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.