Discrete chopper switch

Hello,

I want to use some single chopper switches in my prototype PCB. However, when I searched in ADI product list, there are only chopper-stabilized amplifiers which usually consist of two chopper switches.

I just want to use one chopper switch in my design which seems like a mixer. So I was wondering if there is a product as I want. For instance, an IC integrates several chopper switches and several clock control signals.

Thanks and look forward to your reply.

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  • Hi Victor,

    If you don't mind, I'll study the LTC6943 datasheet myself, it might take a while, okay?

    You mean this table?

    It is not necessary to determine the output resistance with it, because the short-circuit current and the output voltage in the absence of a load are indicated here. You can refer to this graph

    Apparently, the output resistance in differential mode will be equal to twice the value on the graph. By the way, why do you use this driver? Should it be high frequency for your application?

    Regards,

    Kirill

  • Hi Kirill,

    Of course, I'd like to know your opinions after you studying the LTC6943 datasheet.

    I didn't find this graph of output resistance. Thank you for reminding. "Ctrl+F" is a good shortcut that I often forget to use...

    The reason why I plan to use AD8138 is that I need to convert an analog voltage to differential voltage. You can refer to the figure below which is my basic idea. I want to drive each capacitor with a random bit stream (about 5MHz). Then the top-plate voltage is converted and amplified to a differential voltage.

      

    Actually I think lower input impedance of single-to-differential amplifier is better considering the settling error (total capacitance of capacitor array is about 2μF). But the single-to-differential amplifiers I find in ADI product list https://www.analog.com/en/products/amplifiers/adc-drivers/single-ended-differential-amplifiers.html are with high impedance.

    Does my point of view make sense? What do you think about the parameters I should care about S2D amplifier? I'd like to hear from you.

    Thank you so much Kirill.

    Victor

  • Hi Victor,

    Unfortunately, I attached the wrong link to the parametric search for switches, note this, there are 25 parts, I have already fixed this. 

    Do you want to get pulse differentiation or do you want to transmit the tops of the pulses lossless? If you want differentiation, it makes sense to have low resistance on the input side of the amplifier to get a small time constant. If your goal is the opposite, all reasoning is reversed.

    It's not hard to get a low input impedance just by adding an external resistor. Getting high resistance from an unsuitable amplifier is much more difficult.

    Regards,

    Kirill

  • Hi Kirill,

    Thanks for being so meticulous. I have opened the link that you re-edited.

    Could you explain more about the reason why it should have low resistance for getting pulse differentiation. What did you mean by differentiation? Actually, the top plate voltage will change after the PRBS is input to bottom plate. I just want this signal converted to differential signal. I must misunderstand something...

    Victor

  • Hi Victor,

    I found on page 4 an interesting note

    You can select multiple contact configurations that meet or do not meet this requirement. In any case, both sections have the same clock signal and you will have to apply one LTC6943 to each integrator. And in any case, it goes beyond typical applications and will be very cool if you get great results. I can suggest such a configuration as an example, but it is not the only way

    I saw analog switches that have four keys and four separate control contacts, and at the same logical level on all these contacts, two keys are closed while the other two keys are open. It's like it's made for chopper:)

    There are a few remarks about the injected charge. For LTC6943, the condition of proximity of the input signal to half of the supply voltage must be fulfilled - only in this case the charge is minimal. For analog switches it is necessary to study each datasheet of the device of interest. As a typical example:

    You want to apply to the integrator 100 μA, please note:

    Regards,

    Kirill