JPH0633703Y2 - De-emphasis circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a de-emphasis circuit used on the receiving side of an emphasis circuit used for FM transmission.

[Conventional technology]

The emphasis circuit is used for improving the signal-to-noise ratio in FM transmission. Generally, the characteristic of the emphasis circuit is defined by the expression T microsecond. Furthermore, in international communication using satellites, the emphasis circuit specified in CCITT Recommendation (J.17) is used. In recent years, satellite communication has been used not only for international communication but also for regional communication. For this reason, it is desired that various emphasis characteristics can be easily changed.

The characteristics of the emphasis of T microsecond and CCITT Recommendation J.17 will be described with reference to FIGS. 2 and 3.

FIG. 2 shows a T microsecond de-emphasis circuit composed of one operational amplifier 3, two resistors R ₁ and R ₂ and one capacitor C. The gain frequency characteristic of this circuit is expressed by the following equation.

Since | G | = 1 at the crossover frequency (x), FIG. 3 shows a characteristic de-emphasis circuit according to CCITT Recommendation J.17 which is composed of one operational amplifier 3, three resistors R ₁ , R ₂ , R ₇ and one capacitor C. The gain frequency characteristic of this circuit is expressed by the following equation.

On the other hand, the de-emphasis characteristic according to CCITT Recommendation J.17 is
It is specified by the following formula. The crossover frequency is 1.
42KHz.

Therefore, C (R ₂ + R ₇ ) = 1/3000 From the above three formulas, R ₁ = 9.932 × 10 ⁻⁵ / CR ₂ = 2.948 × 10 ⁻⁴ / CR ₇ = 3.849 × 10 ⁻⁵ / C Therefore, these are the conventional circuits shown in FIGS. 4 and 5. The case applied to the example is shown. Here, an example is shown in which three types of de-emphasis characteristics can be set.

First, the circuit example of FIG. 4 will be described.

In this circuit example, resistors R ₁ , R ₂ ,
The R _4, R _6, R ₇ and capacitor C _1, C _2, C ₃ are configured to be switched connection. When the terminals 11 and 12 are connected, the CCITT recommendation J.17 de-emphasis characteristic is obtained. Further, when the terminals 13 and 14 are connected, the T ₁ microsecond characteristic is obtained, and when the terminals 15 and 16 are connected, the T ₂ microsecond characteristic is obtained.

Therefore, if the above-mentioned calculation formula is applied to FIG. 4, each constant can be sequentially calculated if one constant is appropriately determined. For example, if the capacitance of the capacitor C ₁ is set to an appropriate value,
Each constant can be calculated by the following formula.

R ₁ = 9.932 x 10 ^-5 / C ₁ R ₇ = 3.849 x 10 ^-5 / C ₁ R ₂ = 2.948 x 10 ^-4 / C ₁ R ₄ = T ₁ / C ₂ R ₆ = T ₂ / C ₃ As can be seen from these equations, in order to make the gain of each de-emphasis at unity at the crossover frequency equal to 1, not only the resistance value of each resistor but also the capacitance of each capacitor should be different. Must be set. The de-emphasis characteristic requires high accuracy in order to faithfully restore the modulated signal on the transmitting side. Therefore, each resistor and capacitor have a resistance value,
High accuracy is required so that the calculated capacitance values are the same. High precision capacitors are expensive. Moreover, since the capacitance of each capacitor is a value related to each other, it is highly possible that one capacitor cannot be set to a desired value and a plurality of capacitors are required.

Next, the circuit example of FIG. 5 will be described. In this circuit example, the resistances R ₂ , R ₄ , R ₆ , R ₇ , R ₁₁ , R with respect to the operational amplifier 3 are used.
₁₂ , R ₁₃ and the capacitor C are configured so that they can be switched and connected by interlocking with the changeover switches 21a to 21c. Then, here, the electrostatic capacitance of the capacitor of the de-emphasis circuit shown in FIG. 2 and FIG. 3 which is the basic is fixed to a constant value, and the resistance value of each resistor is changed by the changeover switch to obtain various de-emphasis characteristics. I am trying to switch. For each constant in this case, if the electrostatic capacitance of the capacitor C is appropriately determined, the resistance value of each resistor can be obtained by the following formula.

_{R 4 = T 1 / CR 7} = 3.849 × 10 -5 / CR 6 = T 2 / CR 2 = 2.948 × 10 -4 / CR 11 = 9.932 × 10 -5 / C This de-emphasis circuit can be realized with one capacitor, and the capacitance of the capacitor can be set arbitrarily.
However, when switching the de-emphasis characteristics, it is necessary to change all resistance values of each resistor,
Requires multiple changeover switches.

[Problems to be solved by the invention]

In conventional de-emphasis circuits, the capacitance values of the capacitors that make up each de-emphasis are related to each other, so multiple expensive capacitors with high accuracy are required, or various de-emphasis characteristics can be achieved with a single capacitor. In order to do so, it is necessary to change the resistance value of each resistor that constitutes each de-emphasis circuit, so that there is a problem that a multiple changeover switch is required and the changeover becomes complicated.

An object of the present invention is to provide a de-emphasis circuit which can easily change the de-emphasis characteristic and can be constructed at a low cost by reducing the number of expensive and highly accurate capacitors.

