General description

TSH512

24/31

Doc ID 8120 Rev 7

5.6

PEA section: pre-emphasis

The amplitude-regulated audio coming from the ALC feeds the positive input of the

operational amplifier called PEA (pre-emphasis). The pre-emphasis consists in a high-pass

filter in order to compensate the behavior of the FM transmission.

Figure 32.

Pre-emphasis schematics

50 µs or 75 µs time constants are generally used.

Choosing the gain of the PEA stage also allows one to set the right modulation level to the

varicap diode. The gain in the passband is: