Mixer Design Overview - Oregon State...
Transcript of Mixer Design Overview - Oregon State...
![Page 1: Mixer Design Overview - Oregon State Universityphysics.oregonstate.edu/.../Lec10-11_Mixer_rev3_Yue_ece594_ucsb.pdf · Prof. C. Patrick Yue Slide 1 Mixer Design Overview qNoise Figure](https://reader031.fdocuments.in/reader031/viewer/2022031211/5bcb953c09d3f2e1348c4136/html5/thumbnails/1.jpg)
Prof. C. Patrick Yue Slide 1
Mixer Design Overview
q Noise Figure – impacts receiver sensitivityq Linearity (IIP3) – impacts receiver blocking performanceq Conversion gain – lowers noise impact of following stagesq Power match – want maximize voltage gain rather than power match for
integrated designsq Power – want low power dissipationq Isolation – want to minimize interaction between the RF, IF, and LO portsq Sensitivity to process/temp variations – need to make it manufacturable
in high volume
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Prof. C. Patrick Yue Slide 2
Types of Mixer
q Multiplication through device non-linearityq Multiplication through switching
� Active mixers� Passive mixers
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Prof. C. Patrick Yue Slide 3
Ideal Mixer Behavior
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Prof. C. Patrick Yue Slide 4
Non-Ideality in Mixers
q Image problemq LO feedthroughq Self mixing due to reverse LO feedthrough
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Prof. C. Patrick Yue Slide 5
Mixer Based on Non-Linearity
q Drain current of an MOSFET exhibits a square dependence on gate overdrive
q Collector current of an BJT exhibits a exponential dependence on base-emitter voltage drive
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Prof. C. Patrick Yue Slide 6
Single-Device Mixer Using MOSFET (Square-Law Mixer)
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Prof. C. Patrick Yue Slide 7
Practical Configuration for Single-Device Mixer
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Prof. C. Patrick Yue Slide 8
Single-Device Mixer Using BJT
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Prof. C. Patrick Yue Slide 9
Design Considerations for Mixer Based on Device Non-Linearity
q Design simplicityq Noise Figure
� The square law MOSFET mixer can be designed to have very low noise figure
q Linearity� By operating the square law MOSFET mixer in the square law region the
linearity of the mixer can be improved considerably� BJT mixer is less linear as it produces a host of non-linear components due
to the exponential nature of the BJT mixer
q Power Dissipation� Very low power dissipation due to single device operation
q Power Gain� Reasonable power gain can be achieved
q Isolation� Poor isolation from LO to RF port – by far the biggest short coming
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Prof. C. Patrick Yue Slide 10
Mixing Through Switching
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Prof. C. Patrick Yue Slide 11
Spectral Components Due to Mixing
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Prof. C. Patrick Yue Slide 12
Simple Switching Mixer (Single-Balanced Mixer)
q M1 acts as a transconductance to convert the RF voltage signal to a current q M2 and M3 commute the current between the two output branches.
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Prof. C. Patrick Yue Slide 13
The Issue of Balance in Mixers
bias
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Prof. C. Patrick Yue Slide 14
Achieving Balanced LO Signal with DC Baising
)()()()(])()([)( tLOtRFtLOtRFtLOtLOtRF ×−×=−×
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Prof. C. Patrick Yue Slide 15
Single-Balanced Mixer
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Prof. C. Patrick Yue Slide 16
LO Feedthrough in Single-Balanced Mixers
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Prof. C. Patrick Yue Slide 17
Ideal Double-Balanced Mixer
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Prof. C. Patrick Yue Slide 18
Achieving Balanced RF Signal with Biasing
)()()()(])()([)(
)()()()(])()([)(
])()([])()([
tLOtRFtLOtRFtLOtLOtRF
tLOtRFtLOtRFtLOtLOtRF
tLOtLOtRFtRF
×−×=−×⇒
×−×=−×⇒
−×−
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Prof. C. Patrick Yue Slide 19
Double-Balanced Mixer ImplementationI1+I4 I2+I3
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Prof. C. Patrick Yue Slide 20
Gilbert Cell (Four Quadrant) Mixer
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Prof. C. Patrick Yue Slide 21
Mixer Voltage Conversion Gain
q Voltage conversion gain of a mixer depends on several factors� Input transconductance� Multiplication factor� Load resistance
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Prof. C. Patrick Yue Slide 22
Common-Source Transconductance Stage in Mixer
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Prof. C. Patrick Yue Slide 23
CS Transconductance Stage with Degeneration
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Prof. C. Patrick Yue Slide 24
Transconductor Stage in Mixer
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Prof. C. Patrick Yue Slide 25
Common-Gate Transconductance Stage in Mixer
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Prof. C. Patrick Yue Slide 26
Mixer Multiplication Factor
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Prof. C. Patrick Yue Slide 27
Mixer Voltage Conversion Gain
q If the sinusoidal LO swing is sufficiently large to completely switch the current, we can approximate the LO by a square wave
q Consider only the fundamental term in LO
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Prof. C. Patrick Yue Slide 28
Mixer Noise Analysis
q Three contributors to mixer noise� Transconductance stage� Switching pairs� Load resistance
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Prof. C. Patrick Yue Slide 29
Design Consideration for Minimizing Mixer NF
q Design the transducer for minimum noise figureq Noise from M2 and M3 can be minimized through fast switching of M2 &
M3 by� making LO amplitude large to ensure complete (> 90%) current commuting � making M2 and M3 as small as possible (i.e. increasing fTof M2 and M3)
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Prof. C. Patrick Yue Slide 30
NF Expression for Double-Balanced Mixer [1]
where
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Prof. C. Patrick Yue Slide 31
Mixer NF for Single-Sideband Systems
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Prof. C. Patrick Yue Slide 32
Mixer NF Double Sideband Systems
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Prof. C. Patrick Yue Slide 33
Design Consideration for Mixer Linearity
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Prof. C. Patrick Yue Slide 34
Design Consideration for Mixer Linearity
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Prof. C. Patrick Yue Slide 35
Measured IIP3 for a 0.8-µm SB Mixer [2]
q At high bias current, the switching pair nonlinearity dominatesq At low bias current, the transconductance stage nonlinearity dominates
� For short channel devices, the transconductance stage nonlinearity dominates� IIP3 is proportional to (VRF_DC – Vth)
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Prof. C. Patrick Yue Slide 36
Measured IIP3 for a 0.8-µm SB Mixer [2]
q At high frequencies, excessively large LO amplitude degrades IIP3 due to parasitic capacitive coupling which is nonlinear
q For low-voltage design (< 2V), this is usually not a big concern
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Prof. C. Patrick Yue Slide 37
Passive Mixers
q Very high linearity (assuming the current are completely commuted)� 20–30 dBm of IIP3 achievable
q High noise figure (noise due to the the switching devices)� 20–30 dB of NF
q Voltage conversion loss
(Biasing not shown)
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Prof. C. Patrick Yue Slide 38
Passive Mixers with Biasing Shown
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Prof. C. Patrick Yue Slide 39
References
1. M. T. Terrovitis and R. G. Meyer, “Noise in Current-Commuting CMOS Mixers” IEEE Journal of Solid-State Circuits, Vol. 34, No. 6, June 1999.
2. M. T. Terrovitis and R. G. Meyer, “Intermodulation Distortion in Current-Commutating CMOS Mixers,” IEEE Journal of Solid-State Circuits, Vol. 35, No. 10, October 2000.
3. Prof. M. Perrott, MIThttp://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-776Spring-2005/CourseHome/index.htm
4. Prof. L. Larson, UC San DiegoECE 265A and 265B lecture notes