JPS5847893B2 - Muting warmer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In an FM-AM receiver, the FM receiving section thereof is generally provided with a muting circuit.

This is because when the sensitivity of the FM receiving section is increased, the overall gain inevitably increases, so inter-station noise increases during channel selection operations, and this is to prevent the feeling from becoming worse.

On the other hand, the AM receiving section is generally not equipped with a muting circuit, or for the same reason, or in order to avoid irregularities such as interstation beats and random noise, the AM receiving section is also provided with a muting circuit. It is possible that

However, if a muting circuit is simply provided for the AM receiving section, the FM receiving section and the AM receiving section cannot be integrated into one IC.
If it is converted into an IC, the number of bins of the IC increases, and it may not be possible to convert it into a C, or even if it can be converted into an IC, its effect will be reduced.

The present invention attempts to realize muting of the AM receiving section of an FM-AM receiver by taking these points into consideration.

An example of this will be explained below.

In FIG. 1, 10 indicates an FM receiving section, 11 its antenna tuning circuit, 12 a high frequency amplifier, 13 an interstage tuning circuit, 14 a mixer circuit, 15 a local oscillation circuit, and 16
is its resonant circuit.

When receiving FM, the function switch (band changeover switch) 36 switches to the FM side contact F as shown in the figure.
The voltage from the power supply terminal 39 is supplied to the circuits 12, 14, and 15 as the operating voltage through the switch 36, and although not shown, the voltage from the power supply terminal 39 is supplied to the circuits from the next stage onward regardless of the switching of the switch 36. Operating voltage is always supplied.

Therefore, the intermediate frequency signal of the received FM wave is extracted from the mixer circuit 14, and this intermediate frequency signal is
It is supplied to an FM demodulation circuit 19 through a bandpass filter 17 having an intermediate frequency transformer and a ceramic filter, and further through a limiter amplifier 18 for intermediate frequency amplification to be demodulated, and the demodulated signal is sent to an attenuator 21 for level adjustment. → Addition circuit (OR circuit) 31 → It is supplied to the stereo demodulation circuit 33 through the muting switch circuit 32 described later, and when the demodulated signal is a stereo composite signal, the stereo signals of the left and right channels are output from the stereo composite signal. demodulated - this is output terminal 3
On the other hand, when the demodulated signal is a monaural signal, the monaural signal is taken out as it is to terminals 34L and 34R.

Further, 40 indicates an AM receiving section, 41 its antenna tuning circuit, 42 a mixer circuit, 43 a local oscillation circuit, and 44
is its resonant circuit.

When receiving AM, the switch 36 switches to AM, contrary to the diagram.
The voltage from terminal 39 is switched to side contact A, and the voltage from terminal 39 is connected to circuit 4.
2.43 as its operating voltage, and the operating voltage is always supplied to the circuits from the next stage onwards regardless of the switching of the switch 36.

Therefore, the intermediate frequency signal of the received AM wave is extracted from the mixer circuit 42, and this intermediate frequency signal is passed through a band pass filter 45 having, for example, an intermediate frequency transformer and a ceramic filter, and further passed through an amplifier 46 for intermediate frequency amplification. It is supplied to the detection circuit 4γ and detected, and the detected signal is sent to the attenuator 48 for level adjustment.
-> Addition circuit 31 -> Switch circuit 32 -> Stereo demodulation circuit 33 and output to terminals 3 4L and 3 4R.

Also, at this time, the detection signal from the detection circuit 41 is
is supplied to a voltage forming circuit 49 to form an AGC voltage,
This AGC voltage is supplied to the amplifier 46 to perform AGC.

A muting circuit according to the present invention for the FM receiving section 10 and AM receiving section 40 is configured as follows, for example.

That is, when receiving FM, the front stage of limit amplifier 1B,
Intermediate frequency signals Sa-S obtained at the middle and rear stages respectively
The level of o changes as shown in FIG. 2A with respect to the input field level, and these signals Sa to So, for example, are used as signals indicating the bandwidth of the intermediate frequency stage in the rectifier circuits 51A to 51.
B of FIG.
A DC signal Sd whose level changes as shown in FIG.

Note that since the signal Sd is obtained based on an intermediate frequency signal, the level of the signal Sd is as shown in FIG. 3A with respect to the intermediate frequency.
It changes like this.

Also, the demodulated signal from the demodulation circuit 19 is filtered through the low-pass filter 5.
4, and as shown in FIG. 3B, the DC signal (
A DC voltage) Se is taken out, and this signal Se is supplied to the double-wave rectifier circuit 55, and its positive polarity portion is turned back to the negative side to form a DC signal Sf.
3.

