JPH06140854A - Receiver - Google Patents

Abstract

PURPOSE:To exactly detect the intensity of an input signal by providing a received field intensity signal based on only the level of an IF received signal separated by an IF filter. CONSTITUTION:When tuning is shifted between the frequency of the IF received signal and the frequency of a tuning circuit 3 by fluctuation in the frequency of a local oscillator(OSC) 10 or the like and the IF received signal gets out of the pass band of an IF filter 5, the level of the IF received signal is attenuated by the filter 5. Therefore, the level of a first control signal is attenuated to a value lower than a thershold value 14, and a switch 12 is turned to a non-conductive state by a comparator 11. Thus, the first superimposing of a second control signal is blocked, the level of a signal intensity detecting output 101 is almost turned to '0' and an output characteristic without level shift is provided. Therefore, even when a strong disturbing wave exists in an adjacent frequency when the intensity of the input signal is weak, the intensity of the input signal can be exactly detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for demodulating a received signal, and more particularly to a receiver having a function of detecting a received electric field level of the received signal.

[0002]

2. Description of the Related Art A conventional example of a receiver will be described with reference to FIG. The figure shows an example of the configuration of an AM receiver (tuner). An RF (radio frequency or high frequency) received signal induced in an antenna is amplified by an RF amplifier 2 and is sent to a mixer 4 via an RF tuning circuit 3. Supplied.
A local oscillator 10 supplies a local oscillation signal corresponding to a desired tuning frequency to the mixer 4, and the RF reception signal is converted into an IF (intermediate frequency) signal. The IF reception signal is supplied to the IF amplifier 6 via the IF filter 5 having a narrow bandwidth corresponding to one channel. Before the IF filter 5,
The frequency bandwidth of the IF reception signal and the RF reception signal is wide, but the IF reception signal passed through the IF filter 5 has a narrow bandwidth. The IF received signal is demodulated by the AM detector 7, and the demodulated signal 100 is obtained.

In order to prevent oversaturation in the amplifier of the receiving circuit and maintain the output of the IF amplifier 6 within a certain range, two AGC circuits, that is, an IF-AGC circuit 8 are provided.
And an RF-AGC circuit 9 are provided. IF-AG
The C circuit 8 has a built-in carrier level detection circuit using a time constant circuit, etc.
00 is smoothed to generate a first control signal. The first control signal is applied to the gain control input terminal of the IF amplifier 6. The IF received signal level is the first of the received electric field strength.
The control characteristic is gradually changed so as to suppress the gain of the IF amplifier 6 when it becomes larger than the level. Since the level of the first control signal is proportional to the received electric field strength within a predetermined range, it can be used in another circuit as the input signal strength output 101A.

When it is desired to directly detect the level of only the IF received signal to determine the input signal strength output, I
The input signal strength output 101B can be obtained through the narrow band filter 15, the amplifier 16 and the level detector 17 whose output is the F amplifier 6 with the IF frequency as the center (tuning) frequency.

If the received signal saturates before the IF amplifier 6 due to a strong input signal, the IF-AG
Since the C circuit 8 cannot deal with this, the RF-AGC circuit 9 is provided. The RF-AGC circuit 9 has a built-in carrier level detection circuit for an RF reception signal, and the RF amplifier 2
And a wide bandwidth output level of the RF tuning circuit 3, and supplies a second control signal to the gain control terminal of the RF amplifier 2. When the received electric field strength exceeds the second level, which is higher than the first level, the level of the second control signal is set so as to suppress the gain of the RF amplification circuit 2 as the RF received signal level increases. Increase.

The oscillation frequency of the local oscillator 10 and the tuning band of the RF tuning circuit 3 are controlled by a control circuit (not shown). The local oscillator 10 is configured as a frequency synthesizer having a so-called PLL (Phase Locked Loop) circuit configuration. The control circuit controls the reception operation of the synthesizer tuner by using the input signal strength output 101A or 101B, and performs one-touch channel selection, automatic channel selection, reception band scanning, reception level determination, and the like. A well-known configuration can be used for the control circuit, and it will not be described in detail because it is not the gist of the present invention.

FIG. 5 shows a conventional example of an FM receiver. In the figure, parts corresponding to those in FIG. 4 are designated by the same reference numerals, and description of such parts will be omitted. In this example, the level of the narrowband IF reception signal after the IF filter 5 obtained by the narrowband filter 15, the amplifier 16 and the level detector 17 and the wideband RF reception before the IF filter of the RF-AGC circuit 9 are received. The signal level and the signal strength detection circuit 13
In, the input signal strength output 101 representing the received electric field strength is obtained. The IF amplifier 6 can be configured by a saturation amplifier (limiter amplifier) and the IF-AGC circuit can be omitted.

