• Resolved

ADS9110: What is the frequency of−3 dB Input Bandwidth?

Hello guys,

One of my customers is considering using ADS9110 or ADS9120 for their new products.

They have the following question about the device.

Q. What is the frequency of−3 dB Input Bandwidth of ADS9110_20? Is it 1MHz?

Best regards,

Kazuya.

• Hello Kazuya,

The analog input bandwidth for a non-buffered ADC input is primarily determined by the input sampling stage of the device.  Both ADS9110 and ADS9120 use the same input stage.

Referring to figure 37 in the ADS9110 datasheet, the input resistance, Rs1, is equal to 30ohm, and the sampling capacitor, Cs1, is equal to 60pF.

An estimate for the input analog bandwidth of both the ADS9110 and ADS9120 will then be:

f-3dB = 1/(2*pi*R*C) = 1/(2*3.14*30*60p) = 88.5MHz.

The actual BW will likely be lower, but it will not be higher than this number.  In most cases, the input charge bucket filter and input amplifier usually limit the bandwidth to a much lower frequency.  For example, the input filter used on the ADS9110EVM has a -3dB frequency of 7.2MHz.

In either of the above cases, if the customer expects to have a lot of noise that is greater than the Nyquist rate (>1/2 output data rate), then they will want to design an anti-aliasing filter as part of the input signal chain.

Regards,
Keith Nicholas

• In reply to Keith Nicholas:

Hello Kazuya,

Can you find out from customer what is the maximum input frequency they want to measure?

The datasheets have SNR and THD specified for input frequencies up to 500kHz.

Regards,
Keith

• In reply to Keith Nicholas:

Hello Keith,

I will ask them it and I will inform you their reply as soon as I get it.

Thank you and best regards,

Kazuya Nakai.

• In reply to Kazuya Nakai54:

Hello Keith,

The customer wants to input 1MHz(Typ)~1.5MHz(Max) signal to ADS9110 or 9120.

If there is any problem about the frecuency signal input, could you please give me your comment?

It would be much appreciated.

Thank you and best regards,

Kazuya Nakai.

• In reply to Kazuya Nakai54:

Hello Kazuya,

Both ADS9110 and ADS9120 will still function properly, but the SNR and THD will continue to drop off at frequencies greater than 500kHz.

Would it be O.K. if I contacted you directly at the email address you provided in your myTI Account?

Thank you,

Regards,
Keith

• In reply to Keith Nicholas:

Hello Keith,

Yes, of course. If you send me your comment directly, it would be very helpful for the customer and me.

Thank you very much and best regards,

Kazuya.

• In reply to Kazuya Nakai54:

Hi Kazuya,

O.K., I am going to close this e2e post.

Regards,
Keith

• In reply to Keith Nicholas:

Hello Keith,