Multidisciplinary Senior Design Conference
Kate Gleason College of Engineering
Rochester Institute of Technology
Rochester, New York 14623
SINGLE-BALANCED MIXER
PROJECT
FINAL PRESENTATION
RIT Senior Project
Jared Burdick
May 17, 2012
INTRODUCTION

What is a mixer?



Where are they used?



Communication systems.
Radar applications.
How does a mixer work?



A device used to convert frequencies.
Mixer is a term generally associated with converting higher
frequencies to lower frequencies.
RF
IF
LO
They take advantage of the non-linear properties of diodes.
The signal (RF) is “mixed” with another fixed (or tunable)
frequency (LO) and a “difference” frequency (IF) is produced
along with a number of predictable inter-modulation products.
There are several different configurations for mixers.

A single-balanced configuration was selected for this project.
PROJECT GOALS

Research Mixers


Understand theory, applications, configurations, and design
trade-offs.
Design, Simulate, Prototype Mixer





Choose an appropriate configuration.
Develop design and simulation skills.
Mitigate risks and follow project plan.
Test mixer and compare simulated to actual performance.
Analyze results and offer possible future improvements /
implementations.
CUSTOMER NEEDS
SPECIFICATIONS
Several specifications were modified during the
development (with customer approval)
SYSTEM BLOCK DIAGRAM
COMPONENTS USED

Anaren 90º Hybrid Coupler (XC0900A-3S)

Avago Schottky-Diode (HSMS-2822)

Coilcraft Chip Inductors (0805HT-12NTJB)

DLI Chip Capacitors (C06UL120G and C04UL2R7)

Gigalane SMA Connector (PAF-S05-007)

Murata Chip Inductor (LQW18AN39NG00D)

Rogers Substrate Material (RO4003C)
Lumped Element Filter
AWR MODELS
Lumped LPF
5th Order LPF
Maximally Flat
Degree= 5
Fp= 400 MHz
PORT
P=1
Z=50 Ohm
INDQ
ID=L1
L=12 nH
Q=40
FQ=0.1 GHz
ALPH=0
INDQ
ID=L2
L=39 nH
Q=40
FQ=0.1 GHz
ALPH=0
CAPQ
ID=C1
C=12 pF
Q=50
FQ=0.1 GHz
ALPH=0
Single-Balanced Mixer
INDQ
ID=L3
L=12 nH
Q=40
FQ=0.1 GHz
ALPH=0
CAPQ
ID=C2
C=12 pF
Q=50
FQ=0.1 GHz
ALPH=0
PORT
P=2
Z=50 Ohm
DESIGN TRADE-OFFS & DECISIONS MADE

Configuration
Use commercially available components wherever possible.
 Removed BPF’s from the RF and LO paths due to not readily available.
 Went to lumped-element LPF in the IF path for the same reason.


LO Leakage (LO to IF Isolation)

Increased to 5th order of LPF at IF port


Better rejection (approx. 20dB more) at 1GHz, which improved LO/IF isolation (SBM
configuration offers no natural reduction of the LO).
Conversion Loss Flatness

Added micro-strip quarter-wave transformer to help match the impedance coming
out of the diodes and going into LPF


Varied width of micro-strip line to see which gave the best conversion loss result
Changed the radial RF micro-strip choke into a shorted quarter-wave micros-trip
stub


Tried Various angles for the radial choke and line width and found there was little
improvement
Finally went to a true shorted quarter-wave stub



