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 CVictor914,

    It looks like you want to create a discrete chopper amplifier, which was typical in the last century, because there were no such integrated circuits. I'm correct?

    Regards,

    Kirill

  • Hi KirV,

    Thank you for your reply.

    Acually, chopper amplifier is not my target. I just want to use a chopper to realize the function of multiplication. For clarification,  I have an analog input signal and I want to multiply it with a sequence of 1 and 0. And the output is connected to a differential amplifier.

    I know it's hard to find a discrete chopper switch. Do you have any other suggestions?

    Thanks.

    Victor

  • Hi Victor,

    Note how LTC1043 and 6943 are used in conjunction with capacitors - only the difference of the injected charges can create a voltage on the capacitor. Even a significant but identical injected charge applied to both capacitor plates does not affect performance.

    The same unique property has a differential integrator - if the same charge is injected into both inputs, it will cause a common-mode shift of the output voltages, which is not a useful signal. Only the difference of the injected charges matters.

    I find it difficult to advise you any switch. The difference of the injected charges is important. You can make individual selection of components or add a final adjustment of this parameter using external components. But it's not the best choice:)

    Even more difficult is that the integrator has a small input resistance and the internal resistance of the switch can make an error, in addition, this resistance is nonlinear. What is the value of the input resistors and input currents of your integrator? This is important for selection

    Regards,

    Kirill

  • Hi Victor,

    The product tables are sorted by parameters, and I tried to select the parameters important to you here

    https://www.analog.com/en/parametricsearch/10624#/p4264=-1e-12|1e-12&p4458=|Bidirectional|I%C2%B2C|Latched|LVTTL|Parallel|Serial|SMBus/I2C|TTL/CMOS%20Compatible&p4683=(2:1)%20x%201|(2:1)%20x%202|(2:1)%20x%203|(2:1)%20x%204|SPST%20x%201|SPST%20x%202|SPST%20x%204|SPST%20x%208&d=sel|0|546|2606|4264|4270|4458|4683|4811|4812|4813|4814

    It is a simple interface, suitable contact configuration and minimal injected charge

    I think I know why your message was marked as spam - you gave links to third-party resources and products that are prohibited by the forum rules.

    Regards,

    Kirill

  • Hi Kirill,

    Thanks for your really helpful advice!

    This is my first thread in this forum and I will obey the forum rules. Thanks for noticing me. And so lucky to disscuss with you and learn many stuff from you.

    This chopper is for a function prototype PCB. Optimization will be at next stage. I think I have already known which switch I should use.

    Thank you.

    Victor

  • Thank you Victor!

    By the way, which signal goes through the chopper-is it current or voltage? Does the signal source have a high or low internal resistance?

    Regards,

    Kirill

  • Hi Kirill,

    In my case, signal goes through the chopper is the voltage from a single-to-differential amplifier. Here, I plan to use AD8138. There is no illustration of output resistance in AD8138 datasheet. But from the output voltage swing and output current, it should be in the order of several tens ohm. Could I estimate the ouput resistance by this way?

    For the integrator, I plan to use LTC 1992 you recommended in another thread as the fully differential amplifier. Its input resistance is 500MΩ. For input resistor I will use, its resistance can be tuned from several hundreds to several thousands ohm. Input current for integrator is 10-100μA.

    Do you have some comments for my choices?

    Thanks a lot.

    Victor

Reply
  • Hi Kirill,

    In my case, signal goes through the chopper is the voltage from a single-to-differential amplifier. Here, I plan to use AD8138. There is no illustration of output resistance in AD8138 datasheet. But from the output voltage swing and output current, it should be in the order of several tens ohm. Could I estimate the ouput resistance by this way?

    For the integrator, I plan to use LTC 1992 you recommended in another thread as the fully differential amplifier. Its input resistance is 500MΩ. For input resistor I will use, its resistance can be tuned from several hundreds to several thousands ohm. Input current for integrator is 10-100μA.

    Do you have some comments for my choices?

    Thanks a lot.

    Victor

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