High Frequency Ringing [SOLVED]

Can you summarize in 25 words or less ?
(was it a software problem when you posted ? (or a hardware problem?)
That's all I'm asking. I'm not ranting. I just don't see how the above explains anything.
Are you saying your code induced the ringing which caused you to debug it and solve the issue ?
That's really all I'm asking. There's no need to be annoyed. I'm just trying to make sense of what this post
was about. I know you didn't say "Nevermind". But you essentially said "I solved the ringing by fixing my software"
which, if you ask me, would confuse anyone trying to make sense of this post.
As you can see from my last post, I did not overlook the Parallel RC circuit.

I owe you an apology. I saw you edited your post as well. I came to the same calculation after doing the same math. I substituted the 205 ohms for 220 and still get the damping I needed.

No, the software didn't fix it. The software had been altered because I didn't know it was ringing in hardware. The hardware induced the software problem, then before posting, induced the "now I don't know what's going on, I need help, problem." That's when I posted.

I was flustered due to the previous issue I encountered with someone saying, "For the love of God," and berating me. And I'm sorry, I ranted. I probably wasn't as clear as I thought I was.

Let's just move on. Glad you got the level shifter working.

I substituted the 205 ohms for 220 and still get the damping I needed.

For R4 you mean ?

For the record, I only just now notice the components Dloyd added (R6 + 15pF cap).
Don't know how those factor in.

The ringing ------- or oscillations are associated with 'resonance' --- which the physicists know to be linked to energy being cycled back and forth between two different sorts of energy storage components. In this case - L and C ------ associated with the circuit. L can be from wires in the circuit.

If the ringing 'disappeared' by a software adjustment ----- then should mention what was changed.

Or ------ if the circuit that was actually being used wasn't actually the one shown at the beginning of the post ------ then maybe that has something to do with ringing and/or no ringing. That is, output of the circuit connected to a suitable load ..... or not connected to a suitable load etc.

Adding some suitable amount of resistance at suitable locations can/will 'dampen' or damp out oscillations (the energy that is) ----- and somebody did mention adding resistance earlier on.

raschemmel:
Let's just move on. Glad you got the level shifter working.For R4 you mean ?

For the record, I only just now notice the components Dloyd added (R6 + 15pF cap).
Don't know how those factor in.

Apologies, R6 in dlloyed's post. It is the RC circuit on Q2's output. But we both did the math and came up with ~ 205ohms and 15pf. So I just substitued 220ohms since 205ohms is an oddball number for a resistor.

Southpark:
The ringing ------- or oscillations are associated with 'resonance' --- which the physicists know to be linked to energy being cycled back and forth between two different sorts of energy storage components. In this case - L and C ------ associated with the circuit. L can be from wires in the circuit.

If the ringing 'disappeared' by a software adjustment ----- then should mention what was changed.

Or ------ if the circuit that was actually being used wasn't actually the one shown at the beginning of the post ------ then maybe that has something to do with ringing and/or no ringing. That is, output of the circuit connected to a suitable load ..... or not connected to a suitable load etc.

Adding some suitable amount of resistance at suitable locations can/will 'dampen' or damp out oscillations (the energy that is) ----- and somebody did mention adding resistance earlier on.

It is a subcircuit, however, even testing this circuit straight from the power rails, the same ringing occurred. It wasn't a software issue. It was hardware configuration. And yes, you are right about oscillations :slight_smile: But... when you get down to it, everything is a subcircuit of everything else... all the way from the power station haha.
I revised my comment earlier about what it was to clarify on post #20. My brain has been fried from this issue for the past couple days and my son is struggling with baby mamma issues. Sorry if I'm convoluted and a%%-backwards right now.

So dloyd's addition + the 15pF cap you added DID
eliminate the ringing ?
(CASE CLOSED ?)

supernov ...... thanks for getting back to us on that. Nice to hear you got it sorted.

If found that example of a Schottky clamp level shifter circuit in the OP very interesting since I have never seen this design before. I managed to push it to 25MHz in an LTSpice simulation. I could not replicate the ringing.

For comparison, using a simpler level shifter using again two 2N3904 transistors (but without the Schottky diodes ) , I couldn't get more than about 200kHz out of it.

Simple Level Shifter (max ~ 200kHz)

levelShifter.JPG

Incidentally, get any ringing out of the OP's circuit, I had to make some quite drastic changes to it. I've marked the measuring points I used.

levelShifter.JPG

6v6gt:
If found that example of a Schottky clamp level shifter circuit in the OP very interesting since I have never seen this design before. I managed to push it to 25MHz in an LTSpice simulation. I could not replicate the ringing.

For comparison, using a simpler level shifter using again two 2N3904 transistors (but without the Schottky diodes ) , I couldn't get more than about 200kHz out of it.

Simple Level Shifter (max ~ 200kHz)

levelShifter.JPG

Incidentally, get any ringing out of the OP's circuit, I had to make some quite drastic changes to it. I've marked the measuring points I used.

Wait wait wait! Your simulation results showed ringing? What simulation software are you using? Also, there is still ringing on the pulldown that may need another filter on output. At 1.2 volts and with hysteresis, it may trigger a logical high. And then you also have noise you need to deal with.

With the 3904, you can theoretically get 300MHz out of it according to the datasheet. R1 and R2 values would have to be optimized for this and so would D1 and D2 in my schematic. I've optimized for quiescent power draw. You'd need to increase voltage and power draw to get that switching speed tho.

Also, here is my simulation scope data... I don't get the ringing you got :frowning:

raschemmel:
So dloyd's addition + the 15pF cap you added DID
eliminate the ringing ?
(CASE CLOSED ?)

Well, yes, but @6v6gt's findings are interesting... might take another look at new software but yeah, the main issue is solved.

This is with your circuit, simulated with LTspice XVII at 20MHz.
The attached file SchottkyClamp_V0_01.asc (Renamed .txt so I can attach it here) is the complete model.

It could well be there is a difference between the simulation models for the individual components. Also, since the trick with this design is that the transistors are not fully saturated, so not cleanly switched, they may be more complex to model.

I don't understand how your simulation of my "ringing" example got such a clean result. I put some effort into ensuring it "rang". Maybe the component values are not the same. I'll include that as well: SchottkyClampRing.asc.txt

SchottkyClamp_V0_01.asc.txt (1.74 KB)

SchottkyClampRing.asc.txt (2.93 KB)

Oh oh oh!!! I get what you mean. No I didnt try circuit you put up. I was in a hurry to run some errands. I see what the purpose of your circuit is. To simulate the ringing so we can eliminate on the output.

Initially, I had thought that they were filters to eliminate ringing at different sources and your simulation indicated ringing from my original levelshifters.

Scope data from my sim was the bat_diode level shifter only. Not including the resonators you added. At first glance I thought they were RLC dampers.

Sorry for the misunderstanding.

And good finds @6v6gt!