STWBC2-HP datasheet(32/96 Pages) STMICROELECTRONICS

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Table 23. Main PWM operating parameters

Parameter

Value

Frequency

40 MHz max.

Phase count

Number of signal generation steps

FSK FIFO data size

72-bit

Step coarse time value

2 to 4095

Step fine time value

0 to 16

FSK FIFO cycle count

1 to 1023

2.2.1.6

Configuration register overview

For the HR-PWM complete configuration register list overview please contact our sales representative.

2.2.2

Phase demodulator

2.2.2.1

Overview

The phase demodulator is used to detect the variation of tank phase linked to the Rx modulation. The phase

demodulator provides a digital output being the detected modulation.

2.2.2.2

Feature list

•

Variable input frequency decimator

•

3rd order digital LP & HP filter with programmable cut-off frequency

•

Comparator with programmable hysteresis

2.2.2.3

Functional description

Here below is shown the internal circuit block diagram.

Figure 35. Phase modulator block diagram overview

The Main PWM provides chronometer values. These values are sampled in a form coarse + fine.

The phase/frequency demodulator uses chronometer information. The times captured at each half-wave of Main

PWM are summed together. The sample rate is a direct function of PWM frequency so variable from 100 ks/s to

300 ks/s. A simple decimation is implemented using an exponential average. The average value is sampled at 40

ks/s fixed sample rate. A filtering machine calculates the required LPF & HPF to select the modulation bandwidth.

Finally, a comparator with 0 provides a digital 1bit form of the demodulation.

The exponential average computes the following formulae at each Input sample:

Average=Average+ Input− Average4

When the 40 ks/s sampling time occurs, the Average/4 value is captured and is used by the filtering machine.

After the sampling, the Average value is initialized at the first incoming sample with the following formulae:

Average=4*Input

The filtering machine runs HPF and LPF filters to select the modulation bandwidth. The filters have the following

equations:

STWBC2-HP

Digital AFE functions

DS13825 - Rev 1.0

page 32/96

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