Quote Originally Posted by Brian DK View Post
And again.. Why a lower resistor to lower the output level?
Should it not be a resistor with higher value.?
Hi Brain DK,

The influence of the 'shunt-resistor' can be calculate using the following formulas:

if with Ro we denote 'serial resistor' and with Rs we denote shunt resistor, and if with Rd we denote the driver resistance the
the voltage response Av on the driver (neglecting ALL real and equivalent capacitors and inductors) would be:

Av = 1 / [ 1 + Ro*( 1/Rd +1/Rs)]

so from here as Rs become smaller 1/Rs become LARGER, so the products Ro*( 1/Rd +1/Rs) become larger, and Av become smaller.

Such formula become much more complicate if other elements of the network are included, especially if equivalent impedance and the response of the driver are included too. In such situations some computer programs has to be used..

regards
Ivica