I cannot understand this circuit.!

[ljy4468]

Hi all
I've a question about the attatched circuit.
It isi bicmos.
I'm beginner in bicmos circuit.
So I don't know what book I study because almost my book is about CMOS.
who can show me some article or some books about this circuit?

Thanks,
Regards.

 

[Teddy]

this circuit has same function as fully cmos one. just replace the bibs with moses.
Tha cap there is to add 'peaking" which adds a little peak in ac reponse and so extends the bandwidth of a circuit

 

[Sadegh.j]

I also agree.

The whole circuit can be regarded as a fully differential amp. The rest of the circuit provides DC biasing.

 

[ljy4468]

Oh, Thanks very much.
But I want to know more about this circuit (why using BJT instead of MOS...)
So can you tell me any book about that circuit?

Regards.

 

[yxo]

Oh, Thanks very much.
But I want to know more about this circuit (why using BJT instead of MOS...)
So can you tell me any book about that circuit?

Regards.

BJTs are used to decrease input offset voltage of amplifier

 

[rajanarender_suram]

BJTs can provide higher gain with the same current...

 

[ee_ykhab]

As you know,
For Bjt : gm = Ic/Vt where Vt ~ 25mV
For MOS : gm = 2Id/(Vgs-Vt) = Id/100mV when Vgs-vt = 200mV(typical case)
thus, gm for Bjt is 4 times bigger than MOS.
B.R

 

[yxo]

As you know,
For Bjt : gm = Ic/Vt where Vt ~ 25mV
For MOS : gm = 2Id/(Vgs-Vt) = Id/100mV when Vgs-vt = 200mV(typical case)
thus, gm for Bjt is 4 times bigger than MOS.
B.R

But MOS could be used in weak inversion! Then gm is same

 

[boxxang]

maybe, bjt is useful than mos in terms of gain and bandwidth. but it has leakage current.

 

[ljy4468]

Thanks all.
But Teddy, you said there are peaking capacitor.
I want to know about that compensation method more.
How can this cap give peak in ac response?

Thanks.
Regards.

 

[rajanarender_suram]

As you know,
For Bjt : gm = Ic/Vt where Vt ~ 25mV
For MOS : gm = 2Id/(Vgs-Vt) = Id/100mV when Vgs-vt = 200mV(typical case)
thus, gm for Bjt is 4 times bigger than MOS.
B.R

But MOS could be used in weak inversion! Then gm is same

if the mos used in weak inversion, than it will have lot of noise and the BW decreases

 

[forkschgrad]

it will all depend on the function of the whole circuit or chip.

 

[ee_ykhab]

Adding the capacitor at the drains of the differential pairs --> adding a pole to the AC response.. Or you can recognize adding a feedforward path for any fast changes. Its bandwidth/phase margin may be increased or decreased according to the whole system response.

 

[oxide]

bip are less noisy as well.