Low noise integrating preamplifier with integral ADC

There are several situations where a low noise charge integrating preamplifier is required. In applications where multiple data channels are used, the preamplifier output is often digitised for subsequent processing in a data acquisition system. A good example of such a system is the analogue readout circuitry for a flat-panel active matrix imaging array. To address this type of application we have designed an integrating preamplifier circuit with integral analogue-to-digital converter. By eliminating noisy elements in the feedback loop we have been able to constrain overall noise level while achieving relatively low current consumption with wide bandwidth. The circuit may be operated in linear or logarithmic mode. Results are presented for an implementation of the circuit designed using the 2.4 μm Mietec CMOS process