INA818 datasheet(21/39 Pages) TI1

21 / 39 page

Frequency (Hz)

100

120

140

10M

100M

10G

D048

Frequency (Hz)

100

10M

100M

10G

D047

EMIRR (dB)

RF _ PEAK

100 mV

INA818

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SBOS894 – APRIL 2019

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8.3.1.1 Gain Drift

The stability and temperature drift of the external gain setting resistor (RG ) also affects gain. The contribution of

RG to gain accuracy and drift is determined from Equation 1.

The best gain drift of 5 ppm/

℃ (maximum) is achieved when the INA818 uses G = 1 without RG connected. In

this case, gain drift is limited by the mismatch of the temperature coefficient of the integrated 40-kΩ resistors in

the differential amplifier (A3). At gains greater than 1, gain drift increases as a result of the individual drift of the

25-kΩ resistors in the feedback of A1 and A2, relative to the drift of the external gain resistor (RG.) The low

temperature coefficient of the internal feedback resistors improves the overall temperature stability of applications

using gains greater than 1 V/V over alternate solutions.

Low resistor values required for high gain make wiring resistance an important consideration. Sockets add to the

wiring resistance and contribute additional gain error (such as a possible unstable gain error) at gains of

approximately 100 or greater. To maintain stability, avoid parasitic capacitance of more than a few picofarads at

RG connections. Careful matching of any parasitics on the RG pins maintains optimal CMRR over frequency.

8.3.2 EMI Rejection

Texas Instruments developed a method to accurately measure the immunity of an amplifier over a broad

frequency spectrum extending from 10 MHz to 6 GHz. This method uses an EMI rejection ratio (EMIRR) to

quantify the ability of the INA818 to reject EMI. The offset resulting from an input EMI signal is calculated using

Equation 2:

where

•

VRF_PEAK is the peak amplitude of the input EMI signal.

(2)

Figure 54 and Figure 55 show the INA818 EMIRR graphs for differential and common-mode EMI rejection across

this frequency range. Table 3 lists the EMIRR values for the INA818 at frequencies commonly encountered in

real-world applications. Applications listed in Table 3 are centered on or operated near the frequency shown.

Depending on the end-system requirements, additional EMI filters may be required near the signal inputs of the

system. Incorporating known good practices, such as using short traces, low-pass filters, and damping resistors

combined with parallel and shielded signal routing may also be required.

Figure 54. Common-Mode EMIRR Testing

Figure 55. Differential Mode EMIRR Testing

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