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    What is the conditions for complementary BJTs

    Hi, i am trying to design on-chip output BJT amplifiers using a NPN and PNP BJT pair.
    I have a question for the BJT sizing (or choosing).
    For designing CMOS devices such as inverter, usually, the NMOS and PMOS pair were chosen by comparing the Id vs Vds curves of NMOS and PMOS.
    In the case of BJT amplifier, what are the complementary (matching) pair conditions between NPN and PNP BJT for push-pull amplifier? (I-V curve or other conditions?)

    It is my first time to design BJT amplifier. please give me a guideline.
    Thank you.
    Last edited by Luis_rr; 15th September 2019 at 08:08.

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    Re: What is the conditions for complementary BJTs

    Many complementary transistors have the same range of spec's like 2N3904 and 2N3906, 2N4401 and 2N4403 and 2N3055 and MJ2955. They are not matched so then one might be much more sensitive than the other in a pair.


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    Re: What is the conditions for complementary BJTs

    Depends on whether you're talking IC design (run what
    ya brung) or PCB design (shop 'til you drop).

    A complementary bipolar process development would aim
    for things like roughly-equal Vbe@Ic (look at Class B, Class
    AB outputs for why), roughly-equal beta-vs-Ic curves
    across some useful range.

    There are technologies like old National / Fairchild / everybody
    once upon a time "Standard Linear" which had both NPN and
    PNP, but made very differently (lateral PNP, vertical NPN, very
    little similarity between them, PNPs really slow with poor Rc
    so you see amplifier designs which use a few PNPs only where
    speed doesn't matter (like DC current mirror racks) and the
    whole active gain path is NPNs).

    "Back in the day" RCA et al put out some pretty nice app notes
    about discrete-transistor-based audio amplifiers and some of it
    (as I recall) used transistors called out as matched NPN:PNP
    product-pairs. How well matched, how expensive or whether even
    still in production, I couldn't say offhand. But maybe digging for
    old RCA linear and transistor databooks on archive.org would
    be helpful.


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    Re: What is the conditions for complementary BJTs

    Gain and power rating are probably chief parameters to match, especially if you wish to push your amplifier to its maximum performance. Also the maximum amount of bias current they can tolerate before burning.

    An electronics expert told me that commercial products (low end cost-wise) are often designed with conservative specs. Thus each unit yields satisfactory results from components which are mediocre quality or high quality.


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