AN2744 datasheet(34/56 Pages) STMICROELECTRONICS

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Board description

AN2744

34/56

Table 6

gives the parameters for setting the test conditions.

The received signal and noise level are measured with a spectrum analyzer at both the

ST7538Q RAI pin and the measurement port of the CISPR artificial network. To obtain the

right value, the noise level is measured in absence of the transmitted signal. The 3 kHz

resolution bandwidth of the spectrum analyzer has been chosen to fit the spectrum of the

transmitted FSK signal at 2400 baud.

Figure 30

represents the measured BER vs. SNR curve at both RAI pin and measurement

port of the CISPR network in presence of white noise. It may be noted that a BER of 10-3

corresponds to a value of SNR which is a little higher than 12 dB, as it can be expected for a

non-ideal FSK demodulator. The curve of Figure 30 is valid for both 72 and 86 kHz

channels.

Table 6.

Noise immunity test settings

Parameter

Value

Received signal at RAI pin

78 dBµV rms

Frequency

72 kHz

Baud rate

2400

Deviation

Detection method

Carrier with conditioning

Detection time

3 ms

Sensitivity

High

Input filter

Off

Transmitted sequence

AACC h

S.A. resolution BW

3 kHz

Figure 30.

Measured BER vs. SNR curve (typical), white noise

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

SNR (dB)

RAI

CISPR

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

SNR (dB)

RAI

CISPR

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