AN2583 datasheet(7/18 Pages) STMICROELECTRONICS

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AN2583

Audio characteristics

7/18

The required THD specification for the M41T00AUD is less than 2% at 1 kHz and 300 mW.

The voltage formula was used in the measurement for this, and makes for the more difficult

specification since it tends to yield the higher number.

Example: Let V1 = 1 V, V2 = 0.1 V, V3 = 0.08 V, V4 = 0.06 V and V5 = 0.04 V

Thus the voltage formula makes for a more challenging specification.

2.2

Amplifier primer

Several types of amplifiers are possible for fabrication in semiconductor ICs. The following is

a brief overview of the types and their power capabilities.

2.2.1

Simple amplifier

Figure 7 illustrates a simple amplifier circuit. The input section provides any signal

conditioning - gain and offset - necessary for driving the output transistors shown here. The

midpoint voltage, VX, is biased at VDD/2. At its maximum, VX will swing up to VDD – VDSP-min

when Q2 is fully on, and down to VDSN-min when Q1 is fully on.

Figure 7.

Basic single supply amplifier

For the purposes of analysis, we can assume VDSP-min and VDSN-min are small compared to

VDD and thus ignore them here.

With that in mind, the point VX will swing between GND (0 V) and VDD.

For audio applications, it is necessary that the output signal be purely AC. There should be

no DC component in it. The output signal must swing symmetrically about ground.

147

0.04

0.06

0.08

0.1

THD

2.16%

0.0216

THD

VDD

VIN

VDSP

–

VDSN

–

GND

ai13933

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