The next formulas are used for calculations involving the symmetric-T attenuator.
Formula 1
Rs = Z x [ (k-1)/(k+1) ]
Where:
Rs is the parallel resistance in ohm (Ω)
Z is the impedance (Zin and Zout must be equal) in ohm (Ω)
K is the attenuation factor (ratio of input voltage/current and output voltage/current)
Formula 2
Rp = Z x [ (2 x k)/(k2-1) ]
Where:
Rp is the parallel resistance in ohm (Ω)
Z is the impedance (Zin = Zout) in ohm (Ω)
K is the attenuation factor
Application Example:
Determine the resistance to be used in a T-attenuator where the input impedance and output impedance are 300 Ω and the desired attenuation factor is 4.
Data:
Z= 300 Ω
K = 4
Rp = ?
Rs = ?
Applying formula 1 for Rs:
Rs = 300 x [ (4-1)/(16+1) ]
Rs = 300 x (3/5)
Rs = 180 Ω
Applying formula 2 for Rp:
Rp = 300 x [ (2 x 4)/(16 - 1) ]
Rp = 300 x (8 / 15)
Rp = 160 Ω
