During the work in the switching schemes switching speed completely is defined by RC time constant - lock chains. At field transistors with the isolated lock entrance capacity is much less therefore their frequency properties it is much better, than at field transistors with r-p - transition.
Boundary frequency is determined by a formula fgr. = 159/S11i, where fgr = frequency, MHz; S - the steepness of the characteristic of the transistor, / In; S11i - capacity between a lock and a source at short circuit on alternating current of an output chain,.
In MDP-transistors with the induced channel the carrying-out canal between silnolegirovanny areas of a source and drain and, therefore, noticeable current of a drain appear only at a certain polarity and at a certain value of tension on a lock concerning a source (negative at the r-channel and positive at the p-channel. This tension is called threshold (Uzi.por). As emergence and growth of conductivity of the induced channel are connected with enrichment by its main carriers of a charge, consider that the channel works in the enrichment mode.
Entrance conductivity is defined by conductivity of a site a lock - the ULTRASONOGRAPHY source. = u11 + u12; output conductivity - conductivity of a site a drain - a source of WUXI = u22 + u21; transfer functions - the steepness of the volt-ampere characteristic of S = u21 - u12; function of the return transfer - conductivity through passage = u1 These parameters are applied by UZS for primary parameters of the field transistor used as the two-port network. If primary parameters of the two-port network for schemes with the general source are determined, it is possible to calculate parameters for any other scheme of turning on of the field transistor.
Service life of semiconductor triodes and their profitability is many times more, than at electron tubes. At the expense of what transistors found broad application in microelectronics — TV, video, audio-, radio equipment and, of course, in computers. They replace electron tubes in many electric chains of the scientific, industrial and household equipment.
At MDP - transistors of all types substrate potential concerning a source has noticeable impact on volt-ampere characteristics and respectively parameters of the transistor. Thanks to impact on conductivity of the channel the substrate can carry out function of a lock. Tension on a substrate concerning a source has to have such polarity that r-p transition the source - a substrate joined in the opposite direction. Thus r-p transition the channel - the substrate works as a lock of the field transistor with the managing director r-p transition.
In MDP - transistors with the built-in channel the carrying-out canal, is made in the technological way, formed at a tension on a lock equal to zero. Current of a drain can be operated, changing value and polarity of tension between a lock and a source. At some positive tension a lock - a transistor source with - the channel or the negative tension of the transistor with n - the channel current in a chain of a drain stops. This tension is called tension of a cut-off (Uzi.ots). MDP - the transistor can work with the built-in channel both in the enrichment mode, and in the mode of impoverishment of the channel as the main carriers of a charge.
Let's consider the device and the principle of operation of the MOP-field transistor of structure (Metal - Oxide - the Semiconductor) which found broad application as a basic element of all modern integrated chips of KMOP of structure.
Frequency properties of field transistors are defined by RC time constant - lock chains. As the entrance capacity S11i at transistors with r-p transition is great (tens of pikofar, their application in intensifying cascades with a big entrance resistance is possible in the range of frequencies, the exceeding hundreds of kilohertzes - units of megahertz.
The steepness of characteristics of the field transistor S - the relation of change of current of a drain to change of tension on a lock at short circuit on alternating current at the transistor exit in the scheme with the general source.