Skip to content
This repository has been archived by the owner on Oct 21, 2021. It is now read-only.

Front End Main Board Connectors

Jump to bottom
jboone edited this page Mar 5, 2013 · 14 revisions

Goals

  • Co-planar arrangement of front-end and main boards -- no stacking, as it has several potential problems: ventilation, access to SO-DIMM socket, enclosure dimension variations and options (e.g. SoB).
  • Connector-integrated ground plane or nearly 2:1 pin:signal count to support good signal integrity for high-speed buses.
  • Compact width (ideally less than 4" / 100mm), to keep main board size down, and reduce the spread of signal buses across the board, which would require more effort for length matching.
  • Low cost.
  • Durable -- many insertions, and low risk of damage during insertion.

Front-End Scenarios

2 x USB 3.0

  • 78 (2 x 39) 250 MHz signal-ended signals
  • 24 (2 x 12) 60 MHz single-ended signals
  • 44 (2 x 22) configuration signals -- maybe less depending on what signals can be hard-wired, maybe less if we can multiplex some number of these signals serially.

Total interface signals: 146.

Signals Common to All Scenarios

Front-end configuration signals:

  • 2 (1 x 2) EEPROM I2C
  • 8 (2 x 4) Assorted serial interface (I2C or SPI)
  • 8 (4 x 2) Clock reference (four differential clocks -- two in, two out?)

Support for supply and reference voltages:

  • 4 VUSB voltage (enough to carry 1A current).
  • 4 Regulated front-end voltage (enough to carry 1A current).
  • 2 I/O voltage references (variable, connected to FPGA banks).

Total common signals: 28.

Possible Options

Given the above signal requirements and no signal multiplexing, we need a connector that has at least 174 signals, and at least 102 grounds, or a ground plane that is integral to the connector's design.

Stacking

Benefits with stacking connectors

  • Physically smaller, due to smaller contact pitch.
  • Less signal skew due to smaller physical connector and less routing distance.
  • Higher pin count, due to smaller contact pitch. This makes USB 3.0 and HDMI MITM boards possible in a single connector.
  • Integrated ground blade options for controlled impedance and better high-frequency performance.

Complications with stacking connectors

  • More expensive, on average, than edge-card connectors. This assumes asymmetric connector cost of an edge-card interface, where one half of the mating pair requires only edge contacts, not a manufactured connector.
  • Clearance over main board components. Mated stacking heights of as little as 5mm are possible with the Samtech QTH/QSH. This would likely interfere with the SO-DIMM socket, USB 3.0 connector, power connector, and switching regulator inductor.
  • Heat from the main board and front-end board. Lower stacking heights leave almost no opportunity for convection.
  • Spacers are required to mechanically ensure that the front-end board does not contact components on the main board.
  • I assume they are more fragile than edge-card connectors, due to their more delicate design.

Potential options

  • QTH-090-01-F-D-A: $8.06, QSH-090-01-F-D-A: $7.90. Available from Digi-Key. Second sourced by TE Connectivity "MICTOR SB". Samtec offers example single-ended and differential six-layer board layouts that are tested for performance, but only under restrictive (open-source incompatible) license. There are general practices documented in their application notes that appear useful.
  • QTS-075-01-F-D-A: $6.72, QSS-075-01-F-D-A: $6.58.
  • QRM8-078-05.0-L-D-A: $10.41, QRF8-078-05.0-L-D-A: $10.41.
  • QMS-078-05.75-L-D-A: $11.47, QFS-078-04.25-L-D-A: $10.90.
  • QMSS-078-06.75-L-D-A: $15.57, QFSS-078-04.25-L-D-A: $14.80.
  • ERM5-075-02.0-L-DV-TR: $4.70, ERF5-075-05.0-L-DV-TR: $4.91.
  • ERM8-075-02.0-L-DV-TR: $4.70, ERF8-075-05.0-L-DV-TR: $4.91.
  • SEAM8-30-S02.0-S-06-2-K-TR: $14.01, SEAF8-30-05.0-S-06-2-K-TR: $12.96.

Right-Angle and Edge-Mount

Potential options

  • QTH-RA: QTH-090-01-[F|L]-D-RA-WT-[PGP|K] -- not available? Samtec says "preliminary".
  • QSH-RA: QSH-090-01-[F|L]-D-RA-WT-[GP|K] -- not available? Samtec says "preliminary".
  • QTS-RA: QTS-100-01-[F|L]-D-RA-WT[|-SP] -- $13.13@1000.
    • QTS-100-01-F-D-RA-WT is $13.69@1000 via Samtec.
    • QTS-100-01-L-D-RA-WT is $15.96@1000 via Samtec.
  • QSS-RA: QSS-100-01-[F|L]-D-RA-WT -- $16.32@1000.
    • QSS-100-01-F-D-RA-WT is $17.01@1000 via Samtec.
    • QSS-100-01-L-D-RA-WT is $19.86@1000 via Samtec.
  • QRM8-RA: QRM8-078-01[|-L]-RA-GP-[K|TR] -- 156 pins, requires multiplexing
    • QRM8-078-01-L-RA-GP is $18.18@1000 via Samtec.
  • QRF8-RA: QRF8-078-01[|-L]-RA-GP-[K|TR] -- 156 pins, requires multiplexing
    • QRF8-078-01-L-RA-GP is $18.18@1000 via Samtec.
  • QMS-RA: QMS-[078|104]-01[|-SL]-D-RA[|-MG]-[K|TR] -- 156 pin model requires multiplexing
    • QMS-078-01-SL-D-RA is $17.86@1000 via Samtec.
  • QMS-EM: QMS-[078|104]-01[|-SL]-D-EM2[|-PC4][|-TR] -- 156 pin model requires multiplexing
    • QMS-078-01-SL-D-EM2 is $14.29@1000 via Samtec.
    • QMS-104-01-SL-D-EM2 is $17.69@1000 via Samtec.
  • QFS-RA: QFS-[078|104]-01[|-SL]-D-RA-[K|TR] -- 156 pin model requires multiplexing
    • QFS-078-01-SL-D-RA is $18.09@1000 via Samtec.
  • QFS-EM: QFS-[078|104]-01[|-SL]-D-EM2[|-TR] -- 156 pin model requires multiplexing
    • QFS-078-01-SL-D-EM2 is $14.70@1000 via Samtec.
    • QFS-104-01-SL-D-EM2 is $18.19@1000 via Samtec.
  • ERM8-RA: ERM8-075-01[|-L]-D-RA-[K|L][|-TR] -- no ground plane, 150 pins, requires multiplexing
  • ERF8-RA: ERF8-075-01[|-L]-D-RA-[L|EGP][|-TR] -- no ground plane, 150 pins, requires multiplexing
  • ERM8-EM: ERM8-075-01[|-L]-D[|-EM2]-[L|EGPS][|-TR] -- no ground plane, 150 pins, requires multiplexing
  • ERF8-EM: ERF8-075-01[|-L]-D[|-EM2][|-EGPS][|-TR] -- no ground plane, 150 pins, requires multiplexing
  • BTH-090-01-[F|L]-D-RA-WT[|-K], no ground plane(?), may not have enough pins
  • BSH-090-01-[F|L]-D-RA-WT[|-GP], no ground plane(?), may not have enough pins
Clone this wiki locally