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EL9112IL-T7 Datasheet(PDF) 10 Page - Intersil Corporation |
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EL9112IL-T7 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 12 page 10 FN7450.1 May 17, 2005 Applications Information Logic Control The EL9112 has two logical input pins, Chip Enable (ENABLE) and Switch Gain (X2). The logic circuits all have a nominal threshold of 1.1V above the potential of the logic reference pin (VREF). In most applications it is expected that this chip will run from a +5V, 0V, -5V supply system with logic being run between 0V and +5V. In this case the logic reference voltage should be tied to the 0V supply. If the logic is referenced to the -5V rail, then the logic reference should be connected to -5V. The logic reference pin sources about 60µA and this will rise to about 200µA if all inputs are true (positive). The logic inputs all source up to 10µA when they are held at the logic reference level. When taken positive, the inputs sink a current dependent on the high level, up to 50µA for a high level 5V above the reference level. The logic inputs, if not used, should be tied to the appropriate voltage in order to define their state. Control Reference and Signal Reference Analog control voltages are required to set the equalizer and contrast levels. These signals are voltages in the range 0V - 1V, which are referenced to the control reference pin. It is expected that the control reference pin will be tied to 0V and the control voltage will vary from 0V to 1V. It is; however, acceptable to connect the control reference to any potential between -5V and 0V to which the control voltages are referenced. The control voltage pins themselves are high impedance. The control reference pin will source between 0µA and 200µA depending on the control voltages being applied. The control reference and logic reference effectively remove the necessity for the 0V rail and operation from ±5V (or 0V and 10V) only is possible. However we still need a further reference to define the 0V level of the single ended output signal. The reference for the output signal is provided by the 0V pin. The output stage cannot pull fully up or down to either supply so it is important that the reference is positioned to allow full output swing. The 0V reference should be tied to a 'quiet ground' as any noise on this pin is transferred directly to the output. The 0V pin is a high impedance pin and draws dc bias currents of a few µA and similar levels of AC current. Equalizing When transmitting a signal across a twisted pair cable, it is found that the high frequency (above 1MHz) information is attenuated more significantly than the information at low frequencies. The attenuation is predominantly due to resistive skin effect losses and has a loss curve which depends on the resistivity of the conductor, surface condition of the wire and the wire diameter. For the range of high performance twisted pair cables based on 24awg copper wire (CAT-5 etc.) these parameters vary only a little between cable types, and in general cables exhibit the same frequency dependence of loss. (The lower loss cables can be compared with somewhat longer lengths of their more lossy brothers.) This enables a single equalizing law equation to be built into the EL9112. With a control voltage applied between pins VCTRL and VREF, the frequency dependence of the equalization is shown in Figure 8. The equalization matches the cable loss up to about 100MHz. Above this, system gain is rolled off rapidly to reduce noise bandwidth. The roll-off occurs more rapidly for higher control voltages, thus the system (cable + equalizer) bandwidth reduces as the cable length increases. This is desirable, as noise becomes an increasing issue as the equalization increases. Contrast By varying the voltage between pins VGAIN and VREF, the gain of the signal path can be changed in the ratio 4:1. The gain change varies almost linearly with control voltage. For normal operation it is anticipated the X2 mode will be selected and the output load will be back matched. A unity gain to the output load will then be achieved with a gain control voltage of about 0.35V. This allows the gain to be trimmed up or down by 6dB to compensate for any gain/loss errors that affect the contrast of the video signal. Figure 26 shows an example plot of the gain to the load with gain control voltage. FIGURE 26. VARIATION OF GAIN WITH GAIN CONTROL VOLTAGE C ommon Mode Sync Decoding The EL9111 features common mode decoding to allow horizontal and vertical synchronization information, which has been encoded on the three differential inputs by the EL4543, to be decoded. The entire RGB video signal can therefore be transmitted, along with the associated synchronization information, by using just three twisted pairs. 00.8 VGAIN 0.4 1 2 1.8 1.4 1 0.6 0.4 0.6 0.2 1.6 1.2 0.8 EL9111, EL9112 |
Similar Part No. - EL9112IL-T7 |
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Similar Description - EL9112IL-T7 |
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