PLL tricks

If the cycle time of the 10MHz waveform - 100nsec - is equated to a full-s cale of 1V then 1psec is 10uV. A Faulkner and Harding long-tailed pair phas e detector built around a a monolithic dual transistor can do that well wit hout any effort. The equivalent with a dual FET can do better (but you need a bigger gate drive than you need base drive - bigger than you can easily get directly from ECLinPS).

E.A.Faulkner and D.W.Harding - Journal of Scientific Instruments (UK) volum e 43 starting on page 97 (1966). J. Sci. Instr. published two other variati ons in 1968. It wasn't rocket science then, and it certainly isn't now.

In other words the offset performance required is small, but well short of horrendously small. Since - as we've worked out - the PLL is there to keep the 155.52MHz in frequency lock with the 10MHz reference, the absolute offs et doesn't matter (though it won't be big).

He also points out that the gain depends on the jitter level. Designing a s table phase locked loop around a phase detector with uncertain gain is tric ky.

Product detectors have a very stable and predictable gain (in volts per rad ian), and they inject a great deal less random noise into the loop.

My impression is that John got his bang-bang detector to work by his usual exhaustive fiddling, and hasn't explored the other options as carefully as he might have.

We usually do DDS sources in an FPGA, with just an external DAC. That's much cheaper and easier to interface than a bought DDS chip.

We have an upcoming project where we plan to use a little ARM CPU, LPC1768, to do software DDS into its own 10-bit DAC, to generate sine waves around 400 Hz. That should be fun.

DDS chips have a fixed binary modulus or 2^32 or 2^48 or whatever, so that you can't get an exact frequency match to any number that isn't a power of two.

Well i suppose you could look through the data sheets of a few dedicated DDS ICs. Like:

It seems that Analog Devices pretty much owns the market, but seems to have about 50 or so base models. Found some Intersil as well.

Of course there is Wikipedia but they miss a lot or even get some stuff wrong. It points to a good tutorial though:

?-)

Mullard's (now Ferroxcube's) nickel-zinc ferrite cores (blue series) were touted as having an equal and opposite temperature coefficient to polystyrene capacitors.

And if the filtered output of the phase detector is only going to have useful content at around 500Hz and below, you could run an A/D converter on the crudely filtered output and do the serious frequency shaping digitally.

You'd want about 20-bits at the output, but that's easy enough at 500Hz and below.

You seem to be missing my point. I am saying that many DDS circuits are NOT dedicated chips. They are easily built in FPGAs and are even implemented in software using CPU chips. Dedicated DDS chips likely have a small share of the total DDS designs.

I did look at the IEEE link and noticed the paper talks about "truncated" phase accumulator outputs. It made me remember that the last DDS design I did was for a 24 bit ADC/DAC and my look up table capacity was quite limited. I implemented table folding and performed linear interpolation to squeeze as much as I could from my resources.

I'm remembering more of the details now. I didn't want to use a binary accumulator because it would not give me exact rates for the CODEC sample rates in use (multiples of 8 kHz). So the upper N bits were binary but the lower bits had a factor of 3 and maybe some 5s. The binary section had 2 bits to implement the table folding and the rest were used in the table lookup. Some of the lower bits were used for interpolation. The end result was rather better than I first had feared.

So why are you chewing on the ankles of the ankle biter?

The gates and sources shorted together? I'm not familiar with the common gate-source amplifier configuration. I thought I was just not reading the schematic correctly. I think this makes the device into a resistor, no? I could see a negative resistance oscillating maybe. I just have never seen this before.

They are fets, so it makes it easy to combine them.

It's not like dealing with bipolar where you need ballasting resistors, or was that ballerina resistors! :)

Jamie

is.

from LC

have a

filter

on

of 1

native LC

Wow. I really sent that. I meant any frequency or phase parameter that would normally just follow tempco. I must have been really sleepy.

A forcing function versus tempco, how off the wall can i get?

?=(

I think we are not communicating. It looks to me like the sources are connected TO the gates. Is that right? If not, what is connected to what?

You're a tiresome idiot. Bye.

And yet you can't resist biting the ankles yourself.

That's neat. Thanks.

ChesterW

On a sunny day (Tue, 16 Sep 2014 08:27:45 -0700) it happened John Larkin wrote in :

John, I cannot find the original posting of you (yesterday?) with the laser building setup, but I will try to give my (probably wrong) opinion on that setup here anyway. You can verbatim giveittothem as far as I am concerned.

My simple "understanding"

Here it goes: Top down does not work (but you already know that, but do they?).

This is how *I* would go about it.

So, as you want to control room temperature the best place for a thermostat is in the room, IN THE SAME WAY assuming they have some smaller guide (alignment whatever) lasers that can also fire on a pulse, put optical detectors as close to the target as possible, one looking at each laser. Repeatedly trigger one 'guide' laser from wherever (moon if must be), and then use a feedback signal (DC control voltage) to align the other optical pulses so they co-incide as good as possible (femto, atta, you name it), and then when this phase lock in the guide lasers is accurate enough, fire the big ones. That is all.

It does not create so many jobs for industries (like yours), but might make it easier to get the pulses at the same time. no jippyyes (GPS ), no pee-pee-esses, no problems.

OK, the reason Von Braun reached the moon and managed to get people back is that he was interested in the result, not so much in the job creation aspect (of creating a monster project).

And I do not even know if all that laser shooting will ever lead to sustainable fusion.

PS I came up with this in bed last night before falling asleep. Amazing ain't it!

On a sunny day (Tue, 16 Sep 2014 16:45:59 -0400) it happened rickman wrote in :

So what

On a sunny day (Tue, 16 Sep 2014 16:48:23 -0400) it happened rickman wrote in :

I have repeatedly wondered iy you are still in highschool or kindergarten?

What the heck is wrong with *you*? I ask you to explain a hand drawn schematic that I can't understand and you get weird. jeeze

I was hoping to understand what you had done.

On a sunny day (Tue, 16 Sep 2014 18:25:52 +0100) it happened "Kevin Aylward" wrote in :

Well, yes, multiplying will also multiply any deviation in frequency of course.

I can say this about LC based UHF VCOs: I use for example the Firenza vco190-1572t.pdf at 1.5 GHz (GPS frequency):

Frequency Range - 1540 1572 1605 MHz X Tuning Voltage: 1540 MHz 1 1.4 Vdc X 1605 MHz 3.6 3.9 Vdc X Tuning Sensitivity - 29 34 39 MHz/V X Output Power - -3 0 3 dBm X Output Phase Noise: 10 kHz -106 -100 dBc/Hz

On a sunny day (Wed, 17 Sep 2014 03:19:11 -0400) it happened rickman wrote in :

Did you not see the words "in parallel" ? John is right, you really need to pick up some hobby.