JPS6214768Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a multipath noise detection device in an FM receiver that uses a muting drive voltage of an intermediate frequency amplifier as a signal for multipath noise detection.

Conventional multipath noise detection devices include those that detect envelope dips and those that detect distortion components of demodulated signals and noise in high frequencies, but the former requires a separate AM intermediate frequency amplifier. However, it was expensive and had the disadvantage that it operated even when no distortion or noise occurred. In addition, although the latter is stable because it processes at a low frequency, it requires a filter, etc., and is expensive.
The problem was that it could malfunction due to car ignition noise.

The present invention has been made to solve the above-mentioned drawbacks, and uses a multipath detection circuit mounted on a transistor to detect the short muting drive voltage generated by the mute drive circuit of an intermediate frequency amplifier when multipath noise occurs. It is an object of the present invention to provide a multipath noise detection device that obtains a pulse wave as a multipath noise detection signal that notifies the occurrence of multipath noise.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating the multipath noise detection device according to the present invention, including its relationship with an intermediate frequency amplifier, where the dotted line section 100 is the intermediate frequency amplifier, T1 is the input terminal, 101, 102, 10
3,104,105 is limiter, 106,10
7, 108 is a level detector, 109 is an AGC drive circuit, 110 is a signal strength indicator, 111 is an inversion circuit, 112 is a quadruple layer detector, 113
is a Hall detector, 114 is an AFC drive amplifier circuit,
115 is a DC level detector, 116 is an AF amplification, a miute gate circuit, 117 is a miute drive circuit,
118 is a low pass filter, 119 is a multipath detection circuit, and 120 is a mute amplifier. T
2 is AGC output terminal, T3 is AFC output terminal, T4
is a demodulation output terminal, T5 is a signal instruction terminal, T6 is a muting drive output terminal, T7 is a muting drive input terminal, and T8 is an output terminal for a multipath noise detection signal.

FIG. 2 is a graph showing the waveforms of each output for explaining the operation of the multipath noise detection device according to the present invention, where a is the muting drive voltage, and b is the muting drive output via the low-pass filter 118. , c is miute amplifier 1
20, and d is a multipath noise detection signal outputted from the multipath detection circuit 119. Note that the detection positions of these outputs a, b, c, and d are shown in FIG.

The direction of the arrow in the configuration of the intermediate frequency amplifier 100 in FIG. 1 above indicates the input transmission path. The above Mute drive circuit 117 is the AGC drive circuit 1
09, signal strength indicator 110, inversion circuit 111,
The transmission input is monitored via the Hall detector 113 and the DC level detector 115, and the muting drive voltage a is output when the electric field is weak.

It is known that when multipath noise occurs during FM broadcast reception, it generates significant amplitude components, including a drop in the electric field due to phase differences and modulation distortion due to path differences. This amplitude component is affected by the modulation frequency and frequency deviation, and is particularly noticeable during stereo broadcasting, sometimes resulting in 100% amplitude modulation of the IF input. Therefore, at this time, no matter how many stages of limiters are stacked, a uniform amplitude cannot be maintained as a waveform, and the mute signal is supplied to the mute drive circuit 117 with a short width, similar to when the electric field falls. Further, even if the amplitude does not reach 100%, large amplitude components are supplied to the mute drive circuit 117 through the level detectors 106, 107, and 108. However, muting does not work for the above-mentioned skip noise caused by multipath noise.

Normally, the muting drive voltage passed through the mutating drive circuit 117 has a shape as shown in FIG. 2a. Here, a1 is the multipath noise detection level. The above output a is low pass filter 1
18, the waveform is converted into the output b. Note that b1 is the muting detection level here. As shown in FIG. 2, the low-pass filter 118 is originally inserted to prevent muting from occurring due to short-width skip noise generated by multi-path noise. In other words, if muting is operated in response to noise such as the above-mentioned skip noise that occurs in a width of several tens to hundreds of milliseconds, the detection output will become discontinuous and the reproduction output will deteriorate significantly, so this should be prevented. are doing. Therefore, the muting circuit operates only on wide muting outputs such as output c, and the low-pass filter 1
Because of the time constant of 18, there will be a delay of T time with respect to the output a.

