Hi, 

May I know the voltage level of the signal from the analog discovery? The RC filter values of  R83= 160ohms and C121= 10nF are too high for the ADC. When using an external filter such as a one-pole low-pass RC filter on the analog input connected to the AD7091R we recommend R=51ohms and C=4.7nF to achieve the specified performances. Also, the specified value of 70db SNR is tested using high-precision very low-noise equipment. 

Regards,

Andrei

When using internal reference of 2.5V , I am giving signal of 2.5Vpp ( 1.25Vp and 1.25 offset for unipolar input at vin3) 

When using External reference of 3V , I am giving signal of 3Vpp ( 1.5Vp and 1.5 offset for unipolar input at vin3) 

As analog discovery is 14bit source. Moreover the tests performed are when onboard 5V given at Vdd and 3.3V given at Vdrive

Can u please specify the position of R=51ohms and C = 4.7 nF . Is it R83 and C121 as per schematic in data sheet ? 

The reason I selected R = 160 ohms and c= 10nF, because I wanted to keep cuttoff frequency at 100KHz but the third harmonic that is 300KHz kept of causing distortion. 

Please can u specify reason of selecting your recommended values for R and C. ? 

Can you specify the specs for that high precision and very low noise equipment. As we also have sigilent function generator. Are they high precision and low noise? 

The equipment that we use to generate signal is the high performance, low distortion Audio Precision 2700.

We are using 

Siglent SDG6052X function generator and analog discovery pro. Please recommend some filter for this equipment to connect at Vin of ADC evaluation board. Please mention the reason for the selected R and C values u mentioned above. Thankyou . 

Can u please help me with the last reply I did .