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"the basic differential pair" VS " the differential pair with active current mirror"

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sevid

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"the basic differential pair" VS " the differential pair with active current mirror"

can you tell me the differences between "the basic differential pair" and "the differential with active current mirror" ?

i know the latter increases a "mirror pole", i.e., it has worse stability.


what are the other advantages and disadvantages of the two circuits ?

plz help me, thanks in advance.

jeffrey
 

Re: "the basic differential pair" VS " the differential pair with active current mirr

You can save area by using active current mirror load.
Basic differential pairs use resistor load, which is expensive because it occupies large area.
By using active load you save area and thus reduce chip cost, because it's just transistors and you can make them any impedance you want by designing the circuit.
 

Re: "the basic differential pair" VS " the differential pair with active current mirr

Active current mirror is used for increase the output resistance. So it will have higher gain. Also it will lead to lower frequency pole according to bigger output resistance. Pole frequency is related to R.C. Here R is the equivalent resistance, and C is the total capacitance at the node.
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

In addition to higher gain values, the active load (current mirror) provides the best way to change from doubled-ended to single-ended mode without any loss because the current variations in both branches are combined to feed the second stage.
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

Yes, in order to have high gain you need to have high output impedance, and if you use basic differential pair you have to use very big resistances, which occupy large area and therefore is expensive. So the advantage of active load which is basically transistors is that they have high impedance and at the same time small and cheap.
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

differntial pairs having active loads are used to increase gain. also active loads consume less area and provide high output impedence.
if resistors are used instead of current mirrors then they will dissipate heat also cover larger chip area.
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

syeda amna said:
... if resistors are used instead of current mirrors then they will dissipate heat ...
Click to expand...
Actually the same heat as a transistor with the same voltage & current rating :idea: :p
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

Resistive loads are used when you need the bandwidth or speed (ie comparators).
The active loads are superior in most of the other parameters, ie gain, area, headroom etc.
 
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Re: "the basic differential pair" VS " the differential pair with active current mirr

thanks, everyone
 

Re: "the basic differential pair" VS " the differential pair with active current mirr

Dear all, recently I am designing comparator circuit and I read this post.
I have one question here.
when we use basic differential pair (resistor), will input dynamic range become better (widen)?
Because I see a lots of 2 stages diff pair circuit that basic diff pair used in the first stage and active load diff pair used in second stage.
My thinking is first stage increase dynamic range and second stage increase gain. Am I corect?
 

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