LME49880

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SNAS455C – DECEMBER 2009 – REVISED APRIL 2013

Figure 19. Settling Time Test Circuit

Figure 20. Slew Rate Test Circuit

DISTORTION MEASUREMENTS

The vanishingly low residual distortion produced by LME49880 is below the capabilities of all commercially

available equipment. This makes distortion measurements just slightly more difficult than simply connecting a

distortion meter to the amplifier’s inputs and outputs. The solution, however, is quite simple: an additional

resistor. Adding this resistor extends the resolution of the distortion measurement equipment.

The LME49880’s low residual distortion is an input referred internal error. As shown in Figure 21, adding the 10

Ω

resistor connected between the amplifier’s inverting and non-inverting inputs changes the amplifier’s noise gain.

The result is that the error signal (distortion) is amplified by a factor of 101. Although the amplifier’s closed-loop

gain is unaltered, the feedback available to correct distortion errors is reduced by 101, which means that

measurement resolution increases by 101. To ensure minimum effects on distortion measurements, keep the

value of R1 low as shown in Figure 21.

This technique is verified by duplicating the measurements with high closed loop gain and/or making the

measurements at high frequencies. Doing so produces distortion components that are within the measurement

equipment’s capabilities. This datasheet’s THD+N and IMD values were generated using the above described

circuit connected to an Audio Precision System Two Cascade.

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