JPS63129736A - Stereo signal generator - Google Patents

Abstract

PURPOSE:To eliminate the need for the addition of an amplitude control circuit by providing a multiplier detecting an output level of a stereo mixing signal, and adjusting the subcarrier signal output and a multiplier multiplying an audio signal and a subcarrier signal. CONSTITUTION:An output of a subcarrier signal generating circuit 5 and a control voltage generated by a gain control circuit 11 are multiplied by a multiplier 6 and inputted to a non-inverting amplifier 7 and an inverted amplifier 8. The output signal is fed respectively to multipliers 3, 4, where the signal is multiplied with an audio left channel signal and a light channel signal and the result is fed to an adder circuit 10 together with a pilot signal generated by a pilot generating circuit 9. A gain control circuit 11 generates a control voltage to control the output signal level of the multiplier 6. Thus, it is not required to add a limit amplifier to the outside for the prevention of overmodulation, and the level if limited to an amplitude level of a desired stereo mixing signal even when an excess input is left/light channels with inexpensive and simple circuit constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pilot tone type stereo signal generator for FM broadcasting.

[Conventional technology]

Conventionally, this type of stereo signal generator has a left channel input terminal 1 to which an audio left channel signal is applied, and a right channel input terminal 2 to which an audio right channel signal is applied, as shown in FIG. The signals are applied to analog switch 14 and the right channel signal is applied to analog switch 17. On the other hand, the 38 kHz pulse subcarrier signal generated in the subcarrier signal generation circuit 13 is applied to the analog switch 14 via the pulse non-inverting circuit 15, and at the same time performs on/off control of the analog switch 14. After the phase of the signal is inverted by 180 degrees by 16, it is applied to analog switch 17 to control on/off of analog switch 17. The left channel signal and the right channel signal are alternately switched by each analog switch 14.17 controlled by the subcarrier signal, and the adder circuit 17
is applied to The 19 kHz pilot signal generated by the pilot signal generation circuit 9 is applied to the adder circuit 10 together with the above-mentioned left and right channel signals to form a mixed signal. This mixed signal passes through a low-pass filter 18 to remove unnecessary harmonic components, and then is sent to the output terminal 12 to become a stereo composite signal.

[Problem that the invention seeks to solve]

In the conventional stereo signal generator described above, both the left and right channel signals of the audio signal are added after being switched by an analog switch controlled by the pulsed subcarrier signal. There is no need for a low-pass filter to remove unnecessary harmonic components generated by In order to prevent deterioration of the degree of separation of the stereo composite signal, it is necessary to prevent the deterioration of the phase/amplitude characteristics of the low-pass filter up to the high frequency range (53 kHz) of the stereo composite signal. This has the disadvantage that the compensation circuit for preventing deterioration is complicated and expensive.

Furthermore, adding an amplitude control circuit to keep the output level constant to prevent overmodulation requires an external preparation, which is complicated and also increases the price.

[Means for solving problems]

The stereo signal generation device of the present invention includes a subcarrier signal generation circuit that generates a 38kHz sine wave, a multiplier that detects the output level of a stereo mixed signal and adds or subtracts the subcarrier signal output, and a subcarrier signal generation circuit that generates a 38kHz sine wave. It has second and third multipliers that multiply the signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

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

The figure shows a left channel input terminal 1 that applies an audio signal, a right channel input terminal 2, a subcarrier signal generation circuit 5, and a gain control circuit 11 that detects the amplitude level of a stereo mixed signal and generates a control voltage. , a multiplier 6 that multiplies this control voltage by a subcarrier signal, a non-inverting amplifier 7 and an inverting amplifier 8 that non-inverting and inverting amplifying the multiplier output, respectively, and a sum of the output of the non-inverting amplifier and the control voltage. Multiplier 3 that multiplies the left channel signal
, a multiplier 4 that multiplies the right channel signal by the sum of the output of the inverting amplifier and the control voltage, a pilot signal generation circuit 9 that generates a 19kHz pilot signal, and multipliers 3 and 4.
and an adding circuit 10 that adds the outputs of the pilot signal generating circuit and an output terminal 12 that outputs a stereo mixed signal.

