JP2000165147A - Am modem circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a receiver side to generate a signal of the same level at that of a transmitter side without being affected by a high frequency attenuation increasing characteristic of a transmission cable in the case of propagation of the signal through the transmission cable and without being affected by fluctuation in a frequency change. SOLUTION: Left and right side band waves resulting from amplitude- modulating a carrier with an input signal at an AM modulation section 1 provided to a transmitter side P are transmitted trough a transmission cable L. A side wave band balance correction filter 3 corrects unbalanced levels of both the side band waves resulting from difference in attenuation of the levels depending on frequency so as to provide a relation of the level having a prescribed rate of change with respect to the signal frequency. Thus, an AM demodulation section 2 obtains a prescribed level against the frequency for the signal amplitude-demodulated from both the side band waves and obtains the level corresponding to the frequency before the transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AM modulation / demodulation circuit for transmitting and receiving a signal wave as left and right side waves in order to transmit and receive a signal via a transmission cable.

[0002]

2. Description of the Related Art Conventionally, when a signal is transmitted and received using a transmission cable, a carrier wave is AM-modulated by a signal wave on a transmission side and transmitted as a modulated wave to a transmission cable, and a modulated wave is demodulated on a reception side. There is an AM modulation / demodulation circuit for extracting a signal wave. As shown in FIG. 4, such an AM modulation / demodulation circuit includes, as shown in FIG. 4, an AM modulator 11 that amplitude-modulates a high-frequency carrier wave when a signal wave to be transmitted is input and outputs the modulated wave to the transmission cable L1 as a modulated wave. AM demodulator 1 for separating a signal on the receiving side from a modulated wave transmitted to cable L1
And 2.

In such an AM modulation / demodulation circuit, the AM
In the modulation unit 11, as shown in FIG.
When the carrier H1 is AM-modulated with the signal Fc whose frequency is up to fc, the carrier H1 has a frequency f10 as shown in FIG.
Side waves S11 and S12 having signal wave components having frequencies of f11 = f10-fc and f12 = f10 + fc respectively on the left and right sides.
When the frequency of the signal Fc is, for example, an audio signal having a width of about 0 to 10 kHz, the side waves S11 and S12 are included in the left and right sidebands F11 and F12 each having a width of 10 kHz around the frequency f10 of the carrier H1. And have the same level of signal wave components.

[0004]

The transmission cable L1 through which the side waves S11 and S12 containing such signal components are transmitted.
In general, as shown in FIG. 7, the level varies depending on the frequency of a signal to be transmitted. Therefore, even if a signal of the same level is transmitted, the level after transmission fluctuates depending on the frequency, and furthermore, the fluctuation that occurs in the level has a high frequency attenuation increasing characteristic in which there is no fixed relation to the frequency. That is, two-sided waves S11 of the same level having different frequencies f11 and f12, respectively.
When S12 is transmitted through the transmission cable L1, as shown in FIG. 8, since the attenuation rate received from the transmission cable L1 varies depending on the frequency, the level differs, and the level balance between the side waves S11 and S12 is lost. It will be. Therefore, the level F10 at the frequency f10 and the portion m1 surrounded by the straight line of the level due to the frequency characteristics of the transmission cable,
The area of m2 differs between left and right of the frequency f10, and the energy distribution with respect to the frequency is not uniform. For this reason, as shown in FIG. 9, the signal wave Fc demodulated by the AM demodulator 12 is not demodulated to a level corresponding to the level before transmission, but is demodulated to a higher level as the frequency of the signal becomes higher. I have.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and an input signal is transmitted through a transmission cable so that a level attenuation factor with respect to a frequency caused by a high frequency attenuation characteristic of the transmission cable. It is an object of the present invention to provide an AM modulation / demodulation circuit which can correct the fluctuation of the signal and can make the level of the demodulated signal wave unaffected by the change in the frequency and correspond to the level of the signal before transmission.

