Design of a Low-Noise 24 GHz Receiver Using MMICs

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

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

3. Project Background • 23.6-24 GHz is a “quiet” band • Used for passive sensing of water vapor • Making measurements of manmade signals present from 23.3-24.3 GHz • 24.0-24.25 GHz is an ISM band • For maximum sensitivity, the receiver must have as little noise as possible • Previous design had noise figure of 6-8 dB • Want to redesign for a newer first-stage amplifier with better noise performance

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

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

6. Noise in Systems • Most real systems are a series of individual components in cascade • Can be represented by an equivalent network: • The noise figure and equivalent temperature of the cascade is: • The characteristics of the first component dominate the system • In a low-noise system, the first amplifier stage is key G1 F1 Te1 G2 F2 Te2 G1G2 Fcas Te,cas

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

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

9. Microstrip Construction • Microstrips are another form of transmission line • Circuit is created in copper over substrate and ground plane • Substrate is dielectric material, usually low-loss • 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. Substrate Copper

10. Fujitsu LNA MMIC • Monolithic Microwave Integrated Circuit • Fujitsu FMM5701X • Wide bandwidth: 18-28 GHz • High gain: 13.5 dB @ 24 GHz • Low noise figure: 1.4 dB @ 24 GHz • Requires external matching and bias circuitry • Difficult to perform out-of-circuit testing 520 μm 450 μm

11. Design of Matching Networks • For maximum gain, amplifier input should be conjugate matched (Γin= ΓL*) • For optimum noise performance, amplifier input must see a specified reflection coefficient (Γin= Γopt) • Chose to optimize for noise performance • Used single-stub tuner to match 50 Ω to Γopt • Used quarter-wave transformer to match amplifier output to 50 Ω line

12. Design of DC Bias Tees • Amplifier is powered by DC bias injected into RF input and output pins • 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

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

14. Results – S Parameters • Bias Conditions: • VDD=0 V • IDD=0 mA • VGG=-1 V

15. Results – S Parameters (cont.) • Bias Conditions: • VDD=5 V • IDD=72 mA • VGG=-1 V

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

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

18. Questions?