Texas Instruments LM4562 Evaluation Board LM4562NABD LM4562NABD Datenbogen
Produktcode
LM4562NABD
Distortion Signal Gain = 1+(R2/R1)
+
-
LM4562
1000
:
R1
10
:
R2
Analyzer Input
Audio Precision
System Two
Cascade
Generator Output
Actual Distortion = AP Value/100
SNAS326K – AUGUST 2006 – REVISED DECEMBER 2013
APPLICATION INFORMATION
DISTORTION MEASUREMENTS
The vanishingly low residual distortion produced by LM4562 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.
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 LM4562’s low residual distortion is an input referred internal error. As shown in
, 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
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
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.
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 109. THD+N and IMD Distortion Test Circuit
The LM4562 is a high-speed op amp with excellent phase margin and stability. Capacitive loads up to 100pF will
cause little change in the phase characteristics of the amplifiers and are therefore allowable.
cause little change in the phase characteristics of the amplifiers and are therefore allowable.
Capacitive loads greater than 100pF must be isolated from the output. The most straightforward way to do this is
to put a resistor in series with the output. This resistor will also prevent excess power dissipation if the output is
accidentally shorted.
to put a resistor in series with the output. This resistor will also prevent excess power dissipation if the output is
accidentally shorted.
Copyright © 2006–2013, Texas Instruments Incorporated
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