JPS60212047A - Modulator and demodulator for frequency division multiplex communication - Google Patents

Abstract

PURPOSE:To eliminate the need for adjustment at each channel through simple constitution by inputting a frequency division multiplex signal obtained through modulation subcarriers of each channel of the same level to a pre-emphasis circuit and applying pre-emphasis processing so that the level of the subcarrier of high frequency is increased. CONSTITUTION:Outputs (Fig. b)of stereo frequency modulators 10A, 10B...10N are formed into the same level while its level is not adjusted at each channel. Outputs of the stereo frequency modulators 10A, 10B...10N are synthesized into a frequency division multiplex signal as shown in Fig. (c) by a synthesizing circuit 12. The output of the synthesizing circuit 12 is inputted to a preemphasis circuit 14, where it is applied with pre-emphasis processing as shown in Fig. (d) so that the voltage level of the subcarrier having a high frequency is increased. Concretely, the pre-emphasis processing is applied so that the ratio of thevoltage level of each subcarrier signal and the level of the same frequency of a triangle noise N at frequency demodulation is nearly the same.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a modulation device and a demodulation device for frequency division multiplex communication, which can be used in multi-channel FM stereo audio signal transmission/reception systems, 'CAT'V systems, optical communication systems, etc. It is related to.

In conventional frequency division multiplexing communication, the subcarrier assigned to that channel is frequency-modulated or amplitude-modulated using the input signal for each channel, and the modulated subcarriers are synthesized to determine the frequency. Create a division multiplexed signal,
The frequency-division multiplexed signal is used to frequency-modulate the main carrier wave and transmit it. On the other hand, on the receiving side, the main carrier wave is frequency demodulated, and the sub-carrier waves are regenerated through a filter for each channel. Reproduce the signal from.

As is well known, when demodulating a frequency modulated signal, so-called triangular noise, which is unique to frequency modulation, cannot be avoided. Therefore, if the main carrier is frequency modulated with a frequency division multiplexed signal obtained by combining modulated subcarrier signals of the same voltage level, the S/N ratio (signal ratio noise ratio) between channels. That is, the S/N ratio of a reproduced signal of a channel whose subcarrier frequency is high is degraded.

Therefore, in conventional frequency division multiplexing communication, before frequency division multiplexing, the level of the modulated subcarrier signal of each channel is weighted according to the frequency of the subcarrier. was adjusting the output level. Specifically, the output level of each channel modulator is adjusted, or the output of each channel modulator is supplied to a combining circuit that includes an adjustment section that weights the signal level of each channel.

Also, if you play back the frequency division multiplexed signal with level weighting for each channel as it is,
The signal level of the high frequency channel will be high. Therefore, after demodulation, the level of the demodulated signal was adjusted for each channel to cancel out the weighting.

However, adjusting the output level of each channel modulator or using a synthesis circuit that includes an adjustment section that weights the signal level of each channel is cumbersome and increases the complexity of the device. , undesirable. Furthermore, it is also complicated to adjust the level for each channel during demodulation.

Therefore, the present invention solves the above-mentioned conventional drawbacks when frequency modulating a main carrier wave by a frequency division multiplexed signal synthesized from signals of a plurality of channels. It is an object of the present invention to provide a modulation device for frequency division multiplex communication having a pre-emphasis circuit that does not require adjustment for each frequency division multiplex communication.

Furthermore, the present invention solves the above-mentioned conventional drawbacks when frequency demodulating a signal frequency modulated by a frequency division multiplexed signal, and provides a de-emphasis circuit that has a simple configuration and does not require adjustment for each channel. It is an object of the present invention to provide a demodulator for frequency division multiplex communication having the following.

According to the present invention, there is provided a channel modulator for each of a plurality of channels, which modulates the subcarrier assigned to each channel with a human signal and outputs a modulated subcarrier signal of the same voltage level. and a pre-emphasis circuit that receives a frequency division multiplexed signal obtained by combining the outputs of each channel modulator and processes it so that the voltage level of a high-frequency subcarrier becomes high; A modulation device for frequency division multiplexing communication is provided, which is characterized by comprising a frequency modulator that frequency modulates a main carrier wave.

As described above, by inputting the frequency division multiplexed signal obtained by synthesizing the modulated subcarriers of each channel at the same level to one pre-emphasis circuit, there is no need to adjust the level for each channel. Pre-emphasis processing can be performed to raise the level of the subcarrier.

Further, according to the present invention, there is provided a frequency demodulator that receives a frequency modulated signal using a frequency division multiplexed signal and demodulates the frequency, and a frequency demodulator that receives the output of the frequency demodulator to lower the level of a high frequency component. a de-emphasis circuit for processing the de-emphasis circuit; a filter provided for each channel to receive the output of the de-emphasis circuit and output the frequency component of the subcarrier of each channel; A demodulator for frequency division multiplexing communication is provided, comprising a channel demodulator that receives the output of the filter and regenerates the signal of the subcarrier of the channel.

