Warlike
Junior Member level 3
- Joined
- Dec 6, 2006
- Messages
- 31
- Helped
- 2
- Reputation
- 4
- Reaction score
- 0
- Trophy points
- 1,286
- Location
- Moscow, Russia
- Activity points
- 1,515
Warlike said:Hello! I designed Bandgap voltage reference. In attachement is PSRR jpeg. Tell me please: does this PSRR normal or bad? Exactly what about 0 dB crossing?
If it's very bad how correct this without topology and layout change? Maybe capacitance at the Vref node?
It's bandgap for set Vos in the LVDS transmitter that switched by 250 MHz clock. Does this PSRR normal for this application or I should correct it/design new BGVR?If some of your blocks work around 40MHz, and introduce 5mV ripple (which is not uncommon), you will have 30mV error in your reference. If it happens to be an ADC or DAC, this will show up as a huge spur.
If it would be separate supply for Bandgap and other blocks would it work good?It's not practical to filter these frequencies on-chip.
Power supply is 2.5.If you are operating with supply beyond 1.2V
I don't know yet. Will know soon.Having a separate supply for BGR is nice., but do you have that luxury?
Yes. Will try.See whether you could tune up the PSRR of the BGR before taking such a big decision
Ok. Will target for 60 dB. But what about high frequencies? What is a minimum PSRR? (typicaly)With 2.5V supply, you should target atleast for 60dB at low frequencies.
I'll ask they.You should get the specs for the PSRR from the system designers or the one who gave all the other specs of the block to you.
I think I should improve topology and remake layout. It's not good. But not terrible.See how far you are from the spec and then decide what to do.
Warlike said:I had improve my Bandgap. PSRR plot in attachment.
I have some questions.
1) Should PSRR be more smooth?
2) Now PSRR at low frequencies are good. But what about high frequencies? How much should be PSRR at 10 Mhz, at 100 Mhz? In papers I have seen all PSRR plots was from 1 Hz to 1-10 Mhz. Why? There are no ripple at freq. more than 10 Mhz?
saro_k_82 said:The high frequency supply currents are redirected through the low impedance path through the decaps so it's normally left out as a manageable problem.
If you include some decap and then run the sim, you should see the curve moving down after 100MHz or so
PaloAlto said:saro_k_82 said:The high frequency supply currents are redirected through the low impedance path through the decaps so it's normally left out as a manageable problem.
If you include some decap and then run the sim, you should see the curve moving down after 100MHz or so
Yes, that's right, adding decoupling caps will lower the high frequency part of the curve.
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?