JPS6258169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pre-emphasis integrated circuit suitable for recording luminance signals of home VTRs, for example.

The VTR's integrated brightness signal recording circuit, which can switch between standard time recording and playback (hereinafter referred to as SP) and long-time recording and playback (hereinafter referred to as LP), requires significantly fewer peripheral components than a SP-only circuit. This results in the inconvenience of an increase in

The above problems will be explained in detail below.

When recording and reproducing a video tape for a long time by slowing down the running speed of the video tape in a home VTR, the recording track width becomes narrower, and the S/N ratio of the reproduced image quality deteriorates. In order to improve this deterioration, it is necessary to perform so-called dynamic emphasis processing in the recording circuit, which changes the amount of emphasis according to the level of the recorded video signal.

FIG. 1a shows an example of the emphasis characteristic during SP, and FIG. 1b shows an example of the dynamic emphasis characteristic during LP. In the conventional integrated luminance signal recording circuit, in order to be able to switch between SP and LP and to obtain the emphasis characteristics shown in Fig. 1, an additional circuit as shown in the block configuration in Fig. 2 is required. .

In FIG. 2, 1 is a video signal input terminal;
2 is an emphasis circuit having dynamic characteristics, 3 is an SP/LP changeover switch, and 4 is a video signal output terminal. The output video signal is applied to an emphasis circuit having the emphasis characteristics shown in FIG. 1a.

FIG. 3 shows an example of the dynamic characteristics of block 2 in FIG. 2, and FIG. 4 shows an example of the additional circuit shown in FIG. 2. 1 is an input terminal, 4 is an output terminal, and 24 is an SP/SP that has a low potential during SP and a high potential during LP.
This is an LP switching signal input terminal. transistor 5,
Diodes 14, 15, capacitors 12, 13, and resistors 9, 10, 11, 16 constitute an emphasis circuit 2 having dynamic characteristics as shown in FIG. , 20, and 21 constitute the switch 3 in FIG. Further, the transistor 26 constitutes an amplifier, the transistor 29 constitutes a phase inversion circuit, and the transistor 30 constitutes an output emitter follower.

As described above, when attempting to make SP/LP switchable in a conventional integrated luminance signal recording circuit, the number of components increases by approximately 25 as shown in Figure 4, and The luminance signal passes through different amplifiers. In other words, the brightness signal is transmitted from input terminal 1 to capacitor 6 to transistor 26 during SP.
-Transistor 23-Transistor 29 path is amplified, whereas in LP mode input terminal 1-Capacitor 6-Transistor 5-Transistor 22
- amplified in the path of transistor 29; For this reason, variations in resistance cause differences in DC gain. This difference appears as a difference in frequency deviation during FM modulation. As is well known, there are standards for the amount of frequency deviation in home VTRs for compatibility reasons, and this difference reduces the degree of freedom in designing other circuit blocks.

Next, FIG. 5 shows a configuration diagram of the external terminals and peripheral circuits of the IC when the entire emphasis circuit including the changeover switch is integrated using a conventional dynamic emphasis circuit. Elements with the same reference numerals as in FIG. 4 mean elements having the same functions. 3
3 to 36 are external terminals of the IC, resistors 37, 38, 3
9 and a capacitor 40 are peripheral (external) components of the static enhancement circuit. All peripheral components are factors that determine the emphasis constant, so it is not appropriate to use the internal resistance of the IC. Further, the SP/LP switching signal input terminal 24 is not provided as an external terminal because it can normally be used as an external terminal for other functions.

When integrated using conventional technology in this way, the IC
4 external terminals and 12 peripheral components are required, and this results in a difference in the amount of frequency deviation. Furthermore, when the diodes 14 and 15 are integrated, the number of external terminals increases by one more.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a pre-emphasis integrated circuit capable of switching between fixed emphasis and dynamic emphasis with a small number of repeating parts and pins.

In order to achieve the above object, the present invention configures an emphasis circuit with one high-gain differential amplifier and a negative feedback circuit, and switches the frequency characteristics of the negative feedback circuit with a transistor switch to create a fixed emphasis/dynamic amplifier. I am trying to switch assists. As a result, it is possible to realize a pre-emphasis integrated circuit that has no difference in frequency deviation when switching between SP and LP, and has a small number of peripheral components and external terminals.

FIG. 6 shows a block diagram of the present invention. 41
43 is a video signal input terminal, 43 is a pre-emphasized video signal output terminal, 42 is a high gain amplifier, 44 is a negative feedback circuit during SP, 45 is a negative feedback circuit whose feedback rate changes according to the signal level, 46
is a switch that is OFF during SP and ON during LP.

Now, the gain of the amplifier 42 is A, and the feedback circuit 44,4
Assuming that the feedback factors of 5 are β〓 ₁ and β〓 ₂ , the overall gain G of this circuit is, as is well known, at the time of SP...G〓=A/1+β ₁ A≒1/β ₁ (1≪β〓 ₁ A
) At LP...G = A/1 + (β ₁ + β ₂ ) A≒1/β ₁ +
It can be expressed as β ₂ {1≪(β〓 ₁ +β〓 ₂ )A}. Therefore, if β〓 ₁ and β〓 ₂ are designed to obtain the characteristics shown in Fig. 1 a and b, respectively,
It can be seen that a pre-emphasis circuit capable of switching between SP and LP can be realized with the system configuration shown in FIG.

