MINIMIZING INPUT DESIGN PROBLEMS WITH THE TLV5590

Difficulty receiving messages on phases B and D of the FLEXTM signal while successfully receiving messages on Phases A and C usually indicates the receiver audio output is not properly interfaced to the TLV5590. The FLEX chipset requires proper consideration of the TLV5590 input interface to insure the correct digital conversion of the demodulated 4 Level FSK (Frequency Shift Keying) audio output of the RF section.

Understanding the input requirements of the TLV5590 and the typical 4 Level demodulated audio signal from the Receiver can correct this difficulty.

This application note explains these input requirements by discussing the following issues:

- General operation of the TLV5590

- Digital conversion of the 4 Level FSK audio signal

- Higher bit errors for 4 Level FSK

- Design considerations for TLV5590-Receiver interface

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