Discrete chopper switch

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

To use a magnificent amplifier only as a switch is very strange:)

Ok, If you need high-quality switch, I recommend look at this product:

https://www.analog.com/media/en/technical-documentation/data-sheets/1043fa.pdf

And here all similar products:

https://www.analog.com/en/parametricsearch/11487

It is suitable for your purposes?

Regards,

Kirill

Hi KirV,

These two looks helpful.

I don't want to use amplifier as switches. I only want to use switches as the topic of this question requests. Maybe because chopper usually is used in chopper-stabilized opamp, it makes you confused.

In fact, I am searching for a chopper switch which usually consists of four normal switches, for instance, four NMOSs. I can use one control signal to control them. However, if I search "chopper" in ADI product list, it shows chopper amplifier. 

Now I think I should look into the switch list.

Thanks.

Victor

I mean one control signal by one control signal and one signal inverted from it, not just "one".

Hi Victor,

Yes, you're right, it confuses me a bit, thank you. You can also attach at least a simple diagram of your idea. Maybe I can help you with something.

Hi KirV,

Thank you so much for your help.

My idea is shown in the first figure below. I use a chopper (principle shown in the second figure) to multiply analog input voltage with +1 or -1 according to the control signal, say PRBS. And then, the output of chopper goes through a differential integrator. 

I am searching for a device which can achieve the function of chopper above (4 switches and controlled by a logic signal). So far, https://www.electroschematics.com/4066-ic-datasheet/ 4066 is a choice. Do you have some advice?

Furthermore, because here is the group for amplifier, I also wonder which amplifers fit for my differential integrator. 

http://www.ti.com/product/ACF2101/technicaldocuments This is the only integrated integrator chip I found. Do you know any amplifer from ADI can be easily implemented as an integrator with reset switches? It will be very appreciated!

Victor

Sorry KirV, I wrote a lot and used two figure to illustrate my idea. But my reply was determined to be SPAM. So sad. 

Anyway, thank you bro!

Hi Victor,

It's weird, I've never seen anything like it. You can try to attach ZIP archive to the message.

Hi KirV,

Thank you so much for your reply and patience. I am trying to edit it again.

My basic idea is shown as above. I use a chopper, whose principle is shown in below (composed of four switches and they are controlled by a binary signal), to multiply the input analog signal with +1 or 1 according to the bit of PRBS (1 or 0). Then the signal goes through an active RC integrator.

So I want to find a chopper device as above. However, when I search "chopper" in ADI product list, it only shows chopper-stabilized amplifer, which is not my target. I only want "four switches". Do you have any advice for the implementation of chopper?

Furthermore, I also want some advice for the implementation of integrator. The only integrated integrator I found is TI's ACF2101 and it's a little bit old design. So could I use some devices from ADI such as the amplifer to achieve it? Are there switches used as reset switches in my design? Due to a huge amount of amplifer in ADI's product list, I seached something but they don't fit for me. If you know some example designs from datasheets, please let me know. It will be very appreciated!

Victor

Hi KirV,

Thank you so much for your reply and patience. I am trying to edit it again.

My basic idea is shown as above. I use a chopper, whose principle is shown in below (composed of four switches and they are controlled by a binary signal), to multiply the input analog signal with +1 or 1 according to the bit of PRBS (1 or 0). Then the signal goes through an active RC integrator.

So I want to find a chopper device as above. However, when I search "chopper" in ADI product list, it only shows chopper-stabilized amplifer, which is not my target. I only want "four switches". Do you have any advice for the implementation of chopper?

Furthermore, I also want some advice for the implementation of integrator. The only integrated integrator I found is TI's ACF2101 and it's a little bit old design. So could I use some devices from ADI such as the amplifer to achieve it? Are there switches used as reset switches in my design? Due to a huge amount of amplifer in ADI's product list, I seached something but they don't fit for me. If you know some example designs from datasheets, please let me know. It will be very appreciated!

Victor

Hi Victor,

Now I understand your idea. Those devices that I recommended above seem to be perfectly suitable for a chopper. I very much doubt that using four switches as an alternative will get you anything better.

Why are ADI fully differential amplifiers not suitable for your application? What are your requirements for the circuit-supply voltage, permissible error, values of capacitors, speed? I may be able to advise you on suitable reset switches, but I need a little more information.

Regards,

Kirill

I am not familiar with integrated circuits that are called choppers or at least positioned as specially designed for this role. No wonder you couldn't find something like that with a search.

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

Hi Victor,

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

www.analog.com/.../10624

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