Editing MOSFET (section)

==== Analog ====
The MOSFET's advantages in digital circuits do not translate into supremacy in all [[analog circuit]]s. The two types of circuit draw upon different features of transistor behavior. Digital circuits switch, spending most of their time either fully on or fully off. The transition from one to the other is only of concern with regards to speed and charge required. Analog circuits depend on operation in the transition region where small changes to ''V''{{sub|gs}} can modulate the output (drain) current. The JFET and [[bipolar junction transistor]] (BJT) are preferred for accurate matching (of adjacent devices in integrated circuits), higher [[transconductance]] and certain temperature characteristics which simplify keeping performance predictable as circuit temperature varies.

Nevertheless, MOSFETs are widely used in many types of analog circuits because of their own advantages (zero gate current, high and adjustable output impedance and improved robustness vs. BJTs which can be permanently degraded by even lightly breaking down the emitter-base).{{Vague|date=January 2016}} The characteristics and performance of many analog circuits can be scaled up or down by changing the sizes (length and width) of the MOSFETs used. By comparison, in bipolar transistors follow a different [[scaling law]]. MOSFETs' ideal characteristics regarding gate current (zero) and drain-source offset voltage (zero) also make them nearly ideal switch elements, and also make [[switched capacitor]] analog circuits practical. In their linear region, MOSFETs can be used as precision resistors, which can have a much higher controlled resistance than BJTs. In high power circuits, MOSFETs sometimes have the advantage of not suffering from [[thermal runaway]] as BJTs do.{{Dubious|reason=Depends on circuit topology?|date=January 2016}} This means that complete analog circuits can be made on a silicon chip in a much smaller space and with simpler fabrication techniques. MOSFETS are ideally suited to switch inductive loads because of tolerance to [[Counter-electromotive force|inductive kickback]].

Some ICs combine analog and digital MOSFET circuitry on a single [[mixed-signal integrated circuit]], making the needed board space even smaller. This creates a need to isolate the analog circuits from the digital circuits on a chip level, leading to the use of isolation rings and [[silicon on insulator]] (SOI). Since MOSFETs require more space to handle a given amount of power than a BJT, fabrication processes can incorporate BJTs and MOSFETs into a single device. Mixed-transistor devices are called bi-FETs (bipolar FETs) if they contain just one BJT-FET and [[BiCMOS]] (bipolar-CMOS) if they contain complementary BJT-FETs. Such devices have the advantages of both insulated gates and higher current density.