DOM MB Rev 3 Home Page
As built
Changes motivated by testing
of Rev 3.
Pre-Build Testing
Analog Front End Test Results
The ATWD presents an annoyingly high load capacitive to its
driver. Typical operational amplifiers are sensitive to
load capacitance. When the load capacitance exceeds an allowed value,
the amplifier becomes unstable. The instability takes the form of
damped oscillations which become part of fast rising waveforms.
The usual method for dealing with symptom is to place a resistor
between the operational amplifier output and the load. The larger
the resistor, the lower the roll-off frequency... as determined by the
R-C time constant.
The following studies were performed to discover optimum component
values for the Rev 3 main board design.
Output resistance study for HFA1135
driving ATWD Input: (paradigm for signal path of ATWD Ch. 0 signal path)
Output resistance study for HFA1135 driving ATWD Input: (paradigm for
signal path of ATWD Ch. 1 signal path)
Output resistance study for OPA689 driving
ATWD Input: (an exercise in performance evaluation)
The OPA689, a voltage feedback amplifier, and HFA1135, a current
feedback amplifier, both deliver about the
same output current, according to their data sheets. The
OPA689 data sheet depicts it as driving a 500 ohm load, whereas the
HFA1135 data sheet depicts it driving a 100 ohm load (back-terminated
50 ohm output).
The finished result: PMT amplifier
chain performance at various input levels
Part Selection Table
Part changes pending and completed
Some Layout Checks
DOM MB to Delay Board Interface
Schematic as of September 18, 2003
DOM MB (pdf format) Also
available as an OrCAD design file. The Mentor version could be
tar'd up, if needed.
Status Report (powerpoint)
October 14 Change Highlights