My pals over at Linear Tech just released a Silicon Germanium 1.8Ghz amplifier. The LTC6400 kicks butt. It is intended to go in front of LT’s or other high-speed differential input A to D converters. The part is differential in and they have a demo board ready to go. Price is $3.38 in 1000s. Datasheet is here (pdf). As you would expect it uses a hefty bit of power, 90 mA at 3 volts. Heck, the shutdown power is 1 mA. Jaded mob-soldier turned journalist that I am, I asked Erik Soule, Linear’s general manager of signal conditioning products why anyone would use an amplifier instead of a nice cheap passive RF transformer. He mentioned that this part can provide more gain and also provides a very uniform 50-ohm load to the input, as opposed to a transformer that can reflect some of the impedance variations from the A to D converter back out the input. Duh, transformers work in both directions, I should know that.

What else? Well the parts come with fixed 20dB gain, so they could put the delicate summing node inside the chip instead of on your board. The gain is not super-accurate so you would have to cal the thing in software if you were using for a measurement application. You have to do that with discretes anyway and the big application for this chip is the communications industry where the amp is AC coupled anyway. You can also move the output common mode voltage around to help interface with various A to D converters — 1 to 1.6 volts. I also like the 2.1 nV/rtHz input noise—that is pretty good too. Check it out and a big shout-out to my building T buddy Tim Regan, who is the applications manager behind the part.