TSH511C STMicroelectronics, TSH511C Datasheet - Page 15

• Manufacturer Part Number: TSH511C
• Description: HiFi stereo/mono infrared receiver Stereo sub-carrier demodulator
• Manufacturer: STMicroelectronics

The
LNA-OUT1 and LNA-OUT2 pins in parallel (pin 8
and 4 respectively). As the LNA minimum imped-
ance load is 1 k , the load impedance on each pin
LNA-OUT1 or LNA-OUT2 must be 2 k minimum.
The series 50
decouple the LNA supply voltage (pin 5), improv-
ing noise performance.
AMP and LIM sections: Amplifier and Limitor
The first filter output is connected to the intermedi-
ate amplifier AMP. The gain of AMP is typically 20
dB. The second filter is connected between the
output of AMP and the input of the limitor LIM. The
60 dB limitor LIM provides a constant amplitude
signal to the FM demodulator. It reduces the AM
parasitic effects into the FM demodulator.
Figure 4 : AMP and LIM schematic
FM demodulator section
The FM demodulator is a classical quadrature de-
modulator based on a multiplier. The quadrature is
performed with the tank circuit Llo inductor and
Clo capacitor. The tank circuit is tuned on the re-
ceiving frequency.
The Rlo resistor is connected in parallel with Llo
and Clo to reduce the Q factor of the tank circuit. It
LNA
output
resistor and the 100 nF capacitor
is
directly
connected
to
allows to adjustment of the demodulation charac-
teristic. For a given transmitting deviation, a lower
value of Rlo gives a lower demodulated amplitude
and reduces the distortion.
The AC amplitude on pin 18 must not exceed 300
mV
odes of the circuit.
The low output impedance of the demodulator
(MIX-OUT pins) drives the external volume control
and the de-emphasis filter.
Figure 5 : FM demodulator schematic
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 wide-
band ’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 typi-
cally 100kHz. The squelch level depends on the
value of the R
pin of the noise amplifier MUTE-IN (pin 23). The
detected noise is integrated with the Cpeak ca-
pacitor connected to MUTE-INT pin. The DC volt-
age on this pin follows the amplitude of the noise.
RMS
to prevent clipping by the internal ESD di-
MUTE
resistor in serie with the input
TSH511
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