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Sampling Mixer for Software Defined Radio Applications using 0.18µm RF CMOS Technology

Mentors: Dr. Kwang-Jin Koh and Hedieh Elyasi

Virginia Polytechnic Institute and State UniversityBradley Department of Electrical and Computer Engineering

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Overview

REU Cognitive Communications @ Virginia Tech

• Software Defined Radio• Mixer Fundamentals• Project Description• Simulation Results– Graphical– Quantitative

• Conclusions

3REU Cognitive Communications @ Virginia Tech

Concept of Radio• What comes to mind when you here the word “Radio”?

Wireless Communications


Software-Defined Radio (SDR) • What is SDR?– Ability to control RF signals via software as

opposed to custom hardware

• Why SDR?– Flexibility– Adaptability– Low Cost– Lower Power Consumption


Software-Defined Radio (SDR)• How does SDR work?– Ideal Case : Software Radio

• Technology limitations of A/D prevent above implementation– Tx/Rx frequencies up to Giga Hz range

• Input waveform changing up to few billion times per second

• Signal too fast to sufficiently convert to digital

Rx

A/DAnalog-to-Digital Conversion


Software-Defined Radio (SDR)• How do we combat A/D limitations?– Provide RF front end between Antenna and A/D

• Important Functional Unit: Mixer– In Radio Receiver: mixer down converts input

signal to lower frequency (slower signal) sufficient for A/D conversion

LNAMixer

Filter A/D

Rx

LO

RF IF


Mixer: Frequency TranslationMixer

LO

RF IF

600 M Hz 125 M Hz

475 M Hz

Frequency Domain

IF LO RF

𝑃 ( 𝑓 )𝑜𝑟 𝑉 ( 𝑓 )

𝑓

Time Domain

𝑅𝐹− 𝐿𝑂=𝐼𝐹600−475=125


Project Description

• Design, simulate, and analyze a passive direct sampling mixer using 0.18µm RF CMOS technology

• Goal of Research:– Increase commonality of the mixer over various

wireless communication standards while maintaining high degree of re-configurability

ReconfigurableRF CMOS

ADC

IMT-2000

GSM

Bluetooth

GPS

ISDB

FilterLNA

Mixer


What does 0.18µm RF CMOS mean?

Diameter of Penny = 19,050 µm

Substrate Level Diagram Schematic Symbol

Metal-Oxide Semi-Conductor Field Effect Transistor (MOSFET)

Channel Length = 0.18µm!!!


DSM Circuit Diagram


Important Measurable Metrics• Conversion Gain

– The change in output power with respect to the input power (RF IF)

• Noise Figure – How many random signals does our system generate as a result of

the circuit elements

• 1 dB Compression Point– At what input power level (RF Signal) does the mixer functionality

become undesirable (i.e. Output non-linear)

• Third-order Intermodulation Intercept Point (IIP3)– How well the system receives the desired information signal with

other potential RF signals in close frequency proximity


• Time Domain

• Frequency Domain

RF=600 MHz IF=125 MHz

LO=475 MHz

MixerSimulation Results


Direct Sampling Mixer Simulations Results

Metric Simulation DesiredConversion Gain 20.5 dB 15 dB

1-dB Compression Point -16.67 dBm -12 dBm

IIP3 -5.81 dBm -2 dBmNoise Figure 15 dB 10 dB

Power Consumption 3.66 mW 3 mW

Simulation Results


Conclusions

• A Passive Direct Sampling Mixer using 0.18µm RF CMOS technology was designed, simulated and analyzed

• Acceptable Metrics:– Conversion Gain– IIP3– Power Consumption

• Areas to improve:– 1dB Compression point– Noise Figure


Acknowledgements

This research was sponsored by the National Science Foundation (NSF). The authors would like to thank:

• Dr. Kwang-Jin Koh for the opportunity to be a part of his research efforts;

• Dr. Carl Dietrich, Dr. Leslie Pendleton, and Dr. Roofia Galeshi for the oversight and mentoring services provided throughout the duration of the program;

• A special thanks to PhD student Hedieh Elyasi for her patience, as well as her abundant time and effort spent aiding in the learning/research process.


References

• H. Shiozaki, T. Nasu and K. Araki, “Design and Measurement of Harmonic Rejection Direct Sampling Mixer,” Proc. APMC, pp. 293-296, Dec. 2009

• A. Mirzaei, H. Darabi, J. C. Leete, X. Chen, K. Juan, and A. Yazdi,“Analysis and optimization of current-driven passive mixers in narrowbanddirect-conversion receivers,” IEEE J. Solid-State Circuits, vol. 44, no. 10,pp. 2678–2688, Oct. 2009.

• R. Bagheri, A. Mirzaei, M. E. Heidari, S. Chehrazi, M. Lee, M. Mikhemar, W. K. Tang, and A. A. Abidi, “Software-defined radio receiver: Dream to reality,” IEEE Commun. Mag., vol. 44, no. 8, pp.111–118, Aug. 2006.


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1 dB Compression Graph


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𝑰𝑰𝑷 𝟑

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