Author Topic: analog switch  (Read 1801 times)

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Offline MitaliusTopic starter

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analog switch
« on: May 18, 2019, 03:19:01 am »
I have a 2.5V DAC with two channels.
I invert one of these with OpAmp.

So I get:
Channel A: 0V to 2.5V
Channel B: -2.5V to 0V

I would like to have an output on which I can switch these 2 channels at a frequency of 0.5MHz.
I plan to use this to generate a signal for a current source.

Now I use TS12A12511 analog switch to switch DAC channels, but it is very noisy.

It is very important for me to have a good signal quality, but I can't figure out what else to do.

 

Offline OwO

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Re: analog switch
« Reply #1 on: May 18, 2019, 03:35:31 am »
SGM3157
BL1551
Email: OwOwOwOwO123@outlook.com
 

Offline OwO

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Re: analog switch
« Reply #2 on: May 18, 2019, 03:37:37 am »
Noisy during steady state or while switching? Can you try stopping the switching action and see if the noise persists? What kind of noise? harmonics of the switching frequency or just white noise?
Email: OwOwOwOwO123@outlook.com
 

Offline OM222O

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Re: analog switch
« Reply #3 on: May 18, 2019, 04:20:39 am »
a slim fit relay is pretty analog :)
it's less than ideal but provides 0 noise. also if you get the type that only needs current to switch and then latches mechanically, it probably consumes less power than a chip that's constantly powered on as well.
 

Offline Kleinstein

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Re: analog switch
« Reply #4 on: May 18, 2019, 07:07:04 am »
The CMOS switches mentioned so far are very low resistance. This usually comes with a relatively high charge injection. During switching here will be a charge pules going out from the switch. This could effect the DAC or inverting amplifier. Depending one the DAC signal bandwidth one could have a filter / ferrite there to avoid at least the very high frequency part.

Another point is going for a higher impedance and possibly slower switch. So something like  74HC4053 (maybe single gate version of this).
 

Offline David Hess

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Re: analog switch
« Reply #5 on: May 19, 2019, 11:40:49 pm »
Start by lowering the impedance of the analog signals at the input of the analog switch which will absorb more of the charge injection.  An easy way to do this is to use operational amplifiers which can drive a capacitive load as a buffer.

If you want a much higher performance circuit, then look at using currents instead of voltages and switching using a diode bridge like discrete function generators work.

 

Offline MitaliusTopic starter

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Re: analog switch
« Reply #6 on: May 27, 2019, 08:32:41 am »
Noisy during steady state or while switching?

Noise during switching, 0.5MHz.
I see outliers during every channel switch.

Unfortunately, now I have no fee and I can not show the photo oscillogram

 

Offline MitaliusTopic starter

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Re: analog switch
« Reply #7 on: May 27, 2019, 08:34:45 am »
SGM3157
BL1551
But I also have negative voltages.
These switches do not fit  :(
 


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