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.

Parents
  • 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 KirV,

    Thank you so much for your generous help.

    I read carefully the datasheets of LTC1043 and 6943 you recommended. To my understanding, the control clock signal of these two chips are generated internally using pin16 (in 1043) and pin14 (in 6943). Their leakage currents are so low and CMRR are perfect.

    However, for my idea, I need a control signal, say PRBS in the above diagram, that is not a clock signal (say, duty cycle=50%). Its high and low levels are random. So it needs an external control signal. Do you know some devices suitable for my requirement? So far, my choice is a 2-bit bus exchange switch  https://www.onsemi.com/products/interfaces/analog-switches/7wb383. But it is actually used for digital signal. The leakage current is large. If there are analog swiches whose control signal can be given externally, they would be better.

    For the integrator, I have noticed you replied my another thread, so I will disscuss with you in there.

    Best regards,

    Victor

  • Furthermore, the charge injection of switch is also a significant factor in my design. LTC1043 and 6943 surprisingly measure this parameter and have low charge injection. They provide break-before-make action (non-overlapping) as well. I can't find any these measurement data from digital switch datasheets.

    If they can be controlled by the external random digital signal, I would say they are perfect options. If there is possibility that they can be used as I want but I can't come up with?

    Finally, I don't know if you notice. My reply last night which I said it was determined as SPAM came back after my appeal. Yeah!

  • Hi Victor,

    Yes I noticed almost the same thing I had already read, but dated December 9, which confused me a bit. But it's great that everything worked!

    These devices are specifically designed for precision analog devices, and are used, in particular, in the most precision DMM in the world. They can be controlled by an external signal

    It seems to me that when using a non-periodic signal, there should be no big problems if the durations of your signal allow the internal circuit to switch reliably

  • Hi KirV,

    You are totally right!

    I missed something before and now I know how to use them as a chopper. They are perfect choices.

    By the way, did you use some single transistor switches? I know it will be crazy if I use 32 single switches on PCB to make 8 choppers I need. But if you know some high-performance analog switches, it would be better. I can use them as alternatives or use them to compare with LTC1043 and 6943.

    Thanks a lot for your help!

    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

Reply
  • 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

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