improving noise as much as possible question

[yefj]

Hello,given the schematics shown below.purely on reducing noise on the output.
Its a very low frequency driver up to 5MHz with noise, pure operating BW is 1Mhz.
1.As you can see below first i made all the components as dense as possible
2. I put polygon pour and stitching VIAS as shown below.
3. I put 10u 1u 0.1u C0G/NP0 capacitors instead of regular ceramic capacitors and i put then next to the bias Vdd and Vcc on each OPAMP as shown below.
4. I put a pi filter but between the stages but it totally does gain spike in closed loop thus ruins stability so I am thinking to remove it.
5.i put resistor with as much low values a possible to reduce johnson nyquist noise.
Is there more ways you suggest me to improve noise?
Thanks.

 

[danadakk]

What noise level are you experiencing ?

Is the supply "quiet", as freq goes up PSRR drops, more noise coupled
from supply to output. Use DSO, infinite persistence, AC coupled, say
10 mV/box, 10 mS sweep capture pk-pk noise. What is the power supply
noise ?

Not sure how accurate the spice model is (seems to track datasheet) but here is a noise sim your first stage :

Regards, Dana.

 

[yefj]

Hello Dana,this is my power supply 3 DC lines going into a molex connector.
This device stand lie a meter above the circuit so i have an antenna.
But i put decoupling capacitors in my PCB next to the Bias Vp and Vm.
How do i measure PSRR for such device?
do you recommend me to use "RF choke" smd inductors to choke the noise?
Thanks.

 

[danadakk]

PSRR measurement :

https://www.analog.com/en/resources/analog-dialogue/articles/simple-op-amp-measurements.html

Your power supply, do you have a DSO you can use ininite persistence, to see what it
looks like pk-pk ?

Caps are focus, but HF noise L's can help. Bench trials best way to confirm progress. I use L's,
ferrites, only when I confirm that is a problem.

By the way, I have a similar supply, notorious for HV turn off transients. Use scope to capture that in
single shot mode, it is an eye opener.......I never turn mine on/off now when its connected to load,
I connect load after its on. I have blown up steering schottkys on ESP8266 & ESP32 modules with
it.........

Regards, Dana.