JPS5949091A - Filter circuit - Google Patents

Abstract

PURPOSE:To reduce power consumption, by combining a differential amplifier to a transistor (TR) circuit including an impedance circuit, in a filter circuit for video tape recorder recording a color television signal of the SECAM system. CONSTITUTION:In the figure, 1 is an input terminal to which a color television signal of the SECAM system is applied, and connected to a non-inverting input of a differential amplifier circuit 7, and the output of the differential amplifier circut 7 is connected to a base of a TR2. Further, the emitter of the TR2 is connected to an inverting input of the differential amplifier circuit 7 to form a feedback path and grounded via an impedance circuit 3. Further, 6 is an output terminal. In this circuit, the frequency characteristic G'' is expressed as Equation #, where A is a gain of a differential amplifier circuit 7, R is a resistance of a resistor 4, Z is an impedance of the impedance circuit 3, and re is an emitter resistance of the TR2, the effect of the resistor re on the frequency characteristic G'' is less and the stable frequency characteristic is obtained without increasing the emitter current flowing to the TR2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a filter circuit used in a VTR (video recorder) capable of recording, for example, a SECAM color television signal.

Background technology and its problems In the SECAM system, the carrier frequency is 4.4062.
5MHy, FM modulated R-Y signal (red difference signal)
and a BY signal (W color difference signal) FM-modulated with a carrier frequency of 4.25 MIIz are alternately transmitted every horizontal period. In this case, the FM-modulated R-Y signal and IIY signal are transmitted after their amplitudes are suppressed in the vicinity of the carrier frequency by a bandpass filter having frequency characteristics as shown in FIG.

This is to suppress the carrier wave amplitude near achromatic colors to reduce dot interference.

In a television receiver, the signal is processed after passing through a filter circuit having a frequency characteristic as shown in FIG. 2, which is opposite to the frequency characteristic shown in FIG.

Now, when recording this SECAM color preview signal on a VTR, the FM modulated RY signal and B, -Y signals are processed by a filter circuit (bell filter) having frequency characteristics as shown in Fig. 2. ) is used to flatten the signal and then record it. 'This is because the brightness signal is usually FM modulated in a VTR,
The color signals (RY signal, B-Y signal) are low frequency converted and recorded, but in the case of the SECAM system,
The color signal is FM modulated and distributed over a wide band, and if the frequency characteristics shown in Figure 1 were to remain, interference with the luminance signal would occur at the tail of the color signal, which would be inconvenient. It's because I'm busy. If the frequency characteristics remain as shown in Figure 1, then i'J: , When noise is mixed in when recording 7 degrees, the SN near the carrier frequency becomes particularly bad, so the SN in the entire band is This is to ensure that they are equal.

For example, a filter circuit shown in FIG. 3 has been proposed as a filter circuit having frequency characteristics as shown in FIG. 2 for use in this VTR.

In the figure, (1) is an input terminal to which the FM modulated R-Y signal and B-Y signal having the frequency characteristics shown in Figure 1 are supplied, and the color signal is output from this terminal (1). n
It is supplied to the base of the pn type transnoster (2). The emitter of this transistor (2) is an impedance circuit (
3). This impedance circuit (3
), for example, the resistors (3a), (3b), the contactor, and the collector of the transistor (2) are connected to the power supply terminal (5) to which the DC voltage →-B is supplied via the resistor (4). . The collector of this transistor (2) and the resistor (4)
How to get an output signal from the connection point 1.1 child (6)
is derived.

In this example in Figure 3, G= −−・・・・・・・・・・・・ Song・・・・・・
・Song/Listen...Song/Song (1) R: Resistance value z of resistor (4); Frequency characteristic called impedance of impedance circuit (3), that is, the frequency characteristic shown in Figure 2 must be realized. , but actually its frequency characteristic G′
G'-・・・・・・・・・・・・・・・・・・・・・
(2) re +z and the emitter resistance re of the transistor (2) are related. In this case, not only the gain changes but also the Q due to the emitter resistance re, resulting in the inconvenience that stable frequency characteristics cannot be obtained.

Conventionally, the emitter current of the transistor (2) is made quite large (for example, about 5 mA), and the influence of the emitter resistance re on the impedance 2 is made so small as to be negligible, thereby eliminating the above-mentioned disadvantage. 1) Stable frequency characteristics shown by the formula are obtained.

Therefore, in this conventional filter circuit, the emitter current of the transistor (2) is quite low, which has the disadvantage of increasing power consumption.

