The ZLNB200X dual polarisation and tone switch controller is one of a wide range of satellite receiver LNB support circuits available from Zetex. It features two completely independent channels, each providing logic outputs to control LNB polarisation selection, local oscillator selection and downfeed disable. It is intended for use in Twin Universal LNBs, replacing many discrete components to save both manufacturing cost and PCB size whilst improving reliability.
The two polarisation control inputs of the ZLNB200X have a nominal threshold of 14.75V. The threshold is temperature compensated to minimise drift. Each features a low and stable input current that enables transient protection to be achieved with the addition of only a single resistor per channel.
Twin Universal LNBs can be called to operate with one of their controlling receivers powered down/disconnected, with attendant cable mismatch problems. To ease design for this situation, each polarisation input of the ZLNB200X has a second threshold set at 9.5V. An input voltage below this threshold indicates "receiver not present", switching the channels Enable pin low. This logic output can be used to disable the associated downfeed driver, eliminating any problems due to cable mismatch.
Universal LNB local oscillator selection is achieved by detection of a low level AC voltage superimposed on the polarisation control voltage. To facilitate this function, the ZLNB200X includes a separate tone de\tector for each channel. Full control of detector bandwidth and sensitivity is provided using two external resistors and capacitors. In the ZLNB2003/4, additional control of tone switch delays is provided to assist with the rejection of low frequency control signals intended for other systems.
Polarisation switch and tone detector outputs can source and sink 10mA making them suitable to drive TTL and CMOS logic, pin diodes and for IF-amp supply switch
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