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  1. Replies
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    Closed: Re: Differential probe build

    First, the suggestion is one series chain per input (positive and negative)



    [in+/-]
    |
    [1meg]
    |---------o
    [100k]
    |---------o o--------Amplifier + or -
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    Closed: Re: OpAmp BW for Feedback loop

    Have you run into any specific tradeoffs yet choosing amplifiers?

    I ask because for what I care about I don't see a lot of hard choices until about 10mhz and up. See OPA192 for example has low...
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    Closed: Re: Differential probe build

    For one because low C is a figure of merit for a scope probe. You don't want to load the circuit being measured. Have the lowest C possible.

    Second there is no reason you can't get the same...
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    Closed: Re: OpAmp BW for Feedback loop

    1) Both. There is guaranteed to be switching frequency noise. Best to oversample above it if possible and higher sample rate means less delay. Don’t forget that.
    2) General ADC good practice...
  5. Closed: Re: [Microcontroller] Voltage Reading without ADC

    Input voltage thresholds are very widely specified however. Perhaps adding 50% worst case error.

    Could be improved by adding a comparator with reference to the scheme.


    Another scheme is to...
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    Closed: Re: Totem pole pfc challenges

    Still thinking about this?

    I'm curious what your thoughts are.
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    Closed: Re: Digital design of a GPU

    Multiple cores work well only for certain tasks and graphics happens to be one of them. The death of multiple core processing is when your processing depends on the result of other processing and...
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    Closed: Re: Differential probe build

    The AD8130 model may have some parasitics.

    To be clear the 8k should only be in series with the amplifier inputs when the 1k resistor is selected.

    If it 'works' the amplitude rolloff should...
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    Closed: Re: Differential probe build

    Nice trick to see the frequency response in the time domain but I suggest you take a look at LTSpice's AC simulation ability at this point...

    I'm wondering how there is a difference in gain...
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    Closed: Re: Differential probe build

    Every topology has pros and cons but my suggestion is that you don't implement ranges by changing R6/R9. See how I drew the schematic a few posts ago. The 10K and 2K are always in circuit. The...
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    Closed: Re: Differential probe build

    1% is pretty poor. Simulate the common mode rejection with a 1% mismatch.

    If you're on budget and just building a couple maybe you can match them yourself...
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    Closed: Re: Differential probe build

    C stray should be more like 10p probably. You might only need a 1pF or less across the 1megs.

    What are the 12 ohm resistors, that's tiny?

    Be careful with resistor selection: Resistors have...
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    Closed: Re: H-bridge 100khz recommendations

    You should familiarize yourself with what's already available. You can buy these off the shelf, or find chips that do it all and give complete application circuits:
    ...
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    Closed: Re: I/O banks in an FPGA. Is it important for routing?

    In general modern FPGAs and their tools are quite flexible and forgiving in terms of routing.

    Some people have the idea that you should do your FPGA design, let the tool pick the pins and then use...
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    Closed: Re: Differential probe build

    Glad a lot of it is cleared up.

    When it comes to ground I say this: "There is no ground".

    Any two nets have some relationship in terms of voltage, impedance etc but whether they have 'ground'...
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    Closed: Re: Differential probe build

    Ok and from my perspective you understand everything except the conclusion. I try repeating the conclusion and you call me a broken record. So I try a different angle.

    The diodes illustrate the...
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    Closed: Re: Differential probe build

    Again it doesn't matter whether there are clamping diodes or not inside the AD8130. The clamping diodes only act when the input pins exceed the absolute maximum ratings. Either the diodes are there...
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    Closed: Re: Differential probe build

    They're not your zeners they're the ESD protection diodes inside the AD8130 that result in the "Input Voltage (Any Input) −VS − 0.3 V to +VS + 0.3 V" absolute maximum rating (with the diodes having a...
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    Closed: Re: Differential probe build

    Here is a simplified circuit modeling the path between the probe grounds of two of your circuits connected to a single scope.

    V5 is like the battery in the example I gave above. It has no...
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    Closed: Re: Differential probe build

    Even galvancially isolated amplifiers (like ISO124) have peak voltage ratings (1500Vrms for the ISO124).

    Can you show in the datasheet where you think AD8130 is providing isolation and reference...
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    Closed: Re: Differential probe build

    The AD8130 does not provide galvanic isolation!

    If you want galvanic isolation you need an 'isolation amplifier' and an isolated supply to power it.



    If another forum poster jumped in it...
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    Closed: Re: Differential probe build

    I'll modify the example a bit: Your 48V battery is 4 12V batteries in series and you want to measure each with a differential probe. We'll call them battery 0/12/24/36/48V and naturally you want to...
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    Closed: Re: Differential probe build

    If the circuit is galvancially isolated which it would be in the case of a battery powered circuit with no other references then you're good. The non-infinite impediance of your input circuit and...
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    Closed: Re: Differential probe build

    It's not but J1 pin 2 is connected to U1's input. And that input can't be more than 9.3V from "gnd".
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    Closed: Re: Differential probe build

    Your 9V supplies are +/-9V in relation to "gnd".

    "gnd" is tied to scope ground via J3 pin 2.

    Your "Scope Probe" input J1 pin 2 is connected to U1 IN- via a 470ohm resistor.

    U1 AD8130 as...
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