a problem about reference current source

[superleaf]

some paper refers about this kind of reference current source ,they say that Vref is equal to the voltage of source terminal of M62,thus the current draws through the mos M62 will be :Id=Vref/R13,however,using the spectre simulaltion,i can't get this result,actually,i do not understand the principle of this kind of reference current source,could anyone explain it for me?thank you in advanced~~

 

[checkmate]

When the opamp feedback is working, the inputs ill be in virtual short, ie source of m62 is vref.
if things are not working, then opamp is not in feedback.

Is vref within the common mode input?
Can the opamp output swing support vref+vgs(m62)?
Do you have enough headroom for vref+vdsat(m62)+vgs(m63)?

 

[analog-designer]

Hi superleaf,

please add a schematic including the operation point of the internal circuitry of the opamp. You can do this by annotate operation point and voltage in ADE.

Because of feedback the voltage on inverting input node is equal to Vref. So voltage drop at R13 is also Vref. This sets the reference current in the pmos current mirror.