Diodes ZNBG3211 - Manual (Page 10)

For many LNB applications tone detection and band switching is required. The ZNBG3210/11
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 V
POL
). The detector used in the ZNBG32 series has been
specifically designed to reject low frequency signals, DiSEqC

tone bursts and other common
interference signals that may be present on the LNB supply input. This has been achieved without
the need for any additional external components.
67-10
ZNBG3210
ZNBG3211