[Means for solving problems]

The de-emphasis circuit of the present invention comprises an operational amplifier, a resistor and a capacitor connected in series between the inverting input terminal and the output terminal of the operational amplifier, and an even number connected in parallel between the signal input terminal and the output terminal. A series of n resistors (n is a natural number of 2 or more) consisting of a series connected resistors,
N terminals provided at respective intermediate connection points of the n resistance rows, and n terminals provided at the connection point of the inverting input terminal and the resistor and the capacitor to form a pair with the n terminals. And the n terminal pairs are selectively connectable.

〔Example〕

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

FIG. 1 is a circuit diagram of a de-emphasis circuit according to an embodiment of the present invention. Here, an example in which three types of de-emphasis characteristics are obtained is shown.

That is, the operational amplifier 3 has a non-inverting input terminal connected to the ground, and one end of the resistor R ₇ is connected to the inverting input terminal of the operational amplifier 3. And this resistance R ₇
The other end of the capacitor C is connected to the output terminal of the operational amplifier 3 at the other end. In addition, three resistor strings R ₁ and R ₂ , R ₃ and R ₄ , R ₅ and R ₆ connected in parallel between the signal input terminal 1 and the output terminal of the operational amplifier 3, and these 3
Three terminals 11,13,15 at each intermediate connection point of each resistor string
And the inverting input terminal of the operational amplifier 3 or the resistor
Three terminals 12, 14, 16 provided at the connection point of R ₇ and capacitor C
And these three pairs of terminals 11 and 12, 13
And 14, 15 and 16 are selectively interconnectable.

According to this configuration, the de-emphasis characteristic is determined by the interconnection position of these terminals.

First, when terminals 11 and 12 are connected, this arm has resistances R ₁ and R
₂ and R _{7 function} as an inverting amplifier composed of a capacitor C and an operational amplifier 3. The gain G ₁ of this inverting amplifier is expressed by the following equation.

On the other hand, the theoretical formula of the de-emphasis characteristic according to CCITT Recommendation J.17 is as follows.

Therefore, C (R ₂ + R ₇ ) = 1/3000 R ₁ (R ₂ + R ₇ ) / (R ₂ · R ₇ ) = 2.9174 From the above three formulas R ₁ = 9.932 × 10 ⁻⁵ / CR ₂ = 2.948 × 10 ^{− 4} / CR ₇ = 3.849 × 10 ^-5 / C Next, when connecting between terminals 13 and 14, this circuit shows resistors R ₃ and R
_It operates as an inverting amplifier composed of ₄ , a capacitor C and an operational amplifier 3. The gain G ₂ of the amplifier at this time is expressed by the following equation. That is, it shows the de-emphasis characteristic of T ₁ microsecond.

At crossover frequency (x ₁ ) | G ₂ | = 1 R ₄ = T ₁ / C Furthermore, when connecting between terminals 15 and 16, this circuit shows
_It operates as an inverting amplifier composed of ₅ , R ₆ , a capacitor C and an operational amplifier 3. The gain G _{3 of} this amplifier is expressed by the following equation. That is, it exhibits the de-emphasis characteristic of T ₂ microseconds.

(T ₂ = CR ₆ ) At crossover frequency (x ₂ ) | G ₃ | = 1, so R ₆ = T ₂ / C In this way, various de-emphasis characteristics can be obtained by setting the capacitance of the capacitor C to an appropriate value and setting each resistor to the value obtained from each calculation formula. realizable.

The above embodiment is only one embodiment of the present invention, and it goes without saying that the deemphasis characteristic can be switched to a number smaller or larger than this by appropriately changing the number of resistors to be connected.

Here, it goes without saying that an arbitrary type of characteristic can be obtained by setting the number of resistor rows and the number of terminal pairs associated therewith to an arbitrary number.

[Effect of device]

As described above, according to the present invention, any one of the intermediate connection points of each of the n-row resistor arrays, each of which is composed of an even number of resistors, connected in parallel between the signal input terminal and the output terminal of the operational amplifier, A configuration in which an inverting input terminal of an amplifier or one of connection points of a resistor and a capacitor connected between the inverting input terminal and the input terminal is selectively connected to obtain n kinds of de-emphasis characteristics N
The de-emphasis characteristic can be easily changed only by changing the connection point between the individual terminals, and it is possible to use only one expensive and highly accurate capacitor, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams of an example of a basic circuit of a de-emphasis circuit, and FIGS. 4 and 5 are circuit diagrams of a conventional example. 1 ... Circuit input terminal, 2 ... Circuit output terminal, 3 ... Operational amplifier, 11-16 ... Terminal, 21a-21c ... Changeover switch,
R _{1 to} R ₁₃ …… Resistor, C, C _{1 to} C ₃ …… Capacitor.

Claims (1)

[Scope of utility model registration request] 1. An operational amplifier, a resistor and a capacitor connected in series between an inverting input terminal and an output terminal of the operational amplifier, and an even number of series connected in parallel between a signal input terminal and the output terminal. N columns of connected resistors (n is 2
The above natural number), n terminals provided at each intermediate connection point of the n resistance rows, and the n terminals provided at the connection point between the inverting input terminal and the resistor and the capacitor. A de-emphasis circuit comprising: n terminals that make a pair with each other and selectively connect these n terminal pairs.