There is provided a detector substrate for use in a charged particle multi-beam assessment tool to detect charged particles from a sample. The detector substrate defines an array of apertures for the beam paths of respective charged particle beams of a multi-beam. The detector substrate comprises: a sensor unit array. A sensor unit of the sensor unit array is adjacent a corresponding aperture of the aperture array. The sensor unit is configured to capture charged particles from the sample. The detector array comprises an amplification circuit associated with each sensor unit in the sensor unit array and proximate to the corresponding aperture in the aperture array. The amplification circuit comprising a Trans Impedance Amplifier and/or an analogue to digital converter.