JPS60212038A - Receiver - Google Patents

Abstract

PURPOSE:To switch automatically an intermediate frequency pass band to a broad band and a narrow band by using an output signal of a comparator comparing an output voltage of a notch filter and a reference voltage to change over a switch means from the position of a broad band filter to the position of a narrow band filter. CONSTITUTION:A signal of a best component in 9kHz being a frequency difference of adjacent channels is included in an output signal from a detection circuit 19 if an adjacent disturbance takes place in the reception of a radio wave of adjacent channels. Thus, a resonance circuit of the notch filter 21 is resonated and a signal representing a voltage higher than the reference voltage from a connecting point 22 between a capacitor C1 and a coil L1 to the comparator 24 is outputted. Thus, a high-level signal is transmitted from the comparator 24, a common contact (f) of a switch 17 is changed over automatically from a fixed contact (d) to the position of a fixed contact (e) i.e., from the broad band filter 15 to the narrow band filter 16, the best component due to adjacent disturbance is eliminated without being affected by the adjacent waves and only a desired wave is passed.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a receiver capable of automatically switching an intermediate frequency pass band width between a wide band and a narrow band, and particularly relates to a superheterodyne type radio receiver.

Technical Background In general, superhetero gain type receivers, such as AM (
In the receiver (amplitude variable), the passband width of the intermediate frequency filter (IF filter) provided at the intermediate frequency stage is wide enough to satisfy the fidelity and stability (margin against frequency shift) at the dense input level. is set to .

In particular, in an AM stereo receiver, it is necessary to widen the passband width of the IF filter in order to improve the sound quality.

However, in AM broadcasting, the channel separation is 9 KHz in Japan, so if the passband width of the IF filter is set to a wide band (for example, 20 KHz), it will be susceptible to adjacent interference caused by radio waves from adjacent channels, and the noise caused by this effect will continue. It was very difficult to listen to because it appeared as speaker output.

Therefore, there is a need for a receiver that can switch the passband width of the IF filter so that the influence of adjacent interference does not appear in the speaker output.

Prior Art and Problems Conventionally, a configuration as shown in FIG. 2 has been known as a superheterodyne receiver capable of switching intermediate frequency passband widths.

This will be explained below as an AM receiver.

In FIG. 2, a high frequency signal received by an antenna l is tuned amplified by a high frequency amplifier circuit 2, mixed with a local oscillation signal from a local oscillator 4 by a mixing circuit 3, and converted into an intermediate frequency signal. This intermediate frequency signal is supplied to a wideband filter 5 and a narrowband filter 6.
The output signal of the narrow band filter 6 is supplied to the fixed contact a of the switch 7, and the output signal of the narrow band filter 6 is supplied to the fixed contact a of the switch 7.

The output of the common contact C of the switch 7 is detected by a detection circuit 9 via an intermediate frequency amplification circuit 8 and is supplied to an output terminal 10. The output of the output terminal 10 is supplied to a speaker via a low frequency amplification circuit (not shown).

Here, when reproducing AM broadcasting, the common contact C of the switch 7 is connected to the broadband filter 5 side, that is, to the fixed contact a, in order to improve the sound quality of the normally reproduced sound. This results in
The output signal from the broadband filter 5 is amplified by the intermediate frequency amplification circuit 8 as described above, detected by the detection circuit 9, and supplied to the output terminal 1o. Then, information is outputted by a low frequency amplifier circuit and a speaker (not shown) connected to the output terminal 10.

At this time, if noise appears in the speaker output from the speaker due to adjacent interference from the adjacent channel, manually switch the common contact C of the switch 7 to the narrowband filter 6 side, that is, the fixed contact, to eliminate the adjacent interference waves. This allows only the desired wave to pass through, suppressing noise from appearing in the speaker output.

However, in this conventional method, the switch was changed manually, which made the switch operation very cumbersome. In particular, the switch operation by the driver on a car receiver poses a risk of causing an accident. It was something that I had.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional drawbacks, and includes:
The object of the present invention is to provide a receiver that can automatically switch the intermediate frequency pass band width between a wide band and a narrow band.

Structure of the Invention In order to achieve the above object, the present invention includes a mixing circuit that converts a high frequency signal into an intermediate frequency signal, a narrow band filter and a wide band filter connected to the output end of the mixing circuit, and a narrow band filter and a wide band filter connected to the output terminal of the mixing circuit. switch means for selecting one of the output ends of the wideband filter; a notch filter connected to the output of the switch means and having a resonant frequency set to the frequency difference between adjacent channels; and an output voltage and a reference of the notch filter. The present invention is characterized in that it comprises a comparator for comparing the voltage with the voltage, and is configured to switch the switch means from the wide band filter side to the narrow band filter side based on the output signal of the comparator.

