The next application is RF and IF amplifiers.
One of the key specifications you want to look for is noise, at least around 3 nV per root Hz.
- Distortion products should be less than 60 dB below the carrier. If a part has 400 MHz of 3 dB bandwidth, then it is going to fail the distortion specifications down around 40 to 50 MHz.
- You need flat bandwidth to within a tenth of a dB over the frequency range that you are operating.
- Most RF chains are 50 Ohm terminations, at least near the antenna, although once you get into the SAW filters you are looking at around 600 Ohms and A/D converters are around 1000 Ohms of input.
- Use an op amp either as gain or as a buffer. The buffering would be either impedence matching or driving a low impedence stage from a high impedence stage. If you have an oscillator, then you will need some kind of a buffer to buffer it before you drive a mixer with it.
It's True! The following National Semiconductor part is ideal for these types of applications: LMH6702.
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