offset of an op amp coming 0.1uV in 0.18um technology ???

[amic]

I desinged an OTA with a gain of 80dB and bandwidth of 45MHz. but getting offset of 0.1 uV...Is such a low offset possible or am I doing some sily mistake in measuring the offset ?

 

[suria3]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

Hi,

I would say the amount of offset you are getting is already good enough. By the way, how you are measuring the offset of the opamp, method?

Regards,
Suria

 

[Humungus]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

For sure you are not making Monte Carlo simulations. If this is the case what you see is only the systematic offset, which in general can be made very small by proper design.

Offset is s statistic variable, so you need to perform MC simulations considering matching to determine a good estimation of your actual offset.

 

[Alles Gute]

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

 

[amic]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

may be i need to do the monte carlo analysis then as humungus suggested....

but what u think, would be typical values for systematic offset and random offset if the total offset is supposed tobe 0.1mV ?

Sachin

 

[flushrat]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

typical offset is several mV.
for a simple differential pair, the offset is
Vos=delta(Vth)-(Vgs-Vth)/2*delta(beta)/beta (1)
sigma(delta(Vth))=Ath/sqrt(W*L) (2)
sigma(delta(beta)/beta)=Abeta/sqrt(W*L) (3)
for example, l=0.18u W=50u, Ath~=6mV
one sigma of delta(Vth) is 2mV

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

may be i need to do the monte carlo analysis then as humungus suggested....

but what u think, would be typical values for systematic offset and random offset if the total offset is supposed tobe 0.1mV ?

Sachin

 

[Sezi]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

how do you make an autozeroing, chopper stabilization?

 

[sunking]

normal cmos offset is 5mV to 10mV.
you simulation is ideal

 

[Alles Gute]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

how do you make an autozeroing, chopper stabilization?

You can find many papers about these things. try Google it.
I agree with the other guys. Typical opamp input referred offset voltage is several mV.

 

[yuyangjp]

Maybe what you see is the gain error. To find the offset you should know the match accuracy of the input pair.

 

[edajason]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

Would you please give a reference for your quoted equation?

typical offset is several mV.
for a simple differential pair, the offset is
Vos=delta(Vth)-(Vgs-Vth)/2*delta(beta)/beta (1)
sigma(delta(Vth))=Ath/sqrt(W*L) (2)
sigma(delta(beta)/beta)=Abeta/sqrt(W*L) (3)
for example, l=0.18u W=50u, Ath~=6mV
one sigma of delta(Vth) is 2mV

With 45MHz BW and without any special design trick(like autozeroing, chopper stabilization...) in 0.18um process. An offset of 0.1uV is definitely unrealistic. Even 0.1mV is pretty doubtful.

may be i need to do the monte carlo analysis then as humungus suggested....

but what u think, would be typical values for systematic offset and random offset if the total offset is supposed tobe 0.1mV ?

Sachin

 

[pseudockb]

Re: offset of an op amp coming 0.1uV in 0.18um technology ??

Hi edajason, you could refer to Gray and Meyer book for lots of information about systematic and random offset of opamp. Some of the parameters like Ath and Abeta could be obtained from the characterization report provided by the fab. Just ask around. To have a low offset as low as 0.1uV, I do not think it is possible without using techniques like autozeroing and chopper stablization.