Connect with us

bjt question

Discussion in 'Electronic Design' started by R.Lewis, Oct 8, 2003.

Scroll to continue with content
  1. R.Lewis

    R.Lewis Guest

    Is there a small signal bjt that has a particularly small temp dependence of
    Vbe?
     
  2. Jim Thompson

    Jim Thompson Guest

    On Wed, 8 Oct 2003 23:52:58 +0100, "R.Lewis" <h.lewis-not this
    ALL Silicon BJTs have a Vbe TC of approx. -2mV/°C

    ...Jim Thompson
     
  3. No. As Jim said, all bjts are the same. If you want low tc, use a
    differential pair.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  4. R.Lewis

    R.Lewis Guest

    Yes, I know that, but if you needed a tc of 150mV per degC max as much as I
    do then ..... hope springs eternally.
     
  5. Jim Thompson

    Jim Thompson Guest

    On Thu, 9 Oct 2003 18:39:50 +0100, "R.Lewis" <h.lewis-not this
    Why don't you elaborate on your application because hope is the ONLY
    thing that springs eternal ;-)

    ...Jim Thompson
     
  6. Well, you should've said all Silicon BJTs. There are other BJTs that
    are not the same, such as Ge, and more recently, SiGe or GaAs.

    Low tc, Diff pair? More like use a diff pair to cancel out the effects
    of tc.

    --
    ----------------(from OED Mini-Dictionary)-----------------
    PUNCTUATION - Apostrophe
    Incorrect uses: (i) the apostrophe must not be used with a plural
    where there is no possessive sense, as in ~tea's are served here~;
    (ii) there is no such word as ~her's, our's, their's, your's~.

    Confusions: it's = it is or it has (not 'belonging to it'); correct
    uses are ~it's here~ (= it is here); ~it's gone~ (= it has gone);
    but ~the dog wagged its tail~ (no apostrophe).
    ----------------(For the Apostrophe challenged)----------------
    From a fully deputized officer of the Apostrophe Police!

    <<Spammers use Weapons of Mass Distraction!>>

    I bought some batteries, but they weren't included,
    so I had to buy them again.
    -- Steven Wright

    FOR SALE: Nice parachute: never opened - used once.

    (Problem) Evidence of leak on right main landing gear
    (Solution) Evidence removed

    F
    o
    d
    d
    e
    r

    f
    o
    r

    s
    t
    u
    p
    i
    d
    "
    n
    o
    t

    e
    n
    o
    u
    g
    h

    i
    n
    c
    l
    d
    u
    d
    e
    d

    t
    e
    x
    t
    "
    e
    r
    r
    o
    r

    m
    s
    g
    ..
     
  7. Jim Thompson

    Jim Thompson Guest

    ***I*** said all SILICON ;-)
    Matched pairs of any ilk tend to compensate out the TC... even CMOS
    ;-)

    ...Jim Thompson
     
  8. Actually, alot of the characteristic behaviors of BJTs (no matter
    SiGe, Ge, GaAs or Si) are the same. Even the old KT/q type thing is the
    same. The major differences would be related to the Is levels
    and some other measurements like that. (For SiGe, GaAs, vs. Ge
    vs. Si, the old 0.025mhos/ma gm should be essentially the same!!!)

    There are some 'interesting' differences beyond the obvious
    ft and other kinds of circuit measurements -- SiGe with the
    straining tends to have significantly higher Beta -- which
    along with other attributes, provides some improvements for
    noise behaviors.

    John
     
  9. If you actually what a voltage/current variation with temp look up
    "PTAT", that is "Proportional To Absolute Temperature" circuits. They
    are used in all "Band gap" voltage reference circuits. Typically
    constructed by using a "pair" of transistors where one of the pair is a
    multiple device. e.g. 1:8 ratio will get you about 52mv/deg.
    Alternatively one can use identical transistors but operate the
    transistors at different currents.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-