Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Patent
1992-10-23
1994-04-12
Eisenzopf, Reinhard J.
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
4552341, H04B 110
Patent
active
053034155
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a pulse noise detecting circuit provided in an AM receiver for detecting pulse noise signal entering the AM receiver.
More particularly, the present invention alludes to improvement of the pulse noise detecting circuit of the AM receiver to allow greater freedom in construction of the AM receiver and to prevent erroneous operation.
BACKGROUND ART
FIG. 18 is a diagram showing a prior art pulse noise detecting circuit in an AM receiver Note, the same reference numerals and symbols are used to represent the same elements throughout all of the drawings. The construction of the figure includes a tuner 100 of the AM receiver, a pulse noise removal portion 2 for removing pulse noise from an output signal of the tuner 100, and a pulse noise detecting portion 40 for detecting the pulse noise to output a gate signal for removing the pulse noise to the pulse noise removal portion 2.
The tuner 100 includes an antenna 101, a RF amplifier 102 connected to the antenna 101, a mixer 103 connected to the RF amplifier 102, a local oscillator 104 supplying a mixing signal to the mixer 103, a broad band filter 105 connected to the mixer 103, an intermediate frequency amplifier 106 connected to the broad band filter 105, a narrow band filter 107 connected to the intermediate frequency amplifier 106, and, for example, an envelope detector 108 connected to the broad band filter 107. Automatic gain control is performed using the output of the detector 108 to the amplification gain of the intermediate frequency amplifier 106. The output of the detector 108 is made constant.
The pulse noise removal portion 2 includes a gate circuit 21 and a holding capacitor 22.
FIG. 19 is a view illustrating the removal of noise using the pulse noise removal portion of FIG. 18.
As shown in (a) of the figure, in a signal input to the pulse removal portion 2, pulse noise is superposed on a detection signal. This pulse noise is, for example, ignition noise, noise mixed from a transmission line, etc. in a receiver installed in a vehicle. Also, as shown in (b) of the figure, there is a gate signal detected by the pulse noise detecting portion 40 and synchronized with the pulse noise. Further, as shown in (c) of the figure, when the gate signal allows the gate circuit 21 to be open and the pulse noise to be removed, the level of the detection signal before removal of a pulse noise signal is held by the capacitor 22. When the gate circuit 21 is closed, the holding of the detection signal is released As shown in (d) of the figure, the post removal waveform shown in (c) of the figure is corrected by another apparatus not shown.
The pulse noise detecting potrion 40 of FIG. 18 includes an amplifier 41 connected to the output of the broad band filter 105, an envelope detector 42, for example, connected to the amplifier 41, a high pass filter 43 connected to the detector 42, and a level detecting portion 44 connected to the high pass filter 43 and producing a gate signal for operating the gate circuit 21.
The reason why the tuner 100 is provided with the broad band filter 105 is to obtain a greater amplitude of noise in the pulse noise detection portion 40 so as to make the detection of the pulse noise easier.
Also, in order to make the output of the detector 42 constant, automatic gain control is performed to control the amplification gain of the amplifier 41.
Next, the operation will be discussed. A received signal with pulse noise mixed is branched by the band filter 105, passes through the amplifier 41, has the carrier wave removed by the envelope detector 42 to become a demodulation wave, has all but the pulse noise high frequency removed by the high pass filter 43, is shaped into the gate signal by the level detecting portion 44 and is then output to the gate circuit 21.
However, since the prior art pulse noise detecting circuit of the AM receiver is required to amplify the branched signal in the band filter 105 and further perform detection etc., there were the problem of emission of a higher harmonic
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patent: 4910799 (1990-03-01), Takayama
patent: 4965854 (1990-10-01), Glazebrook
patent: 5140704 (1992-08-01), Ueno
Matsunaga Hirokazu
Takayama Kazuo
Eisenzopf Reinhard J.
Fujitsu Ten Limited
Vo Nguyen
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