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TDA8315 Datasheet(PDF) 5 Page - NXP Semiconductors |
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TDA8315 Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 16 page September 1994 5 Philips Semiconductors Preliminary specification Integrated NTSC decoder and sync processor TDA8315T FUNCTIONAL DESCRIPTION CVBS or Y/C input The TDA8315T has a video input which can be switched to CVBS (with internal chrominance bandpass and trap filters) and to Y/C (without chrominance bandpass and trap filters). The switching between CVBS and Y/C is achieved by the DC level of the CHROMA input (pin 15). Integrated video filters The circuit contains a chrominance bandpass and trap circuit. The filters are realised by gyrator circuits that are automatically tuned by comparing the tuning frequency with the crystal frequency of the decoder. The chrominance trap can be switched off by the DC level of the CHROMA input. The luminance delay line is also realised by gyrator circuits. Colour decoder The colour decoder contains an alignment-free crystal oscillator, a colour killer circuit and colour difference demodulators. The gain of the two colour difference signal demodulators is identical and the phase angle of the reference carrier signals is 90 °. This phase shift is achieved internally. It is possible to switch the demodulator angle to 110 ° by an internal matrix circuit. The switching is obtained externally via pin 8. Synchronization circuit The sync separator is preceded by a voltage controlled amplifier which adjusts the sync pulse amplitude to a fixed level. The sync pulses are then fed to the slicing stage (separator) which operates at 50% of the amplitude. The separated sync pulses are fed to the first phase detector and to the coincidence detector. The coincidence detector is used to detect whether the line oscillator is synchronized. The PLL has a very high static steepness, this ensures that the phase of the picture is independent of the line frequency. The line oscillator operates at twice the line frequency. The oscillator network is internal. Because of the spread of internal components an automatic adjustment circuit has been added to the IC. The circuit compares the oscillator frequency with that of the crystal oscillator in the colour decoder. This results in a free-running frequency which deviates less than 2% from the typical value. The horizontal output pulse is derived from the horizontal oscillator via a pulse shaper. The pulse width of the output pulse is 5.4 µs, the front edge of this pulse coincides with the front edge of the sync pulse at the input. The vertical output pulse is generated by a count-down circuit. The pulse width is approximately 380 µs. Both the horizontal and vertical pulses will always be available at the outputs even when no input signal is available. |
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