In addition, in this way, before the frequency demodulated signal is supplied to the filter of each channel, the frequency demodulated signal, that is, the signal in the frequency division multiplexed state is supplied to one de-emphasis circuit. De-emphasis processing can be performed to lower the level of high frequency components without the need to adjust the demodulated subcarrier level.

Embodiments Hereinafter, embodiments of a modulation device and a demodulation device for frequency division multiplex communication according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a modulation device for frequency division multiplex communication according to the present invention. A stereo frequency modulator 10A constitutes a channel modulator.

10B... ION is provided. When these stereo frequency modulators 1□OA, IOB...ION handle stereo audio signals as input signals, they receive R and L signals as shown in FIG. 1(a), or handle audio multiplexed signals. In this case, the main audio signal and the sub audio signal are received and synthesized,
This frequency modulates the subcarrier. However, an amplitude modulator may also be used as the channel modulator.

Each stereo frequency modulator 10A, IOB...ION
The frequencies fn of the subcarriers are different as shown in (c) of FIG. and each stereo frequency modulator 10
As can be seen from FIG. 1(b), the outputs of A, IOB, . . . ION are at the same level without being adjusted for each channel.

Such a stereo frequency modulator 10A, ], OB...
The output of IOH is converted to (C) in FIG.
), the signals are combined into a frequency division multiplexed signal.

The output of the synthesis circuit 12 is input to a pre-emphasis circuit 14, and is subjected to pre-emphasis processing so that the voltage level of the high-frequency subcarrier becomes high, as shown in FIG. 1(d). Specifically, the ratio between the voltage level of each subcarrier signal and the level of the same frequency of triangular noise N during frequency demodulation, that is, the S/ of each subcarrier during frequency demodulation.
Pre-emphasis processing is performed so that the N ratios are almost the same.

The output of the pre-emphasis circuit 14 is input to the frequency modulator 16, and the main carrier wave is frequency-modulated by the frequency division multiplexed signal, resulting in a frequency-modulated signal with a frequency spectrum as shown in FIG. 1(e). It is formed. The output of the frequency modulator 16 is fed to an amplifier 18 and then to an output drive circuit (not shown).

Here, pre-emphasis will be considered.

S/N ratio (signal-to-noise ratio) for each channel signal
When the subcarrier is frequency modulated, S/N=C/N+IFII (dB:] where C/N: carrier-to-noise specification [dB] Δf: maximum frequency deviation of subcarrier (++z) fh:
The highest frequency of the input (audio) signal for each channel [1lz
) B: Occupied bandwidth of frequency modulation signal [:tlz]fn
:Nth channel subcarrier frequency (llz)△F mouth
: The maximum frequency deviation (peak-peak value) of the main carrier by the subcarrier of the nth channel [■z]. In the above equation, factors other than fn and ΔFn are common to all channels.

Therefore, in order to make the S/N ratio of each channel the same, it is necessary to set ΔFn for the subcarrier frequency fn of each channel so that ΔFn/fn becomes equal.

This is because in frequency modulation, the noise spectrum is triangular noise, and the higher the frequency, the larger the noise component becomes.
This indicates that it is necessary to correspondingly increase the voltage level of the high-frequency subcarrier to increase the maximum frequency deviation of the main general transmission.

Here, ΔFn is the voltage level V of the modulated subcarrier of the nth channel when frequency division multiplexing each subcarrier.
Since it is proportional to n, pre-emphasis processing is to adjust the voltage level of the subcarrier of each channel to '' before frequency division multiplexing so that ΔFn/fn is constant. Immediately before multiplexing, an adjustment circuit was provided for each channel to adjust the voltage level of the modulated subcarrier.

However, in the present invention, instead of providing a subcarrier voltage level adjustment circuit for each channel, the subcarriers of each channel at the same voltage level are synthesized and frequency division multiplexed, and then before the main carrier is frequency modulated. In addition, a pre-emphasis circuit 14 weights the voltage level of the subcarrier of each channel.

Specifically, a pre-emphasis circuit 14 whose relative frequency characteristics are expressed as follows may be used. However, the unit of f is (MHz).

For example, as shown in FIG. 2, the pre-emphasis circuit 14 includes a parallel connection of a capacitor C and a resistor R1 connected between an input terminal IN and an output terminal 0LIT, and an output terminal OU
RC consisting of a resistor R2 connected between T and ground
It can be configured with a compensation network.

