JPH0718220Y2 - Luminance signal recording / reproducing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a luminance signal recording / reproducing circuit for a home VTR (video tape recorder), and more particularly to a luminance signal recording / reproducing circuit suitable for use as an IC.

(B) Conventional technology “′” issued by CQ Publishing Co., Ltd. on December 10, 1988
89 Sanyo Semiconductor Data Book Video Equipment Integrated Circuit Edition ”, No. 319
The page shows a block diagram of the luminance signal processing IC LA7323. The IC has a luminance signal recording / reproducing circuit incorporated therein, a part of which is shown in FIG. In FIG. 2, the switch (1) is switched to the R side during recording, and the color video signal from the terminal (2) is applied to the low pass filter (4) via the switch (1) and the first pin (3). To be done. Then, only the luminance signal component in the color video signal is extracted, and the buffer (5) is extracted.
And to the second pin (7) via the clamping capacitor (6). The luminance signal applied to the second pin (7) is clamped by the clamp circuit (8) in the IC and the subsequent processing is performed.

In FIG. 2, the upper side of the one-dot chain line shows the inside of the IC.

During reproduction, the switch (1) is switched to the P side, and the demodulated luminance signal from the FM demodulation circuit (9) is switched to the switch (1),
It is applied to the de-emphasis circuit (10) through the first pin (3) and the low pass filter (4). The low pass filter (4) is used to remove residual carriers. The luminance signal subjected to the de-emphasis in the de-emphasis circuit (10) is transferred to the clamp capacitor (1
1) and the second pin (12) through the clamp circuit (1
3) is applied. The luminance signal applied to the clamp circuit (13) is clamped and thereafter processed.

Therefore, according to the circuit of FIG. 2, two signals can be led to the outside of the IC using a single pin (first pin (3)) and the low-pass filter (4) can be shared.

(C) Problems to be solved by the device By the way, in the circuit of FIG. 2, the low-pass filter (4), the de-emphasis circuit (10) and the buffer (5) are all external to the IC, There was a problem that the number of external parts increased.

(D) Means for Solving the Problems The present invention has been made in view of the above points, and a first transistor to which a recording luminance signal is applied to the base and a reproducing luminance signal to the base are applied. And a second transistor whose collector is connected to the emitter of the first transistor, and a second signal connected to the emitter of the first transistor. The brightness signal recording / reproducing circuit is characterized in that the emitter of the first transistor is connected to a pin of the integrated circuit. , At the time of recording with low impedance,
The luminance signal is derived from the pin with high impedance during reproduction.

(E) Operation According to the present invention, a filter circuit is provided as an external element of the IC on the emitter of the first transistor to which the recording luminance signal is applied to the base, and the reproducing luminance signal is applied to the base. The collectors of the two transistors are connected to the emitter of the first transistor. Therefore, at the time of recording, the recording brightness signal is not affected by the filter
It can be derived to the outside, and at the time of reproduction, the reproduction luminance signal can be de-emphasized by using the filter and the signal can be derived to the outside of the IC.

(F) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. (14) is a low-pass filter built in the IC (15) indicated by the alternate long and short dash line, and (16) is the contact R side during recording. A switch for switching to the contact P side during reproduction, (17) a first transistor to which the recording luminance signal from the switch (16) is applied to the base,
(18) is a second transistor to which the reproduction luminance signal from the switch (16) is applied to the base, ( 19 ) is an IC (15)
A de-emphasis filter connected externally to the first pin (3), (20) a third transistor to which the signal from the filter ( 19 ) is applied to the base, (21)
Is a clamp capacitor, (22) is a clamp circuit which clamps a luminance signal using the clamp capacitor (21), and (23) is a switch which operates in conjunction with the switch (16).

In FIG. 1, the same circuit elements as those in FIG. 2 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, the switches (1), (16) and (23) are switched to the contact R side during recording. Then, the color video signal from the terminal (2) is filtered by the low-pass filter (14) and becomes only the luminance signal component, which is applied to the base of the first transistor (17) via the switch (16). At this time, the second transistor (18) is turned off. Therefore, the first transistor (17) has an emitter follower type configuration in which the filter ( 19 ) serves as an emitter load. The value of the internal resistance of the emitter of the first transistor (17) is much smaller than the impedance of the filter ( 19 ). Therefore, the luminance signal obtained at the emitter of the first transistor (17) is applied to the base of the third transistor (20) without being affected by the filter ( 19 ). The luminance signal generated at the emitter of the third transistor (20) is clamped by the clamp capacitor (21) and the clamp circuit (22) and then led to the terminal (24) via the switch (23). .

Therefore, according to the circuit of FIG. 1, the luminance signal for recording can be clamped.

Next, at the time of reproduction, the switches (1), (16) and (23) are switched to the contact P side. Then, the demodulated luminance signal from the FM demodulation circuit (9) is applied to the base of the second transistor (18) through the low pass filter (14) and the switch (16). Therefore, the second transistor (18) has a configuration in which the filter ( 19 ) serves as a collector load. Since the collector internal resistance of the second transistor (18) is sufficiently large, the second transistor (18)
The luminance signal applied to the base of the third transistor (20) is applied with the de-emphasis characteristic by the filter ( 19 ) and then applied to the base of the third transistor (20). And the third
The luminance signal generated at the emitter of the transistor (20) is
After being clamped by the clamp capacitor (21) and the clamp circuit (22) as in the recording, it is led to the terminal (25) through the switch (23).

Therefore, according to the circuit of FIG. 1, the de-emphasis characteristic can be added to the luminance signal for reproduction and clamping can be performed.

The resistor (26) connected to the emitter of the second transistor (18) is arranged for adjusting the level of the reproduction signal. (26) may be external to the IC (15).

(G) Effect of the Invention As described above, according to the present invention, it is possible to provide a luminance signal recording / reproducing circuit that can be integrated into an IC, because external components can be reduced and the number of pins does not increase. I can. In particular, according to the present invention, the clamping capacitor and the clamping circuit can be shared during recording and reproduction, which is suitable for use in an IC.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional luminance signal recording / reproducing circuit. (17) …… First transistor, (18) …… Second transistor, ( 19 ) …… Filter, (22) …… Clamp circuit.

Claims (3)

[Scope of utility model registration request] 1. A first transistor having a base to which a recording luminance signal is applied, and a second transistor having a base to which a reproducing luminance signal is applied and a collector connected to an emitter of the first transistor. A luminance signal recording / reproducing circuit having a built-in integrated circuit,
A luminance signal recording / reproducing circuit, wherein an emitter of the first transistor is connected to a pin of the integrated circuit, and a luminance signal is derived from the pin with low impedance during recording and with high impedance during reproduction. 2. A first transistor having a base to which a recording luminance signal is applied, and a second transistor having a base to which a reproducing luminance signal is applied and a collector connected to an emitter of the first transistor. A luminance signal recording circuit, wherein a luminance signal for recording and reproducing is derived from an output end of the filter, by incorporating a filter into the integrated circuit, the filter being provided outside the integrated circuit at the emitter of the first transistor. Reproduction circuit. 3. A luminance signal recording / reproducing circuit according to claim 2, wherein a clamp circuit is provided at a stage subsequent to said filter, and a luminance signal for recording and reproducing is derived from an output end of said clamp circuit.