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