This subproject is one of many research subprojects utilizing theresources provided by a Center grant funded by NIH/NCRR. The subproject andinvestigator (PI) may have received primary funding from another NIH source,and thus could be represented in other CRISP entries. The institution listed isfor the Center, which is not necessarily the institution for the investigator.In late 2003, ACERT acquired new 170 and 240GHz phase-locked, tracking millimeter-wave sources from Virginia Diodes, Inc. (VDI). With respect to our previous millimeter-wave sources, these sources feature reduced complexity (single PLL vs. dual PLL), increased power output (+12dB) and greatly expanded reference-to-output tracking range (fc +/- 5GHz vs. fc +/- 0.5GHz). However, these sources, due to their relatively high multiplier power levels, require exacting monitoring and control of the multiplier bias levels and a fast, reliable protective shut-down scheme for instances of out-of-spec operation. At maximum power levels, even a minor violation of the requisite multiplier bias conditions can result in a high-cost, long down-time source failure. Our goal in designing a universal bias driver and power supply for these sources is to provide a means of reproducing output power settings up to the maximum rated value, without incurring significant risk of source failure due to possible operator misadjustment of source operating parameters.To accomplish this goal, we have designed the multiplier bias sources to exhibit voltage-dependent impedance characteristics which are centered on a value which may be manually adjusted over the acceptable bias voltage range for the related multiplier stage. These ranges, along with the maximum permissible diode currents for each of the multiplier stages, are programmed into the respective bias driver sections. Any multiplier current exceeding its diode maximum rating immediately shuts down the source's active multiplier stage, effectively removing r.f. excitation from and protecting the passive millimeter-wave multiplier stages.We have completed bench tests on our initial 240GHz bias driver/power supply, which operates as anticipated, and we are presently constructing a second unit for the 170GHz VDI source. This new 170GHz bias driver/power supply will replace the simple interim bias network which is currently in place for lower-power experimental work.
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