JPS5831133B2 - stereo modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to controlling the occupied bandwidth of a stereo modulation device.

Conventional stereo modulation devices include the following.

That is, the first signal (hereinafter referred to as R
A signal (referred to as the right signal) and a second signal (hereinafter referred to as the lower signal (referred to as the left signal)) are input, and the carrier wave is phase modulated using the difference signal (L-R) of these input signals. (hereinafter referred to as PM modulation), the sum signal (L+R) of the input signals is
Amplitude modulation with a 0° shifted signal (hereinafter referred to as AM modulation)
It was designed to do so.

In addition, the signal modulated in this way is detected as a sum signal (L-1-R) by an AM detector and a difference signal (L-R) by a PM detector, and the sum and difference are calculated by a matrix circuit. It can be played by

As mentioned above, this stereo modulation method has the feature that the modulation/demodulation configuration is simple, but in order to put this into practical use in radio broadcasting, etc., it is necessary to use PM modulation for the first stage modulation. Special measures are required to suppress the spread of sidebands.

For this reason, a low-pass filter is inserted at the input of the PM modulator.
A method has been proposed to suppress the spread of sidebands by suppressing the spectrum of the modulation signal applied to the modulator, but in order to effectively suppress the spread of sidebands, it is necessary to increase the bandwidth of the low-pass filter. Since it has to be set quite narrowly, stereo characteristics cannot be obtained in a modulation frequency range higher than the cutoff frequency of the low-pass filter, resulting in a problem that wideband stereo broadcasting cannot be performed.

This invention has been made in view of the above points, and takes into consideration the spectrum distribution of music, voice, etc. applied as a modulation signal, and normally modulates the modulation signal faithfully so that the high-frequency components of the modulation signal reach a high peak. The amplitude of the modulation signal is limited according to a certain rule only when the value is indicated, and the degree of modulation is limited, so that it is possible to perform stereo modulation over a wide range of modulation signals while suppressing the spread of the spectrum. The present invention provides a stereo modulation device.

Hereinafter, the present invention will be explained in detail based on the drawings.

Reference numeral 100 denotes a limiting amplification section which limits the peak value of the high-frequency component of a signal applied as a modulation signal according to a certain rule, and 200 a modulation section which receives the output signal of the limiting amplification section 100 and performs stereo modulation. , is.

In the limiting amplification section 100, 111 is an L signal input terminal into which the L signal is input, 112 is an R signal input terminal into which the R signal is input, and 121 is an L signal differentiator which extracts the high frequency component of the L signal. 122 is the R signal differentiator circuit.
13 is a matrix circuit that extracts the difference component and sum signal between the high frequency components of the above signal and the R signal; 151 is a multiplier; 152 is a square circuit; 171 and 172 are The first and second resistors together with the operational amplifier 174 constitute an addition circuit that adds the output signals of the multiplication circuit 151 and the square circuit 152 by a predetermined weight, and 173 is a reference voltage application terminal. in,
When the added voltage reaches a predetermined set value, the operational amplifier 17
4 to set the operating point to output the control signal,
181 and 182 are an L signal delay circuit and an R signal delay circuit, respectively, which give predetermined delays to the L signal and R signal, respectively; 191 and 192 are an L signal limiting amplifier and an R signal limiting amplifier, respectively; Each amplitude limiting amplifier 191, 192 is controlled by a control signal from
A predetermined amplitude limit is applied to the L signal and R signal passing through.

In the modulation section 200, 211 and 212 are an L signal modulation input terminal and an R signal modulation input terminal, which are used to input the L signal to the modulator.
A terminal for inputting signals and R signals, 22 is a matrix circuit, which generates a sum signal (L+R) and a difference signal (L -R), 23 is a carrier signal generation circuit that generates a carrier signal that carries modulated signals (L signal and R signal), and 24 is a PM modulator that generates the carrier signal by using a difference signal (L-R). 25 is a 90° shifter that shifts the sum signal (L+R) by 90°, and 26 is a width modulator that modulates the PM output from the PM modulator 24 using the sum signal (L-1). 27 is an output terminal that performs AM modulation on the received signal.

Next, the operation will be explained.

First, the modulation section 200 will be explained. The multi-IJ rack circuit 22 generates a sum signal (L + R) from the L signal and the R signal.
A difference signal (L-R) is created, and the PM modulator 24 outputs the difference signal (L-R).
After performing PM modulation by L-R), the sum signal shifted by 90° by the 90° shifter 25 is used for AM modulation by the AM modulator 26, so that the modulator output signal (2).

(1) becomes as follows.

Vo(t)=sin(ωt+β5inpt).

