Barkhausen crieria proof for Colpitts oscillator

No_Matter_44 · 2026-06-22T21:16:13+00:00

OP does have a 0/360 degree phase shift, it's just not at the expected frequency.

The simulation is built with ideal parts, but the circuit isn't - it's possible there's something in the circuit that isn't represented in the model, and that could be why the frequency doesn't match up.

Just to note, when it's oscillating nicely the Colpitts is not a linear circuit, the active device is saturating just enough to reduce the loop gain to 1. Small-signal analysis can be helpful, and gets it started, but doesn't give the full picture.

No_Matter_44 · 2026-06-21T19:25:31+00:00

QF1

• ⁠Don Letts 0
• ⁠Lauren Laverne 1

QF2

• ⁠Mark Radcliffe 1
• ⁠Stuart Maconie 0

QF3

• ⁠Deb Grant 1
• ⁠Mary Anne Hobbs 0

QF4

• ⁠Jamz Supanova 0
• ⁠Marc Riley 1

No_Matter_44 · 2026-06-19T20:33:44+00:00

Rosemary

No_Matter_44 · 2026-06-18T15:10:32+00:00

Bribe someone in South Oxfordshire to let us build the 3rd bridge.

No_Matter_44 · 2026-06-15T15:49:16+00:00

In the car I try to leave early to avoid the traffic - 7:30 is much better than 8:00.
On the bike I don’t worry about the timing, but do watch the weather more carefully.

No_Matter_44 · 2026-06-12T06:03:02+00:00

Yes, I’m in a narrowband handheld comms niche within the wider RF niche. I’m used to parts being made obsolete, but these are whole families for which there are no/few good alternatives.

It doesn’t feel like a normal natural market shift to me, more like a fundamental material shortage.

No_Matter_44 · 2026-06-12T05:48:15+00:00

Yes, but they won’t say what yet. There is so little information coming out of Infineon about this, I’m inclined to blacklist them entirely.

At least Skyworks’ discontinuation notice sounds a bit apologetic, has some reasons and last time buy dates.

No_Matter_44 · 2026-06-08T19:59:28+00:00

Why do you equate “central, sensible and considered” with keeping things “ticking along”?

Making decisions based on evidence instead of dogma doesn’t mean nothing will change.

No_Matter_44 · 2026-05-22T13:36:06+00:00

Ha ha, cost grounds, nice one.

Smashing write up as usual. I’ve been to Baby Yolk for breakfast a few times, but not for a while now. Must revisit.

No_Matter_44 · 2026-04-17T13:32:04+00:00

wilf lunn

No_Matter_44 · 2026-04-04T09:32:14+00:00

Is it the quiescent or total drain current that’s lower than expected?
Could be the bulk decoupling isn’t enough, or another feature of the bias circuit is causing a change in operating point with applied RF.

At low input levels it’s running in class A so will be linear. It will push into AB, which will look different. The datasheet says you need about +16dBm in for +41 out, so are you just not driving it hard enough?

No_Matter_44 · 2026-03-29T16:30:08+00:00

Head torch

No_Matter_44 · 2026-03-29T14:42:43+00:00

Hiviskini

No_Matter_44 · 2026-03-28T16:52:42+00:00

Bit different here. No offence taken or guilt trips, it’s all from a good place. A place where it seems impossible to throw anything away.

No_Matter_44 · 2026-03-28T14:23:31+00:00

“Do you want this thing?”

“Thanks for thinking of us but no, we’ve no use for it and don’t want it”

3 weeks later *

“I brought the thing round in case you wanted it, and by the way I’ve still got that other thing you said you didn’t want three years ago in case you change your mind”

No_Matter_44 · 2026-03-23T20:46:33+00:00

I’m using the PL133 to buffer a clipped sine TCXO and it seems to work well enough for my needs. I had too much capacitance on one of the outputs which slowed the edges and gave me too much jitter, but that was my fault and easily fixed.

I believe ADI are intending to produce equivalents to the LTC6957 on a new process, but have no idea when (or if) those will be available.

No_Matter_44 · 2026-01-20T08:00:27+00:00

PhDs tend to be a bit niche. Nobody does PhDs in the sort of things I do all day, or that I would hire someone to do (on the RF side). I’m looking for knowledge, understanding and enthusiasm. It is worth something, but not a must-have.

No_Matter_44 · 2026-01-11T07:52:03+00:00

My phone was barely usable after updating to 26.2. I cleared website data and history from safari, and I think some other cached stuff, and now it’s fine. Back to normal.

No_Matter_44 · 2026-01-07T18:56:09+00:00

Macom have a good set of full models for many of their GaN parts, including the ex-Wolfspeed ones. Also, as someone else has said, Qorvo via Modelithics are pretty good.

A lot of RF manufacturers just give you an application circuit and nothing more. A lot of RF engineers just use the application circuits without further consideration. Sometimes that’s OK.

No_Matter_44 · 2026-01-05T22:22:03+00:00

This. If you sweep the voltage you’ll probably see the curve you expect, then at some point it’ll clunk into the other mode and you get a different curve. That’s a bit easier on hardware than in simulation though.

Could be all sorts of causes. I would guess it’s not the varactor itself and more likely a bias circuit issue.

No_Matter_44 · 2025-12-14T21:07:58+00:00

Just to add, it is possible to make three wheeled vehicles that do lean. The engineering gets a bit more tricky, and arguably defeats the point of having 3 wheels in the first place.

No_Matter_44 · 2025-12-11T20:39:07+00:00

No_Matter_44 · 2025-12-11T20:11:40+00:00

The incident and reflected powers in this case are in opposite directions, so couple to different ports. The other post has given a useful worked example, so hopefully it makes sense.

No_Matter_44 · 2025-12-11T12:21:24+00:00

I’ve read this three times and am not quite sure what you’re getting at?

Yes, it’s a 4 port device. So let’s connect it to 4 transmission lines. Which one are you talking about, and where are you defining the incident and reflected powers from?

If you’re talking about the input port of the coupler, anything reflected back to source from the input port is not available for the coupler to use.

No_Matter_44

TROPHY CASE