JPS6257323A - Squelch circuit - Google Patents

Abstract

PURPOSE:To eliminate the readjustment of squelch by impressing a reference level most suited to a detection noise output of a signal passing through a selected filter to a comparator circuit in response to a switching signal of IF filters so as to change automatically the reference level to the optimum value. CONSTITUTION:A reception IF signal given to an input terminal 1 is subject to pass band width limit by either a narrow band pass filter 4 or a broad band filter 5 selected switchingly by a switch 3 controlled by a control signal from a terminal 13 and demodulated into an audible signal by a demodulator 6. A part of the demodulation signal passes through a variable resistor 7, sent to a noise detector 8, where the noise component is detected and the result is fed to one input terminal of a comparator circuit 9. On the other hand, the control signal from the terminal 13 is fed to a storage section 16, a reference voltage having a level corresponding to the data is generated, it is fed to the other input terminal of the comparator circuit 9, compared with the reference level and the squelch gate 11 is switched from the result.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a squelch circuit for a receiving device that receives signals by selectively switching a plurality of intermediate frequency filters having different bandwidths.

[Prior Art] FIG. 2 is a block diagram showing a conventional squelch circuit of this type. In the figure (1) is the intermediate frequency (
(hereinafter referred to as IF) signal input terminal, (2) is a filter switching signal input terminal, (3) is a switch controlled by the filter switching signal from this terminal (2), (4) is a narrow band IF filter, (5) Moon, wideband IF filter, (
6) is a demodulator; (7) is a variable resistor that adjusts the squelch operating point; (8) is a noise detector that uses a filter to separate the demodulated signal into a signal component and a noise component, and detects only the noise component;
(9) is a comparison circuit, (10) is a reference level input terminal, (
11) is controlled according to the output from the comparator circuit (9),
This is a squelch gate that passes the demodulated signal (audible signal) output from the demodulator (6) to the output terminal (12) or blocks it.

Next, the operation will be explained. IF signal input terminal (1)
The received IF signal to the input terminal (2) is controlled by a switch (3) controlled by a filter switching signal to the input terminal (2), so that the passband is changed by either the narrowband IF filter (4) or the wideband IF filter (5). After being limited, it is demodulated into an audible signal by a demodulator (6).

A part of the demodulated signal passes through a variable resistor (7) and is sent to a noise detector (8), where the noise component is separated and detected.
The detected noise level voltage is applied to one input terminal of the comparison circuit (9). The other input terminal of the comparison circuit (9) (
A predetermined reference level voltage is applied to 10), and the levels of both input terminals are compared, and the squelch gate (11) is opened or closed depending on the result.

That is, when the detection noise level is above the reference level, the squelch gate (11) is closed and the passage of the demodulated signal from the demodulator (6) to the output terminal (12) is blocked, and when the detection noise level is below the reference level, the squelch gate (11) is closed. At this time, the squelch gate (11) is opened and a demodulated signal is output to the output terminal (12).

Figure 3 is a characteristic diagram showing the relationship between the IF input signal level to the input terminal (1) and the detection noise level from the noise detector (8).
), the reference level to terminal (10) is A.
When the IF input signal level is at the level of 0 to 6 points, the squelch gate (11) is closed, and when it is 0 or more, it is open. If the narrowband filter (4) is selected in this state, the detected noise level of the noise detector (8) will be below point A over the entire range of the IF input signal, so the squelch gate (11) will remain open and the demodulation The noise can be heard and become annoying. Therefore, the user increases the output level of the noise detector (8) with the variable resistor (7), and uses the broadband filter (5) to increase the output level of the noise detector (8).
When the IF input level is below 6 points, the squelch gate (11) is closed to prevent noise from being heard.

[Problems to be Solved by the Invention] Since the conventional squelch circuit is configured as described above, in the case where a plurality of IF filters are switched and used, each time the filters are switched, the noise caused by the difference in passband width is reduced. There is the hassle of having to adjust the variable resistor each time to compensate for fluctuations in the detection output level of the component and to optimize the squelch function's operating point, and if the structure does not allow variable adjustment, the squelch function's optimal operating point may not be adjusted properly. In order to obtain this, it is necessary to use only one IF filter, which poses a functional problem.

This invention was made to solve the above-mentioned problems, and aims to obtain a squelch circuit that always performs optimal operation by switching between a plurality of filters with different bandwidths, and which filter is switched to. With the goal.

[Means for Solving the Problems] The squelch circuit according to the present invention stores a plurality of reference levels corresponding to a plurality of IF filters, respectively, and selects an IF filter according to a control signal.

A reference level generating means is provided for extracting a reference level corresponding to a filter selected from the plurality of stored reference levels as a reference level to be compared with the detection noise level.

