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Advice on Replicating Signal

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eetjd

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Hello everyone! This is my first time posting here, my name is Justin.

I need help replicating a signal on a system I'm currently working on. The line, when idle, sits at +8VDC; when the line is active, the system transmits data on the line by modulating it and creating a very rough sin wave. The voltage swings from about +5.5V to about 9.7V when it's transmitting. The wave has a period of about 8uS so that gives it a frequency of 125k HZ. I've included two pictures of the line when it's active; the data was captured using a logic analyzer that can do analog.

What circuit could I use to replicate this signal? Should I use transistors, OP AMPS or something else? I'll admit I'm somewhat weak in analog circuits, so this is a learning process for me.

Thanks for you time!
signal_snip.PNG
signal_snip2.PNG
 

kemiyun

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Hello,

I think there are questions you need to answer for yourself: "Are you doing this for test purposes?" or "Am I trying to model something and give it as an input to my circuit, or am I modelling a circuit that is doing this behavior?"

If you are doing it for test purposes or if you're going to use this as a stimuli, no you shouldn't use transistors opamps or anything that has a physical correspondence. They would just slow your simulations down and they're unnecessary complications. Also this is what many people would understand when you say I want to replicate a signal in simulation. At least that's what I thought. In this case you can write a verilogA model or just put two ideal switches, one connected to 8 VDC and the other connected to a sine wave of your choice. And then you can switch between them using a square wave signal. It's the most basic thing I can think of.

The second thing you might have asked for is the real circuit that can do this. The implementation of this circuit completely depends on your specifications and I don't think you have enough data to come up with solid specifications. For example it's easy to do this with a Wien oscillator with an on/off switch, but the problems are: "What is this circuit going to drive?" "How much accuracy do I really need?" "Do I really need to turn this off at a very weird voltage like 8V?"

I'm assuming you want the first one. For the second one, I can't design a circuit for you, but I can help you with a few problems you might face in the process. Depends on what you're trying to do really.
 

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