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sigma delta dac　harmonics
Dear all
There is a strange problems when testing 2 order 1bit sigma delta dac:
When applying -3dB signal, there are harmonic distortion in the base band. This is normal. But when applying -60dB signal, there are still large harmonic distortion, which leads to poor...
pmos ldo current limit
Hi, WindRay
Thanks for your reply.
I have used such a method to design current limit circuit. The most important issue is the stability of the negative feedback loop. The best condition is that when the current limit circuit begins to work, the main feedback loop should...
ldo with pmos pass gate
I have simulate the transient loading variation, it seems no problem. I have not simulate the output noise, but only power supply rejection, which is decreased about 10dB than the condition that the pmos pass transistor operating in saturation region.
If I can accept...
pmos pass transistor
Hi, all
I am designing a LDO regulator, the minimal power supply voltage is 4.75V, and the output voltage is 4.5V, the maximum output current is 20mA. In order to assure the pmos pass transistor operating in saturation, I have to set a large W/L, but i can not provide this...
A method of simulating CMRR of opamp directly is provided in Allen's book. The circuit configuration is as figure.
The equations are:
vout = (vp-vn)*Av+0.5*(vp+vn)*Ac
vp = vcm
vn = vout+vcm
so we have, (1+Av-0.5*Ac)*vout = vcm*Ac.
and vout/vcm = Ac/Av = 1/CMRR
The spice netlist is listed as...
Yes, this circuit has a positive feedback. My question is why this loop is stable and the gain is boosted from 50dB to nearly 90dB. How can I analyze this circuit? Thanks.
Hi, hr_rezaee.
NBIAS is the bias voltage of tail current.
When I applied a constant voltage to NBIAS, the gain of opamp is nearly 50dB, but when self biasing as the figure above, the gain boosted to 90dB.
The meaning of 'failed' is that I can not explain it with small signal model analysis...
Consider the simple condition, that Av=gm*rds, gm=2Id/Vov, ro=1/(lambda*Id), so Av=2/(lambda*Vov). From this, we can see that the gain is determined not by Id, but Vov. Vov changed with W/L.
Hi,all. Thanks for your help. This opamp is used in bandgap. I simulated a simpler circuit as the figure below. The same phenomenon occured. I tried to analyze it using small signal model, but failed. Please help me to check it, thanks a lot!
When simulating opamp, I found that when applying a constant voltage to NBIAS, the gain of the opamp is nearly 50dB, but when self biasing the gain of the opamp boosted to nearly 90db.
Who can explain this problem detailed for me, thanks!
When I select an option in a list box,the option has been highlighted,but the option is not really selected,e.g I can not select any option.Has anyone encountered such a problem?Please help me,thanks a lot.
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