JPS6233773B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an FM receiver capable of receiving FM radio broadcast waves and television broadcast waves. An object of the present invention is to provide an FM receiver that can effectively eliminate the adverse effects caused by the subcarrier being interrupted by a pulse noise removal circuit.

Generally, FM receivers use FM receivers to remove pulse noise such as car ignition noise.
A pulse noise removal circuit is provided after the detection circuit. However, when an FM receiver equipped with a pulse noise removal circuit is configured to be able to receive audio signals of television broadcast waves, subcarriers for TV audio multiplex broadcasting are interrupted by the pulse noise removal circuit. Therefore, there was a problem in that the noise increased on the contrary. In other words, the multiplex signal for television audio multiplex broadcast waves is FM.
Unlike radio broadcast signals, it has an FM-modulated subcarrier signal, and this subcarrier signal is switched by the gate signal to open the gate circuit in the pulse noise removal circuit, generating new switching noise. There was a problem.

This problem will be explained in detail with reference to FIGS. 4 and 5. FIG. 4 shows the pulse noise removal operation in the case of a normal audio signal. First, when an FM detection signal containing pulse noise with large amplitude and narrow pulse width, such as ignition noise, is input as shown in A, the pulse noise removal circuit uses a high-pass filter, etc. The presence of the pulsed noise is detected, and the detected output triggers a gate signal generation circuit such as a monostable multivibrator to generate a gate signal B having a constant width T. Then, by gating the input signal A using the gate signal B, a signal like C from which pulse noise has been removed is output. At this time, during the gate period, the previous signal level is held. By doing this, even if there is a pulse noise with a magnitude of X ₁ in the input signal A, it can be reduced to a level difference of Y ₁ in the output signal B, thereby reducing the auditory noise. I can do it.

However, when this pulse noise removal circuit receives the audio multiplexed signal of the television broadcast wave as shown in Figure 5A,
When an FM detection signal is input, the following problems occur. That is, in this case, a signal with a waveform in which an FM-modulated subcarrier signal with a constant amplitude Z is superimposed on the main audio signal is input, and pulse noise is mixed into this, and the above-mentioned problem also applies to this. If a similar noise removal operation is performed, the gate signal B removes the subcarrier signal, resulting in a large level difference in the output signal C, such as _Y2 . This is because the frequency of the subcarrier signal is higher than that of the audio signal as shown in FIG. 4, and the level of the subcarrier signal varies greatly during the pulse width T of the gate signal B. When there is a step fluctuation with a large level difference in the output signal, the distribution width of the frequency spectrum is wide, so that it is mixed into the voice band as a noise component, causing noise. In particular, since the subcarrier signal of the audio multiplexed signal of the television broadcast wave is an FM modulated signal,
Even when the main audio signal is unmodulated or close to it, the subcarrier signal remains at a constant amplitude Z, and the above-mentioned noise due to sudden changes in the subcarrier signal becomes extremely unpleasant to the ears.

The present invention eliminates such conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments.

FIG. 1 shows an embodiment of the present invention, in which 41 is an antenna, 42 is a high frequency amplification circuit, 43 is a frequency conversion circuit, 44 is an intermediate frequency amplification circuit, and 45 is a high frequency amplification circuit.
is an FM detection circuit, 46 is a pulse noise removal circuit,
47 is a stereo demodulation circuit for FM radio broadcast waves;
48 and 49 are low frequency amplifier circuits, 50 and 5
1 is a speaker. Here, from 76MHz
It is configured to be able to receive FM radio broadcast waves up to 108 MHz and television broadcast waves from channels 1 to 3 in the low band, and television channels 4 to 12 in the high band. D ₁ is a variable capacitance diode as a tuning element, VR ₁ is a variable resistor as a tuning voltage changing means, and the tuning voltage applied to the variable capacitance diode D ₁ is changed from the voltage for receiving FM radio broadcast waves to the voltage for receiving TV broadcast waves. Control voltage up to the desired voltage. _S1 is a switch that switches between the low band and high band. _Q1 is a field effect transistor (hereinafter referred to as a field effect transistor) which is a switching element.
FET), its gate is connected to the common terminal of switch S ₁ through a resistor R ₂₁ , its drain is connected to the power supply +B ₂ through a resistor R ₂₂ , and its source is connected to a Zener diode. D ₂
It is grounded via a capacitor _C21 and connected to an external terminal 3 of a semiconductor integrated circuit constituting a pulse noise removal circuit 46.

