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# Using Voltage Reference to do a wide-swing current mirror?

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#### sakuragi

##### Newbie level 4
wide swing current mirror

Hello, I want to design a wide-swing current mirror. So I use this architecture as shown in figure. But with wide-swing, Vg1=Vdd-Vt-Vov, Vg2=(Vdd-Vov)-Vt-Vov, which are all function of Vdd, but Vbg is indepenct of Vdd. So this architecture is wrong. Is there any other idea about this even replace this kind of current mirror?

Vbg is a voltage with the reference of GND. It is not difficult to convert Vbg to Vbg2 with the reference of Vdd.

### sakuragi

Points: 2
Re: Using Voltage Reference to do a wide-swing current mirro

I think that the opamp output connect a nmos which create a constant reference current, then use this current to create cascode pmos bias(such as the left picture ), which the swing can be maximum.Hope it is useful for you.

### sakuragi

Points: 2
Yes, combine the two structre together can meet your requirement.
Use bandgap to a contast current while the left for wide swing current mirror

### sakuragi

Points: 2
Re: Using Voltage Reference to do a wide-swing current mirro

I think may be the figure shown in the attachment may be useful.

### sakuragi

Points: 2
Re: Using Voltage Reference to do a wide-swing current mirro

marshel said:
I think may be the figure shown in the attachment may be useful.

This helps me so. But I wonder the purpose of R1 and R2 because N1 and N2 may be pushed into linear region at low Vdd and large current. I think R1 and R2 can force the current between N1 and N2 to be matched more than without them, right?

yeah.Just want to help make a matching, you can use the R1 and R2 or not.

Re: Using Voltage Reference to do a wide-swing current mirro

I think these two resistor is added for esd protection.

Re: Using Voltage Reference to do a wide-swing current mirro

hi, marshel , why the Iref branch of ur circuit become two? what is the advantage?

in marshel's circuit, i think the W/L of p1 is twice as p2 and p4 to get the proper bias.

Re: Using Voltage Reference to do a wide-swing current mirro

rambus_ddr said:
I think these two resistor is added for esd protection.

Good point!

If considering esd protection, a resistor should also added to the negative input of opamp.

regards,
jordan76

hi,
this is a V/I the voltage on the Rext is equal to Vbg (provided by the used buffer in a -ve feedback loop)
since the Voltage on Rext is constant then the current passing through it is constant too and equal to Vbg/Rext
so u converted the Vbg into constant current this constant current is passed to the pmos and mirrored for further usage.
regards,
A.Safwat

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