Transcript Limitations of Op Amp Large-Signal Operation

Adaptive Optics
Deformable Mirror
Electronics Simulation
Pearl Yamaguchi
Subaru Telescope
National Astronomical
Observatory of Japan
Mentor: Stephen Colley
Outline
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Project Scope
Adaptive Optics
Deformable Mirror
Protecting the Deformable Mirror
Determinations
Project Scope
• Investigate ways of
protecting the
Deformable Mirror
– From sharp changes in
voltage
– Slew rate limit
• Concern
– Possible damage due to
rapid changes in drive
signals
Adaptive Optics
• Primary Components
of AO System
– Wavefront Sensor
– Control Computer
Image without AO
Image with AO
– Deformable Mirror
Bimorph Deformable Mirror
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Two piezoelectric wafers
Oppositely polarized
Array of electrodes
Dynamically compensates
for aberrations
• Expanding or contracting
with stimulus
Deformable Mirror Actuators
• Current AO System
36 actuators
• Second Generation AO
188 Actuators
Electrode pattern
– Inner and Outer segments
– Load on electronics appears
as pure capacitance
Project Objective
• Manufacturer suggested slew rate limit
100 Volts/ms
• Full scale range
+/- 400 Volts
• Ramping
insures limit
V
200V
100V
1ms
2 ms
time
Protection from Voltage Jumps
• Control Computer
• Digital to Analog Converters
• High Voltage Amplifiers
Control
Computer
D/A
Converter
HV
Amplifier
DM
Ideal safety feature here
High Voltage Amplifiers
• Current Limiting
to limit charging of
segment
• Capacitive Load
• Non-Linear
operation of
amplifiers
Electronics Simulation for
Deformable Mirror
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Implemented and expanded circuit
Using PSpice
Models behavior of circuit elements
Time and frequency response
Test validity of design considerations
Current Limiting
High Voltage Amplifiers
Significant Results
• Oscillates
• Unstable
• Eliminated as a
solution
Digital to Analog Converters
• Determine if digital logic implemented slew
rate limit is feasible
• Continue simulation of D/A Converters
• Test step limited slew rate
Control
Computer
D/A
Converter
HV
Amplifier
DM
Stepping Approximation
• Approximate ramp with Stepping
• Implement in digital logic
• D/A Converters
V
200V
100V
1ms
2 ms
time
Summary
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Protect the mirror
Created PSpice model
Ruled out High Voltage Amplifiers
V
Investigated
D/A
200V
Converters 100V
1ms
2 ms
time
Acknowledgements
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Stephen Colley, AO Project Engineer
Hideki Takami, AO Project Manager
Subaru Telescope, NAOJ
Center for Adaptive Optics
University of Hawaii, Manoa
This project is supported by the National Science Foundation Science
and Technology Center for Adaptive Optics, managed by the
University of California at Santa Cruz under cooperative agreement.
No. AST - 9876783