JPS588620B2 - The Tsuonjiyokiyo Cairo - Google Patents

Description

[Detailed Description of the Invention] When receiving an FM broadcast with a low input level, the reproduced sound contains a lot of noise and becomes very difficult to hear.
The M tuner is provided with a noise removal circuit generally called a high blend circuit.

This circuit is configured as shown in Fig. 1, that is, 1 is an FM signal including a high frequency amplifier to a demodulation circuit.
The tuner circuit 2 indicates a stereo demodulation circuit, and from the tuner circuit 1, a sum signal of a two-channel stereo left channel signal EL and a right channel signal ER, and a difference signal between these signals EL and ER are used to perform carrier suppression amplitude modulation. A composite signal with the modulated signal is extracted, and this composite signal is supplied to the stereo demodulation circuit 2, where the signals EL and ER are demodulated by switching, for example, and these signals EL and ER are extracted to output terminals 3L and 3R.

Further, 4L and 4R indicate line amplifiers, whose input terminals 5L and 5R are connected to terminal 3 through resistors 6L and 6R, respectively.
A series circuit of a capacitor 7 and a switch 8 is connected between the terminals 5L and 5R.

Note that 9L and 9R are output terminals.

Therefore, when there is no noise, switch 8 is turned off.

Then, the signals EL and ER from terminals 3L and 3R are connected to resistor 6.
Connect terminal 9 directly through L, 6R and amplifier 4L, 4R.
It is taken out to L and 9R.

On the other hand, when there is noise, switch 8 is turned on.

Then, the high-frequency component of the noise signal included in the signal EL and the high-frequency component of the noise signal included in the signal ER are added to each other through the capacitor 8, but in this case, the terminals 3L and 3R Then, since the phases of the noise signals are opposite to each other, the high-frequency components of the noise signals are canceled out through the capacitor 7, and therefore the terminals 9L and 9R receive a signal from which the high-frequency components of the noise signals have been removed. EL and ER are taken out.

In this case, the low frequency and middle frequency components of the noise signal are transmitted to the terminal 9.
Although these components appear in L and 9r, the S/N ratio is good even with these components.

Furthermore, the high-frequency components of the signals EL and ER are mixed with each other through the capacitor 7, which worsens high-frequency crosstalk, but this also poses no problem for auditory separation.

In this way, according to the circuit shown in FIG. 1, it is possible to listen to broadcasts with a good S/N ratio even if the input level is low.

However, in this circuit, when the switch 8 is turned on, a low-pass filter is formed by the resistors 6L and 6R and the capacitor 7, so the level of the high-frequency components of the original signals EL and ER decreases. .

That is, R: Value of resistors 6L, 6R Xc: Impedance of capacitor 7 EN: Level of noise signal EL': Level of signal EL at terminal 9L, then Impedance can be approximately regarded as R, so when switch 8 is turned on, it becomes, and therefore signal EL'
The high frequency level of decreases, and its maximum value is 6 dB (R≫1
Xc1).

In view of these points, the present invention attempts to remove noise signals without reducing the high frequency level of the output signal.

An example of this will be explained below.

In FIG. 2, 14L and 14R are operational amplifiers that function as an adder circuit, so the common-mode input terminal is grounded, and resistors 24L and 24R of equal value are connected between the opposite-phase input terminal and the output terminal. Resistors 6L and 6R are connected between the anti-phase input terminals of the amplifiers 14L and 14R and the terminals 3L and 3R, respectively.

And between the terminal 3L and the negative phase input terminal of the amplifier 14R,
A series circuit of switch 8A, resistor 16A, and capacitor 17A is connected, and a series circuit of switch 8B, resistor 16B, and capacitor 17B is connected between terminal 3R and the negative phase input terminal of amplifier 14L. .

In this case, the switches 8A and 8B are interlocked, the values of the resistors 6L, 6R, 16A, and 16B are made equal to each other, and the values of the capacitors 17A and 17B are also made equal to each other.

In such a configuration, switches 8A and 8B are turned off when there is no noise.