Next, the operating characteristics of the AGC circuit of the conventional receiver will be described. FIG. 7A shows the distribution of the frequency components of the IF reception signal that has passed through the IF filter 5 of the AM receiving apparatus shown in FIG. 4 by the deviation from the intermediate frequency (the center frequency of the IF filter 5). The same figure (b)
Further, indicates the distribution of frequency components of the IF reception signal that has passed through the narrow band filter 15. By using the peak value of this distribution characteristic, it is possible to determine the matching of the received electric field level and tuning. The first control output of the IF-AGC circuit 8 is proportional to the peak value within a predetermined range. Further, by utilizing the output of the narrow band filter 15 having a narrower band width, it is possible to more accurately determine the tuning of the reception frequency with respect to the target signal.

However, when the RF-AGC circuit 9 starts to operate, the IF reception signal level after passing through the IF filter 5 becomes substantially constant. Therefore, as shown in FIG. 6B, the input signal strength outputs 101A and 101B do not increase any more as the RF-AGC circuit 9 operates, and the increase in the received electric field strength cannot be detected. Therefore, the range in which the input signal strength can be detected is narrow.

In order to solve the drawback that the dynamic range of the input signal strength output is narrow, the circuit structure of the signal strength detection shown in FIG. 5, that is, the first control signal which is the output of the narrow band level detector 17 is used. And a second control signal of the RF-AGC circuit 9 are added in the signal strength detection circuit 13 to obtain the input signal strength output 101. According to this configuration, even when the increase of the first control signal stops, the second control signal follows the received electric field strength, so that the input signal strength output 101 is input as shown in (C) of FIG. It is possible to follow over a wide range of signal strength.

[0011]

However, when the received electric field strength (input signal strength) is particularly large in the above configuration, the RF-AGC circuit 9 continues to operate, so that the IF received signal is out of synchronization and the IF received signal is filtered by the IF filter. Even if it is out of the pass band of 5, the input signal strength output 101 does not become the “0” level as shown in FIG. It has the drawback that it cannot be detected. Therefore, the signal strength detection circuit 13 is further configured by a multiplication circuit which inputs the first control signal and the second control signal, and when the level of the first control signal becomes "0" due to the misalignment, the signal strength output is performed. It has been considered that the above level shift is suppressed by also setting the level to "0". However, even in the above configuration, when a strong interfering wave signal exists at an adjacent frequency when receiving in synchronization with a weak broadcast signal, the interfering wave signal enters the RF stage together with the RF received signal. Due to the error output of the RF-AGC circuit 9 that follows the level of the strong interfering wave signal, the weak intensity of the input signal cannot be detected. For this reason,
In particular, an electronic tuning type receiving apparatus that controls the tuning operation by detecting the tuning state according to the input signal strength is a cause of malfunction and the like.

Therefore, a first object of the present invention is to expand the dynamic range of the input signal strength output to detect a change in the input signal strength in a wide range while receiving a received signal with a strong level. Another object of the present invention is to provide a receiving device capable of accurately detecting the tuning deviation of the received signal.

A second object of the present invention is to expand the dynamic range of the input signal strength output so that a wide range of changes in the input signal strength can be detected. It is an object of the present invention to provide a receiving device capable of accurately detecting the intensity of a target received signal even when a strong interfering wave signal is present.

[0014]

In order to achieve the above object, the receiving apparatus of the first aspect of the present invention provides a wideband received signal in a receiving circuit preceding the intermediate frequency filter when the received electric field strength exceeds a predetermined reference level. IF reception signal for detecting the level of the IF reception signal separated from the wideband reception signal by the intermediate frequency filter and for generating a first level detection signal according to the signal level. Level detection means, wideband signal level detection means for detecting the level of the wideband received signal and generating a second level detection signal corresponding to the signal level, and the above-mentioned based on the first and second level detection signals A reception level detecting means for obtaining a reception electric field intensity signal representing the reception electric field intensity, and the reception electric field intensity is the predetermined reference level or the predetermined reference level. As long as it does not exceed the value near Le, and a suppressing signal blocking means said second level detection signal.

Further, the receiving device of the second invention is a narrow band AGC for starting the level adjustment of the IF received signal separated by the intermediate frequency filter when the received electric field strength in the selected channel exceeds the first level. A loop, and a wide band AGC loop for starting level adjustment of a wide band received signal in a receiving circuit preceding the intermediate frequency filter when the received electric field strength exceeds a second level higher than the first level, IF reception signal level detection means for detecting the level of the IF reception signal and generating a first level detection signal corresponding to the signal level, and second reception signal level detection means for detecting the level of the wideband reception signal and corresponding to the signal level. Wideband signal level detection means for generating a level detection signal, and reception field strength indicating the reception field strength based on the first and second level detection signals. A reception level detecting means for obtaining a signal; and a signal blocking means for suppressing the second level detection signal unless the reception electric field strength exceeds the second level or a value near the second level. .