Then, in the subtraction circuit 53, the signal Sf is converted from the signal Sd.
is subtracted to form a DC signal Sg whose level changes with respect to the intermediate frequency as shown in FIG.
2 is supplied to the collector of the transistor γ1 through an attenuator 56 for setting the muting level during FM reception.

Further, the detection signal from the detection circuit 4γ is supplied to a low-pass filter type time constant circuit 61, and from the detection signal, a DC signal (DC signal) S1 whose level changes in the same way as the signal Sd with respect to the intermediate frequency is generated. The signal Si is taken out and supplied to the collector of the transistor γ1 through an output signal 62 for setting a muting level during AM reception.

This transistor γ1 constitutes a current mirror circuit γ0 together with the transistor l2, and the collector of the transistor γ2 is grounded through a parallel circuit of a variable resistor for muting level adjustment and a capacitor γ6, and It is connected to one contact a of the switch γγ, and the other contact b of the switch γγ is connected to a terminal 39 through a resistor γ8, and the signal obtained at the parent contact of the switch 1γ is sent to the switch circuit 32 through a Schmitt circuit γ9 to control the switch. Supplied as a signal (muting signal).

In this case, the muting level for FM broadcasting is the same as that for general muting, but the muting level for AM broadcasting is set as shown in FIG. 4, for example.

That is, when muting is not applied to the AM receiving section 40, the characteristics of the output signal (including the noise signal) due to the AGC characteristics are shown as curve 1S in FIG. 4A, and the characteristics of the noise signal are as follows. As shown by curve 1N, the range of human power level that is 5 dB lower than the shoulder of curve IS, that is, the input level where the S/N is 20 to 30 dB is considered to be the muting level, and therefore muting When multiplied by , the characteristics are as shown in FIG. 4B.

Further, at this time, a hysteresis of about 3 to 6 dB is added to the muting level by the Schmitt circuit γ9.

Furthermore, when changing from a tuned state to a detuned state due to a tuning operation, or conversely from a detuned state to a tuned state, muting noise may occur due to a change in the signal S2 or Si, but this is caused by the capacitor. This can be reduced or eliminated by selecting the value of γ6.

Note that this capacitor T6 is also for removing intermediate frequency signal components contained in the signals Sg and Si.

Further, the muting switch 77 is provided, for example, on the front panel (decorative panel) of the receiver as shown in FIG.

Note that 81 is a tuning knob, 82 is a power switch, and 83 is a high blend switch.

In such a structure, to perform muting,
Connect switch γγ to contact a.

Then, when the switch 36 is switched to the contact F, the FM broadcast reception state is entered, but when the FM broadcast is received by the channel selection operation, the subtraction circuit 53 obtains the signal S2, which is the current Since the signal is supplied to the Schmitt circuit γ9 through the mirror circuit γ0 and the switch γγ, as shown in FIG. That is, a signal rising within a range of, for example, ±100 KHz with respect to the center frequency of the intermediate frequency is extracted as the muting signal Sh.

Then, this muting signal Sh is transmitted to the switch circuit 3.
2, the switch circuit 32 is turned on, and therefore, the stereo signal or monaural signal of the FM broadcast is taken out at the terminals 34L and 34R.

However, when FM broadcasting is not received, or even when it is received, the reception level is low, the signal Sg does not reach the threshold level ■TH of the Schmitt circuit T9, so the muting signal Sh from this point falls. It will remain as it is.

，Do you obey? At this time, the switch circuit 32 is off, and the terminals 34L. No signal is taken out from 34R, that is, muting is applied.

In addition, when the switch 36 is switched to contact A, the AM broadcast reception state is reached, but when the channel selection operation is performed, A
When the M broadcast is received, a signal Si is obtained from the time constant circuit 61, and this signal Si is sent to the current mirror circuit 1.
Since the muting signal Si from the Schmitt circuit T9 is supplied to the Schmitt circuit γ9 through 0 and the switch γγ, the muting signal Si from the Schmitt circuit T9 is in a rising state. Therefore, the switch circuit 32 is on, so the AM broadcast signal is taken out to the terminals 34L and 34R. .

However, when AM broadcasting is not received, or even if it is received, the reception level is low, the signal Si does not reach the threshold level ■TH of the Schmitt circuit γ9, so the muting signal Sh falls from this point. It will remain as it is.

Therefore, at this time, the switch circuit 32 is off,
Terminal 34L. 34R. No signal is extracted, that is, muting is applied.

