PSoC 5LP Instrumentation amplifier (IA) onchip

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Anonymous
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Hello!

   

I would like to get a little help to build a onchip IA with PSoC 5LP. I made a search and found this excellent article http://www.cypress.com/file/53376/download. I repeated the Figure 3 circuit and it worked well for Vp = 400 mV and Vn = Vss. But let suppose that need to amplify a signal 3000 times, how would I do ?

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rola_264706
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Here is a complete guide in PDF format enjoy!

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Anonymous
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Hi bobgoar!

   

Thanks for the ebook, but I'm looking for some technical information about designing IA on PSoC Creator. My biggest limitation is that I don't wish to use external components, like resistors. In this way I'll just use the Cypress Component Catalog available on PSoC Creator.

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rola_264706
Level 8
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Daniel: You are limited with the on chip resistors that limit the gain to 50 for each PGA. So if you want gains in the 3000's you will need external resistors of .1%.

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Anonymous
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My initial thought was to make an arrangement of PGA that allows to increase this gain, but I guess you are right. Thanks!

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Anonymous
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I tried t use the Two Opamp Topology from that article that I said before with an Opamp that uses external resistors of %1, but it did'nt works. The OpAmp separately works and the 2 PGA separately works, but when I try them in series it don't work.
 

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        Most likely culprit is OPAMP1 offset voltage, if you set high gain its output will be saturated. Do not use high gain settings with INSAMPs - their goal is to suppress CMRR and bring down voltage from unruly sources such as high-side current sensing resistor.   
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odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted
        Daniel, the INSAMPs based on PSoC internal amplifiers are not great. For the 3-AMP topology that you referenced, PSoC73 reported 43db CMRR, which is not that great compared to of-the-shelf INSAMPs with 120db CMRR. With PSoC, 43db CMRR can be achieved using correlated double sampling technique, which is combination of analog + digital approaches. Check if this works for your application. http://www.cypress.com/documentation/application-notes/an66444-psoc-3-and-psoc-5lp-correlated-double...   
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Anonymous
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Hi odissey1! I'll study the CDS technique that is on that url, but I am not sure if I have enough experience to deal with it because it looks like an advanced design technique. Is there any other factors that should I considerate on INSAMP designing?

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Anonymous
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I already have ina118, that's pretty good, but my goal is to build the IA inside psoc whatever using external resistors or not on it. I know that designing IA inside psoc can be more painful, but at least I'll get less components.

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odissey1
Level 9
Level 9
First comment on KBA 1000 replies posted 750 replies posted

Daniel,

   

DelSigADC already has differential input. This is enough for most applications like voltage bridge or low-side current sensing. It also has buffer gain 1-8, with 20bit 1.024V setting you can reach 1.024V / 8 / 2^20 = 122nV (theoretically!)  Due to the CPU noise the figure will likely be worth than estimated. Therefore, I doubt that INSAMP will help you much to increase S/N. Then you can apply Correlated Double Sampling approach (there is nothing special there, just take fast 2 measurements one after another, second time with DelSigADC buffer inverted, and sum them). Typical CDS technique improves DC offset drift by ~300 times.

   

Again, unless your sensor is sitting at some high voltage which is out of PSoC Vdda range (e.g. +15V), or has high-frequency noise spikes (>1kHz),  INSAMP is not necessary. If you still pursue this route, try to use matching resistor pairs like ORNT-10K/5KCT-ND or similar. But in my view it is waste of time.     

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Anonymous
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I will consider what you said and make some tests with DelSig ADC. I don't know if the ADC sample rate will be enough for my project, considering these configurations of buffer gain. I'm insisting on using a IA because it's pretty common using it to capture emg signals. Would be great if it works!

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