The U2860B includes two identical sound IF channels.
Each consists of a limiter amplifier, PLL FM demodulator
and AF amplifier. Additionally, this circuit contains a
squelch function, mute switch and internal voltage
The intercarrier signals are fed through external ceramic
bandpass filters to a 7-stage limiter amplifier. This
guarantees high input sensitivity and excellent
PLL FM Demodulators
The alignment-free “Phase Locked Loop” (PLL) demo-
dulator covers a wide frequency range of 4.5 MHz up to
6.5 MHz with low noise performance. The linear voltage
to frequency characteristic results in low harmonic
distortion. The free-running frequency of the internal
VCO circuit is about 5.5 MHz. For this frequency, the
input sensitivity and VCO locking is optimal. An addi-
tional external resistor at Pin 10 allows a frequency shift
of ±1 MHz via an internal offset current. With this option,
it is possible to shift the optimum conditions to the upper
frequency (6.5 MHz) or to the lower frequency
(4.5 MHz). The offset current acts simultaneously on
both VCO circuits. If no resistor is connected, the offset
current is disabled.
The demodulated signals are amplified to 500 mVrms
with low output impedance at the audio outputs (Pin 6 and
Pin 7). AC decoupling at Pin 8 and Pin 9 of the audio am-
plifiers leads to high common mode rejection.
For channel 2 the audio output amplifier and VCO2 is
muted automatically (squelch) when the second sound
carrier is not present. This avoids a wrong identification
for stereo and dual sound in the stereo decoder. Therefore,
with mono sound, there is no output signal at Pin 6. The
automatic squelch function can be disabled by switching
Pin 4 to ground.
Simultaneously muting of both circuits is possible by
switching Pin 3 to ground.
Internal Voltage Stabilizer
The internal bandgap reference ensures constant
performance independent of supply voltage and
Extended Type Number
Rev. A1, 17-Jun-96