Patent attributes
A write driver circuit (38) uses a matching resistors (R0, R1) to match the impedance of the head (32) disposed between output nodes (OUTP, OUTN). Control circuitry (Q4, Q5, Q6, Q7, R2, R4, R6 and R7) maintains the voltage at reference voltage nodes (VREFP, REFN) at essentially the same voltage as its corresponding output node. The matching resistor is disposed between the reference voltage node and the output node along with a driver (40a, 40b), which may be implemented as an AB driver. Since the voltage between the reference node and the output node is generally zero, very little current is shunted by the matching resistors, and thus, there is very little power wasted by the matching resistors. In the preferred embodiment, the output transistors of the AB drivers are driven by switched current sources (Q28 and Q29) to provide enhanced current to the bases of the output transistors on an as needed basis.
