Experimental results of gain fluctuations and noise in microwave low-noise cryogenic amplifiers

1. Experimental results of gain fluctuations and noise in microwave low-noise cryogenic amplifiers Juan Daniel Gallego, Isaac López-Fernández,Carmen Diez, Alberto Barcia Centro Astronómico de Yebes Observatorio Astronómico Nacional Apartado 148, 19080 Guadalajara, SPAIN Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

2. Contents • Introduction • Noise Measurements • Gain Fluctuation Measurements • Experimental data and results • Device Technology • Temperature • Statistical Analysis • Bias conditions • Conclusions Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

3. Introduction: Cryogenic Amplifiers • Cryogenic Receivers: • Space communications • Radioastronomy • 60s: Maser, Parametric (18 K @ 8.45 GHz in 1964, JPL) • 70s: GaAs FET amplifiers (13 K @ 1.3 GHz in 1979, NRAO) • 80s: GaAs HEMTs ( 5.5 K ! @ 8.5 GHz in 1988, GE-NRAO) • 90s: InP HEMTs (4.6 K @ 8.5 GHz in 1999, ETH-CAY) (3.0 K @ 8.5 GHz in 2002, TRW-CAY) (2.0 K ! @ 4-8 GHz in 2002, TRW- CAY) • Higher frequencies: SIS, HEBs Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

4. MICROTECH DC connector 1 2 3 SMA connector Input matching circuit Interstage matching circuits Output matching circuit Transistor area detail.See source inductive feedbackand drain resistive loading ETH transistorwith bonding wires Bias cavity with biasing circuits Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

5. Introduction: Transistor characterization • Cryogenic S parameter measurements to model devices • In-house test fixture with microstrip lines to allow two-tier TRL calibration • Device measured with bonding wires • DC and coldFET complete the small signal model • Noise model according to Pospieszalski • The noise measured in a wide band test amplifier sets the TD of the model Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

6. EXAMPLE OF CRYOGENIC S PARAMETERS (1 – 40 GHz) MODEL Circuit model MEAS Raw data MEASG Time domain filter Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

7. Introduction: Radiometer Sensitivity • Radiometer model • Radiometer • Radiometer sensitivity Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

8. Introduction: Gain Fluctuations Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

9. Introduction: Specs of Gain Fluctuations • HERSCHEL: • Far Infrared and Submillimeter 3.5 m Telescope orbiting in L2 with 3 cryogenic instruments • HIFI: Heterodyne Instrument for the Far Infrared with 7 dual polarization submillimeter SIS and HEB receivers • Our contribution: low noise, wide band 4-8 GHz cryogenic IF preamplifiers • Sensitive parameters: • Gain fluctuations: impact in the chopping frequency • ALMA: • Atacama Large Millimeter Array (USA, Europe, Japan), 64 Antennas, 35-850 GHz • Our contribution: 4-8 , 4-12 GHz cryogenic IF preamplifiers Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

10. Introduction: Gain Fluctuations dependence • Improvements in Noise • Shorter gate length • HEMTs • InP substrate • Cryogenic Temperature • Improvements in Gain Stability • Larger gate area • Non HEMT • GaAs substrate • Ambient Temperature • Conclusion: • Advances in the reduction of Noise Temperature have contributed to increase Gain Fluctuations Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

11. Noise Measurements (1) • Room temperature methods: • Hot/cold loads • Diode noise sources • Cryogenic temperature methods: • Hot/cold loads • Diode noise sources • Variable temperature cryogenic load • Diode noise source and cold attenuator Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

12. Noise Measurements (2) Cold Attenuator Method Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

13. Noise Measurements (3) • Cold Attenuator Method: • Advantages: • Reduces the error caused by transitions • Minimizes sensitivity to changes in reflection of noise source • Allows fast sweep measurements in automatic systems • Takes advantage of features of existent Noise Figure Meters • Disadvantages: • Needs careful calibration of noise source, lines, attenuator • Accuracy: • Repeatability: ± 0.2 K • Absolute Accuracy: ± 1.4 K Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