[Function] In this invention, in response to the switching signal of the IF filter, the reference level most suitable for the detection noise output of the signal passing through the selected filter is applied to the comparison circuit. In this way, the reference level is automatically changed to the optimum value each time the IF filter is switched, eliminating the need for squelch readjustment and ensuring an optimum squelch setting point.

[Example code] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, (1) (3) to (9) (11) (12)
is similar to the conventional device shown in FIG. 2 above. (1
3) is a control signal input terminal containing filter switching information;
(14) is a controller that receives a control signal to the input terminal (13) and outputs an address signal corresponding to the reference level information thereof;
A storage unit (16) that stores reference level data corresponding to the routers (4) and (5) and outputs the reference level data in response to an address signal from the controller (14), and data from this storage unit (16). The base P! generates a reference level voltage corresponding to this data. This is a reference level generating means consisting of a voltage generating section (17).

Next, its operation will be explained. The received IF signal applied to the input terminal (1) is passed through either a narrow band filter (4) or a wide band filter (5) which is switched and selected by a switch (3) controlled by a control signal from a terminal (13). After the passband width is limited by
demodulated into an audible signal.

The demodulated signal passes through the squelch gate (11) when it is open and is sent to the output terminal (12). A part of the demodulated signal is sent to a noise detector (8) through a variable resistor (7), where a noise component is detected, and the detected noise level is applied to one input terminal of a comparison circuit (9). - The control signal from the right terminal (13) is also applied to the controller (14), where the predetermined address signal corresponding to the selected switch is stored in the storage section (16) of the reference level generating means (15). The reference level data stored at that address is read out, and the reference voltage generator (17) generates a reference voltage at a level corresponding to the data, which is then applied to the other inputs of the comparator circuit (9). Applied to the terminal. The comparison circuit (9) compares the detected noise level with a reference level corresponding to the switching filter, and the squelch gate (11) is opened or closed based on the result. That is, when the control signal selects the wide band filter (5), the output level from the reference voltage generator (17) is set to point A in FIG. 3, and when the control signal selects the narrow band filter (4), To reach point B in Figure 3,
Address signals are output from each controller (14). Therefore, no matter which way the IF filter is switched, I
When the F input signal level is from O to C, the squelch gate (1
1) is closed, and above 0 points it is open.

Note that although the above embodiment includes a variable resistor for adjusting the squelch set point, this may be a fixed resistor. or,
Although the case where there are two IP filters has been described, there may be two or more IP filters, and the output level obtained from the storage unit (16) may be appropriately set according to the filter switching information of each filter. Further, although the storage unit in the above embodiment stores necessary data in advance, it may also have a function of storing the data shown in FIG. 3 in response to an external command if necessary.

Further, in the above embodiment, only the noise squelch was described, but the same effect as the above embodiment can be obtained also in carrier squelch and the like.

[Effects of the Invention] As described above, according to the present invention, the reference level, which is the squelch setting point, is controlled from the outside according to the switching of the IF filter, so there is no need to perform manual adjustment every time the IF filter is switched. , a receiver equipped with a plurality of IF filters having different bandwidths has the advantage that an optimum squelch operation can always be automatically performed no matter which filter is switched.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
The figure is a block diagram showing a conventional squelch circuit, and FIG. 3 is a characteristic diagram for explaining the operation of the present invention and the conventional example. In the figure, (1) is an intermediate frequency (IF) signal input terminal. (4) (5) is an intermediate frequency (zF) filter, (6) is a demodulator, (8) is a noise detector, (9) is a comparison circuit, (II
) is a squelch gate, (I2) is an output terminal, (13) is a control signal input terminal, (14) is a controller, (15) is a reference level generation means, (16) is a storage unit, and (17) is a reference voltage. This is the generating part. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] (1) Equipped with multiple intermediate frequency filters with different bandwidths,
One of these filters is selectively connected by an external control signal, and the level of the noise component of the demodulated intermediate frequency signal received through the selected filter is detected, and the detected noise level is In the squelch circuit, which compares the noise level with a predetermined reference level and blocks the output of the demodulated signal when the noise level is equal to or higher than the reference level, a plurality of reference levels are stored corresponding to the plurality of intermediate frequency filters, respectively. , further comprising a reference level generating means for extracting a reference level corresponding to the filter selected from the plurality of stored reference levels as a reference level to be compared with the detection noise level in response to a control signal for selecting the intermediate frequency filter. A squelch circuit characterized by: (2) The reference level generating means includes a storage section that stores data corresponding to the plurality of reference levels, and a reference voltage that corresponds to the data taken out from the address specified by the control signal from the storage section. The squelch circuit according to claim 1, further comprising a reference voltage generating section that generates a reference voltage.