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TEA7650H Datasheet(PDF) 8 Page - NXP Semiconductors |
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TEA7650H Datasheet(HTML) 8 Page - NXP Semiconductors |
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8 / 23 page  September 1990 8 Philips Semiconductors Preliminary specification Video signal processor for CD-video/laser vision TEA7650H frequency.The phase of the line synchronization pulses (CS1, pin 2) can be used to control the speed of the turntable motor. However, with this method it is not possible to obtain an acceptable reduction of timing errors for frequencies of 25 Hz and above. To reduce errors, use is made of an external Electronic Time Base Corrector (ETBC) between pins 27 and 31 which functions as a variable delay line driven by an error signal. This error signal can be extracted from the output signal CS1 (pin 2), CHR1 (pin 48), CS2 (pin 46) and CHR2 (pin 44). Since the line sync pulses (CS1) are not suitable to achieve an accurate enough measurement of time difference, use is made of the 3.58 MHz burst signal derived from the chrominance signal CHR1. If the same zero crossing of the burst signal is used in every line, the actual time can be measured with sufficient accuracy. The CVBS signal leaving the ETBC might still have small timing errors due to residual control error. A second (feedback) loop is therefore required. The CVBS signal is fed into an AGC circuit (pin 31) that compensates for gain tolerances in the ETBC. As in the first loop, the line synchronization pulses (CS2) and the chrominance signal (CHR2) are derived from the CVBS signal by using second sync and chrominance separators. The error signal obtained by comparison in this feedback loop is added to the error signal obtained in the first loop. Using the burst signal for accurate measurements is a problem in the PAL format due to its alternating phase. A special 3.75 MHz (240 fh) burst has therefore been added to the video signal recorded on the PAL disk. This burst is inserted on the top level of the line sync pulses. In dual standard applications, the resonant circuits of the chrominance separators (pins 1 and 45) should be tuned to 3.67 MHz to ensure good separation of the special burst or the chrominance subcarrier. When the timebase-corrected CVBS signal has by-passed the second sync and chrominance separators, it reaches the special burst suppressor which removes the special burst. The signal is then fed into the noise reduction circuit. Noise reduction A noise reduction circuit can be used to improve the apparent picture quality of a noisy signal. It operates as follows: First the timebase corrected CVBS signal is buffered (pin 33) and then fed into an external network which removes the chrominance subcarrier and all low-frequency components. It is then fed into a limiter (pin 35) which ensures that only small amplitudes (mainly noise) are removed from the main signal. The chrominance subcarrier trap is switched to either the PAL subcarrier frequency (4.43 MHz) or the NTSC subcarrier (3.58 MHz) by the PAL/NTSC system selector (pin 37) using the additional small capacitor at pin 34. An external resistor at pin 36 is included so that manufacturers can select their preferred level of noise reduction, or none at all, by grounding the pin. Picture insertion The CVBS signal containing the information to be displayed is applied to pin 40. A clamp circuit ensures that the black level of this signal is the same as that of the main signal. Both signals are applied to the insertion switch. When, for example, a character is to be displayed the 6 dB attenuation (pin 39) is first activated to generate a reduced contrast background area around the character (with respect to the black level so that the original picture is still visible). Next, the insertion switch (pin 38) is activated and the character appears at the output. By switching back to the original picture, the procedure operates in the reverse sequence. Other examples of the picture insertion facility are displaying a background picture during start-up of the video disk player or the use of picture-in-picture. A buffer is provided at the CVBS output (pin 42) which delivers a CVBS signal clamped to black level and controlled to a peak-to-peak amplitude of 1 V. Reference voltage A reference voltage of 1.6 V is provided by a bandgap circuit. Internally, all control circuits are supplied with this reference voltage. Externally, it can be used for various purposes. |
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