JPH0513049Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a de-emphasis circuit used on the receiving side among emphasis circuits used in FM transmission.

[Conventional technology]

Emphasis circuits are used to improve the signal-to-noise ratio in FM transmission. Generally, the characteristics of an emphasis circuit are defined in terms of T microseconds. Furthermore, in international communications using satellites, emphasis circuits specified by the CCITT Recommendation (J.17) are used. In recent years, satellite communications have been used not only for international communications but also for regional communications. For this reason, it is desirable to be able to easily change the emphasis characteristics to various types.

This T microsecond and CCITT recommendation
The characteristics of each emphasis of J.17 will be explained with reference to FIGS. 2 and 3.

Figure 2 shows one operational amplifier 11 and two resistors.
This is a T microsecond de-emphasis circuit composed of R ₁ , R ₂ and one capacitor C. The gain frequency characteristic of this circuit is expressed by the following formula.

At the crossover frequency ( _X ), |G|=1, so R ₂ /R ₁ =√1+( _X ) ² ( _ωX = _2πX ) Figure 3 shows one operational amplifier 11 and three resistors.
This is a de-emphasis circuit consisting of R ₁ , R ₂ , R ₄ and one capacitor C and having characteristics according to CCITT Recommendation J.17. The gain frequency characteristic of this circuit is expressed by the following formula.

On the other hand, the de-emphasis characteristic according to CCITT Recommendation J.17 is defined by the following equation. Note that the crossover frequency is 1.42KHz.

Therefore, C (R ₂ + R ₄ ) = 1/3000 (R ₂ + R ₄ )/R ₄ = √75 R ₂ / R ₁ × R ₄ / R ₂ + R ₄ = 1/2.9174 From the above three equations, R ₁ =9.932×10 ^-5 /C R ₂ =2.948×10 ^-4 /C R ₄ =3.849×10 ^-5 /C Therefore, these can be converted into the conventional circuit examples shown in FIGS. 4 and 5. Shows the case where it is applied. Note that here, an example is shown in which three types of de-emphasis characteristics can be set.

First, the circuit example shown in FIG. 4 will be explained.

In this circuit example, a resistor is connected to the operational amplifier 11.
R ₁ , R ₂ , R ₅ , R ₇ , R ₉ and capacitors C ₁ , C ₂ ,
It is configured so that C ₃ can be switched and connected. When terminals 3 and 4 are connected, a de-emphasis characteristic of T ₁ microsecond is obtained, and when terminals 5 and 6 are connected, a de-emphasis characteristic of CCITT Recommendation J.17 is obtained. Furthermore, when terminals 9 and 10 are connected, emphasis is turned off.

Therefore, when the above-mentioned calculation formula is applied to FIG. 4, each constant can be calculated sequentially by appropriately determining one constant. For example, if the capacitance of capacitor _C1 is set to an appropriate value, each constant can be calculated using the following formula.

R ₁ =9.932×10 ^-5 /C ₁ R ₄ =3.849×10 ^-5 /C ₁ R ₇ =2.948×10 ^-4 /C _{1 R5} = _T2 / _C2 R ₂ = T ₁ / C ₃ R ₉ = R _1As can be seen from these equations, in order to make the gains of each de-emphasis equal to 1 at the crossover frequency, not only the resistance value of each resistor but also the capacitance of each capacitor is required. Each must be set to a different value. The de-emphasis characteristic requires high accuracy in order to faithfully restore the modulated signal on the transmitting side. Therefore, each resistor and capacitor are required to have high precision so that the calculated resistance and capacitance values are the same. High precision capacitors are expensive. Furthermore, since the capacitances of the capacitors have values that are related to each other, it is highly likely that a desired value cannot be set with a single capacitor, and that a plurality of capacitors will be required.

Next, the circuit example shown in FIG. 5 will be explained. In this circuit example, resistors R ₂ ,
R ₄ , R ₅ , R ₇ , R ₉ , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and the capacitor C are configured so that they can be switched and connected by switches 21a to 21c. Here, the capacitance of the capacitor of the basic de-emphasis circuit shown in FIGS. 2 and 3 is fixed to a constant value,
The resistance value of each resistor is changed by a changeover switch to switch various de-emphasis characteristics. In this case, each constant can be determined by appropriately determining the capacitance of the capacitor C, and the resistance value of each resistor can be determined by the following formula.

