A high output current wideband output stage/buffer amplifier that has reduced quiescent current requirements. The output stage/buffer amplifier includes a diamond follower circuit having a pair of complementary output load-driving bipolar junction transistors (BJTs), a pair of pre-driver BJTs, and a plurality of current boost BJTs. As the base current of one of the driver transistors starts to increase in response to an increasing load current, the current through a corresponding pre-driver transistor decreases, thereby increasing the collector current of a corresponding boost transistor. The increased collector current of the boost transistor is fed back to a current mirror, causing a concomitant increase in the base current of the driver transistor.

A bias device that modifies the bias of a device based on an input signal to the device. The device may have a fixed bias, and the bias device can be connected in parallel with the fixed bias. The device can be an amplifier, such as a linear amplifier or a class AB amplifier. The bias device can be configured to provide maximum bias during the device's crossover time period.

A bipolar high output current buffer is disclosed using a negative feedback current mirror to supply the base drive to an output transistor. Small quiescent currents are used wherein the buffer demonstrates low quiescent power dissipation. The current mirror supplies the incremental base drive to the output transistor to support high output currents. When the output drive may source or sink the high output currents, two current mirrors may be used, one for each of the source and the sinking circuitry. This invention provides for minimal loss of dynamic range.

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.