Preliminary

TMPA2155DM

Rev.1.0

December 24, 2007

Copyright ©2005, Tai-1 Microelectronics Corp.

9

Automatic output Power Control (APC)

The voltage gain is self adjusted in the chip over voltage range. This means that, regardless

supply voltage change, the output power keeps about the same for a given input level from

Differential input VS single ended input

Differential input offers better noise immunity over single ended input. A differential input

amplifier suppresses common noise and amplifies the difference voltage at the inputs. For

single ended applications just tie the negative input end of the balanced input structure to

ground. If external input resistors are used, the negative input has to be grounded with a series

resistor of the same value as the positive input to reduce common noise.

Output filter

Ferrite bead filter can be used for EMI purpose. The ferrite filter reduces EMI around 1 MHz and

higher（FCC and CE only test radiated emissions greater than 30 MHz）. When selecting a

ferrite bead, choose one with high impedance at high frequencies, but low impedance at low

frequencies.

Use an LC output filter if there are low frequency（＜1 MHz）EMI sensitive circuits and/or there

are long wires from the amplifier to the speaker. EMI is also affected by PCB layout and the

placement of the surrounding components.