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Feature #5892

open

design/build ext clock input board for PlutoSDR Rev.B

Added by laforge about 1 year ago. Updated 4 months ago.

Status:
Stalled
Priority:
Low
Assignee:
Target version:
-
Start date:
02/06/2023
Due date:
% Done:

70%

Resolution:
Spec Reference:

Description

We have a number of plutosdr devices at sysmocom, unfortunately all of them still RevB which unlike current RevD has no external clock input. Most of our use cases require a proper reference clock input, so I thought it might be a good idea to build a small board which contains the LTC6957HMS-3#PBF based input circuitry that was added in RevD. This circuit ensures that any square or sine clock can be used, at proper 50 Ohm impedance, over a wide range of levels.

The ext in / ext out ports should be SMA connectors, so that the resulting PCB can be panel-mounted by bulkhead-mounting those two SMA connectors to a face plate of whatever enclosure we're putting the plutosdr into.

The interconnect between the clock board and plutosdr can be made via u.fl as shown in https://coherent-receiver.com/wp-content/uploads/2018/01/umc-pluto-site.jpg

https://wiki.analog.com/university/tools/pluto/hacking/hardware


Files

plutosdr-revb-clkin.png View plutosdr-revb-clkin.png 71.8 KB laforge, 02/12/2023 04:55 PM
pluto-revb-orig.jpg View pluto-revb-orig.jpg 2.22 MB laforge, 07/02/2023 12:08 PM
pluto-revb-xo_removed.jpg View pluto-revb-xo_removed.jpg 2.18 MB laforge, 07/02/2023 12:08 PM
pluto-revb-pad_removed.jpg View pluto-revb-pad_removed.jpg 2.09 MB laforge, 07/02/2023 12:08 PM
pluto-revb-copper_scratched.jpg View pluto-revb-copper_scratched.jpg 2.52 MB laforge, 07/02/2023 12:08 PM
pluto-revb-ufl.jpg View pluto-revb-ufl.jpg 2.47 MB laforge, 07/02/2023 12:08 PM

Checklist

  • schematics
  • pcb layout
  • order pcb prototypes
  • order parts
  • assemble prototypes
  • test prototypes
  • test prototype attached to plutosdr RevB
Actions #1

Updated by laforge about 1 year ago

  • Checklist item schematics added
  • Checklist item pcb layout added
  • Checklist item order pcb prototypes added
  • Checklist item order parts added
  • Checklist item assemble prototypes added
  • Checklist item test prototypes added
  • Status changed from New to In Progress
  • % Done changed from 0 to 20

schematics finished; components arranged on 40x40mm PCBA. routing still pending

Actions #2

Updated by laforge about 1 year ago

  • Checklist item pcb layout set to Done
  • Checklist item order pcb prototypes set to Done
  • Status changed from In Progress to Stalled
  • % Done changed from 20 to 50
Actions #4

Updated by laforge about 1 year ago

  • Checklist item order parts set to Done
Actions #5

Updated by laforge 8 months ago

has been waiting for parts for months, now finally the U1 (LTC6957HMS-3) has arrived yesterday.

Actions #6

Updated by laforge 8 months ago

  • Checklist item assemble prototypes set to Done
Actions #7

Updated by laforge 8 months ago

  • Status changed from Stalled to In Progress

so, sadly the prototypes don't work. Debugging it now. Supply voltage of 3.3V is stable, input clock signal can be traced all the way up to the LTC, but no output is observed.

Actions #8

Updated by laforge 8 months ago

ah, ok. rather obvious: SD1/SD2 (shutdown1/shutdown2) are both pulled high using R1 (R85 in original schematics), but as we don't have the Q3 FET that can (under digital control) pullt them down, they are permanently in shutdown.

We should replace R1 to VCC with a 0R to GND.

Actions #9

Updated by laforge 8 months ago

  • Checklist item test prototype attached to plutosdr RevB added
  • Checklist item test prototypes set to Done
  • % Done changed from 50 to 70

laforge wrote in #note-8:

We should replace R1 to VCC with a 0R to GND.

and it works. I've reworked the prototypes and changed the design in https://gitea.osmocom.org/electronics/osmo-small-hardware/commit/dbd53d6df52089065254c2a5830343b423d3d5b8

Actions #10

Updated by laforge 8 months ago

Pictures of actual PlotoSDR side U.FL rework:

Original PlutoSDR RevB

XO removed using hot air

VCC pad removed

GND soldermask removed for U.FL

U.FL socket soldered

Actions #11

Updated by laforge 4 months ago

  • Status changed from In Progress to Stalled
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