High-Speed Readout Circuit for PIN Single Electron Detector in Voltage Mode

Abstract

This thesis proposes the design of a new type of read-out circuit for a PIN diode used in Scanning Electron Microscope (SEM) applications. The circuit operates in voltage mode (with high input impedance), which offers significant power-saving advantages over the traditionally used current mode (with low input impedance). The final read-out circuit can detect the incoming charge of ∼1000e− with a temporal resolution of 2.5 ns at a frequency of 400 MHz. Post-layout simulation
results indicate a promising reduction in power consumption to 188 µW per pixel.

At the core of the read-out circuit is a dynamic comparator. The dynamic comparator is designed to operate with low noise at high frequencies while still having a low power consumption. The final comparator has a delay of 240 ps and 140 µV of input-referred noise while consuming 71 fJ/conversion.
The comparator has active offset compensation which reduces the offset from 1σ = 5.87 mV to 1σ = 172 µV in 100 ns.

The threshold for the dynamic comparator is created by inserting a small charge of 500e− on the detector, whose polarity is opposite to that of the signal. By creating the threshold as a charge, the ratio between the threshold and the signal is made independent of the detector capacitance.

The final pixel is implemented in 40 nm TSMC CMOS technology and occupies an area of 80 µm x 98 µm which includes additional circuits designed to measure and quantify the performance of the pixel. The measurement setup is designed but unfortunately, due to delays in the chip delivery, no measurements could be performed