The application of the capability of low-temperature poly-Si TFT circuits for high resolution X-ray active matrix sensor is explored. The integration of poly-Si TIFT circuits oil the glass enables an easy connection for the sensor array with fine pixel pitch. A novel charge sensitive amplifier circuit employing poly-Si TFTs is proposed for the readout system of the active matrix sensor. It can considerably increase the circuit's immunity to the unavoidable threshold voltage variations of the poly-Si TFTs.. The V-TH mismatch effect of the TFTs, which results in the offset voltage of the charge amplifier, can also be suppressed by the proposed circuit. However, the noise arisen from the V-TH mismatch can be even larger than that from the V-TH variation after compensation. It reflects that, for higher bit digital X-ray image sensors, the mismatch effect of the devices must be properly taken into consideration. (c) 2007 Elsevier Ltd. All rights reserved.