FIG. 7 shows an example of a circuit embodying the present invention.
Elements with the same symbols as in FIG. 6 have the same functions. Transistors 47, 48, 51, resistor 4
9 and current source 50 to form the amplifier 42 in FIG.
The negative feedback circuit 44 in the figure is composed of diodes 60, 61,
The resistors 63, 65 and capacitors 54, 62, 64 form the negative feedback circuit 45 in FIG.
6, 59 and resistors 57, 58 to switch 4 in Figure 6.
6 respectively. Terminal 66 is SP/LP
This is a switching signal input terminal, and the potential is low when SP and high when LP.

In the above circuit configuration, when SP, terminal 66
becomes the ground potential, so the transistors 56, 5
9 is OFF. At this time, the feedback circuit is
2, 53, 55 and a capacitor 54, it becomes independent of the signal level. That is, by appropriately setting the constants of each of the circuit elements described above, the characteristics shown in FIG. 1a can be obtained.

On the other hand, during LP, a high voltage is supplied to the terminal 66. The transistor 51 constitutes an emitter follower, and since its emitter side has a low impedance, the transistor 56 as well as the transistor 59 performs a switch operation and is turned on. When the transistors 56 and 59 are turned on, a nonlinear element composed of diodes 60 and 61 whose conduction impedance changes depending on the signal level is inserted into the feedback circuit. Therefore the resistance 63,6
5. By appropriately selecting the constants of the capacitors 62 and 64, dynamic enhancement characteristics as shown in FIG. 2b can be obtained.

When integrating the circuit shown in FIG. 7, the circuit with the highest cost performance can be obtained by considering the following three terminals as external terminals.

(1) The connection point between the emitter of the transistor 51 and the resistor 52 (point A in Figure 7) (2) The connection point between the base of the transistor 48 and the resistor 52 (point B in Figure 7) (3) The anode side of the diode 60 and the resistor 63 connection point (point C in FIG. 7) Corresponding points of the three terminals A to C in FIG. 6 are indicated by the same reference numerals in the same figure.

Note that, as in the case of the circuit shown in FIG. 5, the SP/LP switching signal terminal can also be used as an external terminal for other functions. Also, the DC gain of this circuit is
Since both SP and LP are determined by the ratio of the resistors 52 and 53, there is no difference in frequency deviation due to SP/LP switching.

As mentioned above, by adopting the configuration shown in Fig. 7, there are 3 external terminals and 9 peripheral components (52 resistors, 52 resistors,
53, 55, 63, 65, capacitor 54, 6
2,64, transistor 59), the emphasis constant is determined by the constant of the peripheral circuit, and
It is possible to realize a pre-emphasis circuit that does not cause a difference in frequency deviation due to SP/LP switching. In addition, if this circuit is used exclusively for SP, it is only necessary to remove the peripheral components shown in Fig. 7, such as resistors 57, 58, 63, 65, capacitors 62, 64, and transistor 59, and to remove unnecessary elements from the circuit inside the IC. is 3 elements (transistor 56, diode 60, 6
1) It is only necessary and has high cost performance.
IC can be realized.

As is clear from the above explanation, according to the present invention, it is possible to switch between static emphasis and dynamic emphasis, and there is no difference in the amount of frequency deviation at SP and LP, and the emphasis constant is It is possible to realize a pre-emphasis circuit that is determined by peripheral circuits and has a small number of external terminals and peripheral parts. Furthermore, it is possible to make the IC dedicated to SP by simply removing peripheral parts, and even in that case, there is almost no redundant circuitry within the IC, making it possible to create an IC with high cost performance.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of static emphasis characteristics and dynamic emphasis characteristics.
Figure 3 is a block diagram of a conventional dynamic emphasis circuit, Figure 3 is a characteristic diagram of the dynamic emphasis circuit shown in Figure 2, Figure 4 is a diagram showing an example of a conventional pre-emphasis circuit, and Figure 5. FIG. 6 is a block diagram of an embodiment of the present invention, and FIG. 7 is a specific circuit diagram of an embodiment of the present invention. 42...Amplifier, 44, 45...Negative feedback circuit,
46...Switch.

Claims (1)

[Claims] 1. An amplifier having an input terminal and an output terminal;
A series circuit including a first negative feedback circuit extending from the output terminal to the amplifier, a switch circuit connected in parallel with the first negative feedback circuit, and a second negative feedback circuit whose feedback rate changes depending on the signal level. The pre-emphasis characteristic is switched between fixed emphasis and (fixed emphasis + dynamic emphasis) according to opening and closing of the switch circuit, and the output terminal and the first and second negative feedback circuits are connected to each other. A pre-emphasis integrated circuit characterized in that a connection point to an amplifier and a connection point of IC internal parts and peripheral parts in a second negative feedback circuit are respectively external terminals. 2 A resistor whose one end is connected to the power supply is connected to the collector of the second transistor of the differentially coupled first and second transistors, and the base of the third transistor is connected, and the emitter is connected to the emitter of the third transistor. , the collector of which is connected to one end of a parallel circuit of diodes having opposite polarities, the base of the second transistor, the emitter of the third transistor, and the diode. 2. The pre-emphasis integrated circuit according to claim 1, wherein the other end is an external terminal.