[0006]

In order to achieve this object, an AM modulation / demodulation circuit according to the present invention modulates an input signal by an AM modulator on the transmitting side, transmits the modulated signal as a double-sided signal to the transmission cable, and transmits the signal to the transmission cable. An AM modulator-demodulator circuit for demodulating a signal transmitted via a cable by an AM demodulator on a receiving side, wherein one of a transmitting side and a receiving side is provided with a left and right channel due to a high frequency attenuation increase characteristic of a transmission cable. The sideband balance correction filter for correcting the balance of both sidebands and flattening the frequency characteristics after demodulation is inserted.

[0007] An AM modulator provided on the transmitting side modulates the carrier wave into left and right side waves by an input signal and transmits the same to a transmission cable having a high frequency attenuation increasing characteristic. A sideband balance correction filter is provided on the receiving side that extracts a signal wave from the receiver. It is assumed that the sideband balance correction filter has a characteristic of correcting a fluctuation of the level of a signal wave transmitted by the frequency due to the high frequency attenuation increase characteristic of the transmission cable so as to have a fixed relation. For this reason, by transmitting the transmission cable, the level variation caused by the difference in the frequency of the signal wave after transmission is set to a constant rate of change corresponding to the frequency, thereby disturbing the level balance generated between the left and right side waves. And the signal wave demodulated on the receiving side can be set to a level corresponding to the frequency before transmission.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an AM modulator / demodulator according to the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the AM modulation / demodulation circuit of the present invention includes an AM modulation section 1 provided on a transmission side P, an AM demodulation section 2 provided on a reception side Q, and an AM modulation section 1 and an AM demodulation section 2. And a transmission cable L to be connected, and a sideband balance correction filter 3 is provided on the receiving side Q.

As shown in FIG. 2 (a), the AM modulator 1 provided on the transmitting side P modulates the amplitude of a carrier H having a frequency f0, which is a high frequency, when an input signal Fc having a frequency up to fc is input. It is. As shown in FIG. 2B, the carrier H in the AM modulator 1 has f1 = f0-fc and f2 on the left and right, respectively.
= F0 + fc Side waves S1, S2 having signal wave components of frequency
It is said. The side waves S1 and S2 have the frequency of the input signal Fc,
For example, in the case of about 0 to 10 kHz, the left and right sidebands F of 10 kHz around the frequency f0 of the carrier H
1, which are included in the sideband F2 and have the same level of signal wave components.

The transmission cable L is the same as the above-mentioned transmission cable, and has a high frequency attenuation increasing characteristic in which the level of the transmitted signal wave fluctuates according to the change in the frequency of the signal to be transmitted. When the same level double-sided waves S1 and S2 having different frequencies f1 and f2 are transmitted to the transmission cable L, as described above, the attenuation factors received from the transmission cable L differ, and the level after transmission varies. It becomes.

The AM demodulation unit 2 provided on the receiving side Q removes a carrier component from the side waves S1 and S2 transmitted through the transmission cable L, and extracts a signal wave. Such an A
The sideband balance correction filter 3 provided on the receiving side Q of the M modulation / demodulation circuit operates in the frequency band of the sidebands F1 and F2, and as shown in FIG. It has a frequency characteristic in which the increase characteristic is corrected and the level of the signal is constant at a constant rate with respect to the frequency at frequencies f1 to f2, that is, flat. Therefore, the area of the level F0 at the frequency f0 and the areas M1 and M2 surrounded by the corrected level line become equal on the left and right sides of the frequency f0, and the energy distribution with respect to the frequency becomes uniform. Therefore, the frequencies f1 = f0-fc, f2 = f0 +
The level of the signal demodulated from the side waves S1 and S2 of fc is constant as shown in FIG. Therefore, by transmitting the transmission cable L having the high frequency attenuation increasing characteristic, the side wave S
1. If the level after transmission is not related to the level before transmission due to the fact that S2 has a different level attenuation factor for that frequency, the sideband balance correction filter 3
, The level fluctuation occurring before and after transmission can be corrected to a level corresponding to the level before transmission.

