Small-signal and other circuit design techniques realized by carbon nanotube field-effect transistors (CNFETs) to create analog electronics for analog signal handling, analog signal processing, and conversions between analog signals and digital signals. As the CNFETs exist and operate at nanoscale, they can be readily collocated or integrated into carbon nanotube sensing and transducing systems. The resulting collocation and integration may be at, or adequately near, nanoscale. One embodiment implements an analog differential amplifier having transistors which include carbon nanotubes, electrical contacts, and insulating material. The differential amplifier may be used in isolation or as an element of an operational amplifier. Negative feedback may be used to implement a wide range of analog signal processing functions, and to provide conversions among analog and digital signals. In some cases, an entire analog differential amplifier is implemented with a single carbon nanotube.