Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsDev KitsPCB design board

100 mV

EMIRR = EMIRR

+ 20 log

= EMIRR

± 20 dB

100 mV

RF_PEAK_B

100 mV

= EMIRR

100 mV

RF_PEAK_B

= 20 log

EMIRR = 20 log

+ 20 log

RF_PEAK

EMIRR

RF_PEAK

C·V

RF_PEAK

C·V

RF_PEAK

= 20 log

EMIRR Measurement

www.ti.com

The effect of the quadratic relation (between applied RF level and resulting offset voltage shift) on the

EMIRR is easily illustrated. In the definition of EMIRR, ΔV

is replaced by an expression accounting for

the quadratic dependency on the RF signal level, yielding:

(2)

Equation 2 shows that for a double RF signal level the EMIRR is 6 dB lower, that is, doubling the RF level

quadruples the offset voltage shift.

For the EMIRR a standard test condition of 100 mV

is used, which is equivalent to −20 dBV

. For EMI

hardened op amps it might be necessary, however, to use larger signals for obtaining an offset shift well

beyond the noise level of the measurement test circuit. In that case it is required to indicate the used RF

level when specifying the EMIRR. It should be noted that EMIRR numbers obtained for different RF signal

levels hamper the comparison of the corresponding op amps. Therefore, it is preferable to convert the

EMIRR obtained for an RF signal level other than 100 mV

to the standard EMIRR. The expression for

this conversion is obtained by scaling the used signal level, V

RF_PEAK_B

, to 100 mV

according to:

(3)

For example, assume EMIRR

is measured for an op amp. Converting this to the standard EMIRR yields:

(4)

The interpretation of the EMIRR parameter is straight forward. When two op amps have an EMIRR that

differ by 20 dB, the resulting error signal as a result of EMI, when used in identical setups, differ by 20 dB

as well. So, the higher the EMIRR the more robust the op amp.

4 EMIRR Measurement

Measuring EMIRR is straightforward and requires three basic actions:

1. Applying an RF signal in a well defined way to an op amp pin under test.

2. Measuring the offset voltage with the RF signal switched off and again with the RF signal switched on.

3. Calculate the resulting offset voltage shift from which the EMIRR can be obtained.

The EMIRR is a measure to compare the EMI performance of op amps. To have a fair comparison, it is a

prerequisite that the conditions for these EMIRR measurements are equal, and that the influence of the

test setup, such as instruments and test board, are kept to a minimum. The presented measurement test

circuit and method ensures that the EMIRR measurements are accurate and repeatable. The core is a

simple board with standard components. The equipment used is standard off the shelf as well, such as a

power supply, an RF generator, and a multi-meter. Special attention needs to be paid to the way the RF

AN-1698 A Specification for EMI Hardened Operational Amplifiers SNOA497B–September 2007–Revised April 2013

Submit Documentation Feedback