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Alan Stummer
Research Lab Technologist |
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AOM Driver Redesign |
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I am curious who uses what. Are these webpages a waste of time, or are they any help to others? Are the circuits, software and utilities appearing in other labs? Please send your comments or suggestions or what you have used (or not) or schematics of your version or pictures or anything! Email me, or be creative and send a postcard! I want to hear from the vacuum! |
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NOTICE: This webpage and associated files are provided for reference only. This is not a kit site! It is a collection of my work here at the University of Toronto in the Physics department. If you are considering using any schematics, designs, or anything else from here then be warned that you had better know something of what you are about to do. No design is guaranteed in any way, including workable schematic, board layout, HDL code, embedded software, user software, component selection, documentation, webpages, or anything. All that said, if it says here it works then for me it worked. To make the project work may have involved undocumented additions, changes, deletions, tweaks, tunings, alterations, modifications, adjustments, waving of a wand while wearing a pointy black hat, appeals to electron deities and just plain doing whatever it takes to make the project work. |
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Started 2013 September for Amir in Aephraim's lab. The model DE-70BM AOM drivers ("VCO Defelector Driver") from IntraAction has a good amplifier but questionable oscillator. This projects replaces the oscillator section and adds further AM attenuation. The driver puts out up to 2W at 50-200MHz with AM and FM inputs (100KHz bandwidth) plus switches to kill the output fast with residual RF below the noise floor.
There are three front panel controls: AM input and AM potentiometer ("pot"), FM input and FM pot and RF band selection switch. The AM control is the sum of the AM pot and the AM BNC input, with the latter 0V to +10V. Similarly, the FM control is the sum of the FM pot and the FM BNC input, with the latter 0V to +10V. It is recommended to set the associated pot to zero when using the BNC input so that the BNC input is at a known range.
The unit puts out 50-200MHz at up to 1W. This is split into two bands: 50-100MHz and 100-200MHz, with a slight overlap region. Each band has a Minicircuits VCO, sharing the FM control input. Each output is attenuated by 12dB to bring their hefty outputs into the working range of the variable attenuators, used to normalize the VCOs. An RF switch, controlled by a front panel switch, selects the band. The RF goes through another variable attenuator, which give AM control. Following this atenuator is an RF switch which ensures a high attenuation of the RF. The switch output goes to a BNC connector, plumbed to the input of the RF power amp. The output of the RF power amp is on the front panel. It can be used directly or plumbed back into the circuit where it goes through another RF switch to ensure even further attenuation. These two latter RF switches are controlled by the AM control input. When the AM control is below +7.5mV (±2.5mV hysterisis), the RF switches kick in to kill the RF output.
At a convenient frequency from 50-100MHz, monitor the RF output ampliude. This can be a RF power meter, a 'scope with a 50 Ohm input capable of +33dBm or the effect of an AOM on light. Set the power at full by turning the AM pot fully up or by putting +10V into the AM BNC input. Select the low band, 50-100MHz. Adjust the internal low band trimpot gain for the desired output power, probably 1W or +33dBm. Repeat with the high band: 100-200MHz and the high band trimpot.
The other calibration is the FM transfer curve. On the low band, step the FM BNC input from 0V to +10V in 1V steps and record the frequency. Repeat with the high band.
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| Sorry, no more chance for asking direct questions, queries, broken links, problems, flak, slings, arrows, kudos, criticism, comments, brickbats, corrections or suggestions. |
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