Noise figure is something that can be assured over a wafer a little easier than things like Idss, Vp and g_subm (gm), and these last two parameters are something that can be probed on-wafer whereas NF (on a discrete part such as this) cannot owing to the fact that there are no pads/RF structures to bring in the 'stripline RF probes' and perform this high-frequency measurement at frequency (like 1 GHz). To assure a wafer is at a particular NF value testing is done on specialized transisitor test-structures that possess the necessary RF pads in test reticles that allow just a few easy, quick RF measurements (RF measurements take more time per part, require specialized RF probes versus the simpler "probe cards" used for DC tests and also requires a Noise Figure Measuring Test Set, plus DC supplies to bias the part during testing). Since the gain of the device can be tracked via so-called "DC on-wafer tests" (that don't require specialized conditions like on-wafer RF testing does) the gm (transconductance), Vp (gate pinch-off voltage) and Idss (drain current with zero gate voltage) parameters can be measured and logged - - tests which also assure device functionality - I'd say that those marks were for gain-binning. But, I could be wrong. I don't know what this manufacturer was doing - and I was just extrapolating based on what our foundry did (our product was GaAs devices, including discretes and MMIC's (Microwave Monolithic Integrated Circuits - almost RF SOIC's in some cases!). RF Jim ----- Original Message ----- From: "Brendan Moran" To: Sent: Thursday, August 22, 2002 5:56 PM Subject: Re: [EE]: RF transistor colouring > > Looking at the HP data sheet for these - these > > are 6 GHz Low Noise Silicon Bipolar Transistors > > and *not* gain blocks as I was guessing! > > > > I still think it's a gain-grading perhaps > > screened for the app you've got ... > > Hmm... Could they be graded for noise, rather than gain? The white one is > the first stage, and the black is the second. > > --Brendan > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.