Preamplifier Prototype I

• PCB Layout and Schematic – ​PCB • ​SCH
• Photos of prototype: ​Photo 1 • ​Photo 2 • ​Photo 3 • ​Photo 4

Prototype passed a signal, though not without an oscillation at ~350MHz. Pictured is the result of sending a 500mV square wave with a 1ms period and a 10% duty cycle.

• Oscillation photos: ​Photo 1 • ​Photo 2

Preamplifier Prototype II

• PCB Layout and Schematic – ​PCB • ​SCH • ​PDF
• BOM – ​PDF • ​CSV
• PCB Photos: ​Front • ​Back

New PCB layout uses a 4-layer board design, and strictly adheres to board layout suggestions in TI datasheets for both the OPA847 and THS3201. This design does not oscillate. A -200mV DC offset exists when the test pulse cable is connected. If undesirable, can be corrected with a simple offset nulling circuit connected to U1-3 (non-inverting input of OPA847).

Update: 9/26/2011 An oscillation has been discovered at 700MHz with a peak to peak voltage of ~120mV. Removal of the .36pF capacitor (C3) in the feedback loop of the OPA847 solves this problem. Smaller oscillations still exist at ~20mV at close to 100MHz, and are currently being addressed.

Update: 9/28/11

• Oscillation at ~100MHz with 2nd opamp disconnected (R11 removed)

​pic

• R11 changed to 1k
  • 5pF input ​pic
  • 10pF input ​pic

• 100 ohm resistor was placed in series between the output of the photodiode and input of OPA847 (U1-2).
  • 10pF input ​pic

• 100pF bypass capacitor added in parallel to both power supplies

10pF input ​pic 1 ​pic 2 ​pic 3

• R11 changed to 4k - severely decreased oscillation, added 30mV offset.
  • 10pF input ​pic
  • 10pF input (avg) ​pic

CompactPCI Power Board

The CompactPCI Power Board is a two slot wide 6u cPCI backplane that provides ATX power and RS232 breakouts for a single XCalibur 4301 module. Please note that on the version 1 board the ATX 5VSB is connected to ATX 5V. This will prevent the ATX power supply from starting up. Therefore you must not supply the 5VSB to the version 1 board. It is recommended to cut the 5VSB wire ATX pin 9 purple (see ​http://en.wikipedia.org/wiki/ATX#Power_supply). This problem is resolved in version 1.1.

• ​cPCI_backplane_v1.1.dxf
• ​cPCI_backplane_v1.1.zip
• ​cPCI_backplane_v1.zip
  • ​cPCI_backplane_v1_sch.pdf
  • ​cPCI_backplane_v1_pcb.pdf
• ​cPCI_backplane_v1_BOM.xlsx

The original idea was to design a one-slot backplane-like board which would hold two connectors to mate with the J1 and J2 CompactPCI connectors on the processor board to supply power.

• ​Mouser order
• ​CompactPCI Draft Standard
• ​XCalibur 4301 manual
• ​XIt4103-DS.pdf

Other Documents

• ​ADC3925 User Manual
• ​EVI_ReceiverAmpCircuit.pdf
• ​SBOA122
• ​Photodiode Amplifiers
• ​DWEL-1.ods
• ​G8376
• ​OPA847
  • ​PSPICE model

Design Notes

ADC3925 input is 50 ohms, 0dBm full scale (225mV). 10 bits implies 0.2mV or so LSB.