The transfer function of the circuit in Figure 2 is: However, τl = R, C A: constant It is expressed as

Further, the theoretical frequency characteristics of the pre-emphasis circuit 14 are as shown in FIG.

From the graph in FIG. 3, in the frequency division multiplex modulation device in FIG. 1, the capacitor and resistance values of the pre-emphasis circuit 14 in FIG. 2 are appropriately selected for all frequency division multiplexed subcarriers. It can be seen that this allows the necessary pre-emphasis processing.

Next, the case of eight audio channels will be specifically considered.

Considering the frequency arrangement of the audio subcarrier signals of the 8 channels to minimize the influence of distortion in the transmission system and to fit them within the given band, the frequency f6 of the 8th channel is set to 6.
When the frequency is 5 MHz, the frequency of each channel is selected as follows.

1st channel: L = 2.10MHz 2nd channel 1st
Channel: = 2.45MHz 3rd channel 1st channel: = 2.95MHz 4th channel 1st channel: 3
．． 35MHz 5th channel 1st channel: = 3.95M
Hz 6th channel 1st channel: "" 4.85M) Iz
7th channel: f7 = 5.60MHz 8th channel 1st channel: 6.50M1lz When frequency-division multiplexing and frequency modulating the 8-channel subcarrier with this frequency arrangement, the RC circuit in Figure 2 has the following problems. Then, τ, =R,C -1/2rr (μsec) -0,159μ5e
The values of R11R2 and C are selected so as to satisfy c-1/(2πX12)[μSeC] =0.0133μseC. The pre-emphasis characteristic at that time is shown by a solid line in FIG.

In this case, the deviation of the S/N ratio between each channel is 1.2d.
I was able to get it within B.

FIG. 5 is a block diagram showing an embodiment of a demodulator for frequency division multiplex communication according to the present invention. Receiving device (not shown)
The received signal from the frequency demodulator 2 is passed through an amplifier 20 to
2 and is frequency demodulated. If the received signal is a frequency division multiplexed frequency modulated wave and has been subjected to pre-emphasis processing, the frequency demodulated signal is as shown in FIG.
The frequency spectrum is as shown in a). On the other hand, the noise spectrum at the time of frequency demodulation is as shown in (c) of FIG. It will be seen that the ratio of the level of each carrier signal to the noise level of the same frequency is the same for all carriers.

The frequency-demodulated frequency-division multiplexed signal from the frequency demodulator 22 is supplied to a de-emphasis circuit 24, and the level is adjusted so that the voltage level of each subcarrier becomes the same.

The output of the de-emphasis circuit 24 is supplied to filters 26A, 26B, . . . , 26N for each channel, and only the subcarrier of the corresponding channel is extracted.

The output of each filter 26A, 26B, . . . 26N is connected to a channel demodulator 28A, 28B, . . . 28N, and the original signal is reproduced. When the subcarrier is frequency modulated, the channel demodulators 28Δ, 28B...2
8N is a frequency demodulator, while when the subcarrier is amplitude modulated, channel demodulators 28A and 28B.
-28N is an amplitude demodulator. Furthermore, when the input signal of the frequency division multiplexed modulated signal is a stereo audio signal, the channel demodulators 28Δ, 28B, . . . , 28N output R and L signals as shown in FIG. 5(d). Also,
When the manual signal of the frequency division multiplexed modulation signal is an audio multiplexed signal, channel demodulators 28A, 28B...28N
outputs a main audio signal and a sub audio signal.

As described above, before supplying the frequency demodulated signal to the filter of each channel, it is necessary to adjust the demodulated subcarrier level for each channel by supplying the frequency demodulated signal to one de-emphasis circuit. Instead, de-emphasis processing can be performed to lower the level of high frequency components.

The de-emphasis circuit 24 may have frequency characteristics opposite to those of the pre-emphasis circuit 14 of the modulation device shown in FIG. 1 described above. That is, if the characteristics of the pre-emphasis circuit 14 are as shown by the solid line in FIG. 4, the de-emphasis circuit 24 is configured to have frequency characteristics as shown by the dotted line in FIG.

FIG. 6 is a circuit diagram showing an example of the de-emphasis circuit 24. The de-emphasis circuit 24 connects a resistor R3 between an input terminal IN and an output terminal OUT, and connects a resistor R3 between an input terminal IN and an output terminal OUT.
It can be constituted by an RC compensation network in which a series connection of a capacitor c1 and a resistor R4 is connected between the capacitor c1 and the ground.

Effects of the Invention As is clear from the above explanation, the modulation device and demodulation device for frequency division multiplex communication according to the present invention perform pre-emphasis processing and de-emphasis processing on frequency division multiplexed signals, respectively. Therefore, there is no need to adjust the subcarrier level for each channel, and the configurations of the modulation device and demodulation device are simplified.