Then, the signals EL and ER from the terminals 3L and 3R are taken out as they are to the terminals 9L and 9R through the resistors 6L and 6R and the amplifiers 14L and 14R.

In this case, if the values of the resistors 6L to 16B are R1 and the values of the resistors 24L and 24R are Ra, the signals EL and ER are multiplied by -Ra/R by the amplifiers 14L and 14R.

On the other hand, when there is noise, switches 8A and 8B are turned on.

Then, the signal EL containing the noise signal from the terminal 3L becomes
It is supplied to the amplifier 14L through the resistor 6L, and
The high-frequency component of the noise signal is transmitted from the terminal 3R to the amplifier 14L through the switch 8B, resistor 16B, and capacitor 17B.
Since the high-frequency component of the noise signal included in the signal EL is canceled by the high-frequency component of the noise signal from the terminal 3R, the signal EL from which the high-frequency component noise signal has been removed is supplied to the terminal 9L. ′ is obtained.

Similarly, in the amplifier 14R, the high-frequency component of the noise signal included in the signal ER is canceled by the high-frequency component of the noise signal from the terminal 3L, so the high-frequency component of the noise signal is removed from the terminal 9R. A right channel signal ER' is obtained.

In this case, since the negative phase input terminal of the amplifier 14L can be regarded as a virtual ground point, the capacitor 17 is connected to this negative phase input terminal.
Even if B and the resistor 16B are connected, the signal EL is not bypassed to the terminal 3R side through these, and therefore the high frequency level of the signal EL' is not lowered.

That is, if the impedance of the capacitor 17B is Xc, then the high frequency level of the signal EL' will not drop.

This also applies to the signal ER' at the terminal 9R, and the high frequency level of the signal ER' does not drop.

Furthermore, when the frequencies of the signals EL and ER and the noise signal are equal, comparing the S/N of the circuit in FIG. 1 with the S/N of the circuit in FIG. 2, the S/N of the circuit in FIG. N=(R+Xc)1XcS/N of the circuit in FIG. 2-(R+Xc)1Xc, and the circuit in FIG. 2 can obtain the same S/N as the circuit in FIG. 1.

The same applies to crosstalk.

Thus, according to the present invention, noise signals can be removed without deteriorating high-frequency characteristics, and in this case, S/N and crosstalk will not deteriorate, so it is possible to listen to broadcasts with good sound. can.

In addition, the amplifiers 14L and 14R are line amplifiers 4L and 4R.
Therefore, the configuration is not particularly complicated compared to the circuit shown in FIG.

Although the above description deals with the case of FM 2-channel stereo, the present invention can also be applied to the case of FM 4-channel stereo of the Dahlen system. The above-mentioned circuits may be provided between the channel and the right rear channel, respectively.

Furthermore, the switches 8A and 8B can also be switched automatically.

[Brief explanation of drawings]

FIG. 1 is a connection diagram of a conventional example, and FIG. 2 is a connection diagram of an example of the present invention. 1 is a tuner circuit, and 2 is a stereo demodulation circuit.

Claims (1)

[Claims] 1 First and second output terminals 3L of stereo demodulation circuit 2
, 3R and the opposite phase input terminals of the first and second operational amplifiers 14L14R, first and second resistors 6L and 6R are respectively connected, and the first and second resistors of the stereo demodulation circuit 2
A first switch 8A, a third resistor 16A, and a first capacitor 17A are connected in series between the output terminal 3L and the negative phase input terminal of the second operational amplifier 14R,
between the second output terminal 3R of the stereo demodulation circuit 2 and the negative phase input terminal of the first operational amplifier 14L,
A second switch 8B, a fourth resistor 16B, and a second capacitor 17B are connected in series, and between the negative phase input terminals and output terminals of the first and second operational amplifiers 14L and 14R, Fifth and sixth resistors 24L and 24R are connected to the first and second operational amplifiers 14L and 14, respectively.
The first signal demodulated from R by the stereo demodulation circuit 2
and a noise removal circuit from which signals of the second channel are respectively extracted.