PRECISION FAST PULSED FIELD GRADIENT DRIVER FOR ESR MICROSCOPY

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 在我们的脉冲ESR显微镜研究和开发工作中，我们计划通过向谐振器梯度线圈组提供精确、快速的恒流脉冲来降低高收集速率下的线圈损耗。在实践中，该目标难以实现，因为梯度线圈表示基本上电感性的负载，要求脉冲驱动器能够在几十纳秒左右内将线圈的磁场充电到必要的能量水平，并且还要求线圈的电感在高“Q”下不与寄生系统驱动器和电缆电容谐振。此外，在梯度“开启”时间期间，脉冲幅度变化必须保持小于1%，以避免降低显微图像分辨率。最后，驱动器必须在梯度脉冲周期结束后快速“转储”所存储的线圈能量。 为了解决这些问题，我们已经开发了几种可能的实施方案的快速脉冲梯度驱动器。目前，我们正在评估一种新型的快速恒流驱动器核心，作为我们目前设计方案的基础。驱动器核心网络由电流编程“共源共栅”配置组成，本质上是一种串联开环MOSFET拓扑结构。这种类型的宽带驱动器级本身具有电流调节功能，因此其恒流特性不依赖于离散闭环反馈网络。因此，它的带宽和稳定裕度相对较高，轻松超过了我们的应用要求。我们目前正在评估这一核心网络，以确定在开环形式下，它是否能够充分保持我们的显微镜应用所需的脉冲幅度调节，同时在整个编程输出范围内驱动代表性负载阻抗。如果开环驱动器幅度变化超过我们的规格，我们将探索增加门控快速电流反馈环路，以进一步降低幅度变化。 该项目的工作将持续到2005- 2006年。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. In our pulsed ESR microscopy research and development work, we plan to reduce coil dissipation at high collection rates by providing precise, fast constant-current pulses to the resonator gradient coil sets. In practice, this objective is difficult to achieve because the gradient coils represent a substantially inductive load, requiring that the pulse driver be capable of charging the coil's magnetic field to the requisite energy level in several tens of nanoseconds or so and also that the coil's inductance not resonate at high "Q" with parasitic system driver and cable capacitances. Also, during the gradient "on" time, the pulse amplitude variation must be held to less than 1%, in order to avoid degrading the microimage resolution. Finally, the driver must rapidly "dump" the stored coil energy following the end of the gradient pulse period. To address these issues, we have developed several possible implementation schemes for the fast pulsed gradient driver. Currently, we are evaluating a novel fast constant-current driver core as the basis for our present design options. The driver core network consists of a current-programmed "cascode" configuration, essentially a series-connected, open-loop MOSFET topology. This type of wideband driver stage is inherently current-regulating and therefore does not rely on a discrete closed-loop feedback network for its constant-current characteristic. As a result, its bandwidth and stability margin are relatively high and handily exceed the requirements for our application. We are presently evaluating this core network to determine if, in its open-loop form, it will adequately maintain the pulse amplitude regulation that our microscope application requires while driving a representative load impedance over the full programmed-output range. If the open-loop driver amplitude variation exceeds our specification, we will then explore the addition of a gated fast current feedback loop to further reduce the amplitude variation. Work on this project will continue through the 2005-6 year.