[Main reference number]

10A, IOB...ION stereo frequency modulator: 1
2: Synthesis circuit, 14: Emphasis circuit: 16: Frequency modulator, 18: Amplifier 18: 20: Amplifier, 22:
Frequency demodulator: 24: De-emphasis circuit, 26A, 26B...26N = filter, 28A, 28B
...28N two-channel demodulator Patent applicant: Sumitomo Electric Industries, Ltd. Agent: Masahiko Arai, patent attorney Figure 2 However: T=CR. α・-C'R, +1'2U. 1985, Commissioner of the Japan Patent Office, Mr. Kazuo Wakasugi ■, Indication of the case, 1981 Patent Application No. 67866 2,
Title of the invention Frequency division multiplex communication modulator and demodulator 3, relationship to the amended case Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (21)
3) Sumitomo Electric Industries Co., Ltd. 4, Agent 6, Subject of amendment Claims column 7 of the specification, Contents of amendment Claims (1) Provided for each of a plurality of channels, each with an input signal A channel modulator that modulates the subcarrier assigned to the channel and outputs a modulated subcarrier signal of the same voltage level, and a frequency division multiplexed signal obtained by combining the output of each channel modulator, Modulation for frequency division multiplexing communication, comprising: a pre-emphasis circuit that processes the sub-carrier so that the voltage level becomes high; and a frequency modulator that receives the output of the pre-emphasis circuit and modulates the frequency of the main carrier. Device. (2) The pre-emphasis circuit includes a parallel connection body of a capacitor and a resistor connected between an input end and an output end;
2. The modulation device for frequency division multiplex communication according to claim 1, characterized in that it is constituted by an RC circuit comprising a resistor connected between the output end and ground. (3) The modulation device for frequency division multiplex communication according to claim 1 or 2, wherein the channel modulator is a frequency modulator or an amplitude modulator. (4) A frequency demodulator that receives and demodulates the frequency of a frequency-modulated signal using a frequency division multiplexed signal, and a de-emphasis system that processes the output of the frequency demodulator so that the level of high frequency components is lowered. a circuit, a filter provided for each channel to receive the output of the de-emphasis circuit and output the frequency component of the subcarrier of each channel, and a filter provided attached to each filter to receive the output of the filter. 1. A frequency division multiplexed signal demodulator comprising: a channel demodulator for reproducing a subcarrier signal of the channel. (5) The de-emphasis circuit is composed of an RC circuit consisting of a resistor connected between the human power end and the output end, and a series circuit of a capacitor and resistor connected between the output end and the ground. A demodulator for frequency division multiplex telecommunication according to claim 4, characterized in that: (6) The modulation device for frequency division multiplex communication according to claim 4 or 5, wherein the channel demodulator is a frequency demodulator or an amplitude demodulator.

Claims (1)

[Claims] (1) A channel modulator that is provided in each of a plurality of channels and that modulates the subcarrier assigned to each channel with an input signal and outputs a modulated subcarrier transmission signal of the same voltage level. and a pre-emphasis circuit that receives a frequency division multiplexed signal obtained by combining the outputs of each channel modulator and processes it so that the voltage level of a high-frequency subcarrier becomes high; 1. A modulation device for frequency division multiplex communication, comprising a frequency modulator that frequency modulates a main carrier wave. (2) The pre-emphasis circuit includes a parallel connection body of a capacitor and a resistor connected between an input end and an output end;
2. The modulation device for frequency division multiplex communication according to claim 1, characterized in that it is constituted by an RC circuit comprising a resistor connected between the output end and ground. (3) The modulation device for frequency division multiplex communication according to claim 1 or 2, wherein the channel modulator is a frequency modulator or an amplitude modulator. (4) A frequency demodulator that receives and demodulates the frequency of a frequency-modulated signal using a frequency division multiplexed signal, and a de-emphasis system that processes the output of the frequency demodulator so that the level of high frequency components is lowered. a circuit, a filter provided for each channel to receive the output of the de-emphasis circuit and output the frequency component of the subcarrier of each channel, and a filter provided attached to each filter to receive the output of the filter. A demodulator for frequency division multiplexing communication, characterized in that the de-emphasis circuit comprises a channel demodulator that reproduces the signal of the subcarrier of the channel using the de-emphasis circuit. The demodulation for frequency division multiplexing communication according to claim 4, characterized in that the demodulation for frequency division multiplexing communication is constituted by an RC circuit consisting of a resistor connected to the output end and a capacitor connected between the output end and the ground. (6) The modulation device for frequency division multiplex communication according to claim 4 or 5, wherein the channel demodulator is a frequency demodulator or an amplitude demodulator.