Examples of the invention Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a block diagram of a receiver according to the invention - an AM receiver is shown as an example.

In the figure, 11 is an antenna, 12 is a high frequency amplification circuit,
13 is a mixing circuit; 14 is a local oscillator; 15 and 16 are a wideband filter and a narrowband filter, respectively;
connected to the output end of the Reference numeral 17 denotes a switch means constituted by a relay, which has fixed contacts d and e, a common contact f1, and a relay coil L2. 18 is an intermediate frequency amplification circuit, 19 is a detection circuit, 21 is a notch filter, and a resistor R is connected in series between the detection circuit 19 and the output terminal 2o.
1, a capacitor c1 and a coil L1 connected in parallel between the resistor R1 and the output terminal 20, a C series resonant circuit, and an equivalent series resistor R2 connected to this series resonant circuit. The resonant frequency of the notch filter 21 is set to a frequency difference from an adjacent channel of AM broadcasting, for example, 9KIIz. 24 is a comparator, and the first input terminal 25 of this comparator 24 is connected to the notch filter 2.
1 is connected to the connection point 22 between the capacitor C1 and the coil L1 via the rectifier circuit 23 and the resistor R3,
A reference voltage ■ is applied to the second input terminal 26 . And its output end is connected to relay coil L2. R4 is a feedback resistor, which connects the output terminal of the comparator 24 and the first input terminal 2.
5.

Tr is a transistor whose collector terminal is connected to the first input terminal 25 of the comparator 24 and whose emitter terminal is grounded. In addition, the base terminal is connected to the terminal 27 via the resistor R5.
A muting signal for temporarily suppressing the output signal from the output terminal 20 is input to this terminal 27 when turning on/off the power, changing channels, etc.

With this configuration, the high frequency signal received by the antenna 1 is tuned and amplified by the high frequency amplifier circuit 12, and the high frequency signal received by the antenna 1 is tuned and amplified by the mixing circuit 1.
3, it is mixed with the local oscillation signal from the local oscillator 14 and converted into an intermediate frequency signal. This intermediate frequency signal is supplied to a wideband filter 15 and a narrowband filter 16. The output signal from the wideband filter 15 is supplied to a fixed contact d of the switch means 17, and the output signal from the narrowband filter 16 is supplied to a fixed contact e of the switch means 17. A broadband filter 15 appearing at the common contact f of the switching means 17
, the output of either one of the narrowband filters 16 is detected by a detection circuit 19 via an intermediate frequency amplification circuit 18. The detected output is output from the output terminal 20 via the notch filter 21, and is supplied to the speaker via a low frequency amplification circuit (not shown).

The notch filter 21 converts the detected output from the detection circuit 19 into a signal of the frequency difference with the adjacent channel, which is 9KI in this embodiment.
When the signal Iz is included, it resonates and a signal having a level corresponding to the level of the signal 9Kllz is output from the output terminal 22. When the detection output does not include a signal of 9KIlz, the resonant circuit of the notch filter 21 does not resonate, so that almost no signal is output from the output terminal 22.

The output signal of the notch filter 21 is rectified by a rectifier circuit 23, and the output signal of the rectifier circuit 23 is inputted to an input terminal 25 of a comparator 24 via a resistor R3.

The comparator 24 sends out a high level signal when the voltage of the signal input to the first input terminal 25 is higher than the reference voltage (2). The high-level signal output from the comparator 24 energizes the coil L2, and the common contact f of the switch means 17 is automatically switched to the fixed contact e side, that is, to the narrow band filter 16 side. Further, the output signal from the comparator 24 is fed back to the first input terminal 25 of the comparator 24 via a feedback resistor R4', and the resistance values of the resistor R3 and the feedback resistor R4 are changed by switching the switch means 17. As the output level of the filter 21 decreases, the output level of the comparator 24 also decreases to 1.
When the signal changes from "H" to "L" and a high level signal is sent from the comparator 24 in order to prevent the common contact f of the switch means 17 from switching to the broadband filter 15 side,
Thereafter, the voltage of the signal input to the first input terminal 25 of the comparator 24 is set to be higher than the reference voltage (2). As a result, once the common contact f of the switch means 17 is switched to the contact e side, it always maintains a contact state with the contact e unless an operation described in detail later is performed. transistor T
r is to turn on the power.

