A wide swing charge sensitive amplifier for a prototype Si–W EM calorimeter

A wide swing charge sensitive amplifier (CSA) has been developed, as a part of a front-end electronics (FEE) readout ASIC, for a prototype silicon tungsten (Si–W) based electromagnetic (EM) calorimeter. The CSA, designed in <math display="inline" id="d1e1045" altimg="si189.svg"><mrow><mn>0</mn><mo>.</mo><mn>35</mn><mspace width="1em" class="nbsp"/><mi mathvariant="normal">μ</mi><mi mathvariant="normal">m</mi></mrow></math> N-well CMOS technology using 5V MOS transistors, has a wide linear operating range of 2.6 pC w.r.t the input charge with a power dissipation of 2.3 mW. A noise figure (ENC) of 820 e<math display="inline" id="d1e1060" altimg="si184.svg"><msup><mrow/><mrow><mo>−</mo></mrow></msup></math> at 0 pF of detector capacitance with a noise slope of 25 e<math display="inline" id="d1e1068" altimg="si184.svg"><msup><mrow/><mrow><mo>−</mo></mrow></msup></math>/pF has been achieved (when followed by a CR-RC<math display="inline" id="d1e1077" altimg="si139.svg"><msup><mrow/><mrow><mn>2</mn></mrow></msup></math> filter of <math display="inline" id="d1e1085" altimg="si191.svg"><mrow><mn>1</mn><mo>.</mo><mn>2</mn><mspace width="1em" class="nbsp"/><mi mathvariant="normal">μ</mi><mi mathvariant="normal">s</mi></mrow></math> peaking time). This design of CSA provides a dynamic range (ratio of maximum detectable signal to noise floor) of 79 dB for the maximum input charge of 2.6 pC when connected to a silicon detector with a capacitance of 40 pF. Using folded cascode architecture-based input stage and low voltage high swing current mirrors as the load, the CSA provides an enlarged output swing by biasing the output node towards one supply rail and utilizing the voltage range towards the opposite rail. The design philosophy works for both polarities of a large input signal. This paper presents the design of CSA with a wide negative output swing for an anticipated input signal of positive polarity in the target application with a known detector biasing scheme.