TSH511CF View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TSH511CF' PDF : 25 Pages View PDF
General description
TSH511
The low output impedance of the demodulator (MIX-OUT pins) drives the external volume
control and the de-emphasis filter.
Figure 28. FM demodulator schematics
8.4
Squelch section
To avoid audio FM noise at the speakers when no carrier is received, the TSH511 has a
built-in squelch circuit. The squelch detects the wideband FM noise on the demodulated
output and fades out the audio of both audio buffers.
The audio is filtered from the FM noise using the high-pass RC filter. The cut-off frequency is
typically 100kHz. The squelch level depends on the value of the RMUTE resistor in series
with the input pin of the noise amplifier MUTE-IN (pin 23). The detected noise is integrated
with the Cpeak capacitor connected to MUTE-INT pin. The DC voltage on this pin follows the
amplitude of the noise.
The comparator and the CMUTE capacitor generate the fade-in and fade-out control ramps
for the audio buffers. The squelch was designed with particular attention to avoid audio pop-
noise.
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