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how to implement this circuit?

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Full Member level 3
Nov 15, 2004
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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.

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.


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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?

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?


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“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.

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.


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

how to implement this formula?

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.


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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.


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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.


Added after 10 minutes:

Dear DennisMark,

I dont understand your viewpoint.

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).


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

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.

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.


we just cant think of it as block level

we need schematic info.

whether its MOS implemented or otherwise

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