JPS5831674A - Fm modulation input circuit of rf converter - Google Patents

Abstract

PURPOSE:To compensate modulation degree without disturbing pre-emphasis characteristic, by separating a level adjusting circuit and a pre-emphasis circuit. CONSTITUTION:An audio input signal given to an input terminal 20 is inputted to a level adjusting circuit 22 for level adjustment. The input signal with level adjustment is applied to a non-inverting terminal of an amplifier 30 via a coupling capacitor 28. The amplifier 30 is provided with a feedback circuit 32 which negatively feeds back the amplified output to the input side and the feedback circuit 32 is provided with a pre-emphases circuit 34. The amplified output of the amplifier 30 provided with the pre-emphasis characteristics at the circuit 34 is applied to an FM modulation circuit 42 for FM modulation.

Description

[Detailed Description of the Invention] The present invention relates to an FM modulation input circuit for an RF converter,
41 relates to the modification of the input circuit that corrects the level, high frequency components, etc. of the input signal to the FM modulation circuit that performs FM modulation of the audio signal, etc.

In the video tape recorder f, the RF converter converts the received signal or playback signal into the form of television radio waves and outputs it,
The RF puncher is equipped with an FM modulation circuit. Figure 1 shows the circuit configuration of the input section including this FM modulation circuit. In Figure 0, the audio input signal applied to the input terminal 2 passes through a pre-emphasis circuit 4, The audio input signal with emphasized frequency components is supplied to the FM modulation circuit 10 via the converter 196 and the buffer amplifier 8v.

An FM modulated output is taken out from the output terminal 12.

General KFM modulation j[[ will cause variations, but to correct this, there is a method of adjusting the input level of the input audio signal, or a method of adjusting the constant #! of FM modulation 1lIa path 10. A method of changing L is adopted. In this case, the input level is adjusted by using the resistor 14 and variable resistor of the pre-emphasis circuit 4 and adjusting its value. However, although this method is simple, it may deteriorate the Grien 7 assist characteristics depending on the modulation depth specifications.

That is, the pre-emphasis characteristic shown in the first intention is determined by the six values R14, R1, and 01 of the resistor 14, 16 and capacitor 18 of the pre-emphasis circuit 4, and the time constant 111
T1 (-几l-・01-), τ Cao (-R14・01-
) is changed by the value R14 of the resistor 14. The inclination angle of this straight line is related to the Che/Fasis characteristic, and when the inclination angle of this straight line changes,
There is a possibility that there will be a mismatch between the two characteristics, making it impossible to obtain an appropriate high frequency level.

In addition, in this case, the input of the buffer amplifier 8 sKBrie/7
Since assist 1IjlB4 is provided, depending on the frequency of the audio input signal, [input impedance becomes true,
It is necessary to pay attention to the output impedance of the audio signal.

An object of the present invention is to provide an FM modulation input circuit for an RP converter that maintains a constant pre-emphasis characteristic, performs modulation depth correction by changing the input level, and makes the input impedance independent of the number of people and force. be.

This invention includes a level adjustment circuit that adjusts the level of an input signal, an 8-amplifier that supplies the input signal that has passed through the level adjustment circuit to the FM modulation circuit, and an input section KW of the KFM modulation circuit.
and a pre-emphasis circuit for correcting high-frequency components of the input signal.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an embodiment of the FM converter 111 input circuit of the RF comperme of the present invention. In the figure, input terminal 20
The audio input signal given to the audio input signal is input to the level adjustment circuit 22 and subjected to level adjustment. This level adjustment circuit 22
is constituted by a voltage dividing circuit consisting of resistors 24 and 26, and the level of the input signal can be adjusted by changing the resistance ratio of the resistors 24 and 26. The level-adjusted input signal at the connection point KgA of these resistors 24 and 26 is supplied to the non-inverting terminal (+>) of the amplifier 3o via the converter converter 28t. A feedback circuit 32 is formed which provides negative feedback to the input value which is the amplified output.A pre-emphasis circuit 34 is connected to the feedback circuit 32.This pre-emphasis circuit 34
is composed of resistors 36, 38 and capacitor 40. The amplified output of the amplifier 30 to which the pre-emphasis characteristic is given by the pre-emphasis circuit 34 is the FM modulation circuit w.
142 and undergoes FM modulation, and the modulated output can be taken out from the output terminal 44. The FM modulation circuit 42 is configured to include an FM modulation tracker/jisume that is capable of varying the gm and gm with the audio input signal.
FM modulation is obtained by variable m.

With the above configuration, the level ** circuit 22 can correct the 5 modulation degrees due to variations in the modulation degrees or changes in their specifications.
This can be realized by changing the ratio of each value of resistance 24 and 26 of R4 and R3. Furthermore, since the pre-emphasis circuit 34 is formed in the feedback circuit 32 of the amplifier 30 and is configured independently of the level** circuit 22, the resistor 2
．． Even if the ratio of 26 is changed, the pre-emphasis characteristic is not affected by -1°. In other words, the modulation degree can be corrected by changing the input level while maintaining the pre-emphasis circuit constant.

In this case, if the value of the resistor 36 in the pre-2/7 assist il' 1134 is R3- and the capacitance of the capacitor 40 is 04, then τ in Fig. 2 is given by f, = R, - 04. .

Furthermore, since the input impedance does not change depending on the frequency of the audio input signal and its value can usually be set high, there is also the advantage that no consideration is required for the output impedance.

In the case of the above embodiment, the pre-emphasis circuit 34 was formed in the feedback circuit 32 of the amplifier 30, but as shown in FIG. By performing K in this way, the modulation degree can be corrected by adjusting the level of the input signal without disturbing the pre-emphasis characteristics as in the previous embodiment. In this case, the pre-emphasis circuit 48 , resistors 50, 5 forming a voltage dividing circuit
Assume that a capacitor 54 is connected in parallel to one of the resistors 50 of 2.

Then, if the value of the resistor 50 is R, .., and the capacitance kis4 of the capacitor + 54, then the above τ1 is r1= Rs .
becomes.

As explained above (according to the present invention, it is possible to correct the modulation degree by changing the input level while maintaining the pre-emphasis characteristic at a constant Kfdg, and also to
It is possible to make the frequency independent of the input frequency.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional FM modulation input circuit in an RF converter, Fig. 2 is a graph showing the Freier/Fasis characteristics, and Fig. 3 is a block diagram showing the FM modulation input circuit of the RF converter of the present invention.
FIG. 4 is a circuit diagram showing another embodiment of the modulation input circuit □. 22...Level adjustment circuit, 30.46...Amplifier,
32... Feedback circuit, 34.4B... Preenophasis circuit. Figure ■ Old Figure 2 Input audio frequency f (Hz)

Claims (1)

[Claims] t. 11 level adjustment circuits for adjusting the level of input signals;
It has now been discovered that it is composed of an amplifier that supplies the input signal that has passed through the level tone *a path to the FM modulation circuit, and a pre-emphasis circuit that is provided at the input section of the KFM modulation circuit and corrects the high-frequency components of the input signal. 8F comparator/#)
FM modulation input circuit. The FM modulation input path of an RF3F parter according to claim 1, wherein the Lm plié/7 assist circuit is provided in a feedback circuit formed in the intensifier.