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VPX3220A Datasheet(PDF) 7 Page - List of Unclassifed Manufacturers |
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VPX3220A Datasheet(HTML) 7 Page - List of Unclassifed Manufacturers |
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7 / 80 page  VPX 3220 A, VPX 3216 B, VPX 3214 C PRELIMINARY DATA SHEET MICRONAS INTERMETALL 7 2.1.4. Digitally Controlled Clock Oscillator The clock generation is also a part of the analog front- end. The crystal oscillator is controlled digitally by the control processor; the clock frequency can be adjusted within ±150 ppm if the recommended crystal is used. 2.1.5. Analog-to-Digital Converters Two ADCs are provided to digitize the input signals. Each converter runs with 20.25 MHz and has 8-bit reso- lution. An integrated bandgap circuit generates the re- quired reference voltages for the converters. The two ADCs are of a 2-stage subranging type. 2.2. Color Decoder In this block, the entire luma/chroma separation and multistandard color demodulation is carried out. The col- or demodulation uses an asynchronous clock, thus al- lowing a unified architecture for all color standards. Both luma and chroma are processed to an orthogonal sampling raster. Luma and chroma delays are matched. The total delay of the decoder is adjustable by a FIFO memory. Therefore, even when the display processing delay is included, a processing delay of exactly 64 µsec can be achieved. The color decoder output is YCrCb in a 4:2:2 format. 2.2.1. IF-Compensation With off-air or mistuned reception, any attenuation at higher frequencies or asymmetry around the color sub- carrier is compensated. Three different settings of the IF-compensation are possible: – flat (no compensation) – 6 dB/octave – 12 dB/octave Fig. 2–3: Frequency response of chroma IF-com- pensation 2.2.2. Demodulator The entire signal (which might still contain luma) is now quadrature-mixed to the baseband. The mixing frequen- cy is equal to the subcarrier for PAL and NTSC, thus achieving the chroma demodulation. For SECAM, the mixing frequency is 4.286 MHz giving the quadrature baseband components of the FM modulated chroma. After the mixer, a lowpass filter selects the chroma com- ponents; a downsampling stage converts the color dif- ference signals to a multiplexed half-rate data stream. The subcarrier frequency in the demodulator is gener- ated by direct digital synthesis; therefore, substandards such as PAL 3.58 or NTSC 4.43 can also be demodu- lated. |
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