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Analog Front End Design

Alex52381
Intellectual 810 points
Other Parts Discussed in Thread: OPA381

Hello,

 

I am looking to design an analog front end similar to the input of an oscilloscope. I have been able to get a simulation working in TINA TI, but the design is *not* single supply and requires numerous components and exotic voltages (-2.5V, etc).

The requirements are as follows:

1) Single supply operation (+5V or +3.3V are acceptable)

2) Must present input impedance of 1 Mohm and ~25pF

3) Needs to have an analog bandwidth of 1 MHz

4) Must have AC/DC coupling option

5) Needs to accommodate over voltage conditions

 

The current design's block diagram looks like this:

Input (Probe) -> AC/DC switch ->Attenuator (resistor and capacitor divider circuits) -> Level Shifter (for single supply operation/ADC range matching, I am unsure how to do it)-> Input diode clamp -> Following Op Amp (OPA381) -> Gain Stage (undecided as of now) -> Anti-alising filter (undecided, but probably needs to be 2nd order) -> ADC

 

I am primarily looking for suggestions as to how I could create 100% single supply version of this system. I have seen other circuits that do level shifting in the attenuator stage, but they did not seem to simulate well in TINA TI.

 

Thank you,

Alex

  • 0
    Intellectual 810 points

    Based on further prototyping and simulation, this single supply only design seems difficult. I will be using a dual supply system.

    I've run into the problem that I can't find how to implement an inverse chebyshev filter. I have the coefficients and all, but the TI documents don't cover how to convert those values into an op amp realization (FilterPro and the other documents only seemed to cover "regular" chebyshev filters).

    Is there any support regarding transforming filter design mathematical coefficients into op amp topologies and R/C component values?

    Thanks,

    Alex

  • 0 in reply to Alex52381
    TI__Prodigy 560 points

    Hi Alex,

    You may want to check out our Filter Pro program - this program allows you to evaluate Chebyshev filters amont many others and you can evaluate from the desired poles, resistor values, etc. It doesn't recommend amplifiers for the filter to date, but it is definitely a fast way to get started. Link to Filter Pro.

    Best of luck,

    Gina