[SOLVED] Series current mirrors

[bk781]

Hello

How do 2 series current mirrors with unit W/L matching with diode produce Iref/2 current?

Regards
bk

 

[sutapanaki]

Did you mean NMOS diode to a NMOS current, going into a PMOS diode to a PMOS current?

 

[bk781]

Hi @sutapanaki ,

Lets say, there are 2 branches of pmos current mirrors with a diode w/l size getting a reference current of 1uA. If one branch has 2x pmos with W/l, then the mirrored current here is 2uA.
If the second branch has 2 pmos of w/l in series, then the current here is 0.5uA. Why is this so?

 

[Dominik Przyborowski]

Because of MOSFET physics. This is how it works. For given biasing conditions current is scaled with number of series-parallel devices.

 

[sutapanaki]

Hi @sutapanaki ,


If the second branch has 2 pmos of w/l in series, then the current here is 0.5uA. Why is this so?

Tow transistors with the same L connected in series are equivalent to one transistor with length of 2L and your current multiplication factor is 0.5