As the pulse noise removal circuit 46, dedicated semiconductor integrated circuits are available from various companies, such as AN101 manufactured by Matsushita Electronics Co., Ltd. and the AN101 manufactured by Tokyo Sanyo Electric Co., Ltd.
LA2101 etc. are used. Figures 2 and 3
The block diagram and application circuit example for LA2101 are shown. In FIG. 2, 17 is a semiconductor integrated circuit as a pulse noise removal circuit 46, which includes a buffer circuit 20, a low-pass amplifier 21, a gate circuit 22, an output circuit 23, a high-pass amplifier 24, a noise detection circuit 25, and a monostable multivibrator. 2
6. It is composed of a pilot signal holding circuit 27, and is provided with external terminals numbered 1 to 16.
The above-mentioned semiconductor integrated circuit 17 has an input terminal 18 connected to its external terminal 1 to which the FM detection signal from the FM detection circuit 45 is applied, and delays the signal between the external terminals 2 and 3 for time adjustment. A high-pass filter 29 is connected between its external terminals 2 and 15 for detecting pulse noise components, and a storage circuit 30 consisting of a signal holding capacitor is connected between its external terminals 5 and 8. is connected between external terminals 7 and 8.
A 19KHz filter 31 is connected, and an output terminal 19 is connected to its external terminal 6. Further, the semiconductor integrated circuit 17 determines the pulse width of the monostable multivibrator 26 at its external terminal 10.
An RC circuit 32, a control resistance circuit 33 for determining a noise detection level at its external terminal 11, an RC circuit 34 for noise detection at its external terminal 12, and an RC circuit 35 for determining noise detection sensitivity at its external terminal 13. connected and external terminals 4 and 1
4 is connected to a low pass filter 28 and a high pass filter 29. Note that the external terminal 9 is a power supply terminal, and the external terminal 16 is a common ground terminal. Here, the circuit means 28 to 35 are configured as external additional circuits of the semiconductor integrated circuit 17. This external additional circuit is specifically the third
It is configured as shown in the figure. That is, the low-pass filter 28 includes resistors R ₁ to R ₄ and capacitor C ₁
~ _C4 , the high pass filter 29 is comprised of resistors _R5 ~ _R8 and capacitors _C5 ~ _C8 , the memory circuit 30 is comprised of capacitor _C9 , and the 19KHz filter 31 is comprised of resistors _R9 ~ _R13 and
The pulse width determining RC circuit ₃₂ is composed of a resistor _R14 and a capacitor _C13 , the control resistance circuit 33 is composed of a resistor _{R15 ,} and the noise detection RC circuit 34 is composed of a capacitor _C14 . , C ₁₅ and resistance
The sensitivity determining RC circuit ₃₅ is composed of a capacitor _C16 and a resistor _R17 . Furthermore, the output terminal 19 and the input terminal 18 are connected to external terminals 6 and 1 via coupling capacitors C ₁₇ and C ₁₈ , and a resistor is connected to external terminal 9 as a power supply terminal.
A power supply voltage is applied via R ₁₈ and a capacitor C ₁₉ , and a voltage is applied to the external terminal 15 via a resistor R ₁₉ .

In the pulse noise removal circuit 46 having such a configuration, the FM detection circuit 45 input to the input terminal 18
The output signal is input to a low pass filter 28 and a high pass filter 29 via a buffer circuit 20. The output of the low-pass filter 28 is applied to the gate circuit 22 via the low-pass amplifier 21. On the other hand, the signal component is removed by the high-pass filter 29 (the cut-off frequency of the high-pass filter is 50 KHz or higher), and the pulsed noise is added to the noise detection circuit 25 via the high-pass amplifier 24.
The monostable multivibrator 26 is operated, and its output pulse causes the gate circuit 22 to vibrate for a certain period (the time determined by the CR time constant of the terminal 10, usually 100μ).
sec) open. In the memory circuit 30, the gate circuit 22
The voltage value of the input signal before the gate circuit 22 is opened is stored, and while the gate circuit 22 is open, the voltage value of the input signal before the gate circuit 22 is opened is held as an output signal. 19KHz filter 31 was composed of CR
TWIN-T circuit is generally used, gate circuit 2
If there is a 19KHz signal before gate 2 opens, even if the gate circuit 22 opens and the 19KHz signal disappears,
It is configured to oscillate a 19KHz signal.
Therefore, regarding the 19KHz signal, even if the gate circuit 22 is open, a 19KHz signal close to normal is output. For signals other than 19KHz, the voltage value before the gate circuit 22 is opened is held as described above.

Note that the low-pass filter 28 is necessary to delay the signal so that the gate opens when the signal contains pulse noise, and the cutoff frequency is usually 50 KHz or higher.