Gave the best result in simulation
Easy to provide ground to stub for physical layout
Added RF bypass capacitor shorted to ground after the diode provide additional
filtering prior to the impedance transformation.
SIMULATION RESULTS
Mixer Conversion Loss
Mixer Isolation
-4
-20
-30
-5
Output Level (dBm)
Conversion Loss (dBm)
PRF@IF (dBm)
-6
-7
PLO@IF (dBm)
-40
-50
-60
-8
-70
0.8
0.9
1
Frequency (GHz)
1.1
1.2
0.8
0.9
Mixer Return Losses
1
Frequency (GHz)
1.2
IF Output Power Spectrum
0
0
RF = 0.8 GHZ
LO = 1.0 GHz
0.2 GHz
-16.86 dBm
-20
Power (dBm)
-10
Return Loss (dB)
1.1
-20
-30
0.4 GHz
-61.92 dBm
1 GHz
-40.24 dBm
-40
0.8 GHz
-51.21 dBm
-60
0.6 GHz
-63.94 dBm
LO Return Loss, dB
-40
RF Return Loss, dB
-80
0.8
1.2
Frequency (GHz)
0
1
2
3
Frequency (GHz)
4
4.8
SIMULATION RESULTS
Power Compression
Approximate 1dB
Compression Points
LPF IL RL
0
DB(|S(2,1)|) (L)
LPF
-2.8
-10
-60
-80
0.5
1
1.5
Frequency (GHz)
2
2.5
Coupling (dB)
-20
DB(|S(3,1)|)
Coupler
-3
Return Loss
-40
0
1.1994 GHz
-2.8599 dB
1.0006 GHz
-3.0466 dB
DB(|S(1,1)|) (R)
LPF
-20
Insertion Loss
XC0900A3 Coupling
0
DB(|S(4,1)|)
Coupler
-3.2
1.0003 GHz
-3.1613 dB
-30
-3.4
-40
-3.6
1.1995 GHz
-3.5242 dB
0.8
0.9
1
1.1
Frequency (GHz)
1.2
1.3
CIRCUIT LAYOUT &
ASSEMBLED UNIT
Assembled
Unit
Circuit Layout
SMA
Conn
Launch
(RF In)
λ/4 shorted stub
Diode Pair
λ/4 transformer
Coupler
SMA
Conn
Launch
(LO In)
RF Bypass Cap
LPF
λ/4 shorted stub
SMA Conn
Launch (IF
Out)
TEST RESULTS – SUMMARY COMPARISON
Spec
Specification
Unit of
Spec Simulated
#
(metric)
Measure
S1 RF Frequency
GHz
0.8 - 1.2
OK
S2 LO Frequency
GHz
1
OK
S3 IF Frequency
MHz
DC - 200
OK
Maximum
S4
dB
10
7.2
Conversion Loss
S5 RF/IF Isolation
dB
30
42
S6 LO/IF Isolation
dB
35
50
S7 Minimum LO Power
dBm
10
OK
S8 Maximum RF Power
dBm
-10
OK
Minimum 1dB
S9
dBm
5
8
Compression
S10 Maximum RF VSWR
Ratio
2.0:1
1.40:1
S11 Maximum LO VSWR
Ratio
2.5:1
1.09:1
S12 Maximum IF VSWR
Ratio
1.5:1
-
Measured
Comments
Unit 1 Unit 2
OK
OK
All parameters tested over these ranges.
OK
OK
Several tests looked at performance
OK
OK
beyond specified.
7.6
8.0
37.0
41.0
OK
OK
38.5
43.0
OK
OK
8.6
8.6
1.29:1
1.05:1
1.46:1
LPF rejection less than simulated.
All parameters tested at these levels.
Approximate Value
1.25:1 LO & RF Port VSWR's response similar - LO
1.08:1 port defined at 1.0 GHz only (null)
1.43:1 Not simulated
All specifications were met by both units built.
Both units had very similar performance.
TEST RESULTS
Conversion Loss
RF to IF Isolation
-4.0
60
Conversion Gain (dB)
Unit #1
50
RF - IF Isolation - Unit #1
-5.0
Isolation (dB)
Conversion Gain (dB)
-4.5
-5.5
-6.0
-6.5
40
30
20
-7.0
Measured
Conversion Gain (dB)
-7.5
Simulated
10
Simulation (dB)
-8.0
0
0.800
0.900
1.005
1.100
1.200
RF Frequency (GHz)
RF Frequency (GHz)
RF Input Power Level (dBm)
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
0
6.0
-10
0.8 GHz
8.0
0.9 GHz
1.005 GHz
10.0
1.1 GHz
12.0
1.2 GHz
Spur Level (dBc)
Conversion Loss (dB)
4.0
-20
Frequency (GHz)
Highest Spur Output Level
Unit #1
-30
-40
14.0
16.0
Conversion Loss vs. RF Input Power
Unit #1
-50
Measured
-60
18.0
1-dB Compression
Spurious Output
Simulated
TEST RESULTS
IF Output Power Spectrum
0
RF = 0.85 GHZ
LO = 1.0 GHz
0.15 GHz
-16.27 dBm
-20
Power (dBm)
Unit #1
IF Output Spectrum
LO = 1000 MHz
RF = 850 MHz
Horiz. Scale: 200 MHz/div
1 GHz
-40.24 dBm
-40
0.3 GHz
-72.65 dBm
0.85 GHz
-54.26 dBm
-60
0.7 GHz
-77.27 dBm
-80
0
Spurious Output
1
2
3
Frequency (GHz)
4
4.85
CONCLUSIONS

The prototype mixer met the target specifications.

There were differences between the simulated performance and
the actual measured performance.





In general, the actual measured performance was consistent with the model.
LO to IF Isolation about 7-9 dB less.
 Suspect that the LPF roll-off (rejection at higher frequencies) was less
than modeled – this will need further evaluation to confirm.
RF to IF Isolation 3-5 dB less – LPF roll-off would contribute here as well.
Conversion Loss was slightly higher – connectors not modeled could be a
contributor.
Future Iterations / Investigations.




Add BPF to the LO and RF input paths.
Investigate LPF performance.
Refine the AWR model (connectors, HFSS sub-models, etc.).
Work on final mechanical packaging concept.
LESSONS LEARNED

Do your homework before starting to design



Time is a scare resource





There are many trade-offs that need to be considered and decisions that
need to be made in order to best match the expected performance to the
application and requirements.
Ability to model the circuits accurately was key and greatly increased the
probability of success.
Valuable lessons can be learned even in non-ideal circumstances.
Figuring out project limitations early on in the process helped reduce risk
and deliver the final product on time.
Look at contingency plans (alternate parts, fabrication alternatives etc.)
Identifying concrete action items helped to focus efforts and reduce wasted
time.
Make use of all available resources


Eliciting feedback from other knowledgeable people proved invaluable.
There was a significant amount of information available on-line (technical
papers, forums, etc.).