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TDA8501T датащи(PDF) 7 Page - NXP Semiconductors |
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TDA8501T датащи(HTML) 7 Page - NXP Semiconductors |
7 / 30 page April 1993 7 Philips Semiconductors Preliminary specification PAL/NTSC encoder TDA8501 Fig.3 Low pass filter response for colour difference signals (PAL mode). (1) frequency response. (2) group delay. Fig.4 Low pass filter response for colour difference signals (NTSC mode). (1) frequency response. (2) group delay. Low pass filters The −3dB nominal frequency response level of the low pass filters are different in PAL and NTSC modes. PAL mode: bandwidth = 1.35 MHz nominal (see Fig.3). NTSC mode: bandwidth = 1.1 MHz nominal (see Fig.4). The signal outputs of the low pass filters are connected to the signal inputs of the U and V modulators. U AND VMODULATORS Two four-quadrant multipliers are used for quadrature amplitude modulation of the U and V signals. The level of harmonics produced by the modulated signals are minimal, because of real multiplication with sinewave carriers. The unbalance of the modulators is minimized by means of a control loop and two external capacitors, pin 6 for the U modulator and pin 12 for the V modulator. The timing of the control loop is triggered by the H/2 pulse, so that during one sync period the U control is active and during the next sync period the V control is active. In this way, when U and V are both zero, the suppressed carrier is guaranteed to be at a low level. The internal oscillator circuit generates two sinewave carriers (0 degree and 90 degree). The '0 degree' (0) carrier is connected to the U modulator and the '90 degree' (1) carrier is connected to the V modulator. PAL mode: • switched sequentially by the H/2 pulse, the V signal is modulated alternately with the direct and inverse carrier. • the internal H/2 pulse can be forced into a specific phase by means of an external pulse connected to pin 4 (H/2). Forcing is active at HIGH level. If not used pin 4 can be left open-circuit or connected to ground. If pin 4 is left open, the internally generated H/2 pulse (output) is connected to this pin. NTSC mode: • alternation of the V modulation is not allowed. If pin 4 is not used for set-up control (see Y +SYNC, CVBS and Chrominance outputs), it can be left open-circuit or connected to ground. |
Аналогичный номер детали - TDA8501T |
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Аналогичное описание - TDA8501T |
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