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episode 483: #483 - An Interview with Adrian Tang
This episode is sponsored by Rohde & Schwarz. Check out their reviews of their new product line at AskAnEngineer.us, including a video review from friend of the show Shahriar from The Signal Path.
Welcome, Dr Adrian Tang of NASA’s Jet Propulsion Laboratory (JPL)!
- Adrian is the only CMOS chip designer at JPL (though he has grad students)
- He got his PhD at UCLA working on ultra high frequency devices. Check out some of his projects on his personal website.
- JPL has instruments that can measure these high frequencies.
- Terahertz spectroscopy
- There’s a noise floor in the universe, but gases tend to emit at certain frequencies in the 50-500 GHz region.
- Resonance in the THz range
- Pressure has to be low
- Trying to process as much bandwidth as possible
- Try to get 3GHz of bandwidth out of devices.
- 4000-8000 point FFT
- Power budget might only be 50W on a satellite.
- Was doing commercial CMOS previously
- Horn antenna + lens
- Tempest D mission
- Using cosmic background as a cal point
- What is the output data?
- Time domain data
- Using the LO to remove the movement of the spacecraft
- Doppler properties
- Herschel telescope
- Reflector to focus it down into the feed is about a meter
- Has to be accurate to lambda over 20
- Goes into a receiver feed
- Mixer needs an LO
- IF comes out of the mixer at 3-4 GHz
- Takes it through the IF chain
- Amps and filters
- Apply a window function
- Polyphase filter
- Compute the FFT
- 1 sample isn’t enough to see something
- Average over 1000s of samples
- Rosetta orbiter was put out by ESA
- The more spectrum, the more chance to discover something
- RekTangLE balloon mission
- Measuring NO2 at 570 GHz
- Did have a failure
- This was one of the first CMOS chip to do atmospheric measurement
- Isotopes have different lines
- Heavy water and regular water
- Heavy water is naturally occurring
- Everywhere you go, the ratio is comparable, in the solar system
- Moreau on a jovian comet
- How have things moving into CMOS?
- Active and Passive Receivers
- Northrop Grumman makes some of the only amplifiers that can operate up to 600 GHz
- Past guest Tony Long talked about (relatively) high frequencies and works at NG
- Passive is a mixer first instead of an amplifier first
- Schottky mixer
- Express sensitivity in terms of difference
- Hot electron bolemetric mixers
- Exotic semiconductor junctions
- What has improved?
- Windfreak
- Packaging is not simple
- Waveguide is the only thing that will work at 100G
- They do a lot of the fab in house at JPL
- Measuring snow in the Sierras using Ku band radar
- SWE – Snow water equivalent
- SpectreRF
- Built in self test
- Everything on chip is the best case
- Using different process technologies
- 65 nm process technology cannot work with 180 GHz signals.
- What is this stuff useful for?
- Short range 60 Ghz
- Ken Cooper
- Threat detection, 680 GHz radar, 30 GHz bandwidth
- Another balloon “whatsup” will go up soon. Read about it and other balloon launches (past and present) here.
- Astros – 8 px, multi THz telescope
- Ground penetrating radar
- UAV snow sensor
- Check out more of Adrian’s work on sadcircuitdesigner.com
- Or check out his papers on his “articles” page