JPS6233771B2 - - 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, and its purpose is to receive subcarriers for television audio multiplex broadcasting. An object of the present invention is to provide an FM receiver that can effectively eliminate the negative effects of pulse noise on a pulse noise removal circuit.

Generally, FM receivers, particularly in-vehicle FM receivers, are equipped with a pulse noise removal circuit in order to remove car ignition noise and the like.

When such a car-mounted FM receiver attempts to receive television broadcast waves, the subcarrier for the audio multiplex broadcast has a negative effect on the pulse noise removal circuit, causing a phenomenon that the noise increases instead. There was a problem.

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

FIG. 1 shows one embodiment of the present invention, in which 41 is an antenna, 42 is a harmonic amplification circuit, 43 is a frequency conversion circuit, 44 is an intermediate frequency amplification circuit, 45
is an FM detection circuit, 46 is a pulse noise removal circuit,
47 is a stereo demodulation circuit, 48 and 49 are low frequency amplification circuits, and 50 and 51 are speakers.
Here, it is configured to be able to receive the audio of FM radio broadcast waves from 76MHz to 108MHz and channels 1 to 3 of television broadcast waves in the low band part, and the audio of channels 4 to 12 of television in the high band part. ing. 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 (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 the pulsed noise It is grounded via a Zener diode _D2, which is an operation control element of the removal circuit, and is connected to an external terminal 15 of a semiconductor integrated circuit constituting the pulse noise removal circuit 46 via a capacitor _C21 .

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 4 and 5
The block diagram and application circuit example for LA2101 are shown. In FIG. 4, 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 equipped 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 alignment. A high-pass filter 29 for detecting pulse noise is connected between its external terminals 2 and 15, and a high-pass filter 29 for detecting pulse noise is connected between its external terminals 2 and 15.
A memory circuit 30 consisting of a signal holding capacitor is connected between the 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 to its external terminal 11, an RC circuit 34 for noise detection to its external terminal 12, and an RC circuit 35 for determining sensitivity to its external terminal 13 are connected, respectively. The external terminals 4 and 14 are connected to a low pass filter 28 and a bypass 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 constructed as shown in FIG. That is, the low-pass filter 28 is composed of resistors _R1 to _R4 and capacitors _C1 to _C4 , and the high-pass filter 29 is composed of resistors _R5 to _R8.
and capacitors _C5 to _C8 , the memory circuit 30 is composed of a capacitor _C9 , the 19KHz filter 31 is composed of resistors _R9 to _R13 and _C10 to _C12 , and the RC circuit 32 for determining the pulse width is The control circuit 33 is composed of a resistor R ₁₄ and a capacitor C ₁₃ , the noise detection RC circuit 34 is composed of capacitors C _{14 and} C ₁₅ and a resistor R ₁₆ , and the sensitivity determining RC circuit 35 is composed of a resistor R 14 and a capacitor C 13. Capacitor C ₁₆ and resistor R ₁₇
It is composed of Furthermore, the output terminal 19 and the input terminal 18 are connected to the external terminals 6 and 1 via coupling capacitors C ₁₇ and C ₁₈ , and the external terminal 9, which serves as a power supply terminal, is connected to the power supply via a resistor R ₁₈ and a capacitor C ₁₉ . A voltage is applied to the external terminal 15 via a resistor _R19 .

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 filter 21.
On the other hand, the signal component is removed by the high-pass filter 29 (the cutoff frequency of the high-pass filter is 50 KHz or higher), and the pulsed noise is added to the noise circuit 25 via the high-pass amplifier 24 to operate the monostable multivibrator 26. , the output pulse opens the gate circuit 22 for a certain period (a time determined by the CR time constant of the terminal 10). The memory circuit 30 stores the voltage value of the input signal before the gate circuit 22 opens, and holds the voltage value before the gate circuit 22 opens as an output signal while the gate circuit 22 is open. The 19KHz filter 31 is generally a TWIN-T circuit composed of CR, and if there is a 19KHz signal before the gate circuit 22 is opened, the 19KHz signal will be oscillated even if the gate circuit 22 is opened and the 19KHz signal disappears. is configured to do so. 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~ for television.
This is a 3ch audio broadcast band. At this time, the tuning voltage V of the tuning variable capacitance element _D1 is 90MHz, for example 6V,
8V at 95.75MHz. Therefore, Zener voltage 7V
If you use a Zener diode _D2 of about
When the tuning voltage V is 7V or less and there is a voltage for receiving FM radio broadcasting, FET Q ₁ is turned off and no current flows through Zener diode D ₂ . On the other hand, when the tuning voltage V exceeds 7V and becomes the voltage for receiving television broadcast waves, FET Q ₁ is switched on, current flows to Zener diode D ₂ , and the pulse noise removal circuit passes through capacitor C ₂₁ . 46 is grounded. Capacitor C ₂₁ is connected to external terminal No. 15 of semiconductor integrated circuit 17 shown in FIG.
Therefore, the external terminal 15 is grounded via the capacitor _C21 , and no noise is input to the noise detection circuit of the pulse noise removal circuit 46, and the gate circuit 22 remains closed, eliminating pulse noise. The noise removal operation of the removal circuit 46 is stopped. Therefore, the television audio detection signal input to the pulse noise removal circuit 46 is output as is. In this way, the pulse noise removal circuit 46 does not operate at the reception frequency of television broadcast waves, and therefore, the pulse noise removal circuit 46 malfunctions due to the influence of the subcarrier of the television audio multiplex broadcast, and the noise is suppressed. Never occurs.

As described above, according to the present invention, it is possible to eliminate the negative influence of subcarriers for television audio multiplex broadcasting on the pulse noise removal circuit,
It is possible to easily solve various problems caused by television reception.

[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. It is a wiring diagram. D ₁ ... Variable capacitance diode, VR ₁ ... Variable resistor, S ₁ ... Switch, Q ₁ ... Field effect transistor, R ₂₁ , R ₂₂ , R ₂₃ ... Resistor, D ₂ ... Zener diode, C ₂₁ ...Capacitor.

Claims (1)

[Claims] 1 FM using a voltage variable capacitance element as a tuning element
In an FM receiver that receives radio broadcast waves and television broadcast waves within the same band, a pulse noise removal circuit that detects and removes pulse noise contained in the received signal and a voltage applied to the variable capacitance element are provided. Means for changing the tuning voltage from the voltage for receiving FM radio broadcast waves to the voltage for receiving television broadcast waves, and the tuning voltage being controlled on and off according to the magnitude of the tuning voltage to the voltage for receiving FM radio broadcast waves. A transistor is switched depending on whether the tuning voltage is a voltage for receiving television broadcast waves, and the pulse characteristics are controlled by turning the transistor on or off. An FM receiver comprising: an operation control element that stops the noise removal operation of the noise removal circuit.