We examine how intermodulation distortion of small two-tone signals is a ected by adding degenerative feedback to three types of elementary ampli er circuits (single-ended, push-pull pair, and di erential pair), each implemented with three types of active device (FET, BJT and vacuum triode).
Although high precision numerical methods are employed in our analysis, the active devices are modeled with rather simple models. We have not investigated the consequences of more elaborate models.
Though negative feedback usually improves the distortion characteristics of an ampli er, we nd that in some cases it makes the distortion “messier.” For instance, a common-source FET ampli er without feedback has a distortion spectrum displaying exactly four spurious spectral lines; adding feedback
introduces tier upon tier of high-order intermodulation products spanning the full bandwidth of the ampli er (as suggested by Crowhurst in 1957). In a class-B complementary-pair FET ampli er, feedback mysteriously boosts speci c high-order distortion products.
Small signal distortion in feedback amplifiers for audio by G. Boyk and G. J. Sussman – >>>LINK<<<