Master thesis presentation held on 16-05-2012. In this work a prototipe for a mm-wave mixed signal active load pull working in the frequency range from 50 to 65 GHz is presented. Further work has been accomplished on the topic, and a final version of the measurement setup has been presented at 81st and 83rd ARFTG conferences.

1. Università degli studi di Napoli
Federico II
FACOLTÀ DI INGEGNERIA
CORSO DI LAUREA SPECIALISTICA IN
INGEGNERIA ELETTRONICA
60 GHz mixed signal active load pull
for millimeter wave devices
characterization
RELATORE CANDIDATO
Ch.mo Prof. Niccolò Rinaldi Luca Galatro
Matr. 884/372
CORRELATORE
Ch.mo Prof. Marco Spirito

2. The Load-Pull Technique
 Load pull is the measurement technique where
the load impedance is varied as the
performances of the DUT are measured
 The purpose is to determine the ideal
matching network impedances when the
device is driven into large signal operations
 Useful for determining the DUT operating
characteristics and design parameters for a
given drive level and termination.

3. Passive Load-Pull
Power Meter Power Meter
Signal
Generator
Tuner Tuner
DUT
Reference
planes
•Passive Networks to
synthesize the desired loading
condition
•Allows medium and high
power measurements
Drawbacks
•Slow (Mechanical Tuning)
•Limitations on high Gamma
values
Tuners must be placed as
close as possible to the DUT!

4. Active Load-Pull
 Synthesizes the reflection coefficient at
the output reference plane by means of an
auxiliary signal injected into the DUT
output
 No costraints on the reflection coefficient
magnitude
 Fast active tuning
 Closed Loop and Open Loop

5. Active Load-Pull – Closed Loop
LOS
S
ϕ
b2
a2
ϕ
LOSS
Closed Loop
• Amplified and phase
shifted version of b2 used
as a2
• Independent control for
amplitude and phase of the
load reflectance Fast
tuning
• Feedback topology
Instability
• High linearity amplifiers

6. Active Load-Pull – Open Loop
LOS
S
ϕ
b2
a2
ϕ
LOSS
Open Loop
• The source signal is
splitted, the two resulting
signals are
amplified and phase
shifted to obtain a1 and a2
• Need for iterative
approximations
• No feedback – No
instability
•No need of linear

7. Issues
 Electrical Delay
 Physical Impedance far from the DUT
 Electrical length brings rapid phase variations vs.
frequency
 Dynamic Range
 When working with harmonics and high linearity
devices, a wide dynamic range is needed to
correctely measure all the harmonics

8. Mixed Signal Active Load-Pull
Digital A/DDigital
AWG
Digital
AWG
I signal
Q signal Q signal
I signal
RF RF
To
RF
To
LO
RF source LO source
LO LO L
O
LO
a1 b1 a2 b2
aREF
• Low frequency and
wideband generation and
acquisition
•Upconversion with IQ mixers
– modulated signals can be
used
•No phase variations
due to electrical delays
in the signal paths
• Low frequency acquisition
allows to reduce costs and to
improve the flexibility (low
frequency signal
manipulation is possible)

9. Project Outline
 Realization of a fully synchronized signal
generator module for the I and Q signals
generation using FPGA based modules
 Design of a 60 GHz Mixed Signal Active Load Pull
system
 Realization of a VNA interface for signal
acquisition
 Modification of an existent load-pull software for
the project specifications
 Realization of a prototype

10. Signal Generation
 All the injected signals have to be locked in
phase exhibiting no phase drift among each
other
Synchronization
RF source
sharing
I and Q signals
synchronization

11. Signal Generation
NI Flex-RIO
Modules
FPGA
Module
Adapter Module
(Digital and Analog I/O)
LabVIEW FPGA
Custom controls and
measurement hardware without
any prior knowledge about
Hardware Description Language

12. System Architecture
Digital
AWG
Digital
AWG
I signal
Q signal
Q signal
I signal
RF RF
To RF
RF source
a1b1a2b2
x3
VNA
PA PAHPA
DUT
Reference
planes
• Mixed signal
generation
• VNA acquisition
• x3 multiplication in the
LO loop – lower
frequency generation
• Attenuators to exploit
mixer’s dynamic range
• HPA in the output
loop to maximize the
system’s dynamic
range
• Waveguide Structure

13. System Design

14. System Design

15. System Design

16. System Design

17. VNA Acquisition
 VNA acquisition to take advantage of the
internal IF downconversion mixers so to cut
down the costs
 GPIB controllable
 Need for a special software interface
 Real Time measurements not allowed
 Low IF bandwidth control

18. Gamma convergence routine
•Any desired reflection coeffient
behavior vs. frequency can be created
by iteratively adjusting amplitude and
phase of the injected waveform
independently at each frequency
component of interest.
• Optimization by means of
subsequent iterations
• Injection and acquisition in the time
domain
• I and Q definition, error checking
and optimization in the frequency
domain

19. The Prototype
• Hybrid waveguide-
coaxial setup
•Signal acquisition
performed using
VNA

20. The Prototype
•First waveguide stage: Multiplication – Signal splitting – IQ upconversion –
Attenuation for IQ voltage swing maximization

21. The Prototype
•Second waveguide stage: Signal amplification – Reflectometer for a and b
waves coupling

22. The Prototype
•Third waveguide stage: DUT connection

23. Measurement Results
• Millitech AMP 15-02100
amplifier
Frequency range 50 to 66 GHz
Nominal Gain 22 dB
P1dB at 15 dBm
• 41 loading condition
• Input power sweep from -15
dBm to -7dBm
• Measurements @ 54-57-60
GHz

24. Measurement Results
@ 60 GHz
@ 54 GHz @ 57 GHz

25. Conclusions
 Design of 60 GHz Mixed Signal Active Load-
Pull
 Large Signal Measurements for mm-wave
devices
 High dynamic range
 No phase variations
 Relatively fast
 High ruggedness
 Prototype realization and design
 Proved software functionality, stability and
ruggedness

26. Future Works
 Realization of the full waveguide structure
 On wafer measurements
 Multitone and Modulated signals
measurements
 Introduction of external IF mixers and low
frequency acquisition
 On board signal processing, exploiting Flex-
RIO modules capabilities