Electronics > Projects, Designs, and Technical Stuff
Level shifting
Benta:
Here's a quick little sketch.
If you need to drive your output into a 75 ohm load over longer distances, you need a x2 amplification somewhere.
Concerning DG419B, there are lots of analog switches out there. It's just that I've used them successfully in several CVBS projects. You might even consider just a transistor or MOSFET.
syntax333:
Thank you for the circuit diagram I will definitely try it out.
I just wanted to learn that is there any specific parameter that I need to look while choosing Analog switches for using for my application.
Benta:
I'd say below 100 ohms and as little feed through when off as possible. But that's just an approximation, in this application it's not really critical.
My use of analog switches (DG419B) was directly in the CVBS line, which is much more demanding.
syntax333:
I am assuming the circuit with bjts are for Zout << Zin condition. However, I am worried that bjt switching speed won't keep up with the 4.3Mhz PAL color carrier. I am asking that will the bjts create a problem about switching speed, should I use MOSFET instead of bjt since they have faster switching characteristics?
Benta:
--- Quote from: syntax333 on December 26, 2018, 07:12:27 pm ---I am assuming the circuit with bjts are for Zout << Zin condition. However, I am worried that bjt switching speed won't keep up with the 4.3Mhz PAL color carrier. I am asking that will the bjts create a problem about switching speed, should I use MOSFET instead of bjt since they have faster switching characteristics?
--- End quote ---
Don't worry, in-your-drawer BC547/557 or BC 847/857 will work perfectly. They're 250 MHz fT transistors and operating as emitter followers will give you zero problems.
MOSFETs would be a nightmare. Why are you so down on BJTs?
You'll find this buffer configuration in all kinds of commercial video equipment, it preserves the DC level of your signal. Simple, easy and cheap.
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