AN2744 datasheet(29/56 Pages) STMICROELECTRONICS

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AN2744

Board description

29/56

5.1.5

Input impedance

The input impedance of a power line communication node is another critical point. Figure 22

through 25 show the curves of input impedance magnitude vs. frequency in both Tx and Rx

mode for the two channels.

The impedance magnitude values prove that the ST7538Q dual channel reference design

board is compliant with EN50065-7 normative, which sets the following minimum impedance

constraints for this kind of equipment:

– Tx mode: free in the range 3 to 95 kHz, 3

Ω from 95 to 148.5 kHz

– Rx mode: 10

Ω from 3 to 9 kHz, 50 Ω between 9 and 95 kHz only inside signal 20 dB-

bandwidth (free for frequencies outside signal bandwidth), 5

Ω from 95 to 148.5 kHz

Figure 21.

Simulated frequency response of the Rx active filter for 86 kHz channel with tolerance

effect

4E4

5E4

6E4

7E4

8E4

9E4

1E5

2E5

3E4

3E5

-7

-6

-5

-4

-3

-2

-1

-8

2 dB

4E4

5E4

6E4

7E4

8E4

9E4

1E5

2E5

3E4

3E5

-7

-6

-5

-4

-3

-2

-1

-8

2 dB

Figure 22.

Measured input impedance magnitude of the coupling interface in Rx mode for the 72

kHz channel (typical curve)

100

1000

1E+04

1E+05

1E+06

Freq (Hz)

EN50065

EN50065--7

100

1000

1E+04

1E+05

1E+06

Freq (Hz)

100

1000

1E+04

1E+05

1E+06

Freq (Hz)

EN50065

EN50065--7

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