Reducing System Cost with High Performance Audio Amplifiers
Research Assignement Answers
Q:	Traditional stereo headphone amplifiers use coupling capacitors between their outputs and the speakers.  Together, the value of the coupling capacitor and the speaker's resistance creates the cutoff frequency of a high pass filter.  Refer to the seminar to determine the following: If RL=24 Ohms and the desired frequency response extends to 30Hz, what is the value of Ccoupling? (Round to nearest µF)
A:	221µF See online seminar presentation, page 14  (ppt: 1.9MB).
Q:	RL=8 Ohms and the frequency response extends to 30Hz, what is the value of Ccoupling? (Round to nearest µF)
A:	663µF See online seminar presentation, page 14  (ppt: 1.9MB).
Q:	The LM4867 is available in National Semiconductor Corporation's 24 pin leadless lead frame package (LLP).  When comparing this package to the traditional solution's 24 pin TSSOP, how much board space is saved by using the 24-pin LLP? (in percent)
A:	60% See online seminar presentation, page. 65  (ppt: 1.9MB).
Q:	The LM4910 eliminates output coupling capacitors.  Using the online seminar describe how is this achieved?  Why does this work?
A:	A third amplifier is used to drive one speaker terminal to the same DC potential as the speaker's other terminal. This achieves a 0V DC potential across the speaker. A coupling capacitor is not needed since there is no net DC voltage across the speaker and, hence, no DC current through the speaker. See LM4910 Datasheet, page 10 and online seminar presentation, page 15-16  (ppt: 1.9MB).