UTC L8115

LINEAR INTEGRATED CIRCUIT

QW-R123-005,B

Control Input Switch Function

Input sense

Polarisation

Select

≤

14 volts

Vertical

FET Q2

≥

15.5 volts

Horizontal

FET Q1

For many LNB applications, tone detection for band switching is required. The UTC L8115 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

UTC L8115 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. See the

table

below for recommended values for 22kHz detection, given for a range of supplies.

Lov Input

Output

-

+

-

+

Enable

Enable

OUTPUT DRIVERS

LNB Input

R2

2k

CF1

4.7n

-

+

Ref

-

+

Ref

FILTER

RECTIFIER

UTC L8115

COMPARATOR

Table_1

Supply Voltage (Vcc)

Filter

Components

5V

6V

7V

8V

9V

10V

Cf

4.7nF

4.7nF

4.7nF

10nF

10nF

10nF

Rvpol(R2)

2k

1.8k

1.5k

1.3k

1.1k

1.0k

Note:Optimised for F(tone)=22kHz