Low voltage vertical recording preamplifier for hard disk drives
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Higher data rate hard disk drives(HDD) and improved read channel electronics are demanding preampliﬁer performance be extended well beyond 1 Gb/s. Historically, preampliﬁer power requirements were of low priority; however, with increased demand for battery powered devices such as laptops, MP3 players, personal video recorders, andmanyother wireless hand-held devices, power consumption has become an important design parameter.Furthermore, in order to continue to increase drive capacities, new read-write head technologies(vertical recording and TGMR heads) are demanding innovative preampliﬁer circuitsolutions.Today's production preampliﬁers possess a wide band response of 2.5 MHz-600 MHz; however next generation preampliﬁers willrequire response greater than 250 KHz-1 GHz.Low corner frequencies below 250 KHz present read recovery (sleep-to-read, write-to-read, etc) challenges which can limit drive capacity. This project targets a > 2 Gb/s TGMR (tunneling giantmagneto-resistive) read path for verticalrecording HDDs. A high performance BiCMOS process (IBM's 0.5?m 5HP process)is essential due to the large transconductances, low noise and highspeed requirements of the read path's ﬁrst stage. System frequency limitations at the input are a result of the large TGMR read sensor and preampliﬁer input capacitance. Due to read head and preampliﬁer manufacturingvariations, resistive feedbackaroundthe ﬁrststage is usedto seta controlled input impedance targeted to match the interconnect transmission line. Head resistance variations lead to gain variations; however, the TGMR element becomes more sensitive with larger resistance. This, to a ﬁrst order approximation, acts like an automatic gain control and reduces variations in gain due to the head.
Mellachervu, Ramachandra Murthy (2004). Low voltage vertical recording preamplifier for hard disk drives. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from