Part Number: LM98640
In LM98640 specifications datasheet ,we can find test conditon of dynamic parameter "SNR" is "fs=5MHz" or "fs=15MHz" or "fs=25MHz" or "fs=40MHz" in S/H mode,but now I don't know what is Fin .
This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
Part Number: LM98640
In LM98640 specifications datasheet ,we can find test conditon of dynamic parameter "SNR" is "fs=5MHz" or "fs=15MHz" or "fs=25MHz" or "fs=40MHz" in S/H mode,but now I don't know what is Fin .
Hello
Thanks for contacting us. I will ask the applications engineer who supports this device to respond to your question.
James
First,thank you for your answers.
And then i'm looking for the exact analog input frequencies used of TI's SNR test and characterization details for LM9840.
first,thank you.
1.what's the meaning of "ADC is slightly overdriven"? Or how to achieve "ADC is slightly overdriven"?
2.When I was testing ,the DNL result would be wrong immediately if the inupt level just over 2Vpp,or the output code just was 0/16383.You can see the picture below.
3.Through a series of tests,I find the voltage divider resistor used to generate OSx- common voltage can seriously affects dynamic performance in S/H mode.For example ,20K ohm of R18 and R19 in EVM board can't work within fs=40MHz,but 1K ohm can work,and dynamic performance whin 100ohm will be better. How exactly do you choose the voltage divider resistor value? My OSx- voltage is 1.65 V ,and OSx+ voltage is 2.65V ,PGA=1X,CDS=1X.
As the evaluation board shows,when R1=50ohm and C2 was connected and R18=R19=20Kohm and OSx+=VCLP=2.65V,CLPIN=0V,the EVM can't work in S/H mode.
Through the oscilloscope observation,I find common voltage 1.65V can't be kept,it would be covered by 2.65V of OSx+.And then,Reducing resistance,common voltage 1.65V can be kept whin R18 and R19 less than 1Kohm.The smaller the resistance, the better the dynamic performance.
Hi,
Sorry for late replay. I assume you check it with Vin=2Vpp, CDSgain=0dB PGAgain=0dB.
What happen when Vin=2Vpp, CDSgain=6dB PGAgain=0dB?
Do you have OSx- scope pictures? To my understanding with R18/19=100ohm at OSx- Vcm = 1.65V Vdiff_pp=2V, what is Vcm and Vdiff with R18/19=20kohm?
Thank you,
Costin
I want to know if the dynamic parameter in datasheet specification was tested by TI's evaluation board LM98640CVAL?
I'm waiting for your good news.It is best to find the EVM schematic for specification testing.
Hi,
How wide is the sample pulse? Sample pulse width (sample end - sample start) should be <28dec, otherwise sample and hold may overlap.
There no other know test issue using TI lab set-up.
Did you tried to isolate the signal generator with EVM emitter follower?
Please reply to : costin.cazana@ti.com
Thank you,
Costin