14. Noise Measurements (4) Error Budget in Cryogenic Measurements (f=8 GHz, TN=4 K, G=30 dB) SOURCE OF ERROR CONTRIBUTION Calibration of Noise Source 0.77 K Calibration of cold attenuator 0.54 K Calibration of temperature sensor 1.00 K All other 0.34 K _______________________________________________________ TOTAL (RSS) ±1.40 K Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

15. Gain Fluctuation Measurements (1) • Origins • External • Power supply • Temperature variations • Microphonics • Internal • Intrinsic to the devices • Typical Spectrum Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

16. Gain Fluctuation Measurements (2) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

17. Gain Fluctuation Measurements (3) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

18. Gain Fluctuation Measurements (4) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

19. Experimental data and resultsParameters with impact in noise and fluctuations • Frequency band • Device technology • Semiconductor material: InP vs GaAs • Passivation: • Better noise results with unpassivated devices • Gate geometry: • Gain fluctuations improve with larger gate area • Operating temperature • Illumination: • Necessary to avoid carrier freezing effect in old devices, nowadays noise temperature is immune or improves with light in InP devices • Gain fluctuations worsen with illumination Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

20. Experimental data and resultsFrequency band • Noise temperature decreases with frequency: TN [K] ~ ½ f [GHz] • Low frequency gain fluctuations are insensitive to frequency band • Results of table are contaminated by other parameters (bias, device type) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

21. Experimental data and resultsDevice technology and Temperature (1) 0.2 mm 0.22 mm Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

22. Experimental data and resultsDevice Technology andTemperature (2) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

23. Experimental data and resultsStatistical Analysis:Results of long series (1) • Analyzed two series of 9 and 10 state-of-the-art 4-8 GHz cryogenic amplifiers designed and built at CAY with microstrip hybrid technology: • Development models for Herschel space telescope (all cryogenic LNAs for HIFI) • 2 stages of InP NGST transistors • Design constrained by space qualification • Pre-production phase of ALMA (cryogenic LNAs for the European contribution) • 3 stages of InP NGST and ETH transistors. • Based on HIFI design, with more degrees of freedom Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

24. Experimental data and resultsStatistical Analysis:Results of long series (2) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

25. Experimental data and resultsStatistical Analysis:Results of long series (3) • Mean values of noise and fluctuations are similar in both series • Excellent repeatability in noise and gain • Greater dispersion of gain fluctuations results (value @ 1 Hz and spectral index) • HIFI dispersion in fluctuations significantly wider than ALMA • Bias conditions homogeneous for both series • Different transistor batch used for each series of amplifiers • Some transistor batches exhibit high scattering of gain fluctuations within devices of the same batch not shown in noise results • Observed also a significant batch to batch variation Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

26. Experimental data and resultsBias Conditions (1) • Tested the variation of gain fluctuations and noise with Vd, Id • Found a steep change in gain fluctuations around 0.4-0.5 V • Noise (and gain) are much more insensitive to bias changes • High fluctuation zones could be avoidedwith no penalty in noise or gain • Gain fluctuations  when Id  Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

27. 10 Hz 1 Hz Experimental data and resultsBias conditions (2) • Tested also fluctuations of gate voltage with HP35670A • Found similar bias dependence • Simple measurements of voltage fluctuations may help detecting sensitive bias regions • Correlation with gain fluctuations for different devices useful for pre-selecting least fluctuating devices from a batch Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

28. Conclusions • The reduction in noise and the increase in bandwidth of modern cryogenic amplifiers have made more prominent the problem of gain fluctuations • The reduction of gain fluctuations is possible with an adequate selection of devices and bias • Lack of theoretical model for gain fluctuations of cryogenic amplifiers Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

29. END Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)