Now left channel signal A-L, right channel signal A@
The R subcarrier signal is sinωt (ω=2K・38K0
3), the pilot signal is υpsinωt/2, the amplitude level of the stereo mixed signal at the output terminal is A, the magnitude of the control voltage generated by the gain control circuit is a, and the stereo mixed signal level is B'(A'<C< Assuming that the amplitude is limited to C when B'), sinωt generated by the subcarrier signal generation circuit and the control voltage a generated by the gain control circuit 11 are multiplied by the multiplier 6, and the following equation is obtained. % Formula % (4) The output of the non-inverting amplifier 7 and a are added to obtain the following formula.

J=a(1+sinωt) ・Old...
(5) Similarly, the output of the inverting amplifier 8 and a are added to obtain the following equation.

K= a(1-sinωt) −=
-(6) The signals given by (5) and (6) are applied to multipliers 3 and 4, respectively, and are multiplied by the audio left channel signals A and L and the right channel signals A and R to obtain the following equations.

M=A @L −J =A @L a a (,1+sinωt)
-----・-('!') N=A@R-=A m R11a (1-sinωt')
-.-(8) The signals given by the above equations (7) and (8) are applied to the adder circuit 10 together with the pilot signal generated by the pilot generation circuit 9 to obtain the following equation.

Comp, 4=M+N+t7psin a+t/2=A
*a(L0R+(L-R)sin ωt)+tJpsi
nQ+t/2...(9) Since υp〈kuA-a, A-a=A', Comp, 4=A'(L + R + (L-R) sin ωt
)+υpsinmt/2... (10) It is given by:

Next, when the audio signal becomes B/A times (B>A)
Considering, similarly, the stereo mixed signal output Comp
, 5 are given by the following equation.

Comp, 5=B'(L+R(LR) sinca+t
)+t7 psin ωt/2B'> C, so the gain control circuit 11 generates a control voltage with a magnitude of a/D and lowers the output signal level of the multiplier 6 (however, a(b), that is, the multiplier 3.4 input has 0=-(1+sinωt)...
...-(12)P = -(1-sin6)t)
-=-(13) is not obtained, and the output of multipliers 3 and 4 is the stereo mixed signal output, +υpsinωt/2 -------・(16), Comp, 6=C (L+R+(L-R) sin (4
7t]+t7psin(a+t/2 is obtained.

〔Effect of the invention〕

As explained above, the present invention does not require the addition of an external limiting amplifier to prevent overmodulation, and has a simple and inexpensive circuit configuration, so that even if an excessive input is applied to the left and right channels, the desired output can be maintained. This has the effect of being able to limit the amplitude level of the stereo mixed signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an amplitude limiter self-selecting stereo signal generator according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional stereo signal generator. In the figure, 1... Left channel input terminal, 2
......Right channel input terminal, 3...Multiplier, 4...Multiplier, 5......Sub medium signal generation circuit, 6...・Multiplier, 7...
...Non-inverting amplifier, 8...Inverting amplifier, 9...
... Pilot signal generation circuit, 10 ... Addition circuit, 11 ... Gain control circuit, 1
2... Output terminal, 13... Bias circuit, 14... Bias circuit, 15...
Amplitude limiting amplifier left channel input terminal, 16...
・Amplitude limiting amplifier right channel input terminal, 17...
... Multiplier, 18 ... Multiplier, 19 ...
・Kane control circuit.

Claims (1)

[Claims] a first multiplier generated by a gain control circuit (described later) that controls the level of a subcarrier signal using a control voltage; and a second multiplier that multiplies one of the left or right channel signals by the output of the first multiplier. a third multiplier for multiplying the other signal of the channel signal by a signal having a phase different by 180 degrees with respect to the output of the first multiplier.
a multiplier, a pilot signal generator, an adder for adding the output of the pilot signal generator and each output of the second and third multipliers, and detecting the amplitude level of the adder output to A stereo signal generator comprising: a gain control circuit that generates a control voltage.