AOP

Hi 206_RC,

I tried to look at the parametric search and found the following attached parts which have the same TSOT-23 6 pin package as the LT6233CS6.

Hope this helps you one that is compatible / replacement.

XLSX

I've not looked to make sure the pins are identical or not. But, you can take a look and see if these parametrically satisfy the application or not first.

Regards,

Hooman

Hi,

Thank you, I'll look your XLSX if there is anything compatible. 

Hi 206_RC ,

LT6233 is not an Instrumentation Amplifier. It's a Op Amp.

Regarding the pick up you're seeing: Most of the pickups I've had to deal with are from the way the grounding and PCB layout are done. Sensitive input nodes are especially vulnerable and need to have to have good grounding and shielding.

If you like, you can share more details and see if I (or others on the forum) can lend a hand to help resolve your interference pick up problem.

Regards,

Hooman

Hooman said:

Most of the pickups I've had to deal with are from the way the grounding and PCB layout are done

I'm not speaking for the moment of routing of the card. Can I use this AOP LT6233 to filter a signal coming from a Hydrophone (The Hydrophone already has an integrated preamp). I use this AOP as a high pass filter (the signal is about 1µV to 300µV). Can you answer this question first ?

Thanks for your advice
 

Hi 206_RC ,

I recommend that you take a look at the Filter Wizard program link below to design your High Pass filter using LT6233:

https://tools.analog.com/en/filterwizard/

Let me know if you have any specific question regarding this design.

Regards,

Hooman

Hi Hooman,

Your link I already tried but It can't give me a transient function. I can do it with LTspice and I have a offset with a small signal : 

I have about 32 mV for an output voltage (for input voltage 1mV-1kHz). And an ADC don't like this offset.  

Hi 206_RC,

Please attach your LTspice schematic (*.asc file) in here so that I / others can take a look and see if we can help resolve your offset issue.

To attach a file, use Insert, Image/Video/File, go to the file location and click Upload, Ok.

Regards,

Hooman

Hi Hooman,

Thank you for your helps, please see in this attached the simulation file. Just a point of precision, I add the second AOP to simulate a load with infinite impedance (in theory) and a link capacitance to remove the DC component. But nothing changes. 

 Draft1.asc

Regards.

Hi 206_RC,

Regarding the offset you're seeing from using LT6233 as a Sallen Key High Pass Filter:

Most of that is due to the input bias current of LT6233 (3uA max) flowing through the 22.5kohm input resistor (R1).

I've added a dummy current source to your schematic to allow you to change that current and see the output offset go away or increase (depending on the magnitude and direction of that current).

Here is the simulation file:

LT6233 Sallen Key Filter Offset EZ 7_11_22.asc

To resolve this issue, you can do one or both of the following:

1. Scale your R's lower and your C's higher (to maintain the same filter response) by the same factor (e.g. 22.5k ->2.25k and 1uF --> 10uF, etc.) to reduce the impact of input bias current on output shift.

2. Switch to another Op Amp with CMOS / JFET input structure where the input bias current reduces to the pA range. Let me know if you need help selecting a usable device?

Additionally, I added a shunt resistor to your 2nd stage (R3) to allow for input bias current flow.

Regards,

Hooman

Hi,

Thank you for your helps (I had not seen this bias current). In fact my signal from the hydrophone ( is about 1µV to 300µV). And after your simulation that I modified to have 1µV at the input :

I think it is impossible to satisfy the maximum variation and the minimum variation. In fact I don't know if I must amplify the signal before before attacking the high pass filter. But what is the minimum voltage level that AOP LT6233 can accept ?

I think, the better solution is to have a component with with adjustable offset and very low bias current. I don't know if it exists.

You add a dummy current source : -1.5µA 

But how do we do it electronically ? Is there a dedicated component for this or a specific assembly ?

But now, I see the problem more clearly thanks to your advice.

Regards

Hi Hooman,

Sorry to bother you but I'm still looking for a -1.5µA current source and haven't found it yet.

Thank for your helps

Regards

Hi 206_RC,

206_RC said:

Sorry to bother you but I'm still looking for a -1.5µA current source and haven't found it yet.

Response: The -1.5uA current source I added was only there to demonstrate that the input bias current of LT6233 (about 1.5uA in its model) is responsible for your output offset. Once I added the -1.5uA current source, I was able to null the output offset. So, that's why I recommended choosing a device with CMOS / JFET inputs where the input current is in the pA or nA range (much lower) so that you won't have this offset.

Regards,

Hooman

Hi 206_RC,

206_RC said:

Sorry to bother you but I'm still looking for a -1.5µA current source and haven't found it yet.

Response: The -1.5uA current source I added was only there to demonstrate that the input bias current of LT6233 (about 1.5uA in its model) is responsible for your output offset. Once I added the -1.5uA current source, I was able to null the output offset. So, that's why I recommended choosing a device with CMOS / JFET inputs where the input current is in the pA or nA range (much lower) so that you won't have this offset.

Regards,

Hooman

Hooman said:

I recommended choosing a device with CMOS / JFET inputs where the input current is in the pA or nA range

Probably at the inputs of AOP, but how can I know if the inputs are CMOS/JFET ? In the datasheet ?

After searching I found these selections :
www.analog.com/.../11080

There are 2 components that correspond to my selection : AD8233/AD8428

The AD8233 with 'CHIPS OR DIE,20-Ball WLCSP (2.04mm x 1.705mm)' What is this box ? I just need boxes of types SOT-23 or equivalent.

And for the second AD8428, you advised me in another Topic which I am trying to understand for the moment. 

Thanks you for your helps

Regard

Hi 206_RC,

If you're looking for Instrumentation Amplifiers with low input bias current, you can look at this list sorted for the lowest noise voltage on-top, and input bias current < 400pA:

www.analog.com/.../11080

AD8233 that you mentioned is offered in WLCSP packaging or die only (not in SOT23). The closest packages to the SOT23 that you want which I can find is in 8-pin MSOP are:

LT6370

AD8220

AD8428 is only offered in the 8-pin SOIC package.

Regards,

Hooman

Hooman said:

AD8428 is only offered in the 8-pin SOIC package.

Hi Hooman,

For this package there is no problem for the manufacture and also MSOP. Sorry I don't know all package for cms components.  
I'll see the LT 6370 and AD8220 and I will do the simulation with these components. Just one precision I use this AOP only for High pass filter not for Amplifier (or 1) 

Thank you