Wide band, ultra low noise cryogenic InP IF amplifiers for the HERSCHEL mission radiometers

1. Wide band, ultra low noisecryogenic InP IF amplifiersfor the HERSCHEL mission radiometers Isaac López-Fernández, Juan Daniel Gallego, Carmen Diez, Alberto Barcia, Jesús Martín-Pintado Centro Astronómico de Yebes Observatorio Astronómico Nacional Guadalajara, SPAIN Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

2. Outline • Introduction • Device characterization • Amplifier design • Amplifier fabrication • Amplifier performance • Noise and gain measurements • Reflection and stability measurements • Gain fluctuations measurements • Isolator measurements • Conclusions Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

3. Introduction: HERSCHEL requirements • 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 for each mixer channel (14) • Sensitive parameters: • Noise temperature: the contribution to the receiver noise is significant • Power dissipation: mission life limited by liquid helium mass • Gain fluctuations: impact in the chopping frequency • Other mechanical and electrical constraints Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

4. Introduction: CAY experience • More than 150 cryogenic LNAs built for different applications(not including to HERSCHEL developments) • IRAM: Grenoble, PdB interferometer, 30m (IF amplifiers) • ESOC: New Northia DSN antenna (Rosetta, SMART) • Burdeos Observatory • EMCOR (Atmospheric sensing) • PRONAOS (mm receiver in stratospheric balloon) • INPE: 14m Brazil • CAY: VLBI receivers (X and K band) • Wide experience with HEMT devices • More than 30 batches of commercial GaAs transistors tested • Several models of InP transistors measured • JPL-TRW (CHOP program): 14 batches, 9 models • ETH Zürich: 7 batches, 4 models • Chalmers University: 1 batch Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

5. Introduction: Initial developments • Prototypes in the 8 – 12 GHz band • Successful testing of InP in this band and comparison with GaAs results • Demonstration of InP in the 4 – 8 GHz band Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

6. Device characterization: TransistorsMeasurement procedures • InP technology selected based on previous experience in IF amplifiers • lower power dissipation, factor of 2 better noise, higher gm • 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)

7. 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)

8. Device characterization: TransistorsResults 0.19 mm 0.22 mm Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

9. Device characterization: Components • Selection of components based on previous experience at cryogenic temperatures • SOTA thick film resistors • ATC 111 parallel plate capacitors with CA dielectric • ATC 100 multilayer porcelain capacitors • RT/Duroid 6002 substrates 20 mils thick • Simple models of concentrated elements are adequate for this frequency range Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

10. Amplifier design • Microstrip hybrid design simulated by MMICAD software • Developed cryogenic models for transistors, connectors, critical capacitors, resistors and bonding wires • Each InP device is independently stabilized by resistive loading and inductive feedback • Input circuit: wideband noise matching • Tuning elements incorporated in the design (adjustable bonding wires, microstrip islands) • Box resonances avoided with careful EM design and the use of microwave absorbers • Multiple bias networks requirements • Contribute to the unconditional stability of the amplifier • Comply with EMC mission requirements • Provide ESD protection of sensitive InP HEMTs • Have a low drain voltage drop • Filter RF Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

11. Amplifier fabrication: several series • 37 4-8 GHz YCF amplifiers fabricated at CAY in different series • All processes performed in our labs • Design transferred to Alcatel Espacio to build Flight Models • Series analyzed here: • YCF 2 – ETH transistors (Mixer Program Amplifiers) • YCF 6 – TRW transistors (Development Models) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

12. MP amplifier YCF 2 • 2 stages ETH 200 µm • Gold plated brass • 61.4×35×11.5 mm, 149 g • Duroid 6002 substrates • DM amplifier YCF 6 • 2 stages TRW 200 µm • Gold plated aluminum • 58×32×15 mm, 65 g • Duroid 6002 substrates • Improved bias circuits • Additional cavity for filtering Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

13. Amplifier fabrication: reliability • Reliability is a priority over performance for the selection of components, substrates and mounting techniques • Spatial design • Cryogenic operation • Past experience in cryogenic designs obviates most of the work in testing, modeling and pre-qualifying components • An example: ‘O’ ribbon connection in the SMA tab contact: • Allows mobility in three axis • Excellent electrical properties compared with traditional SMA connections Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

14. Performance: Noise and GainMeasurement procedures • Measurement procedure:Cold attenuator • Two measurement systems available at our labs: • System 350: • Older • More pessimistic • Used to keep traceability with past measurements • All noise tests shown here were performed with 350. • System 1020: • Newer calibration. • Gives 0.75 K better results • Estimated error (both) 1.4 K(repetitivity < 0.2 K) Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

15. Performance: Noise and GainResults • Average of 3.57 K mean noise in the band for the complete DM series Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

16. Performance: Reflection and Stability • Worst case output reflection • Average MPAs: -14.3 dB • Average DMs: -13.0 dB • Model prediction of output return losses needs refinement • Isolator at the input (not designed for low input ref.) • Unconditionally stability for most bias points checked with sliding shorts Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

17. Performance: Gain fluctuationsCryogenic measurements of DMs (TRW transistors) • Characterized by spectral density of normalized gain fluctuations: • Measure S21 @ 6 GHz with HP8510 VNA (attenuator and air lines) • Normalize and FFT each VNA scan (0.012-2.34 Hz) • Average 50 spectra and subtract the system fluctuations • Fit, in the region where 1/f noise dominates, the expression β represents the fluctuatons @ 1 Hz and is used as a reference for comparison between amplifiers Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

18. Performance: Gain fluctuationsCorrelation with voltage fluctuations • Fluctuations of gate voltage measured with HP35670A • Moderate correlation with gain fluctuations for different amplifiers measured at the same bias point • This simple DC measurements may be useful for pre-selecting least fluctuating devices from a batch 1 Hz 1 Hz Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

19. Performance: Gain fluctuationsBias dependence • Tested the variation of gain and voltage fluctuations with drain voltage • Found a steep change in gain voltage around 0.5 V • The behaviour of gain and voltage fluctuations is similar as Vd varies • High fluctuation zones could be avoided with no penalty in noise or gain • Voltage fluctuations may help detecting these bias regions Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

20. Performance: IsolatorsImpact in overall performance • Isolators measured @ 14 K (PAMTECH gives data @ 77 K) • Good agreement between measurement and estimation of isolator noise: • Mean contribution 1.1 – 1.4 K Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

21. Performance: IsolatorsResults Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)

22. Summary • 34 InP HEMT 4-8 GHz cryogenic amplifiers fabricated for HERSCHEL, including the Development Models with TRW transistors • Cryogenic S parameters of InP transistors measured in microstrip and noise models developed • Cryogenic isolators used at the input allow wide-band mixer-independent design with small penalty in noise • Exceptional performance and repeatabilityFor the final DMs 3.5 K noise and 27±1.1 dB gain dissipating 4 mW • Gain fluctuations exhibit a greater dispersion • Low frequency noise of gate bias may help selecting more stable devices • High sensitivity of gain fluctuations to bias point • Gate bias noise measurements could detect bias regions of high fluctuations Centro Astronómico de Yebes, Obs. Astronómico Nacional, IGN (Spain)