I am working on a THS4131 design and have a question. I wanted to see if my numbers were on track. I attached what we have implemented, we are expecting a 8V rms signal to come in that needs to be attenuated to the 1V rms being fed into our ADC. C2852, C2853, C2860, and C2861 are all not placed in the project, but the pads will be on the PCB. My question is what is the worst case CMRR, and SINAD with 0.1% resistors? Documentation for a single ended calculation are readily available, but once you get into fully differential op amps documentation drops out.
Any feedback or input is welcomed and appreciated.
The THS4131 is a high-speed device, therefore I will move it to the appropriate forum.
Precision Analog Applications
The THS4131 is compensated to be unity gain stable. If you want to use it as an attenuator, please refer to the following series written 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)
As far as the AC specs, you can simulate this device in TINA-TI. The CMRR would be 53.9dB for 0.1% resistors
I've attached a simulation showing the CMRR for nominal, 0.1%, and 0.01% resistors for the THS4130.
7725.THS4130 - CMRR.TSC
The SINAD is the SNR + THD. Each of these will be dependant on the final design of the amp + filter. However, the THS4130 model includes input voltage noise and input current noise. You can model the noise performance in TINA-TI by selecting Analysis --> Noise Analysis. Here you can model the SNR as well as the total noise. Keep in mind though that this is just a model and it is only meant to give you an idea of performance. Actual results may vary.
Regards,Luke LapointeHigh Speed Amplifiers
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