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LM1209 データシート(PDF) 9 Page - National Semiconductor (TI) |
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LM1209 データシート(HTML) 9 Page - National Semiconductor (TI) |
9 / 24 page Applications Information (Continued) Figure 5 shows the block diagram of a typical analog RGB color monitor The RGB monitor is used with CADCAM work stations PC’s arcade games and in a wide range of other applications that benefit from the use of color display terminals The RGB color monitor characteristics may differ in such ways as sweep rates screen size CRT color trio spacing (dot pitch) or in video amplifier bandwidths but will still be generally configured as shown in Figure 5 Separate horizontal and vertical sync signals may be required or they may be contained in the green video input signal The video input signals are usually supplied by coax cable which is terminated into 75X at the monitor input and internally AC coupled to the video amplifiers These input signals are ap- proximately 1V peak to peak in amplitude and at the input of the high voltage video section approximately 5V peak to peak At the cathode of the CRT the video signals can be as high as 60V peak to peak One important requirement of the three video amplifiers is that they match and track each other over the contrast and brightness control range The Figure 5 block labeled ‘‘VIDEO AMPLIFICATION WITH GAIN AND DC CONTROL’’ describes the function of the LM1208LM1209 which contains the three matched video amplifiers contrast control and brightness control The LM1208LM1209 also provides the capability to blank at the cathode of the CRT Functional Description Figure 6 is a detailed block diagram of the green channel of the LM1208LM1209 along with the recommended external components The IC pin numbers are circled and all external components are shown outside the dashed line The other two video channels are identical to the green channel only the numbers to the pins unique to each channel are differ- ent The input video is normally terminated into 75X The termination resistor depends on the impedance of the coax cable being used 75X being the most common impedance used in video applications The video signal is AC coupled through a 10 mF capacitor to the input pin 6 There is no standard for the DC level of a video signal therefore the signal must be AC coupled to the LM1208LM1209 Internal to the LM1208LM1209 is a 28V reference giving the input video an offset voltage of 28V This voltage was selected to give the input video enough DC offset to guarantee that the lowest voltage of the video signal at pin 6 is far enough above ground to keep the LM1208LM1209 in the active region The 200X resistor at the input is for ESD protection and for current limiting during any voltage surge that may occur at the input driving pin 6 above VCC The input video signal is buffered by bA1 In this circuit description an in- verting amplifier is shown with a ‘‘b’’ (minus sign) in front of the amplifier designation The output of bA1 goes to the contrast and drive attenuator sections The contrast and drive control sections are virtually identi- cal Both sections take a 0V to 4V input voltage 4V giving the maximum gain for either the contrast or the drive This is a high impedance input allowing for an easy interface to 5V DACs One may also use 100k potentiometers with no deg- radation in performance The contrast control section is common to all three channels It converts the input voltage at pin 12 to a couple of internal DC voltages that control the gain of the contrast attenuator Referring to the Attenuation vs Contrast Voltage under typical performance characteris- tics note that a 4V control voltage results in no attenuation of the video signal A 025V control voltage results in an attenuation of 40 dB Again note that these internal control voltages are common to all three channels To minimize crosstalk these voltages go to pins 1 and 2 Minimizing crosstalk is done by adding the RC network shown in the block diagram (Figure 6) TLH11884 10 FIGURE 5 Typical RGB Color Monitor Block Diagram http www nationalcom 9 |
同様の部品番号 - LM1209 |
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同様の説明 - LM1209 |
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