During operations such as OFF and channel conversion, a muting signal is input from the terminal 27 and the base side becomes "H", which causes conduction, and the first input terminal 25 of the comparator 24
Forcibly ground the signal input to the

When receiving AM broadcasting, operations such as turning on the power and changing channels are performed, so the signal input to the first input terminal 25 of the comparator 24 by inputting the miniting signal from the terminal 27 is Forced to ground,
The common contact f of the switch 17 is connected to the fixed contact d side, that is, to the broadband filter 15 side. As a result, the output signal from the wideband filter 15 is amplified by the intermediate frequency amplification circuit 18, detected by the detection circuit 19, and provided to the output terminal 20. Information is then output by a low frequency amplifier circuit and a speaker (not shown) connected to the output terminal 20.

In this way, when receiving AM broadcasting, a wideband filter is selected, and it is possible to listen to reproduced sound with excellent sound quality.

However, if adjacent interference occurs due to reception of radio waves from adjacent channels, the output signal from the detection circuit 19 will be 1. A beat component signal of 9, kHz, which is the frequency difference between adjacent channels, is included. Therefore, the resonant circuit of the notch filter 21, which is set to resonate due to the frequency difference between adjacent channels, resonates, causing the capacitor C1 and the coil L to resonate.
A signal indicating a voltage higher than the reference voltage V applied to the comparator 24 is output from the connection point 22 with 1. As a result, a high level signal is sent from the comparator 24, and the common contact f of the switch 17 is automatically switched from the fixed contact d side to the fixed contact e side, that is, from the wideband filter 15 side to the narrowband filter 16 side. Therefore, the beat component due to adjacent interference is removed without being affected by adjacent waves, and only the desired wave passes through.

By switching from the wideband filter 15 side to the narrowband filter 16 side, the output signal from the detector 19 no longer includes a signal of 9 KHz, which is the frequency of the adjacent channel, and no signal is output from the notch filter 21.
As mentioned above, when a high-level signal is sent from the comparator 24, the voltage of the signal inputted to the input terminal 25 of the comparator 240 becomes higher than the reference voltage V. A high level signal is still output, and the common contact f of the switch 17 maintains the contact state with the narrow band filter 16 side.

When the power is turned on or off or the channel is changed, a minting signal is input from the terminal 27 and the base side of the transistor T'r becomes "H".
The transistor Tr is turned on and the input terminal 25 of the comparator 24
Since the input signal is forced to ground,
The output signal from the comparator 24 becomes low level, and the common contact f of the switch 17 is switched to the fixed contact d side, that is, to the broadband filter side.

In addition, in AM broadcasting, a blood signal may be included in the frequency difference 9 between channels adjacent to the frequency of the modulating audio signal, but the level of the modulating audio signal is a beat component signal due to adjacent interference. 9 of the modulating audio signal, by setting the reference voltage (2) applied to the comparator 24 between the voltage of the modulating audio signal and the voltage of the beat component signal. This prevents the notch filter 21 from malfunctioning. Note that the present invention is applicable not only to AM receivers but also to FM receivers or other receivers.

Effects of the Invention As explained in detail above, the receiver according to the present invention is provided with a notch filter whose resonance frequency is set to the frequency difference between adjacent channels, and the level and mute of the output signal from this notch filter are adjusted. Since the switching between the wideband filter and the narrowband filter is performed based on the switching signal, the switching between the wideband filter and the narrowband filter can be automatically performed by detecting adjacent interference waves, improving operability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a receiver according to the present invention, and FIG. 2 is an intermediate frequency band switching type receiver. In the figure, 1.11 is an antenna, 2.12 is a high frequency amplifier circuit, 3.13 is a mixing circuit, 4.14 is a local oscillator, 5.15 is a wideband filter, 6.16 is a narrowband filter, and 7.17 8 and 18 are intermediate frequency amplifier circuits, 9 and 19 are detection circuits, 21 is a notch filter, 23 is a rectifier circuit, and 24 is a comparator. Patent applicant Fujitsu Ten Ltd.

Claims (1)

[Claims] A mixing circuit that converts a high frequency signal into an intermediate frequency signal, a narrowband filter and a wideband filter connected to the output end of the mixing circuit, and a switch means for selecting the output end of either the narrowband filter or the wideband filter. a notch filter connected to the output of the switching means and having a resonant frequency set to the frequency difference between adjacent channels; and a comparator for comparing the output voltage of the notch filter and a reference voltage; 1. A receiver according to claim 1, wherein said switch means is configured to switch from a wideband filter side to a narrowband filter side in accordance with an output signal of said receiver.