Analog Frontend Circuits for Avalanche Photodiodes

The aims of this work is to design low noise electronics for optical sensing and X‐ray spectroscopy using Sheffield‐grown Avalanche photodiodes(APD). A transimpedance amplifier(TIA) for a 2.0 μm LIDAR system is designed and tested as part of a project funded by ESA. Numerical analysis is provided for the TIA in addition to SPICE and experimental analysis. Characterisation of the TIA shows that a noise equivalent power of less than 100 fW/√Hz can be achieved with an optimised InAs APD. Preliminary results of a TIA‐InAs module at 2.0 μm is presented. A low noise charge sensitive preamplifier(CSP) with a novel local feedback is designed and characterised. The CSP shows a better noise performance than commercially available CSP such as the CoolFet 250. The CSP is also characterised for APD dark current of up 4 μA and the CSP is found to behave well for such relatively high dark current. Discrepancies between the SPICE model and measured characteristic of the CSP’s input JFET is presented and discussed. The first ever Aluminium Indium Phosphide (AlInP) APD X‐ray spectroscopy measurement is presented in this work. AlInP is the widest band material that can be grown latticematched on a GaAs substrate. Due to its wide bandgap, AlInP can offer reverse dark current of less than 2 pA at gain of 100 for a 200um device, making it desirable for room temperature operation. An energy resolution of 647 eV is obtained for AlInP APD coupled to the CSP and exposed to 55Fe X‐rays. Using the CSP presented in this work, previously reported GaAs/AlGaAs APD is characterised and compared with results obtained using a commercial CSP. A 21% improvement in X‐ray energy resolution is reported, despite degradation in the APD.