One giga ohms resistor

Or, I imagine, any application where small currents (as low as several pA) are to be measured.

Mark

The very high input impedance of MOSFET stages often specify these very high value bias resistors, IIRC. Helps to prevent loading down previous hi-output impedance stages.

I've seen very high resistors used as feedback in sensitive photodetector and electrometer-type circuits. Biggest I ever used was 100 Meg, and even at that it was non-trivial to actually get the resistance you paid for. The problem is that it doesn't take much leakage current to knock down these high values in the actual circuit. You need to be fanatical about cleaning the outside of the glass resistor body (these are always in glass bodies), since any sort of film will cause leakage. You need may exotic circuit board and teflon mounts, etc, etc. And it's hard to know when things have gone wrong, since you typically don't have a femtovolt or picocandela calibration source!

Best regards...

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

I remember seeing them in some early B&W Vidicon type TV cameras.

Perhaps they are making the worlds highest voltage 'Phase pencil' ??

They are used as feedback resistors in photodiode transimpedance amplifiers (current to voltage converters.) One nanoamp into an op amp with a 1 G feedback resistor comes out as one volt.

I Gigohm's are even available in chip form and in 1% tolerance. I have used as high as 10 Gigohm 1% resistors in photodiode test equipment. Victoreen, now owned by Ohmite, is one manufacturer. Digi-Key carries them through 5 gig 1%.

Steve Noll | The Used Equipment Dealer Directory: |