how to implement this circuit?

[samuel]

NOW, the output of Circuit A is current signal, how to implement Circuit B so that Circuit C gets what it want current signal from Cuircuit A. Note, we hope that Circuit B is controlable from outside chip.

 

[DenisMark]

It isn't clear what u want to control in B. I can suggest u to look for current amplifier (with gain = 1) or current conveyor citcuits.

 

[samuel]

ok. thankyou for your reply.

i want to design a Circuit B, which can control freely current from Circiut A to Circuit C。

Can you give me some advice?

 

[DenisMark]

What's "freely"?
What function of circuit B do u expect?
It's a switch (turn-on, turn-off), amplifier with controlable gain. What range of node voltage for link between A and B. U'll need specify this voltage controlable (current conveyor function) or link one with some supply.
Is It PCB circuit or citcuit for on-chip implementation?

 

[samuel]

ok.
(1)
“freely” just means, for example, if Circuit C needs 300nA current, you can get 300nA current signal from Circuit A through controlling Circuit B; if Circuit C needs 301nA ,you can also do it through controlling Criuit B； and so on. That is to say, controlled continously。(Note: the current signal from Circuit A is larger than the current into Circuit A.)
(2)this circuit is implemented on chip.

(3) the voltage relation between A and C is not important.


thanks again.

 

[DenisMark]

This description looks doubtful. How can i decide what current circuit C is needed? And how can i make control through B, add some fix current value or it's a part of feedback?
It'll better if u show relations by formulas.

 

[samuel]

Ic=a×Ia （0<a≤1)
(Ia>Ic)
Ia is constant.
Ic is current into Circuit C;
Ia is curretn outof Circuit A;

how to implement this formula?

 

[mdcui]

looks like a current mirror is what you are looking for, and by control the configuration of current mirror, you can get whatever current you want from B to C, but I am not quite clear about the detailed requirements.

 

[DenisMark]

How is "a" related with B?
If u need voltage control I think u need diff. pair circuit like at picture.
(1-a)=Vb/R. Or u can witch diff. pair completely.

 

[samuel]

ok.

but curent mirror may implement it, but it is discretely controlled, not continously.

that is to say, you can set a=0.1, 0.2, 0.3, and so on. Thus is discrete number, not a real number.

thankyou.

Added after 10 minutes:

Dear DennisMark,

I dont understand your viewpoint.

 

[DenisMark]

Excuse me, I hurried. The previous schematic is incorrect.
But now, your problem becomes more clear.
If current flow direction is appropriate for you, as mentioned before you can use diff.pair to switch/divide current IA and deliver part of one to sink as IC.
If the N mosfets turned on the left and M mosfets turned on the right that IC=(M/N)*IA, a=M/N.
For a=0.1, 0.2, 0.3, and so on u need 10 pair of mosfets (10 mosfets on each side).
Using biasing voltage for turnon switching allows u utilize more simple schematic of current sinker (IC).

 

[samuel]

can you exlain this circuit?

 

[samuel]

now, a is still discrete number, not a real number.

 

[DenisMark]

It's requred about 10 posts to understand what u want. And up to now it isn't clear how u suggest to control "a".
U should master to pose a problem more clearly from begining.

As i take ur explanation u need this function: Ic = Ia * A.
A changes continuously in dependence of controlling voltage Vb or current Ib. U don't explain what is controlling amount.

So we can reformulate this for linear dependence: Ic = Ia * K * Vb or Ic = Ia * K * Ib, K - factor. I don't know what dependence u need.

As u can see the result function is curent with current or current with voltage multiplication.

I think u work with large signal. So for voltage processing this kind of circuits is named variable gain amplifier (VGA). But i haven't known VGA equvalent for current processing. I need a time to think about.

 

[leo_o2]

What's the transfer function for from Current A to Current C with external controlling? What's the external controlling? It can be adjustable resistor or a voltage? Do you need linear controlling or nonlinear controlling? You need to make clear of your requirement.

 

[IBO]

hi

we just cant think of it as block level

we need schematic info.

whether its MOS implemented or otherwise