Transcript ECE 6361:Mixer Design Review 2.4 GHz Single Balanced Mixer Jan Brosi Vasileios Iliopoulos

ECE 6361:Mixer Design Review
2.4 GHz Single Balanced Mixer
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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)
Project Objectives II
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
Board:4-layer PPE (1.7x2.6 inches)
Schottky diodes: dual series connected
Physical Construction I
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
27mm
Physical Construction II
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Board parameters:
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Diodes:
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εr=2.85 ±0.5
tanδ=0.002-0.003
core thickness=1mm
resin thickness=50μm
copper thickness=12μm
Zetex ZC2812ECT
IS=9.5nA, RS=16.3Ohm
N=1.27, Cj0=1.1pF
Lumped Elements
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Toko 2021 series chip inductors
Panasonic chip capacitors
Model Description & Simulation
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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, Tjunctions, 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
Simulation Results
LO
freq=2.345GHz
dBm(V_RF)=-29.697
RF
freq=2.485GHz
dBm(V_RF)=-8.614
10
RF
0
dBm(V_RF)
-10
-20
Spur2
freq=2.065GHz
dBm(V_RF)=-60.577
-30
-40
-50
LO
Spur1
freq=2.765GHz
dBm(V_RF)=-50.357
Spur1
Spur2
-60
-70
-80
1.4
2.4
freq, GHz
Simulated circuit meets all specs
3.0
Conversion Loss Measurement
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Measurement of conversion loss in down-conversion
using the frequency offset function of HP89441 Network
analyzer
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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: ± 0.2dB
Total accuracy: ± 0.7dB
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Conversion Loss
Measurement Results
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 increases with
increasing LO-frequency
Spurious & Isolation
Measurement
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Measurement of spurious signals and LO-RF isolation
for up-conversion using HP8994E Spectrum Analyzer.
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Measurement of LO-IF isolation for down-conversion
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Sweep over the LO frequency range
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Accuracy of the spurious signals measurement
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Relative accuracy of spectrum analyzer: ±0.5dB
Accuracy of the LO-RF isolation measurement
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Absolute accuracy of spectrum analyzer: ±1dB
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Signal generator: ±0.5dB
Total accuracy: ± 1.5dB
Spurious & Isolation
Measurement Graph
LO-IF
LO
RF
LO-2IF
LO-3IF
LO+2IF
LO+3IF
LO+4IF
Spurious Measurement Results
Signal
Worst value in
frequency range
Uncertainty range
Spec
Spurious
LO-3·IF
-29.7dBc
-29.2 to -30.3dBc
-30dBc
Spurious
LO-2·IF
-20.3dBc
-19.8 to -20.8dBc
-30dBc
Spurious
LO +2·IF
-27dBc
-26.5 to -27.5dBc
-40dBc
Spurious
LO + 3·IF
-30.9dBc
-30.4 to -31.4dBc
-40dBc
Spurious
LO+4·IF
-41.7dBc
-41.2 to -42.3dBc
-40dBc
Isolation Measurement Results
Signal
Worst value in
frequency range
Uncertainty range
Spec
Isolation
LO-RF
-12dB
-10.5 to –13.5dBc
-20dB
Isolation
LO-IF
-21.5dB
-20 to -23dBc
-30dB
Changes made to the Circuit
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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
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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
Comparison to Simulations
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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
Summary & Conclusions I
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A single-balanced mixer using a reduced-size ratrace 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 II
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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