This paper presents an ultra low noise instrumentation based on cryogenic electronic integrated circuits (ASICs: Application Specific Integrated Circuits). We have designed successively two ASICs in standard BiCMOS SiGe 0.35 mu m technology that have proved to be operating at cryogenic temperatures. The main functions of these circuits are the readout and the multiplexing of TES/SQUID arrays. We report the cryogenic operation of a first ASIC version dedicated to the readout of a 2 x 4 pixel demonstrator array. We particularly emphasize on the development and the test phases of an ultra low white noise (0.2 nV/sqrtHz) cryogenic amplifier designed with two multiplexed inputs. The cryogenic SiGe amplifier coupled to a SQUID in a FLL operating at 4.2 K is also presented. We finally report on the development of a second version of this circuit to readout a 3 x 8 detectors array with improved noise performances and upgraded functionalities. (C) 2009 Elsevier Ltd. All rights reserved.