AN2317 - Application

External Circuit Design

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1.4

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 it will interfere with the actual signal to be measured. Typically, this shows as

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

At unity power factor, 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 will have a non-linear effect on the

measurements, which cannot be calibrated.

Crosstalk is minimized by means of good PCB planning and the proper use of filter

components in the crosstalk network. Recommended filter components are shown in

Figure 10. The network subtracts a signal proportional to the voltage input from the current

input. This prevents crosstalking within the STPM01. The signal subtraction is calculated in

Equation 25 and Equation 26.

Equation 25

Equation 26

Note:

This network must be applied to every STPM01 design, from the voltage channel to each

current channel.

Figure 10.

Crosstalk Network

V

R15

R15

R19

R15

+

----------------------------- V

VCI

R15

R19

----------- V

VC I

⋅

≅

⋅

=

V

CC I

R1

R21

R1

+

------------------------- V

R15

R1

R21

----------- V

R15

⋅

≅

⋅

R1

R21

-----------

R15

R19

----------- V

VCI

1.18e

6

–

V

VCI

≅

⋅⋅

==

R19

42.2k

–

+

VVCI

Voltage

Channel

Input

VCCI

Current

Channel

Input

+

–

R15

100

R1

1k

R21

2M

AI12908