1/8

May 2004

AN589

APPLICATION NOTE

CROSSTALK BEHAVIOUR OF

ITA25 IN RS232 TRANSMISSION

REV. 2A - 3601

INTRODUCTION

Crosstalk is a digital interference phenomenon between data lines. The signal transmission by one data

line produces parasitic voltages on nearby channels. These disturbances are due mainly to capacitive

coupling or electro magnetic interference. This phenomenon occurs particulary when a great number of

lines are located in a small area, notably in the case of multiline protection circuits having a high density.

The decrease of available area and the increase in the number of lines managed by a board forces the

use of a single chip configuration to realize the protection function.

The goal of this paper is to quantify the parasitic effect of STMicroelectronics monolithic protection prod-

ucts.

TEST DIAGRAM

To analyse the crosstalk behavior we will take as an example the most commonly- used interface: RS232.

Figure 1. Test circuits

Figure 1 shows the test circuits used to do the crosstalk measurements.

The equivalent circuits of the drivers and receivers have been determined from the RS232C standard. So

the following tests are done with:

R1 + R’1 = 500 Ohms and R2 + R’2 = 3 k Ohms.

ITA25B3

R1

R'1

R'2

+/- 12V

R2

+/- 12V

Driver 1

Driver 2

Receiver 2

Receiver 1