Video Transmitter (Driver)
The video transmitting circuitry can be accomplished by utilizing one LMH6733 to transmit the HD analog component video configured for a gain of 2 V/V. Each of the three op amp channels convert the Y, Pr, and Pb video signal into a pseudo-differential output signal with one of the twisted-pair wires connected to ground through a 50Ω resistor to shield the signal and maintain signal integrity. Figure 3 shows the video transmit circuit.
Figure 3: CAT5 Video Transmitter Circuit
Video Receiver & Equalization
The video receiver circuit on the far end of the CAT5 cable can be implemented by using one LMH6733 device. Each amplifier channel can be configured for a gain of
-2 V/V to handle a differential input signal from each of the three twisted-pairs for the Y, Pr, and Pb video signals. A simple RC, low-pass filter with a -3dB roll off of 200MHz can be place between the receiver output and equalizer input to filter out high frequency noise components. Due to the non-inverting input capacitance of 1pF, an inverting gain topology is recommended for the equalization circuit to minimize gain peaking and potential oscillation due to excessive parasitic capacitance and inductance associated with device package and board routing.
The equalization circuit can be implemented with another LMH6733 channel along with a network of RC branches in parallel with the gain resistor, RG, to provide a zero-pole compensation for attention of higher frequency signals in the CAT5 twisted-pair wires. Each branch compensates for the set frequency of attenuation depending on the cable length, such that the video signal maintains a flat frequency response to accommodate the 31MHz of large signal bandwidth required for a 1080i HD signal.
To transmit HD video signal up to 500ft of CAT5 cable the three set frequencies can be 1MHz, 10MHz, and 100MHz. Figure 1 shows that the extra boost in gain at these frequencies is approximately 2.5dB, 9dB, and 31dB, respectively. Because of its high slew rate value, the advantage of using CFB amplifiers as the equalizer is its ability to boost equalization gain at high frequencies. The output of the equalization drives a RO=75Ω load to match the input impedance of the video display.
Figure 4: CAT5 Video Receiver & Equalization Circuit
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