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ECE 6361:Mixer Design Review
2.4 GHz Single Balanced Mixer
Jan Brosi Vasileios Iliopoulos
Project Objectives I
IF Frequency 140MHz
IF Bandwidth 5 MHz
RF Frequency 2400-2485 MHz
LO Frequency 2260-2345 MHz
LO Power 8 dBm (max)
Conversion Loss >-9.5 dB
RF Power -10 dBm (max)
LO-RF Rejection <-20dB
LO-IF Rejection <-30 dB
IF Input power 0 dBm (max)
Spurious Signals at RF port
Relative to desired RF with 8 dBm LO power
1000-2120 MHz <-30dBc
2325-2400 MHz <-40 dBc
2400-2485 MHz <-50 dBc
2485-2900 MHz <-40 dBc
Project Objectives II
Board:4-layer PPE (1.7x2.6 inches)Schottky diodes: dual series connected
Physical Construction I
27mm
Reduced-size rat-race balun with coupled lines on different layers
Radial stubs for matching at RF/LO frequency
Lumped elements for matching at IF and for DC-return
Physical Construction II
Board parameters: εr=2.85 ±0.5 tanδ=0.002-0.003 core thickness=1mm resin thickness=50μm copper thickness=12μm
Diodes: Zetex ZC2812ECT IS=9.5nA, RS=16.3Ohm N=1.27, Cj0=1.1pF
Lumped Elements Toko 2021 series chip inductors Panasonic chip capacitors
Simulation with Agilent ADS using a combination of Multilayer & Microstrip models
Diode Model: ADS P-N diode model with parameters from manufacturer’s data sheet
Inclusion of parasitic elements (bends, steps, T- junctions, vias, pads, parasitics of lumped elements).
Balun design with S-parameter simulation and gradient method optimization for best performance
Mixer harmonic balance simulation with 8 orders and gradient method optimization
Model Description & Simulation
Simulation Results
RFfreq=2.485GHzdBm(V_RF)=-8.614
LOfreq=2.345GHzdBm(V_RF)=-29.697
Spur2freq=2.065GHzdBm(V_RF)=-60.577
Spur1freq=2.765GHzdBm(V_RF)=-50.357
RFfreq=2.485GHzdBm(V_RF)=-8.614
LOfreq=2.345GHzdBm(V_RF)=-29.697
Spur2freq=2.065GHzdBm(V_RF)=-60.577
Spur1freq=2.765GHzdBm(V_RF)=-50.357
2.41.4 3.0
-70
-60
-50
-40
-30
-20
-10
0
-80
10
freq, GHz
dBm
(V_R
F)
RF
LO
Spur2Spur1
Simulated circuit meets all specs
Measurement of conversion loss in down-conversion using the frequency offset function of HP89441 Network analyzer
The LO port is fed by E4432 Signal Generator with 8.5dBm input power (assuming 0.5 dB cable loss)
Use of a low-pass filter at the input port of the Network analyzer to ensure better phase-locking
The filter response was calibrated out Accuracy of the measurement:
Signal generator: ± 0.5dB Network analyzer: ± 0.2dBTotal accuracy: ± 0.7dB
Conversion Loss Measurement
LO Frequency Max. Conv. Loss over IF BW
Uncertainty Range
Specs met
2.26 GHz 8.4 dB 7.7-9.1 dB Yes
2.3025 GHz 8.8 dB 8.1-9.5 dB Yes
2.345 GHz 9.5 dB 8.8-10.2 dB No
Conversion Loss Measurement Results
Conversion loss increases with increasing LO-frequency
Measurement of spurious signals and LO-RF isolation for up-conversion using HP8994E Spectrum Analyzer.
Measurement of LO-IF isolation for down-conversion Sweep over the LO frequency range Accuracy of the spurious signals measurement
Relative accuracy of spectrum analyzer: ±0.5dB
Accuracy of the LO-RF isolation measurement Absolute accuracy of spectrum analyzer: ±1dB Signal generator: ±0.5dB
Total accuracy: ± 1.5dB
Spurious & Isolation Measurement
Spurious & Isolation Measurement Graph
LO RF
LO+2IF
LO+3IF
LO+4IF
LO-IF
LO-2IF
LO-3IF
SignalWorst value in
frequency rangeUncertainty range Spec
SpuriousLO-3·IF
-29.7dBc -29.2 to -30.3dBc -30dBc
SpuriousLO-2·IF
-20.3dBc -19.8 to -20.8dBc -30dBc
SpuriousLO +2·IF
-27dBc -26.5 to -27.5dBc -40dBc
SpuriousLO + 3·IF
-30.9dBc -30.4 to -31.4dBc -40dBc
SpuriousLO+4·IF
-41.7dBc -41.2 to -42.3dBc -40dBc
Spurious Measurement Results
SignalWorst value in
frequency rangeUncertainty range Spec
IsolationLO-RF
-12dB -10.5 to –13.5dBc -20dB
IsolationLO-IF
-21.5dB -20 to -23dBc -30dB
Isolation Measurement Results
Circuit assembled as designed has bad performance and does not meet any of the specs
Slight change of inductor & capacitor values and interchange of their position increased mixer performance
The mixer seems to be shifted to lower frequencies, it works much better at fLO=1.9 GHz
Thus it was tried to reduce the size of the mixer Coupled lines were shortened by use of new vias Line edges were smoothened with copper material to
reduce length
Resulting circuit had best performance and was used for measurements
Changes made to the Circuit
Comparison to Simulations
The measurements don’t match with the simulations
Trying to fit ADS-model to measurements by change of dielectric constant, distance between layers, coupled line offset, length and width of lines, stub length and width, vias and pads, losses and diode model.
This should account for production tolerances and previously not considered effects
Changes didn’t have a significant effect on the simulated mixer performance
Indication that ADS multilayer-model is not accuarate
A single-balanced mixer using a reduced-size rat-race balun with mulilayer coupled-lines was designed, simulated, fabricated and measured
Great differences between model and measurements of the produced mixer occurred
Performance could be increased by change of lumped elements and reducing the size of lines
Specifications for Conversion loss are almost met, for Isolation and some spurious signals not
Re-simulation was not successful
Summary & Conclusions I
Summary & Conclusions II
The ADS multilayer-model does not seem to work well in our case, another software or model should be tried
Board parameters like layer thickness and dielectric constant should be reevaluated
The mixer works much better at lower frequencies, the balun seems to be downshifted
For the next production cycle, the line lengths should be decreased to account for that