PRECISION SIGNAL AMPLIFY AND REMOVE DC OFFSET

Hi Reza,

I have some ideas on how to approach this but I need to better understand your sensor before I can make a recommendation. Could you provide a datasheet for the sensor? If not, can you tell me the following:
1) What is the sensor interface? i.e. 2-wire/3-wire. Is one side grounded while the other requires a 12V excitation voltage?
2) What is the impedance of the sensor?
3) How fast does this signal change and how accurately do you need to track it? This will influence what kind of bandwidth and slew rate you need.
4) What supply voltages do you have available, or is this flexible?

Hi

thanks for reply.

i send a schema and you can get whole answers

when pules turn on Q2 and L2 changed, signal on output line as in past mention change along x axis.

sincerely

Hi Reza,

Here is a concept that might work for you:

Inductive sensor OPA354 + OPA388.TSC

I'm not sure how sharp of an edge you have to your sensor signal or how narrow the pulse is so it's hard to say exactly how much bandwidth you need, but I think something like this will accomplish what you are after with some tweaking for your signal. The OPA388 is configured as an integrator that integrates the output and feeds it back to the input of the OPA354. Note the phase inversion effectively makes this negative feedback. This strips off the dc offset without loading your sensor. There will be a long startup time associated with this depending on where you choose the cutoff frequency with R1 and C1. You want the response time to be relatively slow so that you filter out the dc and don't distort your sensor signal. You will likely need to adjust things to get the optimum response for your sensor.

Thanks for reply.

In my circuit maximum rise time is 70 Nano seconds.

I complete your circuit and resend two schemes for you. please verify these .

In scheme 1.tsc I add sensor and change R1 and C1(integrator) because circuit respond is slow and when signal fall ,pass lower from base line.

In scheme 2-sw.tsc  I SHIFT 200uS VG1 and add a switch for sampling base line of signal.(we can add any SPST).you can simulate.

I send two schematics for you, please verify and give your VIEWPOINT.

1-What scheme is best? (your scheme or scheme I send for you)!

2-how can divide exponential fall two segment and verify each segment?(I think when amplify this signal max 5v have not enough dynamic range).

3-if I change D1 ,D2 with BAT86 (OR LOW VOLTAGE SCHLOCKY_DIODE)can give best dynamic range.

THANKS

Sincerely.

1.TSC0160.2-sw.TSC

Hey Reza,

Sorry for the delayed response. I like the idea of switching the integrator in and out to avoid issues with the input voltage shifting because of the transistor turning on and off. The dynamic range problem can be tricky to address. One way you could approach it is to have multiple stages: one stage that runs in a high gain meant for amplifying low signal levels, and another that feeds into a difference amplifier and subtracts a reference voltage from the signal before amplifying it again. See attached for rough example. If you scale things accordingly, then only one channel would have a valid signal while the rest would be saturated so you could use that to determine which range you are in and what the actual signal level is.

0160.2-sw ZK.TSC

Hi

Thanks for replay

I am in a hurry! Sorry.

I did not understand your writing. Please explain again.(explain about switching and transistor)

This scheme I send for you detect ferromagnetic from paramagnetic metals.

If paramagnetic near to sensor the transition when fall reduced width, and if ferromagnetic near to sensor, more width of falling transition.

my questions are:

1-if replace D1 and D2 with Schottky diode, can get more dynamic ranges??(Because these diode turn on with lower voltage)

2-i sends a scheme for you. Please tell me what scheme is best?(this or your scheme)

Thanks for the answer sooner.

Sincerely.

loop-negative.TSC

Hi Reza,

I was just commenting on your choice to switch the integrator in and out. I assumed you were doing this so that when the transistor switches on the integrator doesn't start drifting in attempt to respond to the shift in the dc voltage caused by the transistor turning on.

Whether you get more dynamic range depends on what you really care about measuring. From simulation, the width of the pulse seems largely unaffected by the diode choice because the LR time constant stays the same, it does however impact the peak signal level. If you are trying to maximize the digitized signal level then a larger diode drop is actually more beneficial.

In the circuit you have attached the scaling doesn't quite accomplish the same thing. You are compressing the signal and level shifting it as opposed to subtracting a reference voltage and amplifying it, so you aren't really gaining any more resolution in the reading. I would also try to avoid saturating the output of the amplifier because there is some overload recovery delay associated with driving the amplifier into the rail and this will skew your pulse width.

Thanks for replay

1-DIODE D2, when used a diode with less forward voltage (Vf) and when switching transistor turn on, so having less voltage drop from other diode. This area have not information’s (Sensor voltage contain information on falling exponential segment you can see in TINA ) and we can more amplify signal for get more dynamic range and saturate op amp and remove other segments.

2-DIODE D2, clamp EMF high voltage when T1 turn off.my questions is: if uses lower Vf diode better or higher Vf diode??this diode turn on with lower voltage is best or turn on with higher voltage?

3-i wants digitizing falling exponential segment of signal not whole segments. (I use ADS8329 1MSPS and 16 bits) So need falling segment more amplify (when more amplify and op amp saturate so width of falling segment be more and on this state if sensor sensing Ferromagnetic, this width will be more and if paramagnetic Sensing , this width will be less, because my digitizer sampling each micro seconds I need more amplify this segment . please give best method.

Please write simple.

Thanks

Regards.

See attached for a recommended circuit that I think will be more applicable for what you are trying to achieve.

Inductive Sensor Analysis.pptx

Rev A attached adds a page documenting the scaling values used.

Inductive Sensor Analysis RevA.pptx