Fully analog function generator project - Page 1
Forum section: electronics / projects

author: ampdoctor
author_rank: Frequent Contributor
timestamp: January 30, 2013, 04:40:38 am
content: Just thought I'd put this out there to see what people here think of the idea. What I'm thinking about is designing a completely analog function generator using discrete components with sine square, triangle, and TTL outputs with a frequency range up to somewhere around 1MHz and distortion figures solidly lower than 1%. Features may include a frequency counter, output level, dc offset, AM and FM modulation, and duty cycle.While I realize it would be much easier to accomplish something like this with a DDS generator, and would certainly be cheaper to go on fleabay and buy a unit, but where's the fun in that?! The idea would be to provide people with a means to understand basic wave shaping and oscillator circuits applied to something useful in the process.So, any comments, opinions etc. Worth taking a shot?

author: ChrisMH
author_rank: Contributor
timestamp: January 30, 2013, 04:48:37 am
content: I was just about to start hunting up some circuits to do just this. I'd love to see what you come up with.Chris

author: Harvs
author_rank: Super Contributor
timestamp: January 30, 2013, 05:15:36 am
content: If you can come up with something that's nice, in a neat box (or designed around an appropriate case that can be bought easily), isolated from ground and has the power to drive a 50ohm output I think it would be a nice little project.The problem with 90% of these things you see out there (like most of the ebay DDS generators) is they've done a half hearted job at it.

author: FenderBender
author_rank: Super Contributor
timestamp: January 30, 2013, 05:19:00 am
content: Square is simple. Triangle would just be integrating the square wave. TTL and sine might be a little trickier, though totally feasible.

author: lowimpedance
author_rank: Super Contributor
timestamp: January 30, 2013, 05:46:24 am
content: Quite a good number of the older analogue designs from wavetek, exact, hp, and many others actually start with the triangle wave.Constant current charging timing cap's through + and - current sources. Square wave was generated from the triangle as was the sinethrough a diode shaper.So if you would like to go the good old discrete way, then I recommend looking at some old manuals from hp, wavetek etc to get some good starting ideas.If you are going to get any reasonable frequency range your PCB and general internal layout is going to be fairly critical for stability.have funLowZ

author: ampdoctor
author_rank: Frequent Contributor
timestamp: January 30, 2013, 05:52:54 am
content: My initial thoughts were to start with some form of a triangle oscillator, to square shaping and TTL out, then send that to possibly a breakpoint sine shaper. From there it would go to an opamp driver with level and offset adjust and into a complementary BJT output. 25v split rail regulated supply should allow for a reasonably large pk-pk signal across 50 ohms. I'm still at the kick the can around/pre-planning stage for now so everything including features and specifications are still mighty loose to say the least.edit: lowimpedance just posted almost exactly what i was thinking

author: ptricks
author_rank: Frequent Contributor
timestamp: January 30, 2013, 12:42:33 pm
content: Some of the older generators got the sine wave by using the sine wave of the power source.I have some schematics I will try to locate that are from about 40 years ago where they use nothing but transistors.