TDA7021 FM Radio Circuit for MTS

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The TDA7021T integrated radio receiver circuit is for portable radios, stereo as well as mono, where a minimum of periphery is important in terms of small dimensions and low cost. It is fully compatible for applications using the low-voltage micro tuning system (MTS). The IC has a frequency locked loop (FLL) system with an intermediate frequency of 76 kHz. The selectivity is obtained by active RC filters. The only function to be tuned is the resonant frequency of the oscillator. Interstation noise as well as noise from receiving weak signals is reduced by a correlation mute system. Special precautions have been taken to meet local oscillator radiation requirements. Because of the low intermediate frequency, low pass filtering of the MUX signal is required to avoid noise when receiving stereo. 50 kHz roll-off compensation, needed because of the low pass characteristic of the FLL, is performed by the integrated LF amplifier. For mono application this amplifier can be used to directly drive an earphone. The field-strength detector enables field-strength dependent channel separation control