Π pad

The topology of an attenuator circuit will usually follow one of the simple filter sections.

However, there is no need for more complex circuitry, as there is with filters, due to the simplicity of the frequency response required.

Circuits are required to be balanced or unbalanced depending on the geometry of the transmission lines with which they are to be used.

For audio and telecommunications, balanced circuits are usually required, such as with the twisted pair format.

However, it can be converted to a balanced circuit by placing half the series resistance in the return path.

Most commonly, the generator and load impedances are equal so that Z1 = Z2 = Z0 and a symmetrical Π pad is used.

The usual requirement in a design is the other way around – the resistor values for a given impedance and loss are needed.

Figure 1. Schematic circuit of a Π-pad attenuator.
Unbalanced source and load. V1o is open circuit voltage of the source.
Figure 2. A general L-section circuit with shunt admittance Y and series impedance Z .
Figure 3. A Π-pad attenuator formed from two symmetrical L sections. Because of the symmetry, R 1 = R 3 in this case.
Pi pads, O pads and split O pads
Conversion of two-port admittance parameters to pi pad
Conversion of tee pad to pi pad