ZLNB2012

The ZLNB2012 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, Quad and multiple feed Universal LNBs, replacing many discrete components to save both manufacturing cost and PCB size whilst improving reliability.

The two highly accurate polarisation control inputs of the ZLNB2012 have a nominal threshold of 14.25V and to meet the required demanding needs from some broadcasters they have a switching range of 14.0V to 14.5V. 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.

Multi Feed LNBs can be called to operate with one or more of their controlling receivers powered down/disconnected, with attendant cable mismatch problems. To ease design for this situation, each polarisation input of the ZLNB2012 has a second threshold set at 9V. An input voltage below this threshold indicates" receiver not present", and switches the relevant control channels high. 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 ZLNB2012 includes a separate tone detector for each channel. Control of detector bandwidth and sensitivity is provided using an external resistor and capacitor for each channel. The tone detector has been designed give excellent rejection of low frequency control signals and DiSEqC™ tone bursts.

The ZLNB2012 has been specifically designed to minimise the solution cost whilst being flexible. The ZLNB2012 only requires two external components per channel to give full user control and functionality. The ZLNB2012 also includes complimentary outputs so that it can directly drive many multiplexer IC's without the need of an inverter. Any unused outputs can be left open circuit without any effect to the remaining circuits operation Polarisation switch and tone detector outputs can directly drive TTL and CMOS logic, pin diodes, IF-amp supply switching and multiplexer IC's.

The ZLNB2012 operates from a single supply which can be anything from 5-8V. Its quiescent current is typically only 9mA and this does not change significantly with load or logic state. It is available in the space saving QSOP16 surface mount package.