How to compare Differential Signal with some threshold value by comparator/Discriminator?

[Ali263]

I am having a chain of differential amplifier stages and at the end a comparator to compare the signal with some threshold value.

For single Ended amplifiers I give amplifier chain output at one input of Comparator and Threshold Voltage at other Input of comparator to get result.

But how do I do it when I have differential Output of Amplifier Chain?
Is it ok to give Vin_P + Vth/2 at one input of comparator and Vin_N + Vth/2 at other end of comparator?



where Vin_P and Vin_N are differential output of Amplifier stages that are to be fed into discriminator


In schematic, circuit in red is Analog chain whose output is intended to be compared with some reference value by discriminator (As seen in blue)

 

[danadakk]

Something like above ?


Regards, Dana.

 

[KlausST]

Hi,

Teoretically you may "add" the threshold at the amp input, at the amp output, at the comparator input...
...at one input (total threshold) or at both inputs (half threshold each).

We don´t know your requiremnts.

Klaus

 

[Ali263]

**broken link removed**

Something like above ?


Regards, Dana.

I added a picture in my question. You can kindly see it

--- Updated Dec 9, 2020 ---

Hi,

Teoretically you may "add" the threshold at the amp input, at the amp output, at the comparator input...
...at one input (total threshold) or at both inputs (half threshold each).

We don´t know your requiremnts.

Klaus

Hey Thank you for your reply.

It means that if my differential output of analog chain is Vin_P and Vin_N, (That is to be fed into discriminator) . I should add Half of threhold to Vin_P and subtract Half threshold from Vin_N?

"Is it ok to give Vin_P + Vth/2 at one input of comparator and Vin_N - Vth/2 at other end of comparator? ""

I tried it and i think it giver good result but I want to confirm the approach and understand logic?

For information the red circle the analog chain and blue circles the discriminator

 

[KlausST]

It means that if my differential output of analog chain is Vin_P and Vin_N, (That is to be fed into discriminator) . I should add Half of threhold to Vin_P and subtract Half threshold from Vin_N?

"Is it ok to give Vin_P + Vth/2 at one input of comparator and Vin_N - Vth/2 at other end of comparator? ""

..as already written:
" ...at one input (total threshold) or at both inputs (half threshold each). "

Klaus

 

[crutschow]

You could also convert the differential out to single ended, and feed that to a standard comparator.

 

[Dominik Przyborowski]

Look for papers about ASD8/ASDBLR, SCT128, ABCD, ABCN25, ABC 130 or CARIOCA.
All these chips processing differential signals into amplitude discriminator.
Depending on architecture, they use or double diff pair (DDA) or unbalanced diff pair for comparator.

 

[Ali263]

I have a differential signal, as shown in figure, which i want to compare with some threshold value. I have a comparator (made up of 2 stage, single ended amplifier) at one input I give signal to be measured and at other input i give threslold value and in this way i can compare single ended signal not differential.
But now since I am having differential signal how can I handle it? (Converting differential signal to single ended is not an option)
I have heard about using two single ended comparators but i do not understand it how.

 

[KlausST]

Hi,

Why asking the same question again?
Threads merged.

Klaus

 

[Ali263]

Hi,

Why asking the same question again?
Threads merged.

Klaus

Because the answer given there did not work, method of applying threshold. Also because as asked , i would like to know if its possible to do it by using 2, single ended, comparators.

 

[KlausST]

Hi,

Adding threshold does work.
Show what you have done, show your test conditions, tell us your expectations, tell us what you see instead.
Give pictures, schematics, values...

Two comparators
.. give two independent outputs. Show your idea how to treat them..

Klaus