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[Discuss-gnuradio] Re: New external clock board for USRP

From: Alexander Chemeris
Subject: [Discuss-gnuradio] Re: New external clock board for USRP
Date: Fri, 30 Oct 2009 15:02:16 +0300

Hi all,

Status update - PCBs for the first batch are ready and we'll start populating
soon. To date we're on time! :)
See some PCB pictures here:
Only when you hold it in hands, you realize how small and densely populated
it is for all its features.

On Tue, Oct 20, 2009 at 01:31, Alexander Chemeris
<address@hidden> wrote:
> Hi all,
> As I wrote in my previous mail, we're working on an universal clock
> source for USRP (and not only for USRP). It is based on 0.28ppm TCXO
> from Connor Winfield [1], National Semiconductor LMX2531 VCO+PLL [2]
> and LMK01000 CD [3] for clock generation and Atmel ATUSB for control.
> So far we've finished PCB design and working on production of the first
> 25 units. We'll reserve 5 of them for our own use and testing of
> different options, 8 others are requested by community people, so there
> are more then 10 left for sale. We plan to finish production at
> the beginning of Dec and take units to 26C3. If you plan to attend it,
> you have a great chance to see them, play with them and take some of
> them with you. ;)
> As we promised, units form this experimental batch will be sold out
> for only $100 or 66EUR (without shipping). We kindly invite everyone
> interested in such unit to get one and try fitting it to your setup.
> Also we need your help determining the best feature set for the unit
> (read on for the ample list of possible features). We aim at creating
> a really flexible and cheap clocking unit, which may used by a broad
> GnuRadio community and will best fit its needs. Unit with open source
> software and open hardware.
> Now, lets get to facts. Board dimensions are 86x44mm (3.4" x 1.7") -
> it is designed to work inside of USRP box with RFX boards installed
> with no external connections.
> Default distribution version includes:
> 1) Clock board with default options
> 2) U.FL to SMA cable to connect to USRP
> 3) Power cable to connect to USRP's fan connector
> Default board options:
> 1) Control from miniUSB or 16-pin connector on USRP daughter boards.
> It will be possible to write a GNURadio block to control clocks right
> from GNURadio flowgraph!
> 2) Power from 2-pin connector for connecting to USRP fan power
> connector and 2-pin pass-throw to connect fan to. That is board is
> connected between USRP and fan.
> 3) One U.FL clock output with ability to generate frequency in the main
> range 2.84-65.83MHz, and additional ranges 65.91-71.82MHz,
> 72.5-79MHz, and more ranges higher with <=0.44Hz step. Output
> levels are CMOS. This means that you can tune your clock precisely
> ti whatever frequency you want.
> 4) Initial frequency calibration 1ppm, temperature stability 0.28ppm,
> holdover stability over 24h 0.32ppm [1]. Clock jitter will be measured
> when first units arrive to us, I'll post measurement results here.
> Pretty simple and flexible isn't it? But what makes this clock unit really
> universal is a set of available options. You may solder them by yourself
> or request ready-to-use units from us - I will make some notes on price
> changes and options compatibility below, mail me for details if you're
> interested in particular configuration. We want to be as flexible as
> possible to fulfill community need in flexible clock source.
> So, basic additional options include:
> 1) Power may be taken from 2-pin connector, 6V jack input or from USB.
> All power options are mutually exclusive.
> 2) COM-port with RS-232 levels for clock control. This will add about 3.5$
> to the price.
> 3) Up to 5 more additional U.FL outputs (6 outputs altogether), which
> share VCO frequency, but may be independently divided in clock
> distributor. 5 additional connectors will add 8-9$ to the price.
> 4*) Output levels may be (a) 4 LVPECL (or CMOS) outputs and 2 LVDS
> outputs, (b) 6 LVPECL (or CMOS) outputs, (c) 6 LVDS outputs.
> 5) SMA connector may be soldered instead of one of U.FL with CMOS
> levels. It will add 4.5$ to the price.
> 6) SMA connector with direct VCO output bypassing clock distributor.
> It will add 4.5$ to the price.
> 7) SMA connector for external clock source. This way onboard
> oscillator should be disabled by resistors soldering or should not be
> present. It will add 4.5$ to the price.
> 8*) Oscillator could be changed to 0.5ppm. This will save you 7.5$.
> 9*) VCO+PLL with clock divider could be changed to clock divider
> and multiplier. In this case you won't be able to tune your clock
> precisely, but you'll be able to generate, e.g. 13MHz, 26MHz and 62MHz
> from a single oscillator.
> 10*) Frequency range could be extended to 1.87-94.75MHz (and more
> ranges higher) at the price of more phase noise.
> 11*) For nerds only - unit may be used without onboard controller by
> direct access to VCO+PLL pins. But this is roughly equivalent to
> a VCO starter kit and obviously is not compatible with features like
> SPI/USB/RS232 control, and can't be used with power from USRP.
> 12) 1pps external signal may be used to tame the clock to external
> GPS unit. It will be passed to ATMega's interrupt input, so you
> should keep in mind that this will need a lot of software work for filtering
> out jitter, generated by it. We don't plan to develop this software at
> least now, but anyone who need this is welcome to take it.
> * These options is not immediately available because of changes in
> components list. Some options need testing before we can offer units
> with them. Some options available for small orders, some available
> only for volume orders. And sure, you can solder them by yourself.
> Mail me for details, if you're interested.
> There are two big options, which touches a big part of the unit and are
> very much experimental. We can't guarantee that they will work,
> but we think they will. :)
> * TCXO with VCO+PLL could be replaced with VCTCXO with DAC.
> DAC can be 12-bit linear or 16-bit delta-sigma. This will make it
> about 20$ cheaper then default bundle if we produce it in volume.
> The downside of this is that frequency range is much smaller and
> more calibration is needed.
> * GPS chip could be actually installed right on board to provide
> 1pps signal. PCB is designed to be used with cheap EB230 GPS
> Module and will add about 40$ to the price. But there are some small
> limitations - you can't use RS232 output with it, only 5 output channels
> are possible. Same notes on software as for 1pps input applies.
> We're working on detailed documentation and will make it available
> as soon as possible.
> 1. http://www.conwin.com/datasheets/tx/tx236.pdf
> 2. http://www.national.com/ds/LM/LMX2531LQ1515E.pdf
> 3. http://www.national.com/ds/LM/LMK01000.pdf
> --
> Regards,
> Alexander Chemeris.

Alexander Chemeris.

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