com, so we'll see in a couple of weeks.
n that some of them aren't very good at it. Paul Horowitz is a physicist, a nd Jan Hall (2005 Nobel) designed all his own stuff, just for starters.
.These very high gain TIAs are intended for use in mass spectrometers, in pa rticular for geochronological dating (see e.g. Argon dating on Wikipedia). High sensitivity is required for low abundance isotopes relative to the maj or isotope and precision ratios are required. The original samples are usua lly also very small so the total number of relevant atoms is tiny. In this high gain region the primary source of noise is the Johnson noise of the fe edback resistor. The general argument is that the gain increases proportion ally with increase in feedback resistance while the noise only increases wi th root of the resistor value so the S/N ratio improves as the root of feed back resistor value increase. This improvement continues until the shot noi se of the IC amplifier bias current presents a limit and this occurs, at pr esent, around the 100Tohm mark (this is also the about the maximum value of resistor available). It indicates that the input IC needs to have very low bias current and the ADA4530-1 is the latest arrival with only femtoamp b ias current. It may be thought that ion multipliers would be better for the lowest abundances but they have a major drawback. The impact (and burying in the surface) of heavy ions changes the secondary emission coefficient so stable cross calibration of isotopic channel gains cannot be achieved and high gain TIAs must be used. It is also necessary that the response time of the amplifiers be short enough that measurement can be made in a few secon ds since the sample introduced into the spectrometer vacuum decays with tim e and the measurement has to be extrapolated back to zero time, a problemat ical procedure if the extrapolation is excessive. My book is aimed primarily at my physicist (and allied subjects) colle agues rather than EEs so there may well be as you say some ?weirdn ess? in the approach. As you slightly obliquely point out Horowitz and Hill is a very successful book indeed, but I wanted to encourage the us e of circuit simulation as an aid for those for whom circuit design was onl y incidental and not a primary skill. This is all getting a long way away from the original topic of cleani ng PCBs and components!