I work on analog amplifier and filter chain for an internal STM32H753VI 16bits ADC. The signal chain is based on ultra-low noise opamp LT6237 and differential driver LT1994. The sample-rate of ADC will be 96 kHz. I cascade opamp to create amplifier stage and sallen & key cells trying to minimize noise spectral density and keep output signal offset very low (I don't have power consumption limit here.) I try my best but I got problem with Low-pass frequency response, I don't know if my output can be connected directly to the ADC and I wonder if I do big mistake and how I can optimize the noise spectral density.
1. LOW-PASS PROBLEM : WHY THIS STRANGE BEHAVIOR ?
The response of the whole chain got a strange behavior @1MH it come from the sallen & key low-pass filter. I don't where the increase of gain came at 1 MHz and I don't know how to correct this.
Can you help me to solve this problem ?
2. ADC ELECTRICAL COMPATIBILITY : CAN I CONNECT MY ADC "AS IS" ?
I don't know if I can connect directly STM32H753VI 16bits ADC to OUT+, OUT- and GND(AVSS). I just put antialias filter a 37kHz but I don't know if ADC and LT1994 impedance are compatible.
Can you help me to adjust my output to the ADC input ?
3. LOOK LIKE "NOT TOO BAD" SIGNAL CHAIN OR NOT ?
Do you see big mistake or misconception at first view on my chain ?
Do I miss basic rules in analog chain design ?
4. NOISE SPECTRAL DENSITY OPTIMIZATION : CAN I OPTIMIZE ?
I try my best to achieve lower noise density but I am not very good in analog world.
Do you think it's possible to lower the noise density ?
In other word, do you think I can build this analog signal chain (notwithstanding opamp power supply decoupling capacitor, LDO and ultra-low noise voltage reference chip, etc..) with average chance of working ?
Thanks in advance for your help to understand what I do, but analog world is not simple and with time I lost all what I learn...