1. RAD Engineering BLM 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.  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% Basic Checks on Signal Lines

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 1’s & 0’s.  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 File Name: BLMBKPLN01.TIF Channel 3 sits at a DC level of about 3.0 Volts. Peak on transients measure around 820 mv. Scope view from slot 12 (slot 9 (halfway) from slot 4, the driven slot).

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 File Name: BLMBKPLN08.TIF Simulating a fully loaded backplane. Channel 1 Overshoot and Preshoot measurements displayed. Scope view from slot 12.

15. RAD Engineering VME J2 Backplane File Name: BLMBKPLN09.TIF Setup same as BLMBKPLN08.TIF Except: Pattern Generator period decreased to 50ns from 100ns. Scope view from slot 12.

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 File Name: BLMBKPLN11.TIF Setup same as BLMBKPLN10.TIF Except: Pattern Generator period decreased to 50ns from 100ns. Scope view from slot 21.

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.