OBJECTS OF THE INVENTION The present invention has been made in view of these points, and it is an object of the present invention to propose a filter circuit that can obtain stable frequency characteristics without increasing power consumption.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention connects an impedance circuit having a predetermined frequency characteristic to the emitter of a transistor whose output side is connected to the base of the differential amplifier circuit, and An input signal is applied to the input terminal, the other input terminal is connected to the emitter of the transistor to form a feedback path, and an output signal is obtained from the collector of the transistor.

By configuring the present invention in this manner, the effect of the emitter resistance r8 of the transistor on the frequency characteristics is reduced, the emitter current of the transistor can be reduced, and stable frequency characteristics can be obtained without increasing power consumption. I can do it.

Embodiment Hereinafter, an embodiment of the filter circuit according to the present invention will be described with reference to FIG. In this Figure 4,
Portions corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this Figure 4, the input terminal (1) is connected to the differential amplifier circuit (
The output side of the differential amplifier circuit (7) is connected to the base of the transistor (2).

In short, the emitter of transistor (2) is connected to the differential amplifier circuit (
7) to form a feedback path.

The rest of the structure is the same as the example shown in FIG. 3 described above.

In the case of the example in FIG. 4, if the gain of the differential amplifier circuit (7) is A, its frequency characteristic σ' is as follows, and the emitter resistance r. The impact of this will be extremely small.

FIG. 5 shows a specific example of the example shown in FIG.

In this example, when the emitter current of transistor (2) was set to 1.1 mA, almost ideal characteristics (actual measurements) as shown by the solid line in Figure 6 were obtained.What is shown by the broken line in Figure 6 is the theoretical value.

Furthermore, even when the impedance circuit (3) was configured as shown in FIG. 7 and the emitter current of the transistor (2) was set to 0.2 mA, substantially the same characteristics as in the example of FIG. 5 were obtained. However, it goes without saying that the dynamic range decreases as the emitter current decreases.

Accordingly, according to the example in FIG. 4, for the frequency characteristic G
The influence of the emitter resistance r8 of the transistor (2) is reduced, and stable frequency characteristics can be obtained without increasing the emitter current flowing through the transistor (2). Therefore, since the emitter current only needs to be small, power consumption can be reduced compared to conventional filter circuits.Next, FIG. This is an example. In FIG. 8, parts corresponding to those in FIG. 4 are designated by the same reference numerals.

In the figure, the impedance circuit (3) includes an npn transistor (8), a resistor (9), On, <
It consists of one, capacitor O→, 03, and coil 0◆. )・A bias voltage Vv is applied to the base of the transistor (8) at terminal 0. And the transistor (
8) and a resistor (9) control the emitter current of the diode (2).

In this case, the transistor (8) and resistor (9) that constitute the impedance circuit (3) are the differential amplifier circuit (7),
to.

It is integrated into an integrated circuit like Runnostar (2). but,
Resistor (IQ+, (1), capacitor H, fi, 1
, the coil 0 is connected to the outside using a pin OQ derived from the emitter of the transistor (2).

This example in FIG. 8 is also constructed in the same way as the example in FIG. 4, and the same effects can be obtained.

Effects of the Invention As is clear from the embodiments described above, according to the filter circuit according to the present invention, the emitter resistance of the transistor constituting the filter circuit has little influence on its frequency characteristics, and the emitter current of the transistor is Even if the frequency characteristics are small, stable frequency characteristics can be obtained. Therefore, since the emitter current may be small, the power consumption can be reduced compared to conventional filter circuits.

[Brief explanation of the drawing]

Figures 1 and 21 are diagrams showing frequency characteristics, respectively.
The figure is a configuration diagram showing an example of a conventional filter circuit, and FIG.
FIGS. 5 and 7 are a configuration diagram showing an embodiment of the filter circuit according to the present invention, and FIGS.
This figure is a diagram showing the frequency characteristics of the example shown in FIG. 5, and FIG. 8 is a connection diagram showing another embodiment of the present invention. (1) is an input terminal, (2) is a transistor, (3) is
In the impedance circuit, (4) is a resistor, (5) is a power supply terminal, (6) is an output terminal, and (7) is a differential amplifier circuit. Same as Hidemori Matsukuma.

Claims (1)

[Claims] An impedance circuit having predetermined frequency characteristics is connected to the emitter of the transistor whose output side is connected to the base of the differential amplifier circuit, and an input signal is applied to one input terminal of the differential amplifier circuit, and an input signal is applied to the other input terminal. is connected to the emitter of the transistor to form a feedback path, and the filter circuit O obtains an output signal from the collector of the transistor.