I need to design an fully differential ADC driver that can handle a +/-15V input signal. I was looking at the THS4130 as an option. I need the design to be as low power and low noise as possible. I was thinking of using power rails lower than +/-15V (due to the fact that more ICs are available) and maybe using a voltage divider on the input signal before the diff driver. Does anyone know what noise implications this would have. I also would like to know what the minimum stable gain of the THS4130 is. I havent seen it noted in the datasheet.
For +/-15V rails, the THS4130 is probably your best bet with 1.3nV/rtHz and 14mA quiescent current. It is also unity gain stable with 150MHz of bandwidth. If you can afford to lower your supplies significantly then there are other options. The next step down would be 15V supply, then 12V, although you might start losing dynamic range depending on the ADC. What is the full scale input for the ADC?
Regards,Luke LaPointeHigh Speed Amplifiers
Thanks for your timely reply. I am more interested in using a gain lower than unity, more like 0.167. I need to fit a +/-15V signal into the ADS1278. I would prefer to do this with just one amplifier instead of multiple stages. The device is 16 channels so the more stages i need for each channel equates to a significant power increase. How would you address this problem?
If you want to attenuate the input signal, your best bet is an input divider stage before the amplifier. There is a good article series in the Analog Applications Journal (http://www.ti.com/general/docs/gencontent.tsp?contentId=29569):
Using fully differential op amps as attenuators, Part 1: Differential bipolar input signals (http://focus.ti.com/lit/an/slyt336/slyt336.pdf)Using fully differential amplifiers as attenuators, Part 2: Single-ended bipolar input signals (http://focus.ti.com/lit/an/slyt341/slyt341.pdf)Using fully differential op amps as attenuators, Part 3: Single-ended unipolar input signals (http://focus.ti.com/lit/an/slyt359/slyt359.pdf)
In addition, the ADS1278 is a 6V max device. If you use this with a 5V supply and Vref of 2.5V, then the FSR input will be +/-2.5V. Most of our fully differential amplifiers can be driven off of 5V as well which would simplify the power aspect of the design.
The THS4521 is a low power device (1.2mA quiescent current) and a very good driver for the ADS1278. Combined performance data can be seen in the applications section on page 34 of the THS4521 datasheet. There is also a dual (THS4522) and quad (THS4524) version of this device.
Let me know if this route works for you!
thank you Luke. Only other question is do you know where i can find the Spreadsheet that is mentioned in slyt336. it is not in the zip folder
The attachments are embedded within the PDF.
sorry to keep coming back to this thread, but i need to make sure of one more thing before i move forward with my design. Do you know the stability problems that will arise (if any) if the THS4130 is run at a gain lower than unity.
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