Physical layer ST7570
20/26 Doc ID 17526 Rev 2
9 Physical layer
The ST7570 embeds a IEC-61334-5-1 PHY layer, which is based on the S-FSK (spread
FSK) modulation technique.
9.1 S-FSK principles
The S-FSK modulation technique is aimed at strengthening the classical FSK by adding
higher robustness against narrow-band interferers typical of a spread-spectrum approach.
Non-return-to-zero (NRZ) coding is used to map the binary data “0” or “1” to sinusoidal
carriers at frequencies f
0
and f
1
(Figure 11).
Figure 11. S-FSK waveform (time domain)
The absolute frequency deviation |f
0
- f
1
| is at least 10 kHz, in order to reduce the probability
that a narrow-band interferer could corrupt both carriers at the same time.
f
0
and f
1
can be set at any value in CENELEC bands A, B, D.
Figure 12. S-FSK waveform (frequency domain)
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