Output Stage Design and Crossover Distortion general class of ring emitter transistors (RETs). This means that they have high fT and good safe operating area. The On Semiconductor data sheet for the NJL3281/1302 complementary par of ThermalTrak transistors shows typical β to be quite flat at about 100 for most operating currents, falling to about 70 at 9 A [9]. Peak fT is about 50 MHz at about 3 A, but is still about 20 MHz at 100 mA. At about 6 A, fT has fallen to about 20 MHz. These transistors suffer much less beta droop and fT droop than most other BJT power transistors. Collector-base capacitance is about 600 pF at Vcb = 10 V. Safe operating area for the device is almost 100 W at 100 V.
References 1. Locanthi, Bart N., “Operational Amplifier Circuit for Hi-Fi,” Electronics World, pp. 39–41, January 1967. 2. Locanthi, Bart N, “An Ultra-low Distortion Direct-current Amplifier,” Journal of the Audio Engineering Society, vol. 15, no. 3, pp. 290–294, July 1967. 3. Self, Douglas, Audio Power Amplifier Design Handbook, 5th ed., Focal Press, 2009. 4. Jung, Walt, “Op-Amp Audio–Realizing High Performance Buffers, Part 2,” Electronic Design, October 1, 1998. 5. Williams, Jim, “High Speed Amplifier Techniques,” Linear Technology Corporation, AN-47, August 1991. 6. Massobrio, Giuseppe, and Paolo, Antognetti, Semiconductor Device Modeling with SPICE, 2d ed., New York, McGraw-Hill, 1993. 7. Otala, M., and Lammasniemi, J., “Intermodulation Distortion in the Amplifier Loudspeaker Interface,” 59th Convention of the Audio Engineering Society, preprint No. 1336, February 1978. 8. Cordell, R. R., “Open-loop Output Impedance and Interface Intermodulation Distortion in Audio Power Amplifiers,” 64th Convention of the Audio Engineering Society, preprint no. 1537, 1982; available at www.cordellaudio.com. 9. ON Semiconductor datasheets for NJL3281D and NJL1302D, www.onsemi.com, June 2006. 10. ThermalTrakTM Audio Output Transistors, Mark Busier, ON Semiconductor, AND8196/D, www.onsemi.com, February 2005.
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