[0016]

If the received electric field strength is below the vicinity of the received electric field strength at which the RF-AGC loop starts to operate, the IF
The received electric field strength signal is obtained based only on the level of the IF received signal separated by the filter, and when the received electric field strength exceeds the vicinity of the received electric field strength, the two received signals of the IF received signal and the RF received signal are received. A signal representing the received electric field strength is obtained based on the level.

As a result, it is possible to accurately detect the deviation of the tuning with respect to the broadcast signal of the strong electric field. Further, even when the strong electric field interference wave signal is present in the vicinity of the intended low-level broadcast signal or the like, the reception level of the broadcast signal or the like can be detected.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which parts corresponding to those shown in FIG.
A description of this part will be omitted. In the figure, an AM demodulation output 100 is an IF-AG that forms a narrow band AGC loop.
It is supplied to the C circuit 8. The IF-AGC circuit 8 has an IF-
The time constant circuit (not shown) in the AGC circuit 8 detects the average level (carrier level) of the AM demodulation output 100, controls the gain of the IF amplifier 6 according to the detection level, and obtains the demodulation output 100 at a substantially constant level. To adjust. At the same time, this detection level is supplied to the comparator 11 and the signal strength detection circuit 13 as the first control signal.

On the other hand, the output of the RF amplifier 2 and the RF reception signal level of the RF tuning circuit 3 are supplied to an RF-AGC circuit 9 forming a wide band AGC loop, and a level is provided by a time constant circuit (not shown) in the RF-AGC circuit 9. To be detected. In addition, the wideband I frequency-converted by the mixer 4
It is also possible to form a wide band AGC loop that controls the output of the RF amplifier 2 using the F received signal. The gain of the RF amplifier 2 is controlled based on the detection level. This detection level is supplied from the RF-AGC circuit 9 to the signal strength detection circuit 13 via the switch 12 as the second control signal. The switch 12 has a first
Is conducted only when the control signal of is greater than the level of the threshold voltage source 14. The threshold voltage is set so that the switch 12 conducts at a reception field strength slightly lower than the reception field strength at which the RF-AGC circuit 9 should start operating.

Therefore, when a broadcast signal or the like arrives at the antenna 1 and the received electric field strength gradually increases, the IF
The AGC circuit 8 starts operating, and the input signal strength output 101 is obtained by the first control signal. At this time, the switch 12 is off. When the received electric field strength increases,
The level of the first control signal increases. When the received electric field strength exceeds a predetermined level, the comparator 11 operates and the switch 12 becomes conductive. Further, when the received electric field strength increases, the RF-AGC circuit 9 starts operating, and the second control signal is supplied to the signal strength detection circuit 13 via the switch 12. The level of the first control signal is saturated as shown in FIG. 6C, but the second control signal is superimposed, so that the input signal strength output 101 is further increased as the received electric field strength increases. 7 shows the output characteristic which is increased and is represented by the curve (C) of FIG. As a result, the input signal strength detection output 101 can be obtained over a wide range of the received signal level.

In the above configuration, if a deviation of tuning occurs between the frequency of the IF received signal and the frequency of the tuning circuit due to frequency fluctuations in the local oscillator 10, etc., and the IF received signal deviates from the pass band of the IF filter 5, The level of the IF reception signal is greatly attenuated by the IF filter 5. Therefore, the level of the first control signal is attenuated to the threshold value 14 or less, and the switch 11 is turned off by the comparator 11. As a result, the superposition of the second control signal on the first control signal is prevented, and the signal strength detection output 101
Level becomes substantially "0", and the output characteristic in which the level shift shown in FIG. 7D is avoided is obtained. Also, I
Even if the frequency of the F received signal and the frequency of the tuning circuit match, if the level of the IF received signal that has passed through the IF filter 5 is weak, the switch 11 is turned off by the comparator 11. . Therefore, even if a strong interfering wave signal exists in the adjacent frequency of the RF reception signal, R
Second controlled by the disturbance wave level from the F-AGC circuit 9
The control signal is blocked, and the intensity of the low-level IF reception signal that has passed through the narrow band IF filter 5 can be accurately detected.

