Hello everyone,
I'm having problems with analysis of one of the circuits presented on this site in the worksheet section, under this link (also see attached screenshot). As you can see it's a BJT differential pair but I'm not interested in small-signal application but large signal DC analysis.
Normally I would start from assumption that these transistors work in linear mode, calculate DC operating point and then apply small-signal model to calculate Vout/(Vinverting - Vnon-inverting). However in this case, such assumptions are not possible (?) as this circuit does not have to operate in linear region and I'm looking for a complete transfer function, regardless of operating state.
That's why I came up with an idea to use Shockley model to characterize emitter currents Ie~Ies*exp(Vbe/Vt) and Vbe voltages. However, despite all my efforts I seem to end up with too many variables and too few equations to find a solution. Maybe it could've helped me if I could somehow assume/calculate constant current flowing through common emitter resistor, but I'm unable to tell if I can do such thing and how to calculate it.
Can someone help me and explain in a step-by-step manner how to approach analysis of such circuit? Some practical engineering tips would be most welcomed. Again, I'm not interested in small-signal analysis - my inputs will have full rail to rail swing. I would like to derive full transfer characteristic, that is Vout as a function of Vinv - Vnon-inv.
P.S.
Intuitively, I know that this circuit is going to be a comparator for most of input voltage range. Nevertheless, I still need my complete transfer function, not just linear approximation.
Thanks in advance!
I'm having problems with analysis of one of the circuits presented on this site in the worksheet section, under this link (also see attached screenshot). As you can see it's a BJT differential pair but I'm not interested in small-signal application but large signal DC analysis.
Normally I would start from assumption that these transistors work in linear mode, calculate DC operating point and then apply small-signal model to calculate Vout/(Vinverting - Vnon-inverting). However in this case, such assumptions are not possible (?) as this circuit does not have to operate in linear region and I'm looking for a complete transfer function, regardless of operating state.
That's why I came up with an idea to use Shockley model to characterize emitter currents Ie~Ies*exp(Vbe/Vt) and Vbe voltages. However, despite all my efforts I seem to end up with too many variables and too few equations to find a solution. Maybe it could've helped me if I could somehow assume/calculate constant current flowing through common emitter resistor, but I'm unable to tell if I can do such thing and how to calculate it.
Can someone help me and explain in a step-by-step manner how to approach analysis of such circuit? Some practical engineering tips would be most welcomed. Again, I'm not interested in small-signal analysis - my inputs will have full rail to rail swing. I would like to derive full transfer characteristic, that is Vout as a function of Vinv - Vnon-inv.
P.S.
Intuitively, I know that this circuit is going to be a comparator for most of input voltage range. Nevertheless, I still need my complete transfer function, not just linear approximation.
Thanks in advance!
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