Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

I cannot understand this circuit.!

Status
Not open for further replies.
L

ljy4468

Full Member level 4
Joined
Jul 20, 2005
Messages
232
Helped
13
Reputation
26
Reaction score
1
Trophy points
1,298
Location
South Korea
Activity points
3,023
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.
 

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
 

I also agree.

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

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.
 

ljy4468 said:
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.
Click to expand...

BJTs are used to decrease input offset voltage of amplifier
 

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
 

ee_ykhab said:
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
Click to expand...
But MOS could be used in weak inversion! Then gm is same
 

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

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.
 

yxo said:
ee_ykhab said:
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
Click to expand...
But MOS could be used in weak inversion! Then gm is same
Click to expand...

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

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.
 

bip are less noisy as well.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top