ZNBG3113
ZNBG3114
For many LNB applications tone detection and band switching is required. The ZNBG3113/14
includes the circuitry necessary to detect the presence of a 22kHz tone modulated on the supply
input to the LNB. Referring to the following schematic diagram, the main elements of this detector
are an op-amp enabling the construction of a Sallen Key filter, a rectifier/smoother and a
comparator. Full control is given over the centre frequency and bandwidth of the filter by the
selection of two external resistors and capacitors (one of these resistors, R2, shares the function
of overvoltage protection of pin VPOL).
Pin Crec makes accessible the output of the tone switch rectifier and provides a means of
controlling tone switch delays (mainly HB-LB). For correct operation of the IC, a capacitor and a
parallel connected resistor should be connected between this pin and ground. A capacitor of
100nF and resistor of 1MW will give a LB-HB delay of around 100µs and a HB-LB delay of 30ms.
The comparator circuit utilises no external components.
4-132
ZETEX [ ZETEX SEMICONDUCTORS ]
