ICL7107 is a high performance, low power, monolithic IC used for analog to digital conversions up to 31/2 digits.  It houses display drive circuitry inside it bypassing the need of connecting an external drive circuit. 

The input impedance is quite high. Polarity and digital drivers, segment decoders, voltage reference, and a clock circuit is already available on its board. ICL7107 is designed to connect LED display directly to it. 

The ADC uses a dual-slope conversion technique which inherently rejects interference signals from the ambiance. Rollover error is minimized less than one count which makes ICL7107 highly accurate.