JP2988375B2 - FM communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM communication system, and more particularly to a millimeter-wave band FM communication system in which an input signal is pre-emphasized and FM-modulated on a transmitting side and de-emphasized after FM demodulation on a receiving side. About.

[0002]

2. Description of the Related Art Generally, in the FM modulation / demodulation system, noise which is added to a signal in a transmission line and appears as a demodulator output and which increases in proportion to the frequency is generated. Also, when transmitting voice and video using the FM communication system, the high frequency components included in the input signal are considerably small. Therefore, by emphasizing and modulating the high frequency component of the input signal in advance and attenuating the high frequency component during demodulation,
S / N (signal-to-noise ratio) of the transmission signal at the receiver output
A method called emphasis is used to improve the image quality.

FIG. 7 shows a configuration of a conventional FM communication system using emphasis. Referring to FIG. 7, a transmitter 1 includes a pre-emphasis circuit 12 for pre-emphasis of an input signal SIN to be transmitted, and an FM modulator 13 for FM-modulating the pre-emphasized signal.

[0004] The receiver 2 comprises an FM demodulator 23 for demodulating a received FM signal, and a de-emphasis circuit 22 for de-emphasizing the FM demodulated output.

FIG. 8 shows the relationship between a transmission signal and noise in an FM communication system using the emphasis system shown in FIG. 7 in baseband. FIG. 8A shows the relationship between the frequency and the level of the input signal SIN of the transmitter 1 at the point a in FIG.

FIG. 8B is a diagram showing a frequency-level relationship between the signal SMOD after pre-emphasis and the phase noise NLO of the oscillator used in the FM modulator 13 at the point b in FIG. FIG. 8C is a diagram showing the frequency versus level relationship of the FM demodulated output (SDEM, NLO, NFM) at point c in FIG. 7 to which triangular noise NFM generated in the FM transmission line is added.

FIG. 8D is a diagram showing the frequency versus level relationship between the output signal SOUT after de-emphasis and the noise NTOTAL at point d in FIG.

As is clear from the characteristic of FIG. 8D, the triangular noise N added on the transmission line by the emphasis process
The high frequency range of FM can be compressed, and S / N of transmission signal
Will be improved.

FIG. 9 is a block diagram of another conventional FM communication system, which is disclosed in JP-A-57-31275. In FIG. 9, the same parts as those in FIG. 7 are indicated by the same reference numerals.

[0010] Referring to FIG. 9, in a transmitter 1, a compression circuit 14 is provided before a pre-emphasis circuit 12.
To compress only the large amplitude and high frequency components of the input signal. Then, in the receiver 2, the decompression circuit 24
The decompression process is performed by. As a result, the signal distortion can be reduced, and the S / N is improved by increasing the emphasis amount.

[0011]

However, even if the emphasis method as shown in FIG. 7 is applied to a millimeter-wave FM communication system, the S / N cannot be improved.

The reason is that the oscillator used in the FM modulator for the millimeter wave has the limitation of the oscillating element and the number of multiplication stages is large, so that the phase noise of the millimeter wave is overwhelmingly compared with the VHF and the microwave. large. For this reason, regarding the noise at the output of the de-emphasis circuit of the receiver, triangular noise is dominant in VHF and microwaves, and the phase noise of the oscillator was not a problem, whereas in millimeter waves, the phase noise of the oscillator was ignored. Can not. In particular, noise that increases in inverse proportion to the frequency in the low frequency region called l / f noise is emphasized as shown in FIG.
As a result, the S / N deteriorates.

In the emphasis method using compression / expansion as shown in FIG. 9, only the distortion of the high frequency region of the input signal is improved, but the low frequency region is not affected. There is no effect on the reduction.

An object of the present invention is to improve the S / N by reducing the amount of emphasis in the low frequency region in an FM communication system in which the low frequency noise of the oscillator is large, such as in the millimeter wave band. To provide an FM communication system.

According to the present invention, there is provided a transmitter configured to supply an input signal to be transmitted to FM modulation means via a pre-emphasis means, and to receive a transmission signal from the transmitter.
FM demodulation and de-emphasis the demodulated output
FM communication system including receiver having emphasis means
A low frequency of an input signal in the transmitter.
Providing low-frequency emphasis means for emphasizing components,
To reduce the low frequency component of the output of the de-emphasis means.
Low-frequency attenuation means are provided, and these low-frequency emphasis means and low-frequency
The transmission at the output of the receiver by means of
The low frequency part of the phase noise of the FM modulation means of the machine to FM transmission
The FM communication system is characterized in that the noise is smaller than the triangular noise .

The low-frequency emphasis means is cascaded before the pre-emphasis means or connected in parallel with the pre-emphasis means.

[0017]

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be described. F
In the low frequency region where the phase noise of the M modulator is a problem,
By emphasizing and modulating the input signal and attenuating it after demodulation, it is possible to prevent the phase noise from being emphasized after FM demodulation even when emphasis is performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention, and the same parts as those in FIGS. 7 and 9 are denoted by the same reference numerals.
Referring to FIG. 1, in a transmitter 1, an input signal SIN to be transmitted is input to a pre-emphasis circuit 12 via an LPF (low-pass filter) 11, and a signal subjected to pre-emphasis processing is input to an FM modulator 13. FM modulation is performed.

In the receiver 2, the FM demodulator 23
The demodulated output subjected to the M demodulation is subjected to de-emphasis processing by a de-emphasis circuit 22, and is input to an HPF (high pal filter) 21. The output of the HPF 21 is the reception output SOUT.

