AN2583

Audio characteristics

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2.4

Gain

There are three stages of gain in the M41T00AUD. The input amplifier's gain is controlled by

the input and feedback resistors chosen by the user. The LPF is at unity gain and thus does

not contribute.

The programmable gain stage can be adjusted from a gain (attenuation) of 0.022x all the

way up to a 4x multiplication. Lastly, the bridge amplifier provides a fixed gain of 2x which is

a consequence of two amplifiers in parallel, one at a gain of 1x and one at –1x, resulting in a

net gain of 2 as shown in Equation 2 on page 12.

Figure 15.

End-to-end audio path

The gain is usually measured in decibels or dB. This is defined as the ten times the log of

the ratio of the output power to the input power

Normalizing the resistances, this reduces to

stage gain of 2. The net gain for these two sections is then 1. The result is that the final gain

is determined solely by the adjustable gain stage and will match whatever value is

programmed into the gain register.

ai13941

LPF

100Hz-8kHz

256Hz

512Hz

256/512

SELECT

TONE

ON/OFF

From internal

RTC timing chain

300mW

@ 8 ohms

2

AOUT+

AOUT–

+6dB

0dB

(1x, @ midband)

(0.022x to 4x)

(2x)

GAIN Register

bbbb

33dB to +12dB

–

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

=

IN

2

IN

OUT

2

OUT

IN

OUT

P

/R

V

/R

V

log

10

P

P

log

10

dB

in

gain

power

A

IN

OUT

2

IN

OUT

2

IN

2

OUT

P

V

V

log

20

V

V

log

10

V

V

log

10

A

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=