Balanced PI-Attenuator (MA065E)

The next formulas are used to calculate the components of a π (PIT) attenuator.

 

Formula 1

Rs = Z x [ (k² - 1)/(2 x k) ]

Where:

Rs is the parallel resistance in ohm (Ω)

Z is the impedance (Zin = Z out) in ohm (Ω)

K is the attenuation factor

Formula 2

Rp = Z x [ (k + 1) / (k – 1) ]

Where:

Rp is the parallel resistance in ohm (Ω)

Z is the impedance (Rin = Rout) in ohm (Ω)

K is the attenuation factor.

Application Example:

Calculate the components of a PI-attenuator with na input/output impedance of 50 Ω and na attenuation factor of 5.

Data:

Z = 50 Ω

K = 5

Rp, Rs = ?

Applying formula 1 for Rs:

Rs = 50 x [ (5² - 1)/(2 x 5) ]

Rs = 50 x (24/10)

Rs = 50 x 2,4

Rs = 120 Ω

Using formula 2 for Rp:

Rp = 50 x [ (5 + 1) / (5 – 1) ]

Rp = 50 x (6 / 4)

Rp = 75 Ω