Datasheet

Distortion Signal Gain = 1+(R2/R1)
+
-
LME49710
1000:
R1
10:
R2
Analyzer Input
Audio Precision
System Two
Cascade
Generator Output
Actual Distortion = AP Value/100
LME49710
www.ti.com SNAS376C –NOVEMBER 2006–REVISED APRIL 2013
APPLICATION INFORMATION
DISTORTION MEASUREMENTS
The vanishingly low-residual distortion produced by LME49710 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 LME49710’s low-residual distortion is an input referred internal error. As shown in Figure 95, adding the 10Ω
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 95.
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.
Figure 95. THD+N and IMD Distortion Test Circuit
Copyright © 2006–2013, Texas Instruments Incorporated Submit Documentation Feedback 25
Product Folder Links: LME49710