NASA Goddard Space Flight Center has developed a digitizer that can process a wide range of low-level signals in the presence of ionizing radiation. This novel digitizer overcomes the disadvantages of current technology including limited gain of the frontend amplifier circuits to fixed values, and amplifier saturation from the use of bandpass filtering rather than autozero.
A unique feature of this innovation is the combination of autozero/chopping with a discrete time integrator in the main path. This integrator allows for variable gain and when combined with the linear amplifiers, can also generate very high and accurate gain. Further, the discrete time integrator can be placed in hold mode after the desired number of integrations has occurred.
Advantages of the technology include flexible and low-cost variable gain digitizing with high accuracy that can be implemented in radiation-hardened-by-design submicron CMOS (complementary metal-oxide semiconductor). The autozero, in combination with the chopper, adapts and adjusts the offset of the linear amplifiers in the presence of radiation-induced threshold voltage changes in the MOSFET devices in the amplifiers. Since chopping alone would not prevent this amplifier saturation caused by large offsets, the addition of autozero makes the amplifier chain more robust in high TID environments.