silicon oscillators

Has anyone used silicon oscillators? I'd like to stock a few SOT-23 oscillators to replace quartz crystal oscillators for non-critical stuff. Something cheap, of course.

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin
Loading thread data ...

I know that MicroChip has some semi-stable oscillators (I designed some for them :-)

Whether they are available stand-alone, I don't know. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

LTC has nice stuff, but it costs as much as an XO.

The MEMS oscillators seem to be expensive, too.

A CMOS oscillator would be a tiny chip with three wire bonds. Why wouldn't that cost 10 cents? OK, it's trimmed, so 11 cents.

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

What kind of frequencies and stability are you looking for? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

Perhaps not what you're looking for, but I put a Silicon Labs Si5340 into a product recently. It has a 14GHz internal VCO with four frac-N output dividers, and a frac-N feedback divider that allows it to synthesise just about any four frequencies up to 800MHz to better than 0.1ppm. If the frequencies you want are integer numbers of Hz, it will synthesise them with 0ppm error. At least it did that for all the test frequencies I tried. The frac-N dividers have dynamic phase adjusters to help reduce the jitter due to the fractional N division process. They don't say how this is done, but I assume that they get multiple phases from the 14GHz VCO and switch between them.

It's programmable over I2C or SPI. It also has a one-time programmable memory so you can get it to power up with the frequencies you want, but I'm not using that in my application.

I used a 48MHz TXCO as the input reference.

The datasheet doesn't give phase noise plots. (The part is new. I expect phase noise plots to turn up in future releases.)

I tried to measure the performance. I couldn't see any but the carrier above the noise floor of my spectrum analyser at any span / rbw setting. Ok, I need a better spectrum analyser. With the four outputs set to different frequencies, I measured crosstalk between adjacent outputs at about -80dB.

I don't have access to a phase noise test set any more so I can't do any real phase noise measurements :(

On my trusty Agilent scope (20GSa/s, not sure of jitter spec), I measured the relative jitter between the Si5340 outputs. This type of measurement shows up the jitter from the output dividers but not the VCO. At 600MHz, with all the test outputs at the same frequency I measured about 30ps p-p on infinite persistence. I repeated the same test with frequency offsets, e.g. output 1 was 600MHz, output 2 was 600.0000001MHz, etc. causing the traces to drift slowly past each other on the scope. The jitter seemed to be about 50ps p-p.

I think the performance is good enough for my needs. A decade back, that sort of performance on four channels would have cost a few hundred dollars [VCSOs, buffers, PLL per channel]. Now it's $20.

Regards, Allan

Reply to
Allan Herriman

10, 25, 100 MHz would be handy. 1% looks do-able in silicon oscillators.
--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

I've been using the Silicon Laboratories parts (like 501BAA16M0000CAF) but they cost about $0.70 @ 1k. Typical crystal oscillator type specs,

20ppm or 50ppm. Where can you get a SOT23 part with a decent (ie better than 0.1%) spec at anything near $0.10. I found some ST parts on Digikey at $0.26 on a 3k reel but they had no stock, 1.5% spec.

Michael Kellett

Reply to
MK

I would imagine 1% would be easy at roughly room temperature, but you could get a lot of temperature dependence for the frequency.

The built-in oscillators (which I /think/ are CMOS oscillators) in Freescale Kinetis microcontrollers are around 0.1% at room temperature, according to the samples I took. Since the cheapest of this chips is a Cortex M0+ microcontroller at about 1mm x 2mm for less than 50 cents, I would not expect a high price for a stand-alone oscillator.

Reply to
David Brown

I'm confused about what you mean by a silicon oscillator. You mean some Schmidt trigger inverter and RC thing?

George H.

Reply to
George Herold

Exactly. We use NXP ARM chips that have excellent oscillators inside.

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

Well, a fancier version, more stable. They are inside lots of uP chips, and LTC sells them as standalone oscillators, but they seem expensive to me.

Looks like I can buy an ARM chip for 50 cents and use it just for the oscillator inside... for 1/3 the price of an LTC oscillator.

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

Are you talking about the micromachined silicon resonator MEMS oscillators, or the tweaked ring oscillators of MCUs? Their jitter behaviour is going to be pretty different, I expect.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
 Click to see the full signature
Reply to
Phil Hobbs

The "silicon oscillators" are just analog circuits, compensated RC oscillators of some sort. Power consumption and TC are low, so they are probably not ring oscillators, I'm guessing. Maybe an integrated

555 sort of thing? Silicon capacitors are excellent, and good current sources can be done on-chip.

MEMS oscillators generally cost more than XOs!

--
John Larkin         Highland Technology, Inc 

jlarkin att highlandtechnology dott com 
 Click to see the full signature
Reply to
John Larkin

AFAIK, there are two main types: LC and MEMS.

In the former case, a shielding can is formed by tracks and vias in every metallization layer, then planar structures such as spiral inductors, transmission lines, etc. are fabricated inside. (The 'tub' structure may not be strictly necessary, but silicon probably makes an awful ground plane. RF chips incorporating tuners and amplifiers would still use shielding for internal isolation though.)

Such inductors have ratty Q (peaking at 5-15 or so in the 4-20GHz range), but they're good enough to make simple things with. So, add varactors and compensation circuitry, and you've got a reasonably stable oscillator (and, as it turns out, a pretty stable one in general).

The MEMS product uses electrostatic deflection on a tuning fork, or something like that, which I presume has much better Q, and probably lower operating frequency. I would think they're sensitive to rotation or acceleration, but that's probably nulled out by design (whereas, MEMS accelerometers optimize for the opposite effect..).

In either case, a DDS or whatever furnishes a programmable output frequency. Such devices are often programmed by the supplier as Value-Add parts.

Both components are comparable to crystal oscillators (which are arguably MEMS devices as well, but not monolithic), though no one really talks about the close-in versus far-out stability / jitter tradeoffs, if any.

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
 Click to see the full signature
Reply to
Tim Williams

[snip]

Most are trimmed RC oscillators... with SiCr resistors and SiO2 capacitors the stability after trimming is quite respectable. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
 Click to see the full signature
Reply to
Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Really, I would've thought that too noisy; it's occasionally even suggested as a TRNG source in MCUs (compare internal RC to external XTAL, siphon off LSBs of frequency counting).

Or maybe that's just the shitty MCUs. :)

Tim

--
Seven Transistor Labs 
Electrical Engineering Consultation 
 Click to see the full signature
Reply to
Tim Williams

I'm surprised to hear you say that. Every time I've looked at them they were very price competitive. I think they would not sell at all if they weren't. It's not like they do much better than an XO in any way.

--

Rick
Reply to
rickman

Everything according to the requirements. Many designs only need timing accuracy good enough to run a UART. Why worry about 100 ppm timing when you are operating a toothbrush, a microwave or many, many other devices.

Oh, I forgot about that special grade, there's A, B and "Shitty" in the oscillator families.

--

Rick
Reply to
rickman

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.