GENERAL DESCRIPTION
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.

FEATUREs
• Wide supply voltage range
• Automatic mono/stereo switching (pilot presence detector)
• Smooth stereo-to-mono change-over at weak signals (signal-dependent stereo channel separation)
• LED driver for stereo/mono indicator
• Suppresses:
   third harmonics (114 kHz) of multiplexed signal to prevent interference from strong adjacent channels;
   phase distortion due to the 57 kHz signal from VWF transmitters
• Pilot cancelling circuit to give added suppression of 19 kHz stereo pilot tone (up to 25 dB)
• IF filter roll-off compensation
• Source selector for radio or cassette input (typ. 90 dB)
• Mute circuit for 90 dB (typ.) muting of the output level
• Matrix and two output buffers with adjustable gain (max. 20 dB).