ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

BJT Vs FET : A Quick Look

Updated on March 4, 2010

Dominant Features

We know that PN junctions have two dominant features : injection of minority carriers with forward bias and variation of depletion width with reverse bias. These 2 features are used in BJT and FET respectively. Like th bipolar counterpart, FET is a 3 terminal device (Drain, Source and Gate) in which current conduction is by one type of majority carriers. (Electrons in the case of N channel type and holes for P channel type). Unlike Bipolar junction transistor, an FET virtually need no input current. Field effect devices are controlled by an electric field (or voltage) and give an extremely high input impedance and this is considered as one of the most important advantages over BJTs. 

Confusing Transistor Types :-

Field effect transistors are of several types such as JFETs, MESFETs, MISFETs, etc. In a JFET, the gate voltage controls the depletion width of a reverse biased PN junction. A MESFET is the same bsic device except that the PN junction is replaced by Schottky barrier rectifying junction.  MISFET is the one in which the metal gate electrode may be separated from the semiconductor by an insulator. MOSFET is a special type of which makes use of oxide layer insulator.      

What's Behind Them?

The current in a JFET is through a semiconductor region called the channel, with ohmic contacts at each end. The basic transistor action is the modulation of the channel conductance by the electric field that is perpendicular to the channel. The modulating electric filed is induced in the space charge region of a reverse-biased PN junction or a reverse biased schottky barrier junction and is, therefore, a function of voltage applied to the gate.

Although the bipolar junction transistors reigned supreme in the early days of semiconductor integrated electronics, it has been gradually supplemented in most applications by Silicon MOSFETs.The main reason is , unlike BJTs, the FETs are characterized by high input impedance, as the control voltage is applied to reverse biased junction. Such devixes are particularly suitable for controlled switching between a conducting state and a non conducting state and that is why they are quite useful in digital circuits. They are also well suited for integration of many devices on a single chip. The MOSFET is, without doubt, the core of the integrated circuit (IC) at the present time. 

Comments

    0 of 8192 characters used
    Post Comment

    • profile image

      deepu 

      6 years ago

      very nyc easily understable

    • profile image

      Vidya.M 

      6 years ago

      THANKS FOR THIS EXPLANANTION..........

    • profile image

      Lama Mahmoud 

      7 years ago

      Thank you for these info

    • profile image

      Akshay 

      7 years ago

      nice work..keep on..

    • lakshanhere profile image

      Lakshan Thiranagama 

      7 years ago from Colombo, Sri Lanka

      Great...useful..thanks for publishing this..!!!!

    working

    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, hubpages.com uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at: https://hubpages.com/privacy-policy#gdpr

    Show Details
    Necessary
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the googleapis.com or gstatic.com domains, for performance and efficiency reasons. (Privacy Policy)
    Features
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Marketing
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Statistics
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)