JP2580570B2 - sin 2 upper 2 waveform shaping circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sin ² waveform shaping circuit used for shaping a waveform of a synchronization signal in a broadcasting station, for example.

[Summary of the Invention]

The present invention relates to a sin ² waveform shaping circuit, a trapezoidal wave shaping circuit having an integrating circuit is provided, Yotsute to supply the trapezoidal wave to the differential transistor circuit, simple structure with good sin ²
A waveform is obtained.

[Conventional technology]

For example, in the NTSC broadcast TV signal standard, the rise and fall of the synchronization pulse are 1 to 10-90% with a level change of 10% to 90%.
It is specified as 40nsec. Also 250ns for PAL method
It is specified as ec.

Therefore, conventionally, a broadcasting station or the like has used a so-called sin ² filter as shown in FIG. 4 to shape a rectangular wave output from an IC or the like into a sin ² waveform conforming to the above-described standard. . However, such a sin ² filter
For example, since the filter is composed of fifth to seventh-order filters, considerable accuracy is required for the selection of constants, and it is often difficult to obtain necessary characteristics with constants in a normal usable constant rank.

Further, in the sin ² filter, the constants of most elements had to be changed between the NTSC system and the PAL system described above, and it was virtually impossible to share a circuit between them.
Further, when the output waveform of the sin ² filter is to be transmitted by using a coaxial line, there is a possibility that the characteristics of the circuit change due to the influence of the capacity of the coaxial line and the sin ² filter cannot be formed.

On the other hand, it has been proposed to supply a rectangular wave to a charge / discharge circuit of a resistor / capacitor, form a trapezoidal wave using a part of the charge / discharge curve, and shape the trapezoidal wave to obtain a sin ² waveform. (U.S. Pat. No. 4,311,921).

However, in this circuit, the trapezoidal wave is not symmetrical due to the use of the charge / discharge curve of the resistor / capacitor, so that a symmetrical output waveform of good quality cannot be obtained.

[Problems to be solved by the invention]

As described above, in the conventional technology, since a trapezoidal wave is formed by using the charge / discharge curves of the resistor and the capacitor, the waveform is not symmetrical and a high-quality output waveform cannot be obtained. Atsuta.

[Means for solving the problem]

The present invention provides a negative feedback circuit comprising an operational amplifier in which an input signal is input to an inverting input terminal via a resistor, a variable capacitor for integration, and two diodes connected in opposite directions for a voltage limiter. A trapezoidal wave shaping circuit having a parallel circuit connected in parallel with the operational amplifier between an output terminal of the operational amplifier and the inverting input terminal; and an input level adjusting resistor connected to the trapezoidal wave shaping circuit. Sin ² consisting of a differential transistor circuit with a circuit
This is a waveform shaping circuit.

[Action]

According to this, since the trapezoidal wave is shaped using the integration circuit, a linearly symmetric trapezoidal wave having a slope can be obtained, and a high quality sin ² waveform can be obtained using the trapezoidal wave.

〔Example〕

In FIG. 1, an input terminal (1) is connected to an inverting input of an operational amplifier (3) through a resistor (2). The output of the amplifier (3) is connected to the inverting input of the amplifier (3) through a parallel circuit of a variable capacitor (4) and diodes (5) and (6) connected in opposite directions. Also, a bias terminal (7) of the midpoint potential of the input waveform is connected to the non-inverting input of the amplifier (3).

Further, the output of the amplifier (3) is connected to the base of one of the pnp transistors (9) and (10) differentially connected through the resistor (8), and the transistor (9)
A bias terminal (7) is connected to the base of (10) through resistors (11) and (12), respectively. The emitters of the transistors (9) and (10) are connected to each other, and this connection point is connected to a positive power supply terminal (14) through a resistor (13). And the collector of the transistor (9) is grounded,
The collector of the transistor (10) is connected to the negative power supply terminal (16) through the resistor (15), and the output terminal (17) is led out of the collector of the transistor (10).

In this circuit, for example, when an input signal vin of a rectangular wave as shown in FIG. 2A is input to the input terminal (1), the input signal vin is input to the inverting input of the operational amplifier (3) through the resistor (2). Supplied to And this input signal vi
when n is 0V, is turned diode (5) is forward of the operational amplifier (3) the bias potential as the intermediate signal v _t obtained at the output is shown in Fig B (2.5V) + V _D (diode Voltage).

When the input signal vin in a subsequent time t ₁ is from 0 to 5V,
A diode (5) is off, resistor (2) an integrating circuit comprised of operational amplifier (3) the capacitor (4) is driven, the intermediate signal v _t is linearly until diode (6) is turned on Descended. The diode (6) When turned on, the intermediate signal v _t is constant at 2.5V-V _D.

When the rectangular wave vin yet time t ₂ is from 5 to 0V, and now is turned off diode (6) is an intermediate signal v _t until diode (5) is turned on is linearly increased.

Connexion intermediate signal v _t in which amplitude is trapezoidal wave of 2V _D Focusing bias potential (2.5V).

And this intermediate signal v _t is converted into two transistors (9).
(10) is supplied to the differential circuit, and the ratio of the input resistors (8) and (11) is appropriately selected, so that the output terminal (17) has a sin ² as shown in FIG. A shaped output signal v _out is taken.

That is, in the above circuit, the transistor (9)
The characteristic curve of the input (v _t ) versus the output (i) of (10) is as shown in FIG. 3, so that when the above-mentioned intermediate signal v _t is supplied to the base of the transistor (9), A current i as shown in the figure flows through the collector of the transistor (10). The current i is converted into a voltage by the resistor (15), and an output signal v _out is taken _out to the output terminal (17).

In this way, sin ² waveform shaping is performed. According to the above-described circuit, a trapezoidal wave is formed by the integrating circuit of the resistor (2), the operational amplifier (3), and the capacitor (4). A symmetrical waveform with good characteristics can be obtained, and this is used to obtain a high quality si
n ² waveforms can be obtained.

Also, the inclination of the slope of the trapezoidal wave can be arbitrarily adjusted by changing the capacitance value of the capacitor (4), so that a desired 140 ns waveform can be easily obtained. Can also be obtained in a single configuration.

Therefore, there is no need to perform a conventional precise setting of a constant or a mounting test, and the circuit can be realized extremely easily.

Further, according to the above-mentioned circuit, there is little possibility that the circuit is affected by the subsequent circuit.

〔The invention's effect〕

According to the present invention, since the trapezoidal wave is shaped by using the integrating circuit, a linearly symmetric trapezoidal wave having a slope can be obtained, and a high quality sin ² waveform can be obtained by using the trapezoidal wave. Natsuta

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an example of the present invention, FIGS. 2 and 3 are diagrams for explaining the same, and FIG. 4 is a diagram for explaining a conventional technique. (1) is an input terminal, (2) (8) (11)-(13) (15)
Is a resistor, (3) is an operational amplifier, (4) is a variable capacitor, (5) and (6) are diodes, (7) is a bias terminal, (9) and (10) are transistors, and (14) and (16) are A power supply terminal and (17) are output terminals.

Claims (1)

(57) [Claims] A negative feedback circuit comprising an operational amplifier for inputting an input signal to an inverting input terminal via a resistor, a variable capacitor for integration, and two diodes connected in opposite directions for a voltage limiter. A trapezoidal wave shaping circuit having a parallel circuit connected in parallel with the operational amplifier between the output terminal of the operational amplifier and the inverting input terminal, and an input level adjusting circuit connected to the trapezoidal wave shaping circuit. A sin ² waveform shaping circuit including a differential transistor circuit having a resistance circuit.