FURTHER INFORMATION

Inputs Vpol1 and Vpol2 are designed to be wired to the

power inputs of an LNB via a high value (1K) resistors.

Input Vpol1 controls outputs HOR1, BHOR1 and ENA1.

Input Vpol2 controls outputs HOR2, BHOR2 and ENA2.

With either input voltage set at or below 14V, the

corresponding HOR pin will be active and the

corresponding BHOR pin will be the inverse of HOR.

With either input voltage at 14.5V or higher, the

corresponding HOR pin will be active and the

corresponding BHOR pin will be the inverse. Should

the voltage applied to either Vpol input fall below 8V,

the corresponding ENA (enable) pin will be low,

otherwise these outputs will remain high. Any input or

output may be left open circuit without any effect on

the remaining circuitry.

The ZLNB2012 includes all the circuitry necessary to

detect the presence of a 22kHz tone modulated on the

supply input to the LNB. The main elements of the

detector are an op-amp, a rectifier/smoother and a

comparitor. The op-amp has a pre-set internal

feedback resistor so that just a simple RC network

wired to the input gives user defined gain and low

frequency cut filter characteristics.

The RC network components also serve two other

purposes. The resistor provides overvoltage

protection for the Vpol pin and the capacitor minimises

tone interference of the Vpol threshold. The upper

frequency roll-off of the op-amp has been set internally

at above 100kHz to allow the amplifier to be used with

other common tone switch frequencies.

The rectifier/smoother/comparitor function is provided

by a complex propriety circuit that allows the

ZLNB2012 to reliably detect wanted tones whilst

ignoring low frequency square wave switch box

signals, DiSEqC™ bursts and supply switching

transients common when using DiSEqC-2™ ready

set-top boxes. This is all achieved without the need for

any further external components. The threshold of the

comparitor is supply dependent, hence the gain of the

preceding op-amp must be adjusted in line with supply

voltage.

Output Truth Table

The ZLNB2012 includes two independent channels, each containing a voltage detector and tone detector. The

following truth table applies to each channel:-

PROVISIONAL ISSUE A - OCTOBER 2001

ZLNB2012

7

Tone

Vpol

TD

BTD

HOR

BHOR

ENA

Off

14V

Low

High

Low

High

High

Off

14.5V

Low

High

High

Low

High

On

14V

High

Low

Low

High

High

On

14.5V

High

Low

High

Low

High

-

<8V

-

-

Low

High

Low