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Switching and amplifiers

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May 8, 2011
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Tehran , Iran
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Dear All :
im looking for a circuit configuration that never goes to saturation region. (either consisting BJTs or other Circuit components) ,
such circuit could never be used as a switching Device (correct me if iam wrong please)
Thanks all.

If is necesary amplify a sonsor signal that in the following stage controls a switching device, tha answear to your questio is NO.
And not necesarly must be in saturation, if your definition if 5V for a logic "1" it doesn't matter the region of the tranasistor.
The equuivalent region of the BJT operation or linear region in the MOSFET transistor is saturation.
For the mosfet as switch the regions are cut off and triode (no saturation).

Thanks For your reply , But i didnt get the answer completely, The question was about a circuit that NEVER goes to saturation region. im looking for the circuit it self, or schematic diagram of the circuit.
thanks anyway

Your question is raising several doubts:
- the term saturation has a different meaning for BJT and MOS transistors, so it's not clear which operation region of transistors you actually mean

I assume, that you mean saturation as it's used for BJT.

- I don't agree to the conclusion, because the operation of some high speed logic circuits is usually descibed as non-saturated switching.

Anyway, it's not clear to me, which kind of circuit you are actuall looking for?
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As all devices are limited in their output by their supply lines, i.e. you can't get 20V out of an amplifier that has a 5V supply line, the only way to proceed is to use a logerithmic amplifier, even these will run out of head room but their dynamic range is very wide.

Thanks FVM,
By the Word "saturation" , i exactly meant saturation as used for BJTs. is it possible to have a circuit configuration for A BJT transistor that never reaches saturation region?
about non-saturated switching, thanks alot, ill search about those high speed logic gates,
You were so helpful ,
Thanks once again.

I think the basic scheme for non-saturated switching is a differential amplifier. It performs current steering to the outputs without saturation (assume Vce > Vbe for simplicity). ECL logic is basically using this operation mode.

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