AN0015 Datasheet, PDF (1/6 Pages) RF Micro Devices – Design of “PI” and “T” Network Attenuators for Inter-Stage Buffering

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AN0015
AN0015
Design of “PI” and “T” Network Attenuators for Inter-Stage Buffering
Design of “PI” and “T” Network Attenuators for Inter-Stage Buffering
The NBB and NDA-series matched amplifiers may be cascaded in a driver chain or used adjacent to other components
such as mixers, oscillators, or filters. In all such instances, it is desirable to provide isolation between adjacent compo-
nents to minimize ripple due to any impedance mismatch. "PI" and "T" Network Attenuators (also known as PAD attenu-
ators) are simple networks to insert between an amplifier chain (see Figure 1) or between an amplifier and adjacent
component to minimize ripple over frequency.
2-STAGE DRIVER AMPLIFIER CHAIN
V_CC1
V_CC2
R_BIAS
R_BIAS
IN
C_BLOCK
L_CHOKE
V_{D CBLOCK}
R₂
R₁
C_BLOCK
R₃
L_CHOKE
V_{D CBLOCK}
OUT
RFMD
NBB-300
RFMD
NBB-300
"PI" Attenuator
Figure 1. Two-stage driver amplifier chain using two NBB-300 amplifiers, along with a "PI" buffer network, used to
minimize ripple in the amplifier chain's response. The "PI" network is symmetric and consists of two resistor
values, R1 and R2.
The following example illustrates a circuit technique to analyze the "PI" network configuration.
R₂
37 Ω
R₁
150 Ω
R₃
150 Ω
Example 1. S-Parameters for a 6dB Pi-Pad Attenuator.
Derive the four s-parameters from the 6dB Pi-Pad attenuator shown.
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Copyright 1997-2002 RF Micro Devices, Inc.
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