10/14

MUTING FUNCTION

Figure 29

muting-off

R5 =

10

Ω

@

0V

≤ VT ≤ 1.3V

muting-on

6V

Referring to the following input stage, the possible attenuationof the input signal and therefore of the output

signal can be found using the following expression:

Ω the attenuation in the

muting-off condition, the attenuation is very low,

typically 1.2 dB.

A very low current is necessary to drive the thresh-

4 is greater than 150 K

Ω. The muting function can

be usedin many cases, when a temporaryinhibition

of the output signal is requested, for example:

– in switch-on condition, to avoid preamplifier

power-on transients (see fig. 22)

=

=

+(

+ 5

)

(

)

where R8

≅ 100 KΩ

– during switching at the input stages.

– during the receiver tuning.

The variable impedance capability at pin 5 can be

useful in many applications and two examples are

shown in fig. 25 and 27, where it has been used to

change the feedback network, obtaining 2 different

frequency responses.

TDA1905