R ₂ =T ₁ /C R ₄ =3.849×10 ^-5 /C R ₅ =T ₂ /C R ₇ =2.948×10 ^-4 /C R ₉ =R ₁₃ R ₁₀ =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 changing the de-emphasis characteristic, all the resistance values of each resistor must be changed, so multiple changeover switches are required.

[Problem that the invention attempts to solve]

In the conventional de-emphasis circuit described above, the capacitance values of the capacitors constituting each de-emphasis are related to each other.
In order to realize various de-emphasis characteristics individually, it is necessary to change the resistance value of each resistor constituting each de-emphasis circuit, which poses a problem in that switching becomes complicated.

[Means for solving problems]

The de-emphasis circuit of the present invention allows the de-emphasis characteristics to be easily changed and can be constructed at low cost by reducing the number of expensive high-precision capacitors.

The de-emphasis circuit of the present invention includes an operational amplifier having an inverting input terminal, a resistor connected between the input terminal of the circuit and the inverting input terminal of the operational amplifier, and a capacitor having one terminal connected to the inverting input terminal. a resistor connected between the other terminal of the capacitor and the output terminal of the operational amplifier; a plurality of resistors connected in series between the inverting input terminal and the output terminal of the circuit; and another plurality of resistors each having one terminal connected to the connection point of each of the plurality of resistors and the output terminal of the circuit, and one of the other terminals of the latter plurality of resistors. Furthermore, a plurality of types of de-emphasis characteristics are obtained by connecting either the output terminal of the operational amplifier or the connection point between the resistor and the capacitor connected to this terminal.

〔Example〕

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

FIG. 1 is a circuit diagram of a de-emphasis circuit according to an embodiment of the present invention, and shows an example in which three types of de-emphasis characteristics can be obtained.

That is, it has an operational amplifier 11 whose non-inverting input terminal is connected to ground, and this operational amplifier 11
A resistor R ₁ is connected between the inverting input terminal of the circuit and the input terminal 1 of the circuit. Further, one end of a capacitor C is connected to the inverting input terminal of the operational amplifier 11. The other end of this capacitor C is connected to the other end of a resistor _R4 , one end of which is connected to the output terminal of the operational amplifier 11.

Further, an inverting input terminal of the operational amplifier 11,
Three resistors R ₂ , R ₅ ,
R ₇ are connected in series. And this resistance R ₂
and R ₅ and each connection point between R ₅ and R ₇ and the circuit output terminal 2 are connected to one end of each of resistors R ₃ , R ₆ , and R ₈ , respectively. The other end of each of these resistors R ₃ , R ₆ , R ₈ is terminal 3,
5 and 7, and these terminals have terminals ₄ and 7 provided at the connection point between the capacitor C and the resistor R4.
6 and the terminal 8 connected to the output terminal of the operational amplifier 11 are arranged to face each other so that they can be selectively connected to each other.

Furthermore, terminals 9 and 10 are provided between the input terminal 1 and the output terminal 2 of the circuit to short-circuit them.

According to this configuration, the de-emphasis characteristics are determined by the interconnection positions of the terminals.

First, when terminals 9 and 10 are connected, the input signal at input terminal 1 is directly guided to output terminal 2. That is, the de-emphasis characteristic is set to OFF.

Next, when terminals 3 and 4 are connected, this circuit operates as an inverting amplifier composed of resistors R ₁ , R ₂ , R ₃ , R ₄ , capacitor C, and operational amplifier 11 . The gain G ₁ of this inverting amplifier is expressed by the formula below. That is, it exhibits a de-emphasis characteristic of T ₁ microseconds.

