Preamplifier for Magnetoresistive Heads Using Series Voltage Bias
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
A new preamplifier design, as shown in the figure, uses fewer I/O leads in the head, cable and amplifier circuit, resulting in lower costs and higher reliability while maintaining constant current density in the magnetoresistive (MR) elements and good common mode rejection of noise. This preamplifier design uses sharing of electrically adjacent MR leads. A group of MR elements are connected in a series configuration and share a common current source 1 and current sink 2 controlled by Operational Transconductance Amplifiers (OTAs) 3 and 4. The OTAs are operated at low frequencies with the use of external capacitors. The voltage Vrefb, which is the reference vp;tage for OTA 4, is set equal to Vb. Current source 2 and OTA 4 produce a current I which is equal to the output current Io minus twice the Ib currents.