On the other hand, when switch γγ is switched to contact b contrary to the diagram, the human power level of Schmitt circuit γ9 will be equal to or higher than its threshold level v, regardless of the presence or absence of signals S, Si. The signal Sh remains high, so the switch circuit 32 is always on, that is, the muting is turned off.

Note that during the muting operation, the muting level is a problem, but this can be set to any level using the attenuators 56 and 62 and the variable resistor γ5.

That is, by changing the values of the attenuators 56 and 62, respectively, the magnitude of the signal Sg or Si supplied to the transistor 1 changes, so that the muting level for FM broadcasting and the muting level for AM broadcasting can be set in advance, respectively. Can be set arbitrarily.

Also, a signal S2 or S is sent from the collector of transistor 2.
When 1 appears, the transistor γ2 works as a constant current source, so the signal Sg or Si is obtained in the form of a constant current.

This constant current signal Sg or Si is applied to the variable resistor 675
Therefore, the constant current signal S or Si is converted into a voltage by the variable resistor gγ5, and its level becomes a level proportional to the value of the variable resistor gγ5, and this voltage signal S2 or Si is connected to the Schmitt circuit. 19, and the level is determined using the level vTH as a threshold level.

Therefore, by changing the value of variable resistor γ5, muting levels for FM broadcasting and AM broadcasting can be set arbitrarily and simultaneously.

In this way, according to the present invention, muting can be applied not only to FM broadcasts but also to AM broadcasts, so that AM broadcasts can be tuned with good feeling.

Moreover, in that case, especially according to the present invention, the FM receiving section 10
The demodulated signal from the AM receiver 40 and the detected signal from the AM receiver 40 are combined into a single signal by an adder circuit 31, and a switch circuit 32 is provided on this single signal path, and the signals S, . Si is also a current mirror circuit TO
Since the circuit is integrated into a single circuit, only the variable resistor γ5, the capacitor γ6, and the switch 77 need to be used as an example when converting into a C. Therefore, it is easy to integrate the circuit into an IC, and the effect is large.

Furthermore, as shown in FIG. 5, the front panel of the receiver is not complicated and is easy to operate.

In the example {2 of FIG. 6, muting can be turned on and off independently for FM broadcasting and AM broadcasting.

That is, switch 36B is a changeover switch linked to switch 36, 17A is a muting switch for AN, and 77F is a muting switch for FM. Although muting is not applied to broadcasting, A
M broadcasting requires muting.

In the example shown in FIG. T, a receiver 90 for television broadcast audio is further provided, and
6 selectively supplies the operating voltage to the receivers 40 and 10.90 to receive TV audio, FM broadcasts, and AM broadcasts, and the demodulated signal from the receiver 90 is also supplied to the adder circuit 31. At the same time, a signal similar to the signals S, , Si is taken out from the receiving section 90, and this signal is also supplied to the transistor T1.

The switch γ7T is a muting switch for audio broadcasting on the television, and in the case of the figure, muting is turned on.

In the above description, the switch circuit 32 is provided separately for the sake of explanation, but it may also be used as a switching element for switching demodulation in the stereo demodulation circuit 33.

Also, the demodulation circuit 33 and the terminal 34L. 34R may be provided with a similar switch circuit.

Furthermore, the attenuators 21.4B and 56.62 may be semi-fixed variable resistors.

Also, the signals S, . Si may be anything that has information regarding the bandwidth or input electric field level of the intermediate frequency stage of the receiving section 40.10.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an example of the present invention, FIGS. 2 to 4 are diagrams for explaining the same, and FIG. 5 is a front view showing the → direction of the present invention.
FIG. 6 is a connection diagram showing a part of another example of the present invention, and FIG. T is a system diagram of another example of the present invention. 10 is an FM transmission section, 40 is an AM receiving section, 32 is a muting switch circuit, and γt is a muting switch.

Claims (1)

[Claims] 1. C), each having a bandwidth from the valley intermediate frequency signal system of two or more receiving sections, is a rectifier circuit that obtains and rectifies signals related to the input electric field level, and a rectifier circuit that rectifies each DC signal from the rectifier circuit. a first coupling circuit that takes out the output to a common output terminal; a muting switch that turns muting on and off;
a second coupling circuit that extracts each demodulated signal from the three or more receiving sections to a common output terminal, and a muting switch circuit provided on the output side of the second coupling circuit,
A muting circuit in which an output signal of the first coupling circuit is supplied to the switch circuit as a control signal through the muting switch to perform muting. 2. In the muting circuit according to claim 1, there is provided another switch that is switched in conjunction with the switch that selectively operates the two or more receiving sections, and the muting circuit that is selected by the another switch, and another muting switch that selectively turns on and off a muting operation for each reception operation of the two or more receivers.