I see I'm not the first to see it this way.

 

View attachment 257550 I see I'm not the first to see it this way.

It seems that the cad person does not understand.

 

I'd be inclined to believe the person who drew the diagram could have only done that deliberately. I can't see any possible way that could be a legitimate mistake.

 

I'd be inclined to believe the person who drew the diagram could have only done that deliberately. I can't see any possible way that could be a legitimate mistake.

My experience has been that not all drafters and CAD operators know anything about anything else. And with Autocad the flip command can do very strange things.

 

I'd be inclined to believe the person who drew the diagram could have only done that deliberately. I can't see any possible way that could be a legitimate mistake.

It could be the CAD operator clicked the op-amp randomly and also clicked the mirror function to caused that the direction of op-amp was opsite.

 

I think that the CAD operator fell asleep on the keyboard and then went home. They never showed back to work because of the pandemic. So that’s how the drawing ended up and it got filed away as completed documentation.

 

The original circuit could be like this.

View attachment 257366

A Horizontal Flip has been done.
A Vertical Flip too is required to make it a amp with Gain 10.

 

A Horizontal Flip has been done.
A Vertical Flip too is required to make it a amp with Gain 10.

Or a single 180° rotation.

 

A Horizontal Flip has been done.
A Vertical Flip too is required to make it a amp with Gain 10.

When I redraw the circuit but I didn't analyze the circuit, I also didn't check the detail, so I said "could be", when I replied in #25, I still felt that there is something wrong there, rotation 180° is more makes sense.

 

Hi team

Trying to understand this circuit, does it make sense to you? U3 output a square, I understand U4A is a low pass filter, what the job of U4B?

Thanks team!

View attachment 257360

"The more i learn the more i dont know".
That means you know a lot more than a lot of people. This is the way of knowledge. We might modify that statement a little:
"The more i learn the more i learn that there is always something new to learn and that i can never know everything, and what i already know may change at any time so i must be completely open to new ideas, viewpoints, and procedures".
Anyone who did not learn that lesson is still lacking.

But to your circuit, it starts out pretty good. First it converts a digital wave probably 0 to 3.3 or to 5v to a wave that rides on one half of the DC buss value, then uses a 2nd order low pass filter to reduce some frequencies of that digital rectangular wave. It will end up looking similar to ocean waves.
The next stage, when connected properly, probably just amplifies the signal a little.
The next stage does not look like it is functional yet.

However, with regard to the 2nd order low pass filter, a low pass filter is not the best idea for obtaining a sine wave. It does reduce some of the higher harmonics but fails short of reducing all of the harmonics needed to obtain a nice sine wave.
The best way to get a sine wave from a single frequency rectangular wave is to use a bandpass filter. You can actually get a pretty clean sine wave out of a 2nd order bandpass filter because it acts to reduce many of the frequencies present in the rectangular wave that are not needed for a sine wave. It in effect only lets the one chosen frequency through, which is a sine wave. The bandpass filter must be tuned to the fundamental frequency to get the best results though. So if you push a 1kHz square wave through a 1kHz bandpass filter you could expect to get a nice sine wave output.
The only caveat is that this setup is made more or less for a single frequency which i assume you are doing. If you have to do more than one frequency then you have to be able to tune the bandpass filter. This can be done by hand with potentiometers or with a switched capacitor filter which allows for somewhat easier adjustment. Follow up with a low pass clock filter and you have a decent setup.
The theory of switched capacitor RC filters is not that difficult either, we could discuss that at some point.

In any case, try the digital wave to DC bias at one half of the DC buss followed by a 2nd order bandpass filter tuned to the fundamental frequency of the digital wave and see how nice it works.

 

The simple lowpass filter has only 2 orders so it does not eliminate the extreme distortion of the input pulses.
Then U4B amplifies the waveform 11 times making another pulsed waveform full of distortion harmonics.
The output of U4B is attenuated to 1/57th by R13 and R14.
The power amplifier has a voltage gain of 111 times to drive a speaker or headphones with the buzzer sound of the squarewave.
Therefore it is a completely useless circuit.