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.

Diff Amp with active load vs diff amp with linear resistors

Status
Not open for further replies.

suhas_shiv

Full Member level 2
Joined
Nov 30, 2005
Messages
136
Helped
11
Reputation
22
Reaction score
4
Trophy points
1,298
Activity points
2,461
Hi all,
What are the pros and cons of Diff Amp with active load when compared to diff amp with resistors?
More gain and less area with active loads are the ones that I know of.

Thanks
 

Re: Diff Amp with active load vs diff amp with linear resist

it is hard to fabricate resistor with tightly-controlled values
 

Re: Diff Amp with active load vs diff amp with linear resist

active load provide large impedance , and influence the output swing less than resistors.
 

Re: Diff Amp with active load vs diff amp with linear resist

One thing more is that the output will either be a single ended or differential output.
The gain between the two are manipulated by current(active load) and resistor(resistor load).
 

Re: Diff Amp with active load vs diff amp with linear resist

the gain of the amp is Gm Rout. if you use a resistor, for example a 100k one, the swing will be like nothing, but an active load can give you a fair swing with a high gain
 

In general, Diff Amp with active load is good for gain,
diff amp with linear resist is good for speed such
as pre-Amp.
 

Re: Diff Amp with active load vs diff amp with linear resist

There is another major difference..

Active loads in general are non-linear.
Non-linear loads convert common mode noise to differential mode noise,
whereas linear loads dont.

Regards Prashanth
 

Re: Diff Amp with active load vs diff amp with linear resist

For resistive loaded differential amplfiers, gain will be gm*Rl, which requires high values of Rl to achieve moderate gain .However, these resistors will consume a voltage drop of Rl*Io/2 which would lead to a very limited headroom and would drive your transistors quickly out of saturation ,besides they consume lots of chip area .
So, for higher gains ,using active loads is more convenient .For active loads implementation, you can either use current sources at loads (MOS transistors each with a constant Vgs and none is diode connected) and in this case you'll need to have a CMFB network (Common Mode Feedback network) which is not easy to design .Or, you can use a current mirror at the load (single ended or unbalanced amplifier) and in this case your o/p will be single ended and more sensitive to Common Mode variation even in the case of perfect matching .
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top