(1+αcospt) Between songs, 1 equation; ω/2π: Same wave number of carrier signal P/2π: Same wave number of modulated signal (L signal, R signal) α=K(L+R)(ku1) β=K (LR) (<1) L: L signal amplitude R: R signal amplitude: Modulation index, and L and R signals are placed in the left and right side bands, respectively.

Now, let's consider the expansion of the sideband.

Now, in the sideband spectrum, there is a large amplitude (ω+2
Looking at the p) component, its amplitude coefficient V2P is as follows, and it is possible to understand how it is influenced by the amplitudes of the L and R signals.

Therefore, as a method of suppressing the spread of the sideband, the amplitude coefficient of this (ω+2p) component ■The amplitude of 2P is set to a predetermined value■
.

It is conceivable to keep it to .

A method to embody this idea is to set the amplitude coefficient of the (ω+2p) component ■2P to a predetermined value ■.

When this happens, the L signal and R signal, which are modulation signals, may be suppressed so that the modulation input does not increase any further.

The amplitude limiting section 100 shown in the figure performs amplitude limiting based on this idea to suppress the spread of sidebands.

That is, the matrix circuit 13 generates the (L+R) signal and the (LR,) signal, and the square detector 152 squares the (L-[) signal to generate the 2(L-R,)2 signal. Also, the (L+R) signal and (L-4t) signal are multiplied by the multiplier 1.
By multiplying by 51, we get 2(L+R,)(LR,
) get a signal.

These signals are added in an adder circuit 174 consisting of an operational amplifier 174 and first and second resistors 171 and 172 that perform weighting to obtain a signal corresponding to the above-mentioned 2P, and then connected to the reference signal terminal 173. The reference voltage to be applied is compared with this V2F, and if V2P exceeds this reference voltage, the amplitude of the passing signal of each limiting amplifier 191, 192 is controlled to be limited.

Note that each delay circuit 181 and 182 transmits the L signal and R signal, which are controlled signals, to a delay of the control signal in order to compensate for a control delay due to a time delay until such a limiting control signal arrives at the limiting amplifier. It is delayed depending on the amount.

Note that since this limiting amplifier 100 is under feedforward control, the output level of the limiting amplifier can be set to any of soft limiting, critical limiting, and over limiting.

The above describes a case in which the spread of the spectrum is controlled by focusing on (ω-2p) and applying an amplitude limit so that the spectrum of this frequency component does not exceed a predetermined value, but control that focuses on the spectrum of other frequency components is explained. A circuit for performing this can also be constructed based on the same idea.

In addition to the extraction of high-frequency components using a simple differentiation circuit, specific high-frequency components can be weighted and extracted according to the properties of the modulation signal, and amplitude limiting control can be performed using this method. I can do it.

For example, if this is applied to a modulated signal in which the high frequency component has a low probability but can be at a high level, faithful stereo modulation will be performed in most cases, and the amplitude will be limited at the high frequency peak that occurs with a low probability. The effect is that the occupied bandwidth can be controlled to a predetermined value while applying deep modulation on average.

As described above, according to the present invention, when the difference component between the high frequency components of the first signal and the second signal constituting the stereo signal exceeds a predetermined value, the first and second signals are applied to the modulation section. Since the amplitude is limited, it is possible to provide a stereo modulation device that can perform stereo modulation over a wide range of modulation signals while suppressing spectrum broadening.

[Brief explanation of drawings]

The figure is a block diagram showing an embodiment of the invention. 100...Limiting amplification section, 200...Modulation section, 111...L signal input terminal, 112...
...R signal input terminal, 121...L signal differentiator circuit, 122...R signal input terminal, 13...
... Matrix circuit, 151 ... Multiplier circuit, 152 ... Exponent circuit, 171 ... First resistor, 172 ... Second resistor , 173...
... Reference voltage application terminal, 174 ... Operational amplifier, 181 ... L signal delay circuit, 182 ...
...R signal delay circuit, 191...L signal amplitude control amplifier, 192...R signal amplitude limiting amplifier, 211...L signal modulation input terminal, 212...
...R signal modulation input terminal, 22...M
- IJ Lux path, 23...Carrier signal generation circuit, 24...PM modulator, 27...Modulator output terminal.

Claims (1)

[Scope of Claims] 1. First and second input terminals into which first and second signals constituting a stereo signal are respectively input; first and second input terminals which are applied to the first and second input terminals; first and second limiting amplifiers that pass the signal and limit the level of the signal to be passed to a predetermined value according to the level of the high-frequency component of the difference signal between the first and second signals; and a phase modulator that phase-modulates the carrier signal with a difference signal between the output signals of the second limiting amplifier;
an amplitude modulator that amplitude modulates the output signal of the phase modulator with a sum signal of the output signals of the limiting amplifiers.