I have some questions about hfe parameter of bjt

hfe parameter of bjt transistor

In any bjt datasheet, we see hfe parameter is a variant parameter because it depends on temparature. Of course, in an analog circuit we would like it mostly invariant. How can we do it?
I really need an answer about it. I think the only thing I don't understand still now on BJT is the question about hfe parameter.

Please help me. Thanks in advance.

amount of bjt hfe variation due to temperature

Try to cancel the hfe...
Because Ic~=hfe* Ib, then if we can make Ib~=constant*hfe then you can make your circuit not depends on temperature.

BR,
TY

Added after 1 minutes:

Sorry,It is Ib=~constant/hfe

you can cancel the variation hfe with temperature with a degradation resistance at the emitter or some sort of feed back
for feedback techniques check sedra chapter 8

How can we make Ic=const? How could we design a circuit in which Ic=const.
Thanks.

Best regards.

to get constant IC

by putting Re negative feed back takes place

if t increased IE & IC will increase so VE winn increase
and VBE decrease causing IC to decrease so u get a const IC

also this stabilizes the gain as the gain in this case ≈ RC/RE
so it depends on the ratio of the resistances not hfe

For example,
You can bias a BJT with its base bias(Vbb) =Vcc*[Rb2/(Rb1+Rb2)], Then Ib=(Vbb-Vbe)/[Rbb+(hfe+1)Re] where Rbb=Rb1 || Rb2. Because Ic=hfe*Ib , as Rbb is small then Ic will be almost constant.

BR,
TY

also it's useful to try biasing the transistor with a current source or a current mirror
that will force IC to be constant

But how do you amplify the input signal by current mirror? Is it a current mode input signal?

no you don't amplify the signal with a current mirror you amplify the signal with an amplifier biased with a current mirror or a current source

check sedra the chapter 5 section 5 page 442 in the fifth edition
biasing bjt amplifier circuits
biasing using a constant current source

Well, if you have a mirror with two BJTs, and the areas are not equal, there will be some "amplification" factor, but in general, you don't use the current mirror to produce large gains.

hi
by temperture variation Bjt's parameter will vary. but how we can reduce these variation?
hfe and Vbe are the parameters that vary with temperature. variation of Vbe will cause variation in Ib and variation in Ib and hfe will cause variayion in Ic. by biasing the bjt by a diode with same Vbe parameter or a same bjt with conected bais and collector we can keep Ib constant against tempereture variation in fact we compensate this variation by variation in diode or bjt in bias circut
but about hfe we can use a resistor in emmiter of bjt the bigger resistor make Ic more constant but bigger resistor make the currnt lower and increase the loss. then we can use a currnt source by desired current and big resistance
note that useing a small resistor in bias circut (Rb) could not be a good sloutuon because decrise the input impedance
be happy

if you bjt is used in the integrated circuit , you can bias it with an internal referece bias current.
if not ,the discrete bjt's bias is normally formed by two big resistors
ratio, with a source feedback resisitor.

but the hfe's variation is not just decided by the temperature, it also varied with the differenct IC current.