In an FM receiver with such a configuration, Switch S ₁
of the low band when is switched to the L side.
76MHz to 90MHz is the FM radio broadcast band,
95.75MHz~107.75MHz is 1~ of television
This is a 3ch audio broadcast band. At this time, the tuning voltage V of the tuning variable capacitance diode _D1 is, for example, 6V at 90MHz and 8V at 95.75MHz. Therefore, if you use a Zener diode _D2 with a Zener voltage of about 7V, when the tuning voltage V is 7V or less, which is the voltage for receiving FM radio broadcast waves, FETQ ₁ will be turned off and current will flow through the Zener diode _D2 . do not have.
On the other hand, when the tuning voltage V exceeds 7V and becomes the voltage for receiving television broadcast waves, FETQ ₁ is switched on, current flows through the Zener diode D ₂ , and the capacitor connected to the pulse noise removal circuit 46 is turned on. One end of C ₂₁ is grounded. At this time,
Since the capacitor C ₂₁ is connected to the external terminal 3 of the pulse noise removal circuit 46, it is connected in parallel to the low-pass filter 28. Therefore, when receiving television broadcast waves, a capacitor is
The cutoff frequency of the low-pass filter 28 including C ₂₁ becomes a low frequency of several KHz, and even if the subcarrier signal of the audio multiplex broadcast wave is applied to the input terminal 18 of the pulse noise removal circuit 46, the subcarrier signal The signal is greatly attenuated as shown in FIG. 5D. Therefore, the pulse noise removal circuit 4
Even if the gate circuit 22 of No. 6 is opened by a gate signal based on the detected pulse noise and the subcarrier signal is interrupted, the subcarrier signal is considerably attenuated, so a new level difference is created by the gate signal.
_Y3 becomes small, and the switching noise becomes so small that it does not become a problem. Note that this receiver demodulates and reproduces FM radio broadcast waves as a stereo signal, but for television broadcast waves, even if it is an audio multiplex broadcast, subcarrier signals are not used, and only the main audio signal is used to reproduce monaural sound. Since it is reproduced, there is no problem even if the audio multiplex subcarrier signal is attenuated as described above.

As described above, at frequencies of 95.75 MHz or higher, the characteristics of the low-pass filter 28 of the pulse noise removal circuit 46 change, and therefore, the subcarrier signal of the television audio multiplex broadcast is interrupted by the gate circuit, resulting in pulse noise. The switching noise newly generated by the static noise removal circuit 46 is significantly reduced. In addition, switch S ₁ to the high band side H and
When receiving 12 channels, the characteristics of the low-pass filter 28 of the pulse noise removal circuit 46 change, and similar effects are achieved.

As described above, according to the present invention, the constant of the low-pass filter constituting the pulse noise removal circuit is changed so as to greatly attenuate high-frequency components when receiving television broadcasting, and the gate open time of the gate circuit is lengthened. As a result, the subcarrier of the audio multiplex broadcast can be attenuated, and there is no remaining pulse noise after the gate is closed, and switching noise newly generated in the pulse noise removal circuit can be significantly reduced. It has the advantage of being able to

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the FM receiver of the present invention, Fig. 2 is a block diagram of a pulse noise removal circuit used in the FM receiver, and Fig. 3 is a specific example of the applied circuit. The wiring diagram, FIGS. 4 and 5 are waveform diagrams for explaining the operation. D ₁ ... Tuning variable cap, VR ₁ ... Tuning volume, S ₁ ... Band switch, Q ₁ ... Transistor, R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ ... Resistor, D ₂ ... Zener diode, C ₂₁ ... Capacitor, 46...
Pulse noise removal circuit, 28... low pass filter, 29... high pass filter, 22... gate circuit, 26... monostable multivibrator.

Claims (1)

[Claims] 1 FM using a voltage variable capacitance element as a tuning element
An FM receiver that receives radio broadcast waves and television broadcast waves within the same band includes a low-pass filter that delays the FM detection signal, a high-pass filter that extracts pulse noise components contained in the FM detection signal, and this high-pass filter. a noise detection circuit that detects the pulsed noise using the output signal of the filter; a gate signal generation circuit that is triggered by the output signal of the noise detection circuit and generates a gate signal for removing the pulsed noise; The gate includes a gate that gates the output signal of the low-pass filter and holds the previous signal to remove pulse noise components contained in the signal and outputs the resultant signal. Means for changing the voltage from the voltage for receiving FM radio broadcast waves to the voltage for receiving television broadcast waves, and whether the tuning voltage is controlled on and off according to the magnitude of the tuning voltage and is within the voltage range for receiving FM radio broadcast waves. It is controlled by a switching element that is switched depending on whether the voltage range is for receiving television broadcast waves, and the on/off of this switching element, and when the above tuning voltage is within the voltage range for receiving television broadcast waves, An FM receiver comprising a time constant control element connected to the low-pass filter so as to switch the time constant of the low-pass filter to a characteristic that greatly attenuates a subcarrier signal of a television audio multiplex signal.