Design of a Low-Noise 24 GHz Receiver Using MMICs Eric Tollefson, Rose-Hulman Institute of Technology Advisor: Dr. L. Wilson Pearson

Overview u Project Description and Background u Introduction to Noise u System Overview u Microwave Components u Design u Results u Future Work u Acknowledgements

Project Background u GHz is a “quiet” band u Used for passive sensing of water vapor u Making measurements of manmade signals present from GHz – GHz is an ISM band u For maximum sensitivity, the receiver must have as little noise as possible u Previous design had noise figure of 6-8 dB u Want to redesign for a newer first-stage amplifier with better noise performance

Introduction to Noise u Noise is a natural phenomenon present everywhere u White noise has Gaussian distribution and equal power at all frequencies u Often referred to as AWGN – Additive White Gaussian Noise u A source can be modeled by a noisy resistor at temperature T e : u All components can also be characterized by an equivalent noise temperature:

Noise Figure u Noise Figure (F) is another way of expressing noise u Defined as the reduction in signal-to-noise ratio: u Can also be calculated from the equivalent noise temperature: u For a lossy component at T o =290K, the noise figure is equal to the attenuation in the component:

Noise in Systems u Most real systems are a series of individual components in cascade u Can be represented by an equivalent network: u The noise figure and equivalent temperature of the cascade is: u The characteristics of the first component dominate the system u In a low-noise system, the first amplifier stage is key G 1 F 1 T e1 G 2 F 2 T e2 G 1 G 2 F cas T e,cas

System Overview Current System Design (J. Simoneau) Amplifier to be replaced

Transmission Lines u T-lines are efficient conductors of RF energy and inefficient radiators u Come in balanced and unbalanced forms u Coaxial cable is a common form of unbalanced line u T-lines have a characteristic impedance –Normally must be matched to other components –50 Ω is the most common u Mismatches at junctions create reflections –Represented by Γ, the reflection coefficient:

Microstrip Construction u Microstrips are another form of transmission line u Circuit is created in copper over substrate and ground plane u Substrate is dielectric material, usually low-loss u Shape determines electrical characteristics –Strip width determines characteristic impedance –Open-ended stubs add reactance –Stubs can also provide virtual short circuits to ground –Combinations form filters, impedance transformers, etc. CopperSubstrate

Fujitsu LNA MMIC u Monolithic Microwave Integrated Circuit u Fujitsu FMM5701X –Wide bandwidth: GHz –High gain: GHz –Low noise figure: GHz –Requires external matching and bias circuitry –Difficult to perform out-of- circuit testing 520 μm 450 μm

Design of Matching Networks u For maximum gain, amplifier input should be conjugate matched (Γ in = Γ L * ) u For optimum noise performance, amplifier input must see a specified reflection coefficient (Γ in = Γ opt ) u Chose to optimize for noise performance –Used single-stub tuner to match 50 Ω to Γ opt –Used quarter-wave transformer to match amplifier output to 50 Ω line

Design of DC Bias Tees u Amplifier is powered by DC bias injected into RF input and output pins u Must design circuitry to provide RF isolation from the DC source and block DC from the RF signal path –Used radial stubs to provide virtual RF short to ground –Used λ/4 sections to transform short into open at transmission line –Will use coupled lines in future versions to block DC from RF connections

Completed Design Single-stub tuner Quarter-wave transformer Bias Tees MMIC

Results – S Parameters Bias Conditions: V DD =0 V I DD =0 mA V GG =-1 V

Results – S Parameters (cont.) Bias Conditions: V DD =5 V I DD =72 mA V GG =-1 V

Future Work u Troubleshoot to obtain correctly working prototype u Verify that matching design is correct u Measure noise figure and gain parameters u Integrate into complete system u Measure whole-system parameters for comparison with previous design u Take new noise measurements

Acknowledgements u Dr. L. Wilson Pearson u Joel Simoneau u Chris Tompkins u Simoneau, J. et al. “Noise Floor Measurements in the Passive Sensor Band (23.6 to 24 GHz)” u Pozar, David. “Microwave Engineering 2 nd Ed.” John Wiley & Sons, 1998.

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