AN3157

Circuit description

Doc ID 17105 Rev 1

7/26

2.2.4

Crosstalk cancellation network

The voltage front-end handles voltages of considerable amplitude, which makes it a

potential source of noise. Disturbances are readily emitted into current measurement

circuitry where they interfere with the actual signal to be measured. Typically, this produces

a non-linear error at small signal amplitudes and non-unity power factors. At unity power

factors, voltage and current signals are in phase and crosstalk between voltage and current

channels merely appears as a gain error, which can be calibrated. When voltage and

current are not in phase, crosstalk has a non-linear effect on the measurements, which

cannot be calibrated.

Crosstalk is minimized through good PCB planning and the proper use of filter components

in the crosstalk network. Recommended filter components are shown in Figure 4. The

network subtracts a signal proportional to the voltage input from the current input. This

prevents crosstalk.

Figure 4.

Daughterboard circuit schematic

1

3

4

5

2

VCC

VCC

VCC

VCC

CLK

CLK

NCLK

NCLK

NCLK

CLK

DAR

R18

0

C13 100n

U1

stpms1

1

2

3

4

9

10

11

12

17

18

vdd_reg

gnd_reg

vdd_ac

gnd_ac

vdd_av

vdd_d

ms0

ms1

e1

e2

J1

Card_Edge_10

F1

F2

F3

F4

F5

F6

F7

F8

F9

F10

S1

S2

S3

S4

S5

S6

S7

S8

S9

S10

C5

1u

C14

1u

VREG

170u

CLK

R7 1K 1%

R16

0

SH1

170u

JP1

1

2

3

4

5

6

7

8

C6

1u

JP2

1

2

3

4

5

6

7

8

TR1

E4622_X503

2

3

C7

5n

C12 100n

R14

10

R8 1K 1%

R6

3.4 1%

C8

5n

DAR

R15

0

D1

C3 22n

R1

82

VCC

C11

1u

N

R4 150k

R11

100 1%

R10

2.2M 1%

R2 150k

GND

R3 150k

D2

L1

220u

VCC

C2 1n

R5

475 1%

R17

10

R9

42.2k 1%

C1 470n

R13 150k

V1

460V

1

2

F

1

3

4

5

2

VCC

VCC

VCC

VCC

CLK

CLK

NCLK

NCLK

NCLK

CLK

DAR

R18

0

C13 100n

U1

stpms1

1

2

3

4

9

10

11

12

17

18

vdd_reg

gnd_reg

vdd_ac

gnd_ac

vdd_av

vdd_d

ms0

ms1

e1

e2

J1

Card_Edge_10

F1

F2

F3

F4

F5

F6

F7

F8

F9

F10

S1

S2

S3

S4

S5

S6

S7

S8

S9

S10

C5

1u

C14

1u

VREG

170u

CLK

R7 1K 1%

R16

0

SH1

170u

JP1

1

2

3

4

5

6

7

8

C6

1u

JP2

1

2

3

4

5

6

7

8

TR1

E4622_X503

2

3

C7

5n

C12 100n

R14

10

R8 1K 1%

R6

3.4 1%

C8

5n

DAR

R15

0

D1

C3 22n

R1

82

VCC

C11

1u

N

R4 150k

R11

100 1%

R10

2.2M 1%

R2 150k

GND

R3 150k

D2

L1

220u

VCC

C2 1n

R5

475 1%

R17

10

R9

42.2k 1%

C1 470n

R13 150k

V1

460V

1

2

F