Analog to digital conversion system having automatically and dynamically

Abstract

In order to digitize with sufficient resolution an analog signal, which may be generated by a photodetector in a spectrophotometer, an improved analog to digital conversion system is provided having an integrator stage, an analog to digital converter, a microprocessor and interface circuits for providing communication between the microprocessor and a host computer. The integrator may include an operational amplifier with a capacitor in feedback relationship therewith for providing an output which varies linearly as function of time. The microprocessor operates the analog to digital converter to sample the integrator output at successive increments of time which increase in accordance with a binary relationship to an increment corresponding in binary value to the desired upper end of the resolution range. The digitized samples from the analog to digital converter are compared with a predetermined value in the upper end of the amplitude range of the converter. Low amplitude analog signals do not reach the predetermined level until the later sampling times and thus are resolved at the upper end of the resolution range. Higher amplitude analog signals are resolved at the lower end of the resolution range. Thus the resolution dynamically and automatically increases inversely with the amplitude of the analog signal being digitized. The digitized value is expressed by two binary numbers, one corresponding to the number of samples until detection of the sample of the integrator output achieving the predetermined amplitude, and the other corresponding to the value which the integrated signal has achieved.