RAD Engineering BLM VME J2 Backplane

1
RAD EngineeringBLM VME J2 Backplane

• Printed Circuit Board
• Backplane Crosstalk Comparison
• January 25, 2005

2
Initial Look at Crosstalk

• How does the RAD Engineering design affect
  crosstalk and signal quality?
• Where to start? Al suggests comparing what we
  have (RAD Engineering) with another commercial
  backplane.
• Fortunately? We have a Bicc-Vero VME J2
  backplane lying around.
• Not great, but something to start with.

3
Test Equipment Used

• Scope HP 54825A Infinium Oscilloscope, 500 MHz,
  2 Ga/s
• Probes HP 1160A Probes 500 MHz,
  10 Meg Ohm, 9pf
• Pattern Generator HP 16520A 50 M/bit
  Second Data Rate
• RAD Engineering VME J2 Backplane

4
Basic Checks on Signal Lines

• Backplane current draw with just built-in (B Row)
  terminations 0.304 Amps.
• Backplane current draw with built-in and Control
  Bus terminations 1.151 Amps.
• Measured termination voltages for Control Bus
  signal lines, D0-D7, pins 19-26.
• Pin 19 D0 2.993V, Pin 20 D1 3.001V, Pin 21
  D2 3.002V
• Pin 23 D3 2.998V, Pin 24 D4 2.999V, Pin 25
  D5 2.997V
• Pin 26 D6 2.994V, Pin 27 D7 2.997V
• VME spec. for termination voltage is 2.94V,
  /-10

5
Test Pulse Pattern

• Backplane Vcc 5.10V
• Input Pulse Level High 3.00V, Low 0.20V
• Output Pulse Level TTL (74F241 Buffer)
• Pulse Pattern has a 50ns or 100ns bit time.
• Initial Pulse Pattern is binary count sequence.
• Pulse Pattern then changes to all 1s 0s.
• Pattern Generator buffered output and signal of
  interest terminated properly at each end of the
  backplane (Standard VME Practice).

6
Test Signal Lines

• Drive Test signals on VME B Row pins.
• Scope Ch. 1, Pin 23 (D24), Color Yellow.
• Scope Ch. 2, Pin 25 (D26), Color Green.
• Scope Ch. 3, Pin 24 (D25), Color Purple.
• Pins 23 and 25 are driven at slot four by a
  74F241 (VME spec.) and properly terminated at
  each end of the backplane.
• Pin 24 (Channel 3) not driven but terminated.

7
Bicc-Vero VME J2 Backplane
Scope view from slot 12 (slot 9 (halfway) from
slot 4, the driven slot).

• File Name
• BLMBKPLN01.TIF
• Channel 3 sits
• at a DC level of
• about 3.0 Volts.
• Peak on transients
• measure around
• 820 mv.

8
RAD Engineering VME J2 Backplane
Scope view from slot 12 (slot 9 (halfway) from
slot 4, the driven slot).

• File Name
• BLMBKPLN04.TIF
• Channel 3 DC
• level is 3.0 V.
• Transients are 380 mv.
• This is less than half of the Bicc-Vero Backplane.

9
Bicc-Vero VME J2 Backplane
Scope Screen Dump viewed from slot 21 (last slot).

• File Name
• BLMBKPLN02.TIF
• With Channel 1 Overshoot and Preshoot
  measurements displayed.

10
RAD Engineering VME J2 Backplane
Scope Screen Dump viewed from slot 21 (last slot).

• File Name
• BLMBKPLN06.TIF
• With Channel 1 Overshoot and Preshoot
  measurements displayed.

11
Bicc-Vero VME J2 Backplane
Scope Screen Dump viewed from slot 21 (Last slot).

• File Name
• BLMBKPLN03.TIF
• Pattern Generator period decreased to 50ns from
  100ns.
• Channel 1 Overshoot and Preshoot measurements
  displayed.

12
RAD Engineering VME J2 Backplane
Scope Screen Dump viewed from slot 21 (Last slot).

• File Name
• BLMBKPLN07.TIF
• Pattern Generator period decreased to 50ns from
  100ns.
• Channel 1 Overshoot and Preshoot measurements
  displayed.

13
RAD Engineering VME J2 Backplane

• How would a fully loaded backplane affect the
  level of crosstalk seen on the signal line?
• How to simulate a fully loaded backplane?
• Slots 5-11 and 13-21 have a 18pf capacitor
  installed on the B Row between pins 22 (GND) and
  23 (D24)
• Simulated load is 16 x 18pf 288pf
• VME spec. is 20pf per slot (For Add/Data)

14
RAD Engineering VME J2 Backplane
Scope view from slot 12.

• File Name
• BLMBKPLN08.TIF
• Simulating a
• fully loaded
• backplane.
• Channel 1 Overshoot and Preshoot measurements
  displayed.

15
RAD Engineering VME J2 Backplane
Scope view from slot 12.

• File Name
• BLMBKPLN09.TIF
• Setup same as
• BLMBKPLN08.TIF
• Except
• Pattern Generator period decreased to 50ns from
  100ns.

16
RAD Engineering VME J2 Backplane
Scope view from slot 21.

• File Name
• BLMBKPLN10.TIF
• Simulating a
• fully loaded
• backplane.
• Slots 5-20 have
• a 18pf capacitor
• installed.

17
RAD Engineering VME J2 Backplane
Scope view from slot 21.

• File Name
• BLMBKPLN11.TIF
• Setup same as
• BLMBKPLN10.TIF
• Except
• Pattern Generator
• period decreased
• to 50ns from
• 100ns.

18
Comparison Summary

• Bicc-Vero VME J2 Backplane
• Crosstalk Amplitude 820 mv.
• RAD Engineering VME J2 Backplane
• Crosstalk Amplitude 380 mv.
• The RAD design uses many ground isolation islands
  between parallel traces.
• RAD Engineering Backplane Design appears to
  minimize the level of crosstalk.