Patent Number: 
Section: claims

1. An apparatus comprising:an X-ray absorption layer comprising an electrode;a first voltage comparator configured to compare a voltage of the electrode to a first threshold;a second voltage comparator configured to compare the voltage to a second threshold;a counter configured to register a number of X-ray photons absorbed by the X-ray absorption layer;a controller;wherein the controller is configured to start a time delay from a time at which the first voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the first threshold;wherein the controller is configured to activate the second voltage comparator during the time delay;wherein the controller is configured to cause the number registered by the counter to increase by one, if the second voltage comparator determines that an absolute value of the voltage equals or exceeds an absolute value of the second threshold. 2. The apparatus of claim 1, further comprising a capacitor module electrically connected to the electrode, wherein the capacitor module is configured to collect charge carriers from the electrode. 3. The apparatus of claim 1, wherein the controller is configured to activate the second voltage comparator at a beginning or expiration of the time delay. 4. The apparatus of claim 1, further comprising a voltmeter, wherein the controller is configured to cause the voltmeter to measure the voltage upon expiration of the time delay. 5. The apparatus of claim 4, wherein the controller is configured to determine an X-ray photon energy based on a value of the voltage measured upon expiration of the time delay. 6. The apparatus of claim 1, wherein the controller is configured to connect the electrode to an electrical ground. 7. The apparatus of claim 1, wherein a rate of change of the voltage is substantially zero at expiration of the time delay. 8. The apparatus of claim 1, wherein a rate of change of the voltage is substantially non-zero at expiration of the time delay. 9. The apparatus of claim 1, wherein the X-ray absorption layer comprises a diode. 10. The apparatus of claim 1, wherein the X-ray absorption layer comprises silicon, germanium, GaAs, CdTe, CdZnTe, or a combination thereof. 11. The apparatus of claim 1, wherein the apparatus does not comprise a scintillator. 12. The apparatus of claim 1, wherein the apparatus comprises an array of pixels. 13. A system comprising the apparatus of claim 1 and an X-ray source, wherein the system is configured to perform X-ray radiography on human chest or abdomen. 14. A system comprising the apparatus of claim 1 and an X-ray source, wherein the system is configured to perform X-ray radiography on human mouth. 15. A cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus of claim 1 and an X-ray source, wherein the cargo scanning or non-intrusive inspection (NII) system is configured to form an image using backscattered X-ray. 16. A cargo scanning or non-intrusive inspection (NII) system, comprising the apparatus of claim 1 and an X-ray source, wherein the cargo scanning or non-intrusive inspection (NII) system is configured to form an image using X-ray transmitted through an object inspected. 17. A full-body scanner system comprising the apparatus of claim 1 and an X-ray source. 18. An X-ray computed tomography (X-ray CT) system comprising the apparatus of claim 1 and an X-ray source. 19. An electron microscope comprising the apparatus of claim 1, an electron source and an electronic optical system. 20. A system comprising the apparatus of claim 1, wherein the system is an X-ray telescope, or an X-ray microscopy, or wherein the system is configured to perform mammography, industrial defect detection, microradiography, casting inspection, weld inspection, or digital subtraction angiography. 21. A system comprising:the apparatus of claim 1,an X-ray detector,a spacer,wherein the apparatus and the X-ray detector are spaced apart by the spacer. 22. The system of claim 21, wherein the apparatus and the X-ray detector are configured to respectively capture an image of an object simultaneously. 23. The system of claim 21, wherein the X-ray detector is identical to the apparatus. 24. A system comprising:the apparatus of claim 1,wherein the apparatus is configured to move to and capture images of an object exposed to incident X-ray at different distances from the object. 25. The apparatus of claim 1, wherein the controller is configured to deactivate the first voltage comparator at a beginning of the time delay. 26. The apparatus of claim 1, wherein the controller is configured to deactivate the second voltage comparator at expiration of the time delay or at a time when the second voltage comparator determines that the absolute value of the voltage equals or exceeds the absolute value of the second threshold, or a time in between. 27. A method comprising:starting a time delay from a time at which an absolute value of a voltage of an electrode of an X-ray absorption layer equals or exceeds an absolute value of a first threshold;deactivating a first circuit at a beginning of or during the time delay, wherein the first circuit is configured to compare the absolute value of the voltage to the absolute value of the first threshold;activating a second circuit during the time delay, wherein the second circuit is configured to compare the absolute value of the voltage to the absolute value of the second threshold;determining an absolute value of the voltage equals or exceeds an absolute value of the second threshold;increasing a count of X-ray photon incident on the X-ray absorption layer by one in response to the absolute value of the voltage equaling or exceeding the absolute value of the second threshold. 28. The method of claim 27, further comprising connecting the electrode to an electrical ground. 29. The method of claim 27, further comprising measuring the voltage upon expiration of the time delay. 30. The method of claim 27, further comprising determining an X-ray photon energy based on a value of the voltage at expiration of the time delay. 31. The method of claim 27, wherein a rate of change of the voltage is substantially zero at expiration of the time delay. 32. The method of claim 27, wherein a rate of change of the voltage is substantially non-zero at expiration of the time delay. 33. The method of claim 27, wherein activating the second circuit is at a beginning or expiration of the time delay. 34. The method of claim 27, further comprising deactivating the second circuit at an expiration of the time delay or at a time when the absolute value of the voltage equals or exceeds the absolute value of the second threshold.