1. A computer system comprising:
a plurality of operational components each having to operate at the same frequency;
a plurality of reference cells, each reference cell coupled to at least one of the operational components for providing a reference frequency; and
a passive network connecting at least one of the reference cells to another of the reference cells such that energy transfer between the plurality of reference cells synchronizes the reference frequency of one another.
2. The computer system of claim 1, further comprising a backup reference cell connected to at least another of the plurality of reference cells.
3. The computer system of claim 1, wherein the reference cells are coupled in a modular grid topology.
4. The computer system of claim 1, wherein the reference cells are coupled in a fault-tolerant grid topology.
5. The computer system of claim 1, wherein the operational components are processing units in a multi-processor computer system.
6. The computer system of claim 1, wherein the passive network includes a bandpass filter.
7. The computer system of claim 1, wherein the passive network is a single-wire network.
8. The computer system of claim 1, wherein the passive network is a multi-wire network.
9. The computer system of claim 1, wherein an output signal from at least one of the reference cells is coupled to the input path of at least another of the reference cells.
10. The computer system of claim 1, wherein the output signals from the reference cells are the same and minimal current flows between the reference cells if the reference cells are synchronized.
11. The computer system of claim 1, wherein energy flows through the reference cells and realigns the frequency of the reference cells.
12. A method comprising:
providing separate reference signals having a frequency for each of a plurality of operational components;
connecting the separate reference frequencies to one another in a modular, fault-tolerant circuit topology via a passive network; and
synchronizing the separate reference frequencies so that each of the operational components operate at the same frequency.
13. The method of claim 12, further comprising phase-aligning the separate reference frequencies with one another.
14. The method of claim 12, further comprising synchronizing a new reference frequency with the separate reference frequencies when the new reference frequency is brought online.
15. The method of claim 12, wherein connecting the separate reference frequencies to one another is via a bandpass filter.
16. The method of claim 12, further comprising coupling the output of one of the separate reference frequencies to the input path of another of the separate reference frequencies.
17. A computer system comprising:
means for connecting individual reference cells to a plurality of operational components via a passive network; and
means for automatically synchronizing the individual reference cells with one another so that each of the plurality of operational components operate at the same frequency.
18. The computer system of claim 17, further comprising means for automatically phase-aligning the individual reference cells.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A scanning electron microscope comprising:
an irradiation optical system for irradiating an electron beam to a sample;
a sample holder for supporting said sample, arranged inside a sample chamber;
at least one electric field supply electrode arranged at a periphery of said sample holder; and
an ion current detection electrode;
wherein said electric field supply electrode is arranged such that said ion current detection electrode covers a part of said electric field supply electrode not opposed to said sample holder.
2. A scanning electron microscope comprising:
an irradiation optical system for irradiating an electron beam to a sample;
a sample holder for supporting said sample;
a sample chamber having said sample holder arranged therein;
an electric field supply electrode for supplying an electric field for accelerating secondary electrons generated from said sample by irradiating an electron beam; and
an ion current detection electrode arranged inside said sample chamber, for detecting ions generated by impingement of said secondary electrons accelerated against a residual gas inside said sample chamber;
wherein said ion current detection electrode has an upper electrode and a lower electrode, and said electric field supply electrode is arranged between said upper electrode and said lower electrode.
3. A scanning electron microscope according to claim 2, wherein said ion current detection electrode has a shape covering the periphery of said electric field supply electrode.
4. A scanning electron microscope according to claim 1, wherein the shape of either one, or both, of said electric field supply electrode and said ion current detection electrode is a mono-filament-like, mesh-like, porous sheet-like or sheet-like one.
5. A scanning electron microscope according to claim 1, further comprising:
means for applying a voltage to said sample holder, said ion current detection electrode or said electric field supply electrode; and
means for controlling said impressed voltage.
6. A scanning electron microscope according to claim 1, further comprising:
a first electrode arranged inside said sample chamber, for forming an electrode field for imparting a desired speed to said secondary electrons generated from said sample by irradiating said electron beam.
7. A scanning electron microscope according to claim 1, further comprising:
a second electrode, arranged inside said sample chamber, for supplying an electric field necessary for accelerating the secondary ions and causing gas multiplication by residual gas molecules, and for supplying an electric field for causing the ions or electrons generated by said gas multiplication to drift towards said sample being charged.
8. A scanning electron microscope according to claim 5, wherein said impressed voltage control means controls the impressed voltage to said first electrode.
9. A scanning electron microscope according to claim 1, further comprising:
means for independently adjusting relative positions of said ion current detection electrode and said electric field supply electrode.
10. A scanning electron microscope according to claim 1, further comprising:
means for adjusting a relative position of said ion current detection electrode or said electric field supply electrode with respect to said sample holder.
11. A scanning electron microscope according to claim 1, wherein said sample holder is used also as said ion current detection electrode.
12. A scanning electron microscope according to claim 1, wherein said electric field supply electrode or said ion current detection electrode can be used also as a secondary electron collector.
13. A scanning electron microscope according to claim 1, further comprising:
an amplifier for amplifying the ion current detected from said ion current detection electrode to an intensity necessary for forming an image, arranged inside said sample chamber.
14. A scanning electron microscope according to claim 2, wherein said residual gas is an atmospheric air, a nitrogen gas or a rare gas.
15. A scanning electron microscope according to claim 7, wherein said impressed voltage control means controls the impressed voltage to said second electrode.
16. A scanning electron microscope comprising:
an irradiation optical system for irradiating an electron beam to a sample;
a sample holder for supporting said sample;
a sample chamber having said sample holder arranged therein;
an electric field supply electrode for supplying an electric field for accelerating secondary electrons generated from said sample by irradiating an electron beam; and
an ion current detection electrode arranged inside said sample chamber, for detecting ions generated by impingement of said secondary electrons accelerated against a residual gas inside said sample chamber;
wherein said ion current detection electrode is a cylindrical shape ion current detection electrode having an opening, and said electric field supply electrode is disposed inside the cylindrical shape electrode such that said electric field supply electrode is opposed to said sample holder via said opening of the cylindrical shape ion current detection electrode.