AN0015
15
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
L
CHOKE
IN
C
BLOCK
RFMD
NBB-300
R
2
V
D
C
BLOCK
C
BLOCK
V
D
L
CHOKE
OUT
C
BLOCK
R
1
R
3
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.
R
2
37
Ω
R
1
150
Ω
R
3
150
Ω
15
TECHNICAL NOTES
AND ARTICLES
Example 1. S-Parameters for a 6dB Pi-Pad Attenuator.
Derive the four s-parameters from the 6dB Pi-Pad attenuator shown.
Copyright 1997-2002 RF Micro Devices, Inc.
15-35
RFMD [ RF MICRO DEVICES ]
