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Feature #3272

next-generation osmo-e1-xcvr board

Added by laforge 9 days ago. Updated about 23 hours ago.

Status:
New
Priority:
Normal
Assignee:
Target version:
-
Start date:
05/15/2018
Due date:
% Done:

100%


Description

Since osmo-e1-xcvr is full of bugs, and it doesn't yet include a microcontroller, it might be worth collecting ideas about a next board version.

As soon as I have my SAM4S firmware code working, I guess it would be a good idea to make a board that contains
  • a (fixed) osmo-e1-xcvr
    • no missing GND on Vref resistor
    • no wrong transformer symbol/layout
    • proper silkscreen
    • make sure IC pin is connected to GND as specified in data sheet
  • a suitable SAM4S
  • a first version of the GPS-DO (@mschramm: we can use the DAC and maybe also the voltage reference from sob-jb, but drive a 30.72 MHz OCXO from it)

For people working on a non-SAM4S approach, that part could simply be DNP, as long as we still have headers (possibly with identical pinout) for SPI + serial data stream, it would remain copatible. Basically one could populate either the LIU+magnetics part, and/or the SAM3+USB part, and/or the GPS-DO part.

GNS2201_datasheet.pdf (1.14 MB) laforge, 05/16/2018 08:07 PM

GNS3301_datasheet.pdf (1.28 MB) laforge, 05/16/2018 08:08 PM

GNS3301B_datasheet.pdf (1.19 MB) laforge, 05/16/2018 08:08 PM

Venus828F_PB_v1.pdf (177 KB) laforge, 05/16/2018 08:08 PM

T604.pdf - Connor-Winfield T604 VCTCXO (280ppb) (1.47 MB) laforge, 05/16/2018 08:11 PM

XO-0040-VT-CMOSTYPE.pdf - Taitien VT VCXO (50ppm) (298 KB) laforge, 05/16/2018 08:13 PM

GNS3301.lbr - EAGLE library for GNS3301/2201 (18.6 KB) laforge, 05/23/2018 10:55 AM


Subtasks

Feature #3275: release connor-winfield + SJ-2523 EAGLE footprints Resolvedmschramm


Related issues

Related to E1/T1 Adapter - Feature #3237: Come up with GPS-DO design for E1 Interface New 05/04/2018

History

#1 Updated by laforge 9 days ago

another idea is to make the LIU usable (Even for transmit) without SPI. There are some strapping options. It is's possible without too much effort, we could witch from SPI to strapping mode - but only if all the related strapping pins would then actually put it in regular E1 mode with Rx/Tx enabled, single-rail, ...

#2 Updated by laforge 8 days ago

In terms of GPS receivers, I would propose the following candidates:

#3 Updated by laforge 8 days ago

  • Checklist item SAM4S added
  • Checklist item GPS receiver with 1PPS output added
  • Checklist item VC[TC]XO driven by DAC [of SAM4?] added
  • Checklist item possibly precision voltage reference for DAC? added
  • Checklist item LIU added
  • Checklist item magnetics matching to LIU and with fixed symbol/footprint added
  • Checklist item SAM-BA capable UART (PA9/PA10?) on 2.5mm jack (SJ-2523-SMT) added
  • File T604.pdf added
  • File XO-0040-VT-CMOSTYPE.pdf added
In terms of 30.72 MHz oscillator, we have identified the following models:

I would think we ideally put both footprints on one board to experiment with.

NOTE: A 30.72MHz clock for the SAM4S means it's USB SAM-BA loader can no longer be used. This means we need to expose SAM-BA on UART (using 2.5mm jack so osomocom-style serial cables can be used for recovery flashing)

#4 Updated by tnt 8 days ago

Precision voltage reference is only required if you want to 'save' a calibration value. When locked to GPS, then it doesn't matter.

And of course that 'saved' value would really only work in the same condition (temp, etc ...) because even if your voltage reference and tune voltage is perfect, nothing guarantees that your xtal is always going to respond to it the same way.

#5 Updated by laforge 8 days ago

On Wed, May 16, 2018 at 08:48:57PM +0000, tnt [REDMINE] wrote:

Precision voltage reference is only required if you want to 'save' a calibration value. When locked to GPS, then it doesn't matter.

yes, I think it's useful to have some kind of "cold start" behavior where the clock is reasonable even in
absence of GPS (or before GPS is locked). In the end we might be able to do without any of that. But at
least for now it seems interesting to keep all options open.

And of course that 'saved' value would really only work in the same condition (temp, etc ...) because even if your voltage reference and tune voltage is perfect, nothing guarantees that your xtal is always going to respond to it the same way.

Is it that bad? I understand there's voltage / load / temperature related implications on frequency, but if
I'm using the same board with the exact same voltage / load / temperature, without having a year of time in
between, then the outcome should be rather close to the situation before?

I guess we need to do some testing on all of this, including how the relevant BTSs react to E1 clock error
[and over what period, ...]

#6 Updated by laforge 7 days ago

  • Related to Feature #3237: Come up with GPS-DO design for E1 Interface added

#7 Updated by tnt 7 days ago

I'm not sure how "bad" it is. But it's more in relation with what the gain of using a precision voltage reference rather than just relying on the "normal" regulator.
If the frequency error you get from saving and restoring a DAC value comes mainly for change in the actual DAC output because of supply variation or not.

#8 Updated by vogelchr 7 days ago

tnt wrote:

I'm not sure how "bad" it is. But it's more in relation with what the gain of using a precision voltage reference rather than just relying on the "normal" regulator.
If the frequency error you get from saving and restoring a DAC value comes mainly for change in the actual DAC output because of supply variation or not.

Taitien VCXO (VTEUALJANF-30.720000)

  • 50ppm stability, pulling range ±50 ppm (0,3 … 3,0V) ≈ 16,7 ppm/V

Connor Winfield VCTCXO (T604-030.72M)

  • 0,28 ppm stability, abs. freq. tolerance ±4,7 ppm
  • stability vs. load, voltage ≤ 0,05 ppm
  • "holdover" ≤ 0,3 ppm
  • pulling range is ±10 ppm (0,3 … 3,0V) ≈ 3,33 ppm/V

Standard voltage regulator: http://www.ti.com/lit/ds/symlink/lm1117.pdf

Page 9, Fig. 6, Temperature Stability is certainly better than ±0,5%,
let's just say it's better than ±10mV for brevity, and let's ignore the
variation with load, because we could use a separate Vreg for Vref + VCXO.

Assume that a voltage regulator with 3,3V±10mV is used as a voltage reference,
this means that a control voltage held at approx. Vcc/2 moves by 5mV which
would be 16ppb (Connor) or 83,5 ppb (Taitien).

#9 Updated by laforge 7 days ago

laforge wrote:

In terms of GPS receivers, I would propose the following candidates: [...]

The GNS2201/3301 appear to be the favorites so far. the Venus828 is less expensive, but is not typically stocked in Germany and we'd have 6-8 weeks lead time for every production, which is not a good idea. GNS GmbH typically has EAGLE library footprints available, so we don't have to create that one. I'll inquire.

#10 Updated by mschramm 6 days ago

(As the ticket has one subticket which is solved, it appears to be 100% solved too which isn't true ,) )

#11 Updated by laforge about 23 hours ago

laforge wrote:

GNS GmbH typically has EAGLE library footprints available, so we don't have to create that one. I'll inquire.

I got a response, see attached library.

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