The characteristic of the LPF 11 in the transmitter 1 is selected so that the transfer characteristic in the low frequency region increases as the frequency decreases. Specifically, at the demodulated output (point c in FIG. 1) of the demodulator 23 shown in FIG.
In a frequency range where the phase noise NLO of No. 3 is larger than the triangular noise NFM, the transfer characteristic of the LPF 11 is increased.

The output of the LPF 11 is applied to the FM modulator 13 with its high-frequency region emphasized by the pre-emphasis circuit 12 and transmitted. FIG. 2A shows L in the transmitter 1.
FIG. 3 is a diagram illustrating a relationship between a frequency and a transmission gain between a PF 11 and a pre-emphasis circuit 12.

On the other hand, in the receiver 2, the output of the FM demodulator 23 is supplied to the de-emphasis circuit 22 to attenuate the high-frequency region to reduce the triangular noise added on the transmission line. HPF with reverse characteristics
By compressing the low-frequency component at 21, the component ΔN corresponding to the phase noise of the modulator 13 can be eliminated as shown in FIG.

FIG. 2B is a diagram showing the relationship between the frequency and the transmission gain of the de-emphasis circuit 22 and the HPF 21 in the receiver 2. FIGS. 3A and 3B are diagrams showing the transmitter 1.
FIG. 4 is a diagram showing each frequency-to-level relationship between a transmitter input signal SIN (point a) and a modulator input signal (point b) in FIG.

FIG. 4A is a circuit diagram showing an example of the LPF 11, which includes an operational amplifier (operational amplifier) 3 and resistors R1 to R1.
This is an active low-pass filter including R4 and a capacitor C1. FIG. 4B is a circuit diagram illustrating an example of the HPF 21. The operational amplifier 4 includes resistors R5 to R8.
And a capacitor C.

It is needless to say that a passive filter configuration using only passive elements may be used in addition to the active filter configuration.

FIG. 5 is a block diagram of another embodiment of the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals. FIG.
In the embodiment, the LPF 11 is connected to the pre-emphasis circuit 12.
5, the LPF 11 is connected in parallel with the pre-emphasis circuit 12 in the present embodiment shown in FIG.

The transfer characteristics of the LPF 11 are shown in FIG.
As shown in (2), the transfer characteristic in the low frequency region is selected so as to increase as the frequency decreases. Specifically, in the demodulated output of FIG. 3C, the phase noise NLO of the modulator is
The transfer characteristic of the LPF 11 is selected so as not to be larger than FM.

In each of the above embodiments, the LPF 11
Although the pre-emphasis circuit 12, the HPF 21, and the de-emphasis circuit 22 are independent circuit blocks, they may be one filter having the same transfer characteristics.

[0031]

According to the present invention, emphasis is suppressed in a low frequency region where the phase noise of the FM modulator is a problem. Therefore, S / S is particularly required in a communication system where phase noise is a problem such as millimeter wave FM communication. There is an effect that N can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

2A is a diagram showing a transfer gain characteristic from the input of the transmitter of FIG. 1 to the FM modulator, and FIG. 2B is a diagram showing a transfer gain characteristic from the demodulator to the output of the receiver of FIG. 1; It is.

FIGS. 3A to 3D are diagrams respectively showing baseband characteristics at points a to d in FIG. 1 as frequency versus level characteristics.

FIG. 4A is a circuit diagram showing an example of the LPF 11 of FIG. 1;
2B is a circuit diagram illustrating an example of the HPF 21 in FIG.

FIG. 5 is a block diagram of another embodiment of the present invention.

6 is a diagram showing a transfer gain characteristic from an input of the transmitter of FIG. 5 to an FM modulator.

FIG. 7 is a block diagram illustrating an example of a conventional FM communication system.

8A to 8D are diagrams respectively showing baseband characteristics at points a to d in FIG. 7 as frequency versus level characteristics.

FIG. 9 is a block diagram showing another example of the conventional FM communication system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmitter 2 Receiver 3 and 4 Operational amplifier 11 LPF 12 Pre-emphasis circuit 13 FM modulator 21 HPF 22 De-emphasis circuit 23 FM demodulator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 1/04 H04B 1/26 H04B 1/62

Claims (7)

(57) [Claims] 1. A transmitter adapted to supply an input signal to be transmitted to FM modulation means via pre-emphasis means.
Receiving the transmission signal from the transmitter and performing FM demodulation.
De-emphasis hand to de-emphasize the demodulated output of
An FM communication system comprising a receiver having stages.
In the transmitter, a low-frequency component of the input signal is emphasized.
Low-frequency emphasis means is provided;
Low-frequency attenuation that attenuates the low-frequency component of the output of the emphasis means
Means provided by these low-frequency emphasis means and low-frequency attenuation means.
At the output of the receiver, the FM modulation of the transmitter
The low-frequency part of the phase noise of the stage
An FM communication system characterized in that it has a small size . 2. The FM communication system according to claim 1, wherein said low-frequency emphasis means is cascaded before said pre-emphasis means. 3. The FM communication system according to claim 1, wherein said low-frequency emphasis means is connected in parallel with said pre-emphasis means. 4. The FM according to claim 1, wherein the low-frequency emphasis unit is a low-pass filter.
Communications system. 5. The low-frequency attenuation means is a high-pass filter.
FM according to any one of claims 1 to 4, characterized in that there
Communications system. 6. The low-frequency emphasis means and the low-frequency attenuation means are each
The FM communication system according to any one of claims 1 to 5 , wherein the FM communication system is provided in each baseband unit . 7. The FM communication system according to claim 1, wherein the FM communication system is used for FM communication in a millimeter wave band .