KR100191215B1 - Apparatus for eliminating broadcast signal in a telephone - Google Patents

Abstract

end. The technical field to which the invention described in the claims belongs:

The present invention relates to a telephone for blocking a broadcast signal received through a telephone line.

I. The technical problem the invention is trying to solve:

Conventional telephones operate as circuits for detecting envelopes of amplitude modulated broadcast signals to reproduce broadcast signals received through telephone lines with the handset of the telephone.

All. The gist of the solution of the invention:

A reception broadcast signal cancellation telephone implemented by short-circuiting a broadcast signal as an alternating current signal by connecting a capacitor in parallel to four diodes forming a bridge rectifier.

la. Important uses of the invention:

cellphone.

Description

Eliminate incoming broadcast signal

The present invention relates to an apparatus for canceling a broadcast signal received by a telephone.

In general, a broadcasting station modulates a voice or video signal to be transmitted into a broadcast signal and transmits the broadcast or broadcast signal, which is received through a receiver and demodulated into an original signal. For example, a radio station transmits a modulated broadcast signal by frequency modulation (FM) or amplitude modulation (AM) of a voice signal to be transmitted. On the other hand, the radio receives and demodulates the broadcast signal transmitted by the frequency modulation (FM) or amplitude modulation (AM) and provides a voice signal as an original signal to the listener.

In general, the amplitude modulation (AM) performed by a radio station uses a modulation scheme that varies according to a waveform of an audio signal (about 300 Hz to 5 Khz) to transmit the amplitude of a carrier wave having a frequency of 800 KHz to 900 Khz. In addition, the radio uses an envelope detector to detect an envelope corresponding to the speech signal from the amplitude modulated signal to receive the speech signal and to reproduce the speech signal. The amplitude modulated broadcast signal is shown in FIG. 3A, and the envelope-detected signal is shown in FIG. 3B. The radio for receiving the amplitude modulated broadcast signal should be provided with an antenna having a predetermined length. Determination of the length of the antenna can be obtained by the following equation.

For example, the voltage (V) is 3 × 10⁸ego, When the signal of 900Khz is received, the length of the λ / 4 antenna can be obtained by using Equation 1 as follows.

3 × 10 ⁸ = 900 × 10 ³ × λ

λ = 3 × 10 ⁸ ÷ 900 × 10 ³ = 333 (m)

λ / 4 = 83 (m)

The configuration of the conventional telephone and the operation of receiving a broadcast signal will be described with reference to FIG. 1 through a bridge rectifier (D1, D2, D3, D4) in which a telephone line incoming from a local exchange (not shown) is a full wave rectifier circuit. It is connected to the telephone circuit 10. A capacitor C1 is connected in parallel between the bridge rectifier consisting of the four diodes D1, D2, D3, and D4 and the telephone circuit 10. The bridge rectifier is used as a circuit for unifying the polarity of the talk current inverted in polarity provided from the local exchange. The telephone circuit 10 generally refers to a circuit that performs the overall function of the telephone.

The telephone having the above configuration can be represented by an equivalent circuit as shown in FIG. The resistance R1 of the equivalent circuit represents the internal resistance of the telephone circuit 10 in an equivalent manner, and the diode 12 is formed in the telephone line of the four diodes D1, D2, D3, and D4 constituting the bridge rectifier. Two diodes D1 and D2 forward connected to the telephone circuit 10 side are shown. The equivalent circuit shown in FIG. 2 is the same as that of a conventional envelope detector. Thus, the phone performs the function of an envelope detector.

When the telephone line is about 83m, which is the length calculated in the above-described example, the telephone line is operated like an antenna to provide a broadcast signal f (t) cosω _c t. The provided broadcast signal f (t) cosω _c t is an amplitude modulated (AM) signal. The telephone operates as an envelope detector, an equivalent circuit as shown in Fig. 2, to detect the envelope of the provided amplitude modulated broadcast signal f (t) cosω _c t. Since the configuration and operation of the envelope detector are conventional techniques, detailed description thereof will be omitted. The detected signal f (t) is a voice signal transmitted from a broadcasting station and is reproduced through the handset when the telephone user hears the handset.

As described above, the conventional telephone operates as a circuit for detecting an envelope of an amplitude modulated broadcast signal and has a problem of being reproduced through a telephone receiver.

Accordingly, an object of the present invention is to provide a telephone having a capacitor having a short circuit characteristic with respect to an AC signal to block reception of a broadcast signal.

1 is a conventional phone configuration diagram.

2 is an equivalent circuit of FIG.

3A is a waveform diagram of a broadcast signal received through a telephone line;

3B is a waveform diagram in which the waveform of FIG. 3A is envelope detected.

4 is a block diagram of a telephone according to an embodiment of the present invention.

5 is an equivalent circuit of FIG. 4.

Hereinafter, a configuration of a phone and an operation of blocking a received broadcast signal according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The configuration of the telephone according to the present invention is a bridge rectifier and telephone circuit composed of four diodes (D1, D2, D3, D4) to unify the inverted polarity of the call current supplied through the telephone line as shown in FIG. And parallel to two diodes D1 and D2 forward-connected from the telephone line to the telephone circuit 10 side among the four diodes D1, D2, D3 and D4 constituting the bridge rectifier. Capacitors C2 and C3 are connected. In addition, capacitors C4 and C5 are connected in parallel to the two diodes D3 and D4 forward connected from the telephone circuit 10 to the telephone line side.

The capacitors C2, C3, C4, and C5 connected in parallel to the four diodes D1, D2, D3, and D4 constituting the bridge rectifier are considered to be shorted to signals having an AC component according to the characteristics of the capacitor. Can be. Thus, the bridge rectifier remains shorted for the amplitude modulated broadcast signal f (t) cosω _c t having the form of FIG. 3A received over the telephone line. The bridge rectifier can detect an envelope corresponding to the voice signal f (t) in the amplitude modulated broadcast signal f (t) cosω _c t by maintaining a short circuit state with respect to the AC signal. Therefore, the received broadcast signal can be removed. When the capacitor maintains a short circuit state for the AC signal, which is the broadcast signal, the equivalent circuit of the telephone according to the present invention may be represented as shown in FIG. 5.

As described above, by preventing the telephone from operating as an envelope detector, it is possible to prevent the broadcast signal from being reproduced through the handset of the telephone, thereby improving call quality.

Claims (2)

A phone comprising a bridge rectifier consisting of four diodes and a telephone circuit for unifying the inverted polarity of the call current supplied through the telephone line, wherein the telephone line is connected to the telephone circuit side of the four diodes constituting the bridge rectifier. And a capacitor connected in parallel to two forward connected diodes. The telephone set as claimed in claim 1, further comprising a capacitor connected in parallel to two diodes forward connected to the telephone line side in the telephone circuit.