ZL40166 Datasheet, PDF (4/33 Pages) Zarlink Semiconductor Inc – High Output Current High Speed Dual Operational Amplifier

Data Sheet
ZL40166
Video transmitter and receiver for twisted wire pair.
Composite video signals can be transmitted down twisted pair cable, i.e. Ethernet (CAT 5), using a differential
transmitter and receiver. The transmitter must be able to drive high currents into the low impedance twisted pair
cable. For video, the amplifiers require flat gain and low phase-shift over the video signal band. To ensure this, the
amplifiers will have 3dB bandwidths well in excess of this. The ZL40166 (dual amplifier) has all of these attributes.
With reference to the differential video driver shown in Figure , the input coax is assumed to have a characteristic
impedance of 75 Ohms, this is terminated with a parallel combination of 110 Ohms and the input impedance of
amplifier IC1 (b) of 255 Ohms, giving 77 Ohms. Low values of feedback resistors are used around the op-amps to
reduce phase-shift due to parasitic capacitors and to minimise the addition of noise.
Baseband PAL or NTSC video signals generally have an amplitude of 2V pk-pk. A gain of two is used to ensure that
the signal level at the end of the (terminated with 100 Ohms) differential pair will be the same as the input level,
neglecting any losses due to the use of long cable lengths.
Composite Video
Co-Ax Input
IC1(a)
110R
510R
510R
510R
50R
510R
510R
50R
IC1(b)
Twisted Pair
Output
Figure 4 - Differential Video Driver
The differential receiver is shown in Figure 5 has a 100 Ohm line termination resistor, followed by a differential
amplifier. Long cables will tend to attenuate the signal with greater losses at the higher frequencies, so the second
amplifier is used to equalise these losses. Initially the amplifier should be built without fitting components R1 and
C1. Select the value of R2 to give the required gain at low frequency. Adjust the values of R1 and C1 to correct for
the frequency dependant attenuation of the cable.
To drive a coax cable the output of the amplifier is connected via a series matching 75 Ohm resistor, again this
second (dual amplifier) ZL40166 provides the required power output for the restored 2Vpk-pk video signal.
Twisted Pair
Input
100R
510R
510R
510R
IC2(a)
510R
C1 R1
510R
R2
IC2(b)
Composite Video
Co-Ax Output
75R
Figure 5 - Differential Video Receiver
Zarlink Semiconductor Inc.
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