TEA5581

The TEA5581 PLL stereo decoder is for car and medium-fi radios. It incorporates all the features provided by the TEA5580 together with a source selector, muting circuit and output amplifiers with adjustable gain. It also features a switch for radio or cassette function and a 228 kHz voltage-controlled oscillator (VCO) that is locked to the 19 kHz stereo pilot tone by a phase-locked loop (PLL) system. Subcarrier frequencies of 19, 38, 57 and 114 kHz are regenerated via I2L logic from the VCO output.

The PLL phase detector suppresses phase distortion due to the 57 kHz pilot tone from the German 'Verkehrs Warnfunk' (VWF) traffic warning system. Typical suppression of the 19 kHz stereo pilot tone is 40 dB. Adjacent channel interference is prevented by the use of two demodulators, one driven by the 38 kHz decoding signal and the other at 114 kHz to suppress the third harmonic of the multiplexed input signal.The gain of the input amplifier can be adjusted by an external resistor and the circuit includes  compensation for an IF filter typical roll-off frequency of 50 kHz (2 dB down at 38 kHz). The supply voltage range of the circuit is 7 V to 16 V.