. A comparator 5 is provided for comparing the gain control signal of the second automatic gain control amplifier 2 with the detection level threshold value, and the output of the gain control signal addition circuit 4 is passed only when the gain control signal is larger than the detection level threshold value. By providing the switch circuit 6, it is possible to output only the reception field strength signal of the desired wave without outputting the reception field strength signal of the interference wave.

In the above description, the example in which the IF filter for detecting the received electric field strength is composed of two automatic gain control amplifiers and one bandpass filter has been described, but a circuit composed of the automatic gain control amplifier and the bandpass filter. It is also possible to make a similar connection by cascading a plurality of capacitors and connecting an automatic gain control amplifier after the final stage bandpass filter.

[0036]

As described above, according to the present invention, the means for discriminating whether the received electric field strength signal is due to the desired wave or the disturbing wave and not outputting the received electric field strength signal due to the disturbing wave is provided. It is possible to obtain the effect that only the received electric field strength signal due to the wave can be output.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an IF filter according to an embodiment of the present invention.

2 is a schematic diagram of a first and a second automatic gain control amplifiers 1 and 2 of FIG.
3 is a block diagram showing a configuration example of FIG.

3 is a diagram showing frequency characteristics of the bandpass filter 3 of FIG.

FIG. 4 is a level diagram when a signal having a center frequency fo within the band of the bandpass filter of FIG. 1 is input.

5 is a level diagram when a signal having a center frequency fo ± Δf outside the band of the bandpass filter in FIG. 1 is input.

6 is a diagram showing an output characteristic of a received electric field strength signal with respect to an input of an input terminal 7 of FIG.

FIG. 7 is a diagram showing output characteristics of the gain control signal of FIG.

FIG. 8 is a block diagram showing a circuit configuration of a conventional IF filter.

[Explanation of symbols]

1, 2 ... Automatic gain control amplifier, 3 ... Band pass filter, 4 ... Gain control signal addition circuit, 5 ... Comparator, 6
... switch circuit.

Claims (2)

[Claims] 1. A means for discriminating whether a received electric field strength signal is due to a desired wave or an interfering wave and not outputting the received electric field strength signal due to the interfering wave so as to output only the received electric field strength signal due to the desired wave An IF filter characterized by being configured as follows. 2. An automatic gain control amplifying means having a predetermined gain range for an input signal, and subjecting an input signal larger than the gain range to a predetermined amplitude limitation, and an output signal of the automatic gain control amplifying means. To a bandpass filter means having at least one circuit composed of a bandpass filter having a predetermined attenuation amount with respect to an interference wave, and an output signal of the bandpass filter means at the final stage of the bandpass filter means. On the other hand, a final stage automatic gain control amplifying means having a predetermined gain range, gain control signal adding means for adding the gain control signals of all the automatic gain control amplifying means to obtain a reception electric field strength signal, and the final stage Means for comparing the gain control signal of the automatic gain control amplifying means with a detection level threshold value; and a gain control signal of the final stage automatic gain control amplifying means for detecting the detection level. 2. The IF filter according to claim 1, further comprising switch means for outputting the received electric field strength signal obtained from the gain control signal adding means only when the value is larger than a threshold value.