New OpAmp circuit to analyse

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,446
Hi...

I have a new OpAmp circuit to analyse and part of the analysis is already done!
It is a "Widow Detector" and we have the circuit split in 3 separate blocks. Block 1 which is a Schimtt Trigger, Block 2 which is an Integrator and the 3rd one I'm still not sure what it is!

I think it is at least an Half-Wave rectifier but it has probably some other function that I don't know!
I need some help to identify it and give an explanation of the role of this block on the whole circuit!



I have tried to simulate Block 3 on LTSpice, first using a sine wave and I tried with a triangular wave. But for the triangular wave I was not able to setup the input voltage source the way I wanted as it is in the attached file!
I have also tried to use discrete values (see picture below) on the right voltage source and tried to use the directive ".param" to make things a bit more simple to read but I couldn't! I can' figure out what's wrong with the parameters in the simulation!

http://i.imgur.com/kDKuvLz.png
 

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Last edited:

MrAl

Joined Jun 17, 2014
6,469
Hello,

The 3rd block looks like a comparator with adjusted output impedance: low impedance source and higher impedance (10k) sink.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,446
Ok, and what about not being able to set the voltage supply for that block like I pretend???
 

GopherT

Joined Nov 23, 2012
7,983
Hi...

I have a new OpAmp circuit to analyse and part of the analysis is already done!
It is a "Widow Detector" and we have the circuit split in 3 separate blocks. Block 1 which is a Schimtt Trigger, Block 2 which is an Integrator and the 3rd one I'm still not sure what it is!

I think it is at least an Half-Wave rectifier but it has probably some other function that I don't know!
I need some help to identify it and give an explanation of the role of this block on the whole circuit!



I have tried to simulate Block 3 on LTSpice, first using a sine wave and I tried with a triangular wave. But for the triangular wave I was not able to setup the input voltage source the way I wanted as it is in the attached file!
I have also tried to use discrete values (see picture below) on the right voltage source and tried to use the directive ".param" to make things a bit more simple to read but I couldn't! I can' figure out what's wrong with the parameters in the simulation!

http://i.imgur.com/kDKuvLz.png

Blocks 1 and 2 are integrator and comparator. Together, they make a triangle wave oscillator. hint: if there is no input terminal, it is usually an oscillator). The block 3 is a rectifier (half wave as you said) that can clip as little or as much of the mountain base off of each triangle as you want (pot control) and that op amp acts as a comparitor to make a square wave - PWM.

This circuit needs a +/- 15 V power supply (not a single supply).
 
Last edited:

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,446
Blocks 1 and 2 are integrator and comparator. Together, they make a triangle wave oscillator. hint: if there is no input terminal, it is usually an oscillator). The block 3 is a rectifier (half wave as you said) that can clip as little or as much of the mountain base off of each triangle as you want (pot control).

This circuit needs a +/- 15 V power supply (not a single supply).
I'm using a split voltage supply with +12V/-12V. If it's not enough, I can use the 15V level, no problem, but I'm using 2 voltage sources!

I wish I would have thought of that.



Any reference to what a PXX circuit is?
I also can't find anything about PXX circuits!
 
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Jony130

Joined Feb 17, 2009
4,969
Have look at my attached file? And do you analyze the results ??
And do you ever herd about Pulse Width Modulation ??
 

crutschow

Joined Mar 14, 2008
23,314
Yes, that's a PWM circuit with the output pulse width determined by the potentiometer setting.
But I don't understand the purpose of the output diode and resistor in that circuit. :confused:
 

AnalogKid

Joined Aug 1, 2013
8,102
(3) is a comparator that can only source current.
While that certainly is a very common approach, there is nothing in the original problem that states or implies that. A03 (note that the A might mean amplifier as opposed to a C for comparator) could be 1/4 of the same quad opamp used for A01 and A02.

ak
 

AnalogKid

Joined Aug 1, 2013
8,102
Maybe they want only a positive PWM at the output.
I agree. I think the output is a converter for a CMOS logic input, but another possibility is that it is a part of the problem included to cover something else being taught.

ak
 

marcf

Joined Dec 29, 2014
256
The title of this thread refers to A0, A1 and A3 as op amps, not comparators. I think the difference is that comparators are open collector devices that can only sink current and op-amps have the ability to both sink and source current.

I understand that while you can use a op amp as a comparator is not necessarily a good idea to do so.

If A0 - A3 are comparators, I would expect to see at least a pull up resistor on A3.
 

crutschow

Joined Mar 14, 2008
23,314
The title of this thread refers to A0, A1 and A3 as op amps, not comparators. I think the difference is that comparators are open collector devices that can only sink current and op-amps have the ability to both sink and source current.

I understand that while you can use a op amp as a comparator is not necessarily a good idea to do so.

If A0 - A3 are comparators, I would expect to see at least a pull up resistor on A3.
A02 must be an op amp since it is being used in the linear mode as an integrator.
A comparator would oscillate in that application since they are not compensated for linear operation.
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,446
Have look at my attached file? And do you analyze the results ??
And do you ever herd about Pulse Width Modulation ??
Yes I have looked into your attached file. I also looked at the results. I just didn't know that PWM was also known as PXX.

I'm not sure if your intent with your .asc file was just the results or if you were trying to tell me something about the way I tried to set the vin voltage source.

I spoke to my teacher and sometimes I think you might be a psychic. That diode is in fact to get a positive only output voltage.

And is the resistor next to the diode, a pull-down resistor or what is it doing there?
What about my attempt to set the Vin voltage as I tried? Why doesn't it work?
 
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