BAW

Of course a crystal oscillator is a BAW device too. ;)

Cheers

Phil Hobbs

They look very nice, but where do you see such low prices? Certainly not at Mouser or Digikey.

John

That's the 1K price on the TI page. Maybe 1/3 the price of a junky XO.

Don't get technical with me!

I wonder if it's all silicon, a sort of bulk MEMS thing. The price is absurd. I guess every one has to be trimmed to frequency.

This has got to crush the XO business. It looks like it's a single chip that's encapsulated like any other IC. XOs are complex and need hermetic cans.

Looking through this BAW app note

XOs used to use handmounted crystals. There's nothing all that complicated about them, but low volume manufacture tends to be a bit knife and fork.

As far as I can see these are surface acoustic wave devices. Integrated circuits are pretty well encapsulated. This one probably dumps any heat it generates into the board it is mounted on, which might run a bit warmer in a vacuum, but that would be the only risk I can see.

It does look more like bulk acoustic waves - hence the name! There is no cavity inside, so they should be immune to the effects of helium, unlike the oscillators that use MEMS resonators where it appears that helium can diffuse through the silicon to clog up the vacuum cavity. Phase noise performance looks excellent as is the temperature stability. John

You can look up the patent:

The patent text is voluntarily vague about the materials used for the reflector and resonator layers. They mention lots of examples, without clearly saying what they really used. I'd expect that most examples don't work.

Jeroen Belleman

The next step might be to have BAWs on uPs or FPGAs or watch circuits or something, super accurate clocks instead of external XOs or bad RC oscillators.

When they quote jitter at 0.1ps, does that translate to phase noise?

Phil's pretty good in that regard. There are some people who see everything in terms of equations and use higher mathematics to explain their function. A xtal oscillator would provide a very simple example for such persons to exhibit this (most unfortunate) character trait.

The data sheet does however: TI’s BAW resonator technology uses piezoelectric transduction to generate high-Q resonance at 2.5 GHz. The resonator is defined by the quadrilateral area overlaid by top and bottom electrodes. Alternating high- and low-acoustic impedance layers form acoustic mirrors beneath the resonant body to prevent acoustic energy leakage into the substrate. Furthermore, these acoustic mirrors are also placed on top of the resonator stack to protect the device from contamination and minimize energy leakage into the package materials. This unique dual-Bragg acoustic resonator (DBAR) allows efficient excitation without the need of costly vacuum cavities around the resonator. As a result, TI’s BAW resonator is immune to frequency drift caused by absorption of surface contaminants and can be directly placed in a non-hermetic plastic package with the oscillator IC in small standard oscillator footprints John

Phil is one of those people who can see equations in motion. I can't. I operate on instinct and simulation.

We have brainstormed on some pretty important projects and generated some ideas that influence most everyone here. The skills are complementary.

His book is good to have if you design electro-optics or low-level analog stuff.

Equations are fine (unavoidable anyway) in this science. But it's not helpful in the first instance to gain an intuitive idea of how something works - unless you're one of the people I mentioned above. This is my main issue with Tom Lee's otherwise superb book, 'Planar Microwave Engineering' where he typically launches into higher mathematics almost from the get-go.

I have that book. It's mostly useless. One equation will be a full page of fine print, and then the next page turns out to be one term of that equation.

Indeed. Not only that, but the mathematics is unfamiliar. I know most of the equations for transmission line theory by sight, but the ones Tom cites are completely different and tend to use a lot of Greek letters which relate to physical constants I've never even heard of. On the other hand, where he doesn't use unfamiliar mathematics, there's a *lot* in there I haven't seen any any other RF books which I find really interesting.

It's easier to design with a geometry for which there are good calculator programs.

We have used ATLC to do e/m simulations of transmission line cases.

I had to google ATLC simulator as I've not heard of it before. Anyway, these plots are all very interesting, but you have no way of verifying their accuracy AFAICS. You mentioned a while ago you had a good source for cheap but reasonable quality edge connectors (Aliexpress?) Can you post a link to them please?