G ₁ = −R ₂ /R ₁ × 1/1 + jωC (R ₂ + R ₃ ) = −R ₂ /R ₁ × 1/1 + jωT ₁ (T ₁ = C (R ₂ + R ₃ )) At crossover frequency ( _X1 ) |G|=1
Therefore, R ₂ ^/ _{R 1} = _√1 + ( _{X1 1 )} ² (ω _X1 = 2π _X1 ) ∴R ₂ = _{R√1 +} ( When connected between 6 and 6, this circuit consists of resistors R ₁ , R ₂ , R ₄ , R ₅ , R ₆ and capacitor C
and an operational amplifier 11. The gain (G ₂ ) of this amplifier is expressed by the formula below. That is, it shows the de-emphasis characteristic of T ₂ microseconds.

G ₂ = −R ₂ +R ₅ /R ₁ × 1/1 + jωC (R ₂ + R ₅ + R ₆ ) = −R ₂ + R ₅ /R ₁ × 1/1 + jωT ₂ (T ₂ = C (R ₂ + R ₅ + R ₆ ) ) Since |G ₂ |=1 at the crossover frequency ( _X2 ), R ₂ +R ₅ /R ₁ =√1+( _{X2 2} ) ² ∴R ₅ =R√1+( _{X2 2} ) ² −R ₂ R ₆ = T ₂ /C - (R ₂ + R ₅ ) Also, when terminals 7 and 8 are connected, this circuit consists of resistors R ₁ , R ₂ , R ₄ , R ₅ , R ₇ , R ₈ and capacitor C
and an operational amplifier 11. The gain (G ₃ ) of the amplifier at this time is expressed by the following formula.

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

Therefore, (R ₂ +R ₄ +R ₅ +R ₇ +R ₈ )/R ₄ =√75 C(R ₂ +R ₄ +R ₅ +R ₇ +R ₈ )=1/3000 R ₁ /R ₄ ×R ₂ +R ₄ +R ₅ +R ₇ +R ₈ /R ₂ +R ₅ +R ₇ =2.9174 From the three equations above, R ₄ = 1/(3000√75C) R ₇ = (√75R ₁ /2.9174) − ( _{R 2} +R ₅ ) R ₈ = 1 −1/√75/3000C−√75R ₁ /2.9174 In this way, set the capacitance of capacitor C to an appropriate value, and select the resistance value of resistor _R1 to satisfy the conditions of the formula below. For example, various de-emphasis characteristics can be realized.

T ₁ < T ₂ Here, the above embodiment is only one embodiment of the present invention, and the de-emphasis characteristic can be changed to a smaller or larger number by appropriately changing the number of connected resistors. Needless to say.

[Effect of idea]

As explained above, the present invention provides the connection point of a plurality of resistors connected in series between the inverting input terminal and the circuit output terminal of an operational amplifier, and the connection point of a plurality of resistors each having one end connected to the circuit output terminal. A plurality of types of de-emphasis characteristics are obtained by connecting any one of the other terminals to either the output terminal of the operational amplifier or the connection point between the resistor and the capacitor connected to this terminal. Because of this structure, the de-emphasis characteristics can be easily changed by simply changing the connection points between the terminals, and moreover, only one expensive high-precision capacitor is required, resulting in an inexpensive structure.

[Brief explanation 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
~10... terminal, 11... operational amplifier, R ₁ ~ _{R 13}
...Resistor, C...Capacitor, _C1 - _C3 ...Capacitor, 21a-21c...Selector switch.

Claims (1)

[Scope of utility model registration request] an operational amplifier having an inverting input terminal; a resistor connected between the input terminal of the circuit and the inverting input terminal of the operational amplifier; a capacitor having one terminal connected to the inverting input terminal; a resistor connected between the terminal and the output terminal of the operational amplifier; a plurality of series-connected resistors connected between the inverting input terminal and the output terminal of the circuit; and a resistor for each of the plurality of resistors. and another plurality of resistors each having one terminal connected to the connection point and the output terminal of the circuit, and one of the other terminals of the latter plurality of resistors and the output of the operational amplifier. A de-emphasis circuit characterized in that it is configured to obtain a plurality of types of de-emphasis characteristics by connecting either a terminal or a connection point between the resistor and the capacitor connected to the output terminal.