Patent ID: 7211802

Claim:
A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising: an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed; a source of a reference voltage; a charge balance capacitor connected at a common node to the pixel intrinsic capacitors; a control unit for varying a level of charge injection to the charge balance capacitor in response to changes in charge balance between the pixel capacitors and the charge balance capacitor for maintaining a constant charge voltage on the common node as determined by the reference voltage; and a control signal generator responsive to the control unit for generating an output control signal indicating presence of impinging X-rays on the imaging panel when the level of charge injection exceeds a predetermined threshold value.