Another embodiment is shown in FIG. In the figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and description of such parts will be omitted. In this embodiment, the narrow band filter 15,
An amplifier 16, a level detection circuit 17, a reference voltage source 18, and a comparator 19 are added. In the figure, I
The IF reception signal that has passed through the F amplifier 6 is further passed through the narrow band filter 15 and the amplifier 16 and then to the level detection circuit 17
Level detected by. Therefore, this narrow band IF
The frequency band characteristic of the received signal is, as shown in (e) of FIG. 7, a narrower band than that of (d) in FIG. In other words, the tuning state can be detected more accurately.

Further, the signal strength detection circuit 13 supplies the input signal strength output 101 to the comparison input terminal of the second comparator 19 to which the threshold level of the reference voltage source 18 is applied to the comparison reference input terminal. When the input signal detection output 101 is larger than the threshold level, the comparator 19 sets the tuning detection output 102 to the “H” level and outputs that the receiving circuit is in the tuning state. By changing the threshold level, it is possible to variably set the tuning input signal strength for tuning determination.

In the configuration of this embodiment, the input signal strength output 10 is set even when a strong interfering signal exists in the adjacent frequency.
1 does not cause the level shift as shown in FIG. 7C and the weak tuning signal strength can be accurately detected, so that more accurate tuning detection is performed.

FIG. 3 shows an example in which the present invention is applied to an FM receiver. In the figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals. Also in this configuration, when the level of the IF reception signal is low, the switch 12 is made non-conductive to prevent the output of the RF-AGC circuit 9. This ensures that even if there is a strong disturbing signal in the adjacent frequency,
The level shift as shown in FIG. 7C does not occur in the input signal strength output 101, and a weak input signal strength can be accurately detected.

In the above embodiment, the switch 12 is used as the blocking means for blocking the second control signal.
The present invention is not limited to this, and it is possible to use a device that exhibits the same effect, for example, a mute circuit that greatly attenuates the level of the second control signal.

[0027]

As described above, according to the present invention, the detection of the input signal strength with a wide dynamic range can be ensured with a simple circuit configuration, and the input signal strength detection caused by the strong input signal with the deviated level can be detected. The error in is prevented. Further, even when there is a strong interfering wave signal in the adjacent frequency when the intensity of the input signal is weak, the intensity of the input signal can be accurately detected. Therefore,
It is suitable for use in electronically tuned receivers.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a third embodiment of the present invention.

FIG. 4 is a block diagram showing a conventional example.

FIG. 5 is a block diagram showing a conventional example.

FIG. 6 is a graph showing operating characteristics of the AGC circuit.

FIG. 7 is a graph showing tuning characteristics of the receiving device.

[Explanation of symbols]

1 antenna 2 RF amplifier 3 RF tuning circuit 4 mixer 5 IF filter 6 IF amplifier 7 demodulator 8 IF-AGC circuit (or first level detection circuit) 9 RF-AGC circuit (or second level detection circuit) 10 Local Oscillator 11 First Comparator 12 Switch 13 Signal Strength Detection Circuit 15 Narrow Band Filter 19 Second Comparator

Claims (3)

[Claims] 1. A wide band AGC loop for starting the level adjustment of a wide band received signal in a receiving circuit preceding the intermediate frequency filter when the received electric field strength exceeds a predetermined reference level, and the wide band reception by the intermediate frequency filter. IF reception signal level detection means for detecting the level of the IF reception signal separated from the signal and generating a first level detection signal corresponding to the signal level; and detecting the level of the wideband reception signal and responding to the signal level Wideband signal level detection means for generating a second level detection signal, reception level detection means for obtaining a reception field strength signal representing the reception field strength based on the first and second level detection signals, and the reception The second level detection signal is suppressed as long as the electric field strength does not exceed the predetermined reference level or a value near the predetermined reference level. And a signal blocking means for receiving the signal. 2. The received electric field strength in the selected channel is first.
Narrow band A that starts the level adjustment of the IF reception signal separated by the intermediate frequency filter when the level exceeds
A GC loop and a wide band AGC loop for starting level adjustment of a wide band received signal in a receiving circuit in a stage preceding the intermediate frequency filter when the received electric field strength exceeds a second level higher than the first level. An IF reception signal level detecting means for detecting a level of the IF reception signal and generating a first level detection signal corresponding to the signal level; and a second reception signal level detecting means for detecting a level of the wideband reception signal according to the signal level. A wideband signal level detecting means for generating a level detecting signal, a receiving level detecting means for obtaining a receiving electric field strength signal representing the receiving electric field strength based on the first and second level detecting signals, The second level or the second
And a signal blocking unit that suppresses the second level detection signal as long as the value does not exceed a value close to the level. 3. The receiving apparatus according to claim 2, wherein the IF reception signal level detecting means and the wide band signal level detecting means are level detection circuits in the narrow band AGC loop and the wide band AGC loop, respectively.