Single Balanced Mixer Design
ECE 6361
July 30, 2002
Prof. J. S. Kenney
L01: Group1
Dennis Mahoney
Adam Toner
Minsik Ahn
Objectives
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Single-balanced mixer
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2.400-2.485 GHz RF, 2.260-2.345 GHz LO,
140 MHz IF (5 MHz bandwidth)
4-layer PPE printed circuit boards
2.6” by 1.7”
Upconversion and downconversion
Description of Design
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Balun was realized as a 380 mil long
broadside coupled line on layers 1 and 2.
RF was fed into diode through a Wilkinson
power divider for balance.
Microstrip stubs were used for reflective
terminations.
Alternate Design
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Similar design, but balun outputs on single
layer
Simulated conversion loss: ~8 dB
Measured conversion loss: ~10.5 dB
Tapered LO input and moved vias in CAD
LO-RF transmission null centered at 2.8 GHz
instead of 2.4 GHz indicating poor balun
performance
Poor RF port return loss
Simulation
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Design, simulation, optimization, and layout
in Agilent ADS 2001
Harmonic balance simulation and optimization
with seven harmonics
Curve fit diode for n, Rs; Cj from datasheet
ADS Simulation Model
Wilkinson Power Divider in
ADS
ADS Simulation Results:
Downconverter
m2
m3
m1
m4
f req=140.0MHz f req=2.162GHz f req=2.302GHz f req=2.442GHz
dBm(VIF)=-19.253 dBm(VIF)=-48.791 dBm(VIF)=-62.161 dBm(VIF)=-75.695
m5
m6
f req=2.302GHz
f req=2.442GHz
dBm(VRF)=-61.356 dBm(VRF)=-11.750
0
0
m6
m1
-20
-20
m2
-40
m3
-60
dBm(VRF)
dBm(VIF)
-40
m4
-80
m5
-60
-80
-100
-100
-120
-120
-140
-140
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
freq, GHz
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
freq, GHz
2.4
2.5
2.6
2.7
2.8
2.9
3.0
ADS Simulation Results:
Upconverter
m3
m4
m1
m2
f req=2.442GHz
f req=2.582GHz
f req=140.0MHz f req=2.302GHz
dBm(VIF)=1.720 dBm(VIF)=-61.796 dBm(VIF)=-70.549 dBm(VIF)=-69.021
m5
m6
m7
m8
f req=2.022GHz
f req=2.442GHz f req=2.582GHz
f req=2.722GHz
dBm(VRF)=-56.781 dBm(VRF)=-9.587dBm(VRF)=-59.499 dBm(VRF)=-56.982
0
20
m6
m1
0
-20
-20
m2
m3m4
-60
dBm(VRF)
dBm(VIF)
-40
-40
m5
m7
m8
-60
-80
-80
-100
-100
-120
-120
4.0
3.9
3.8
3.7
3.6
3.5
3.4
3.3
3.2
3.1
3.0
2.9
2.8
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
freq, GHz
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
freq, GHz
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
Mixer Layout
Specifications and Results:
Downconverter
Actual Results
(Simulated
Results)
RF:2400
MHz
RF:2442 MHz
RF:2485 MHz
Specification
Conversion Loss
8.9 dB
(9.325 dB)
9.5 dB
(9.253 dB)
11.2 dB
(9.456 dB)
< 9.5 dB
LO-RF Rejection
29.4 dB
(33.545 dB)
33.3 dB
(49.606 dB)
38.0 dB
(30.543 dB)
< -20 dB
LO-IF Rejection
36.7 dB
(58.052 dB )
40.1 dB
(42.908 dB)
43.3 dB
(54.393 dB)
< -30 dB
Specifications and Results:
Upconverter Spurious Response
Actual Results
(Simulated Results)
RF:2400 MHz
RF:2442 MHz
RF:2485 MHz
Specification
2400-2485
No Spurs
(No Spurs)
No Spurs
(No Spurs)
No Spurs
(No Spurs)
-50 dBc
2485-2900 MHz
-24.3 dBc
at 2.520 GHz
(-43.461 dBc
at 2.520 GHz)
-25.4 dBc
at 2.582 GHz
(-49.912 dBc
at 2.582 GHz)
-28.4 dBc
at 2.765 GHz
(-48.305 dBc
at 2.765 GHz)
-40 dBc
2325-2400 MHz
No spurs
(No spurs)
No spurs
(No spurs)
Only LO
(Only LO)
-40 dBc
1000-2120 MHz
-21.9 dBc
at 1.980 GHz
(-24.28 dBc
at 1.840 GHz)
-22.0 dBc
at 2.022 GHz
(-38.619 dBc
at 1.882 GHz)
22.2 dBc
at 2.065 GHz
(-32.607 dBc
at 1.925 GHz)
-30 dBc
Measurement Notes
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Downconverter conversion loss measured with VNA,
accuracy ~0.2 dB
Increased signal generator amplitude to compensate
for measured cable loss
Frequency offset mode, calibrated IF output with
filter and cables, connected RF directly to test port
Upconverter conversion loss measured with spectrum
analyzer, results were better than downconverter but
accuracy was ~1 dB
Spurious response measurements with spectrum
analyzer set to appropriate RBW and span
Verified IF bandwidth (>> 5 MHz) with swept input,
measured output on spectrum analyzer
Problems
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Simulated without vias
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One via to ground not drilled
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Vias greatly increased simulation time
Performance margin built into design
Repaired by drilling, inserting wire,
soldering
Top balun trace not centered
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Decreases coupling efficiency, increases
conversion loss and spurious products
Trace moved in CAD
Problems (continued)
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Simulated with straight reactive
terminations, fabricated curved stubs
Mixer operating range shifted down in
frequency
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Conversion loss improved from simulation in
low end but increased in high end
Low end spurs increased to out-of-spec from
simulation (stub tuning offset down)
Simulated with nominal dielectric constant
Improvements
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Increase spacing around stubs to
reduce parasitic coupling
Reduce loss in RF input bends
Optimize further in ADS
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Limited time for first prototype
Agilent diode improved conversion loss
in simulation by ~3 dB
Investigate alternate design problems
Conclusions
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Two designs fabricated
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Primary design met most specifications
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One was consistent with simulation
Conversion loss for alternate design was ~3 dB
worse than simulation
Some conversion loss and spurious specs missed
Room for improvement in both designs
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Can reduce size and improve performance