Iam simulating the circuit using LTSpice software. Need to hold few ns time at the output of the comparator. Do anyone help me?

 

Please post your circuit. (LT SPICE file)
Do you want the output delayed a few ns in time?

 

Attached the LTSpice file. Output of comparator has 2 ns ON time and 6 ns OFF time. I want to hold the output of comparator for 100ns for every 2 ns ON time.

 

i know how to build the 2ns pulse amplifier but the 2ns propagation speed for a comparator sounds suspicious . . . with some kind of a "feed forward" (a positive! HF feedback) . . . perhaps

if your both inputs are varying - then such adds a complexity

also too weak input signal strength may add complexity

+ your input repetition rate may add complexity -- e.g. -- if the "input" occurs every 8ns up to every 8h

↑ the input range specifications are required here -- without no-one can provide you any valid advice ↑

 

if your both inputs are varying - then such adds a complexity
- Only one input of comparator are varying.

Please suggest me how to hold the output of comparator to 100ns when 2ns pulse occurs at the output.

 

Please post your circuit. (LT SPICE file)
Do you want the output delayed a few ns in time?
I have uploaded LTSpice file. I want the output to hold for few ns in time.

 

https://en.wikipedia.org/wiki/Low-voltage_differential_signaling
describe the role of your comparator (it's I/O) with respect to the rest of the system ...
e.g. does it receive it's input from Std. LVDS output . . . ← if so can the otput be intercepted .. or is it "far" away / the output pins of another iC
does it's output go to Std. LVDS input

see also the Pg.14 https://www.analog.com/media/en/technical-documentation/data-sheets/6754f.pdf

 

describe the role of your comparator (it's I/O) with respect to the rest of the system ...

Comparator Output is feeding to Arduino. Arduino can't handle 2ns for every 6ns so I want to hold the output of the comparator for at least 100ns.

 

Need to hold few ns time

I want to hold the output of the comparator for at least 100ns.

Finely; a few does not equal 100.
The comparator you are using has LVDS outputs and will not talk to a Arduino well. You need outputs that from 0 to 5V or 0 to 3V.
100nS is not long enough for a Arduino.
------------------
There are things you have not told us …… so here is my first try.
When those fast pulses happen the output goes low for 7uS.
Few comparators can do 3nS. I used a Schokey diode to peak detect the signal. Changed to a comparator that has 0-5V output. (sorry I should have removed the 10p C1 cap)

 

Thank you. As I am new in building circuits. Sorry for asking basic questions.
-100nS is not long enough for a Arduino.
Arduino Uno has clock frequency 16MHz. When there is change in input it takes approximately 64 ns to respond. Is that not right? If 100ns is not sufficient Can't we make it to 500ns?
-When those fast pulses happen the goes low for 7uS.
I want the 2ns pulse to appear after 500ns or whatever time Arduino can handle. I don't want the output to go low for 7us. I first pulse 2ns hits the Arduino. The other pulse 2ns hits arduino after 6ns. So, every 2ns should be kept hold for few ns.(i.e) It has to wait for some processing time of Arduino

View attachment 204618In this circuit, Why this V2 and R1 are left unconnected?

 

In this circuit, Why this V2 and R1 are left unconnected?

From your circuit.

When there is change in input it takes approximately 64 ns

You must be using an interrupt? How are you using the data? If you are poling the pin it will take a long time. Are you using a counter input?

I do not understand.
There are 4 pulses of 2nS. Total time is about 20nS. The Arduino can do nothing in this time.
Do you want the Arduino to see all 4 pulses?
I can make a circuit where the output goes high on the first pulse. The output will stay until the Arduino reads and resets the circuit back to low.

 

From your circuit.

You must be using an interrupt? How are you using the data? If you are poling the pin it will take a long time. Are you using a counter input?
Yes Iam feeding pulses into the interrupt pin of Arduino.

There are 4 pulses of 2nS. Total time is about 20nS. The Arduino can do nothing in this time.
Yes, Arduino can't do anything. So, only I want the Comparator output to hold for 100/500 ns for every 2ns pulses.

Do you want the Arduino to see all 4 pulses?
yes.

I can make a circuit where the output goes high on the first pulse. The output will stay until the Arduino reads and resets the circuit back to low.
Yes, it should happen for all the N pulses. Not only for first pulse.

 

To delay pulses is very difficult in analog.
You can use a counter. Every pulse will increase the number in the counter.
The counter will have a "clock" input which connects to you 2nS pulses.
The counter will have 4 outputs that go the Arduino.
The counter has a "reset" input where the Arduino can reset it back to zero after a read.

 

Need to program in Arduino using the counter?
If I get more than 4 cycles of input. Can I use this counter?

 

2ns pulse with period of 8ns = 125MHz
Houston we have a problem.
Arduino cannot count at 125MHz. Using interrupt is even worse.
You have to find another solution.

 

How many pulses will there be?
Is there always 4 pulses or is the "125mhz" there for 1000s of pulses?
Where is the signal coming from?
What computer IC are you using in the Arduino? Many different parts.
-----edited------

Arduino Uno has clock frequency 16MHz. When there is change in input it takes approximately 64 ns to respond.

If you want to know how fast the response is. Make a loop: set pin high, set pin low, conditional branch, loop. Watch the pin with a scope. You can do nothing in 64nS.

 

Pulses will be coming from Photodiode. It will have N number of pulses. ATmega328.

In LTspice, Can we use a BUF or BUF1 at the output of comparator?

 

I do not know the ATmega328 well.
You can use Counter/timer1 as a counter. I have not found how fast it can count but not the speed you want. (maybe 16mhz maybe twice that)

You can put a high speed counter on the outside and have it divide the frequency down. There are many ICs that will take 16 pulses and make one pulse. This divide by 16 idea is often used in frequency counters.
----edited-----
I found some information. The 16 bit counter/timer can count up to 8mhz in a 16mhz part. That is assuming a 50/50 duty cycle.

 

a bad* design example /// * -- the comparator is dependent on the LT1252 output level - the least is not specially fixed

 

It seems very complicated circuit. Instead will it be possible to use BUF IC in LTSpice at the output of comparator circuit?