KR790001101B1 - Demodulation circuit for four-channel f m receiver - Google Patents

Abstract

A circuit for demodulating the received FM broadcasting wave to the original 4-channeled signal by Dorren method or the similar way, consisted of a switching signal generating circuit(11), the first switching circuit(2-4), a phase inverting circuit(6), the second switching circuit, and a mixing circuit (12-15) for mixing the output signals with one another. The demodulating circuit removes the unnecessary crosstalk component of the channels and provides high fidelity.

Description

Demodulation Circuits in Four-Channel FM Receivers

1 and 2 show switching signal waveforms used in the demodulation circuit.

3 is a block diagram of a demodulation circuit.

The present invention provides a method for demodulating a received FM broadcast wave into an original four channel signal in a discrete four channel FM broadcasting method by a so-called Doren method (invented by a person named DORREN) or a similar method. It relates to a demodulation circuit.

In addition, an object of the present invention is inevitably between channels when demodulating a signal transmitted from a main channel, a first sub-channel and a second sub-channel of an FM broadcast wave into a 4-channel signal by a switching method. An improved demodulation circuit is provided to eliminate cross talk components of other channels to be mixed and to obtain good separation.

The demodulation circuit of the present invention can be applied to demodulation of four-channel FM broadcasts by the doren method or the like. In the doren system, the signals of left front S ₁ , rear left S ₂ , right front S _3, and right back S ₄ are combined according to a predetermined method, and then FM broadcast waves. As fired. The FM broadcast wave is considered to be able to individually catch signals having at least the following five conditions in order to be compatible with monaural, two-channel stereo and four-channel stereo.

(1) the sum of all the signals of S ₁ -S ₄ ,

(2) a signal obtained by carrying out carrier suppression amplitude modulation of the first carrier by the difference between the sum of S ₁ and S _{2 and} the sum of S ₃ and S ₄ ,

(3) A carrier suppression amplitude modulated signal of a second subcarrier having the same frequency and orthogonal phase as the first subcarrier as a difference between S ₁ and S ₂ and a difference between S ₃ and S ₄ .

(4) A carrier suppression amplitude modulated signal of a third subcarrier having the same frequency and phase as the frequency of the first subcarrier by the sum of the difference between S ₁ and S _{2 and} the difference between S ₃ and S ₄ .

의 주파수이고 위상이 같은 기준신호(pilot signal)이 FM 방송파에 의하여 보내지는 복합신호는 다음 (1)식으로 표시된다.(5) Part 1 carrier

A composite signal in which a pilot signal of the same frequency and phase is transmitted by an FM broadcast wave is represented by the following equation (1).

C (t) = (S ₁ + S ₂ + S ₃ + S ₄ )

+ (S ₁ -S ₂ -S ₃ -S ₄ ) sin 2πfst

+ (S ₁ -S ₂ -S ₃ + S ₄ ) cos 2πfst

+ (S ₁ -S ₂ + S ₃ -S ₄ ) sin 2π · 2fst

fst………(1)+ ρsin 2π

fst… … … (One)

Where C (t): composite signal

fs: frequency of the first carrier

ρ: amplitude of the pilot signal

The composite signal can be demodulated into a four-channel signal by, for example, switching by a switching signal as shown in FIG. That is, the switching signal of FIG. 1 can be expressed by the following equation.

The switching operation can be represented by multiplying (1) by (2)-(5).

Only the audible components of the four demodulated signals obtained by this switching operation are represented by the following formulas (6) to (9).

As can be seen from the above equation, the demodulation signal of each channel includes signals of three different channels as crosstalk components.

According to the demodulation circuit of the present invention, by sending a demodulation signal corresponding to each channel to a signal capable of canceling the crosstalk component included therein, four signals corresponding to the original four-channel signal having high separation can be separated. There is a number.

3 shows an embodiment of a demodulation circuit of the present invention.

In Fig. 3, reference numeral 1 denotes the FM detection circuit of the FM receiver, and the outputs of the FM detection circuit 1 are the first switching circuits 2, 3, 4 (4). ) And (5) and the phase inversion circuit 6 are simultaneously supplied.

The phase inverting circuit 6 inverts the phase of the composite signal output from the FM detection circuit 1, so that the second switching circuits 7, 8, 9, and 10 are made into one pair. Supply the inverted output to.

및

가 스윗칭 신호 발생회로(11)로부터 공급이 된다.The first switching circuits (2) to (5) are the first switching signals f1 (t) generated by the switching signal generation circuit (11) by reference signals included in the output of the FM detection circuit (1). , under the control of f2 (t), f3 (t) and f4 (t), the output O '1-O' 4 shown in the above formulas (6)-(9) is generated. On the other hand, in the second switching circuits 7 to 10, as shown in FIG. 2, the second switching signal inverting the passing section and the blocking section of the first switching signals f1 (t) -f4 (t) is shown.

And

Is supplied from the switching signal generating circuit 11.

This second switching signal is mathematically represented by the following equations (10)-(13).

및

는 다음과 같이 표시된다.In addition, since the input signals of the second switching circuits 7 to 10 are phase-inverted in advance by passing through the phase inversion circuit 6, the output of the second switching circuits 7 to 10 is output.

And

Is displayed as follows.

Also, four for mixing each of the outputs of the first and second switching circuits (2), (7), (3) and (8), (4) and (9), and (5) and (10) The mixing circuits 12, 13, 14, and 15 are set.

If the ratio of mixing two kinds of inputs that are in phase with each other is set to (π-2) / (3π + 2), the next addition is performed in the mixers 12 and 15 so that the four outputs 0 1 , 0 2, 0 3 and 0 4.

That is, in the demodulation circuit of the present invention, the crosstalk component included in the four-channel signal obtained by demodulation by switching is effectively canceled, and as a result, the separation between the channels is good.

In the above embodiment, for convenience of explanation, the gains of the switching circuit, the phase inverting circuit, and the mixing circuit are set to 1, but even when the gain of these circuits is not 1, the component mixing ratio of the mutual antiphases as a whole becomes a predetermined value. You can get the same effect by setting it.

Claims (1)

Four kinds of first switching signals f ₁ (t)... F ₄ (t), which are waveform signals synchronized with the reference signal and sequentially deteriorated in phase, and whose frequency is twice the first carrier frequency. And a switching signal generating circuit 11 for generating four kinds of second switching signals f ₁ (t)... F ₄ (t) inverting the passage section and the blocking section of the first switching signal. In order to derive four kinds of front, rear, left and right signals including cross talk components in a stereophonic sound relationship from the composite signal, the composite signals are input to each of the four kinds of first switching signals. Four first switching circuits 2-4 arranged so as to be sequentially switched by the first step, a phase inversion circuit 6 for inverting the phase of the composite signal and an output signal of the phase inversion circuit, respectively, Four second switching circuits arranged to sequentially switch by four kinds of second switching signals, respectively (7-10) and the four-channel FM receiver canceling out unnecessary crosstalk components included in the front, rear, left and right signals in the stereophonic sound relationship caused by the switching of the first switching circuit and the output signal of the second switching circuit. Demodulation circuit.

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