3.3.6 Interface to TX_DSP

The TX DSP controls the frequency versus time behavior of the PLL in TXMode. The FSK modulation is performed by modifying the ffreq[17:0] input signal to the fractional-N PLL. This block contains a preemphasis filter and a Gauss shaping filter. The preemphasis counteracts the low-pass function of the PLL, whereas the Gauss filter shapes the frequency versus time of ffreq[17:0] to perform GFSK modulation. Because of these features, the ATA8510/15 is able to modulate data rates up to 80 kBit/s Manchester and 120 kBit/s NRZ with a maximum frequency deviation of ±93 kHz.

In RxMode, the TX DSP uses the FFREQ1 and routes it directly to the SDM. In TxMode, the FFREQ1 is used for ASK modulation and routed directly to the SDM. In the case of FSK modulation, the FFREQ1/FFREQ2 are used for the low/high frequency setting (see TX DSP).