公开(公告)号：JPH1166505A

公开(公告)日：1999-03-09

申请号：JP16380798

申请日：1998-06-11

Applicant: ST MICROELECTRON INC

Inventor： PATTI GUISEPPE

IPC: G11B5/09 ,  G01R33/09 ,  G11B5/02 ,  G11B5/39 ,  H03F1/26

Abstract: PROBLEM TO BE SOLVED: To supply a small amount of current from a high load resistance to obtain a large gain at a first stage thereby reducing a noise by supplying a constant amount of current from a pair of current sources to a first stage of a preamplifier to obtain a current sufficient for reducing a bias current applied via an MR readout head so as to disappear. SOLUTION: A preamplifier 50 supplies from first and second current sources 80 and 82 a constant amount of current which is sufficient for reducing a bias current to be applied via an MR readout head 60 (RH) so as to disappear. As a result, a relatively small amount of current is supplied from a load resistance 56 thereby allowing a resistance value RL of the load resistance 56 to increase. Accordingly, it is possible to obtain a relatively large gain at a first amplifying stage 52 composed of the load resistance 56, an NPN bipolar transistor 58 and the MR readout head 60. Thus, noise contribution of the load resistance 56 is reduced and noise contribution of a second amplifying stage 54 can also be significantly reduced.