TSH512

General description

Doc ID 8120 Rev 7

21/31

5.4

ALC section: automatic level control

Both transmitters of the TSH512 include an automatic level control (ALC). When the level of

the audio signal is too high, the ALC compresses the signal in order to avoid over-

modulation of the FM VCO. In this way, the ALC reduces the distortion and maintains a

reduced transmit spectrum with very high amplitude signals.

Figure 28.

Automatic level control schematics

The ALC features a 20 dB gain and an output signal regulated to 700 mVpp in compression.

The attack time is the response time of the ALC to go from the linear amplification to the

page 15).

The decay time is the response time the ALC requires to recover to full gain amplifying

5.5

VOX description: voice operated transmit

The voice operated transmit (VOX) section reduces consumption when there is no audio

signal to transmit. When the VOX detects that no audio signal is present, it mutes the output

buffers of TX1 and TX2 and provides the logic signal VOX-MUTE to switch-off the external

LED drivers if needed.

frequency:

f

HPF

1

2

π R

sens

C

sens

⋅

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