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STV2112B bảng dữ liệu(PDF) 3 Page - STMicroelectronics |
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STV2112B bảng dữ liệu(HTML) 3 Page - STMicroelectronics |
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3 / 24 page  FUNCTIONAL DESCRIPTION 1 - DEFLECTION CIRCUIT Note : [X,Y] : line number referred to the internal line counter numbering - Fully integrated synch. separator, with a low pass filter, a black level alignment of the Y/CVBS input, a slicing level at 2/3,1/3of the sync. pulse amplitude. - Frame sync. pulse locked on 2 fH frequency to perfect interlace. - 500kHz VCO with an external ceramic resonator. - Two phase locked loops • the first PLL locks the VCO on the video signal frequency, • the secondPLLcompensatesthe line transistor storage time. - Three time constants for the first PLL. • thelong timeconstantis usedfornormaloperation • the short time constant is automatically used during the frame retrace and in search mode of VCR when the frame pulse is outside [258,264] and [309,314]. • verylong time constantwhenno video recognition Time constants in normal operation (automatic selection of time constants) : 50Hz input signal : - short time constant : [306, 21] - long time constant : the rest of the field • inhibition of the first PLL : the first locked loop is opened from line 309 to line 4.5 (or 314) in 50Hz mode. • the time constantsvalues are chosenby means of external components. • possibility to force the short time constant through the bus. • possibility to force the very long time constant through the bus. - Video identification : coincidence detector be- tween the line synchro top and a line frequency window from the first PLL. The video identification status is available in the output register of the I 2C bus decoder. - Generation of burst gate pulses and line fre- quency signals from the first PLL to drive the chroma and video circuits. The burst gate pulse is also sent to the sandcastle generator. - Frame synchro window : [248, 352] catching - Field frequency selection windows : [288, 352] 50Hz mode selection window - frame blanking pulse : from line 0 to 21 in 50Hz mode - Vertical output pulse is 10.5 lines long. - Horizontal output pulse : 28 µs line pulse on an open collector output; - Start up circuit : the horizontal output is at a high level when VCC increases from 0 to 6.8V. On shutting down, horizontal pulses are disabled when VCC is below 6.2V. - Soft-start circuit : the duty cycle of the horizontal output is 78 % (Thigh/(Thigh + TLow)) when VCC1 is lower than (0.75 x VCC2), during the rising time. During the falling time, a 78% duty cycle HOUT pulse is provided when VCC1 is lower than (0.60 x VCC2). - Possibility to disable the horizontal output pulse through the bus (force a high level on HOUT). - Horizontal position adjustment controlled by bus. - Bus controlledoutput voltage to adjustthe vertical amplitude ; this voltagepermitsto adjustthe slope of the vertical sawtooth generated by the external frame booster. - Bus controlled vertical position ; the high level of the vertical pulse permits to adjust the vertical position. - Bus controlled 4/3-16/9 selection : the low level of the vertical pulse is 0.1V when 16/9 is selected, 2V when 4/3 is selected. - Combined flyback input and sandcastle output (Pin 37). Two thresholds on LFB/SCO Pin : The lowest threshold (0.7V) permits to extract the line blanking pulse ; the highest threshold (2V) per- mits to extract the line pulse for PLL2. The sand- castle signal at Pin 37 is used to control the external baseband chroma delay line. 2 - FILTERS - Integrated trap filter : Q = 1 fo f−3dB − f−3dB fo Q = 1.7 at sharp. min Q = 3.0 at sharp. max Center frequency : - 4.43MHz for PAL - 4.25MHz, for SECAM (f-3dB = 3MHz; -20dB rejection between 4.1MHz and 4.4MHz) - Integrated chroma bandpass : Q = 3.5, Center frequency= 4.43MHz - Integrated cloche filter for SECAM : Q = 16, Center frequency = 4.286MHz - Integrated delay line : Bandwidth = 8MHz - Integrated low pass filter for deflection part. - Allfilters aretunedwitha referencephaselockedloop. The PLL consists of a lowpass filter, a phasecompa- rator,a loopfilter (with an externalcapacitor).The ref- erence signal is the continuouscarrier wave from the VCO (4.43MHz). The PLL adjusts the center fre- quency of the lowpass so that it is equal to the referencesignal.ThetuningvoltageofthePLLisused to adjust all other filters. The cloche filter is fine tuned with a secondPLLoperatingduring frame retrace. STV2112B 3/24 |
Số phần tương tự - STV2112B |
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Mô tả tương tự - STV2112B |
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