The Amp Hour

An Interview with Adrian Tang

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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
    • ...more
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