RX64DTH - a fully integrated 64-channel ASIC for digital X-ray imaging system with energy window selection

We report on the multichannel IC (RX64DTH) designed for position sensitive X-ray measurements with silicon strip detectors and dedicated to medical imaging applications. This integrated circuit has a binary readout architecture and possibility of selecting energy window for measured signals. The design has been realized in 0.8 μm CMOS process. The core of the RX64DTH chip consists of 64 readout channels. The single channel is built of four basic blocks: charge sensitive preamplifier, shaper, two independent discriminators and two independent 20-bit counters. Each readout channel counts pulses, which are above low discriminator threshold and independently pulses above high discriminator threshold. The energy resolution in such architecture is limited by noise of a single channel and by channel to channel threshold spread. We present noise and matching performance of a single chip and the performance of 384-channel system built of silicon strip detector and six RX64DTH chips. In the 384-channel system an equivalent noise charge of about 200 el. rms has been achieved for shaper peaking time of 0.8 μs and the strip capacitance of 3 pF. The deviation of discriminator thresholds for the whole system is only 87 el. rms. The obtained results show clearly that the energy resolution and uniformity of analog parameters (noise, gain, offsets) are sufficient for medical diagnostic applications such as dual energy mammography and angiography.