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Optimum Equivalent Capacitance at Output Stage9 O$ ?& Q; Q; m7 u
Cellular phone and wireless portable device designers normally place several Radio Frequency filtering capacitors and ESD protection devices between the outputs and the headset connector. Those devices are usually connected between amplifier outputs and ground, or amplifier output and virtual ground. Different headsets with different impedance can be used. 16, 32 and 64Ohm are standard values. The extra impedance resulting of parasitic headset inductance and protections capacitance can affect sound quality. In order to achieve the best sound quality, we suggest the optimum value of total equivalent capacitance:
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6 R( g8 L6 z' R9 b- Between each output terminal to the virtual ground should be less than or equal to 100pF
- Between each output terminal to the ground should be less than or equal to 100pF.
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This total equivalent capacitance consists of the radio frequency filtering capacitors and ESD protection device equivalent parasitic capacitance. Because of their very low parasitic capacitance value, diode based ESD protection are preferred. If for some reason the above requirements cannot be met, a series resistor between each audio output and the protection device can improve amplifier operation. In order to keep dynamic output signal range, the resistor value should be very small compared to the loudspeaker. For example, a 10Ohm resistor for a 64Ohm loudspeaker allows up to 400pF parasitic capacitance load.
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发表于 2015-2-28 11:17
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发表于 2015-3-2 11:14
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