In the multipath detection device according to the present invention, the muting drive output a before entering the low pass filter 118 is introduced into the multipath detection circuit 119,
This is to obtain a multipath noise detection signal. As a result, the multipath noise detection signal has no time delay, as shown in FIG. 2d, and can respond to even short width skip noises to detect all multipath noises.
This configuration eliminates the need for AM intermediate frequency amplifiers and filters, is inexpensive, and prevents external noise such as car ignition noise from increasing the electric field. Since the same effect is applied to the signal transmission system, there are no malfunctions.

FIG. 3 is a circuit diagram explaining one embodiment of the multipath detection circuit, in which R1, R2, and R3 are resistors, and Q
1 is a transistor, T31 is an input terminal, +B is a bias supply terminal, and T32 is an output terminal.

In the above configuration, when a muting drive voltage of a predetermined level or higher is input from the input terminal T31, the transistor Q1 is turned on and outputs a multipath noise detection signal.

FIG. 4 is a circuit diagram explaining an embodiment of a multipath detection circuit using a comparator (voltage comparator), where 44 is a comparator, T41 is an input terminal, T42 is an output terminal, and T43 is a reference voltage supply terminal. It is. In the above configuration, when the mute drive voltage exceeds the reference voltage, a multipath noise detection signal is output.

Note that, as shown in FIG. 2d, the multipath noise detection signal supplies a high level output when multipath noise is detected, but it may be set to a low level when multipath noise is detected.

In addition to the embodiments shown in FIGS. 3 and 4, the multipath detection circuit described above may be one that can take in the output from the mute drive circuit 117, accurately detect multipath noise, and obtain pulse waves. You can also use something else.

The multipath noise detection signal obtained by the multipath detection circuit can be used as an antenna switching signal when detecting multipath noise, or can be used for other multipath noise countermeasures.

As described above, the multipath noise detection device according to the present invention detects multipath noise by directly inputting the muting drive voltage of the intermediate frequency amplifier into the mutating drive circuit described above. It is inexpensive, and does not malfunction even due to ignition noise.

[Brief explanation of drawings]

FIG. 1 is a block diagram explaining the multipath noise detection device according to the present invention, FIG. 2 is a graph showing the output waveform explaining the operation of the multipath noise detection device according to the present invention, and FIG. FIG. 4 is a circuit diagram of the multipath detection circuit. 100... intermediate frequency amplifier, 101, 102,
103, 104, 105... Limiter, 10
6,107,108...Level detector, 109...
...AGC drive circuit, 110...signal strength indicator,
111... Inverting circuit, 112... Quadruple layer detector, 113... Hall detector, 114...
...AGC drive amplifier circuit, 115...DC level detector, 116...AF amplification, miute gate circuit,
117... Mute drive circuit, 118... Low pass filter, 119... Multipath detection circuit,
120...Miute amplifier, a, b, c, d...
Output waveform, T1, T2, T3, T4, T5, T3
1, T32, T41, T42, T43, +B...
Terminal, Q1...Transistor, 44...Comparator.

Claims (1)

[Scope of utility model registration request] A plurality of level detection means for detecting a signal level from an intermediate frequency amplifier of an FM receiver, an AGC driving means for extracting a signal level from the intermediate frequency amplifier for AGC, and a detection signal from a quadruple layer detector downstream of the intermediate frequency amplifier. and DC level detection means for extracting the DC component from the AFC drive amplifier circuit at the downstream stage of the quad layer detector. 1. A multipath noise detection device comprising: a muting drive means for mutating; and means for detecting multipath noise by extracting a level equal to or higher than a multipath noise detection level of the output of each of the means.