The operation of such an AM modulation / demodulation circuit will be described. When an input signal Fc whose frequency is up to fc is input to the AM modulator 1 of the transmitting side P, the carrier H having a frequency f0 is amplitude-modulated, and a signal wave having the same level of f1 = f0-fc and f2 = f0 + fc is generated. It is transmitted through the transmission cable L as side waves S1 and S2 having components. The transmitted side waves S1 and S2 receive the high frequency attenuation characteristic of the transmission cable L, and the level attenuation rate fluctuates due to the difference in frequency. Is converted to a level that does not exist. As a result, the side waves S1 and S2 have a relationship in which the level balance is lost. This unbalanced side wave S
1 and S2 are passed through the sideband balance correction filter 3 to correct the imbalance due to the high frequency attenuation increase characteristic of the transmission cable L, and are converted into a signal having a fixed level with respect to the frequency. Therefore, when the carrier wave is removed and the signal wave is extracted by the AM demodulation unit 2, a signal corresponding to the level of the input signal Fc of the transmission side P which is not changed by the change in frequency is extracted.

The above embodiment is an embodiment of the present invention, and the present invention is not limited to this embodiment. The sideband balance correction filter may be provided downstream of the AM demodulation unit or provided on the transmission side. The same effect can be obtained.

[0014]

As is apparent from the above description, according to the AM modulation / demodulation circuit of the present invention, the AM modulation section provided on the transmission side modulates the carrier wave by the input signal into the left and right side waves. A signal is transmitted through a transmission cable having a high-frequency attenuation increasing characteristic in which the level attenuation rate varies depending on the frequency, and a sideband balance correction filter is provided on a reception side that extracts a signal wave from a sidewave transmitted by an AM demodulation unit. ,
It is possible to correct the imbalance of the level generated in the double-sided waves caused by the fact that the attenuation rate differs depending on the frequency by being transmitted to the transmission cable so that the level has a constant rate of change with respect to the frequency of the signal. .
For this reason, it is possible to correct the level imbalance that occurs between the two-sided waves after transmission by transmitting the transmission cable, and to set the demodulated signal wave to a level corresponding to the frequency before transmission.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an AM modulation / demodulation circuit according to the present invention.

FIG. 2A is a frequency distribution diagram before modulation according to the present invention.
(B) is a frequency distribution diagram after modulation according to the present invention.

FIG. 3 is a modulated wave frequency distribution diagram after correction according to the present invention.

FIG. 4 is a diagram showing a signal wave level after demodulation according to the present invention.

FIG. 5 is a block diagram showing a conventional example.

FIG. 6A is a frequency distribution diagram of a conventional example before modulation.
(B) is a frequency distribution diagram after modulation of a conventional example.

FIG. 7 is a diagram showing a signal wave level after transmission in a conventional example.

FIG. 8 is a diagram showing a modulated wave frequency distribution after transmission in a conventional example.

FIG. 9 is a diagram showing a signal wave level after demodulation in a conventional example.

[Explanation of symbols]

 1 AM modulator 2 AM demodulator 3 Sideband balance correction filter L Transmission cable P Transmission Side Q: Reception side Fc: Input signal

Claims (1)

[Claims] 1. An input signal (Fc) is modulated by an AM modulator (1) on a transmitting side (P) and transmitted to a transmission cable (L) as left and right side waves, and is transmitted through the transmission cable. An AM modulator / demodulator circuit for demodulating a signal transmitted by an AM demodulation unit (2) on a reception side (Q), wherein one of the transmission side and the reception side includes the transmission cable.
An AM modulator / demodulator circuit, wherein a sideband balance correction filter (3) for correcting the balance between the left and right sidebands due to the high frequency attenuation increase characteristic of the bull and for flattening the frequency characteristics after demodulation is inserted.