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RFMW Circuit TutorialSheet 1 of 14

Attenuator Design Tutorial Introduction Attenuators are devices used to adjust signal levels, to control impedance mismatch and to isolate circuit stages. Passive design Passive attenuators consist of two types ‘pi’ and ‘Tee’ attenuators. (1) Pi Attenuator The circuit for the Pi attenuator is shown in Figure 1.

R3

Zout

Zin R1 R2

Zin >= Zout
Figure 1 Pi Attenuator
R3 =
L 1 10 10 1 Zin * Zout L 2 10 10

R2 =

1 10 + 1 1 L 10 R3 Zout 10 1
L 10

R1 =

1 10 + 1 1 L 10 R3 Zin 10 1
L 10

Where L = desired loss in dB Zin = desired input impedance (ohms) Zout = desired output impedance (ohms)

Sheet 2 of 14

(2) Tee Attenuator The circuit for the T attenuator is shown in Figure 2

R1

R2

Zin R3

Zout

Zin >= Zout
Figure 2 Circuit of the T attenuator
L

R