This document discusses selecting the type of notch filter to place at the output of a PA to reject the second harmonic frequency. It analyzes using either a series or shunt notch filter. It determines that a shunt filter is better despite having slightly lower simulated rejection. This is because the series filter actually has more insertion loss due to additional impedance discontinuities compared to the shunt filter. It also finds that adding a stub to the shunt filter reduces its rejection performance. Finally, it notes that placing the filter closer to the PA will affect the PA's load pull characteristics more.

1. PA output Notch Filter
Consideration

2. PA output Notch Filter type selection
n F = 433.2 MHz, 2F = 866.4 MHz
n We need to put notch filter at PA output
to enhance 2 order harmonics rejection
n But, series type or shunt type ?

3. PA output Notch Filter type selection
n Series type is better than shunt type in all aspects
IL (dB) Rejection (dB) Impedance
Series Type 0.12 18.86 50.46 + 14.3j
Shunt Type 0.2 16.06 42.83 – 17j

4. PA output Notch Filter type selection
n Series type has three impedance discontinuity, but
shunt type has only one
n Series type has worse impedance discontinuity
(9mil => 20mil) than shunt type(9mil => 12mil)
n Impedance discontinuity effect leads to mismatch loss.
In other words, series type seems to have less loss in
simulation, but actually it has more loss

5. Stub for notch filter ?
n For shunt type, with stub,
there is still impedance discontinuity effect
n In addition, the 2F rejection becomes worse
than the original one due to
the parasitic inductance.

6. Stub for notch filter ?
2fo Rejection (dB)
With Stub 10.44
Without Stub 16.06
Delta 5.6 dB

7. Notch Filter location
n Case A affects PA’s load-pull more than Case B.