SLOS712I – JANUARY 2011 – REVISED OCTOBER 2016
Typical Applications (continued)
220.127.116.11 Design Requirements
Design a low distortion, single-ended input to single-ended output audio amplifier using the OPA836 device. The
2700-series audio analyzer from Audio Precision is used as the signal source and also as the measurement
OPA836 Unity Gain Config.
Table 6. Design Requirements
1 KHz Tone Frequency
>110 dBc SFDR
300 Ω and
18.104.22.168 Detailed Design Procedure
The OPA836 device is tested in this application in a unity-gain buffer configuration. A buffer configuration is
selected for maximum loop gain of the amplifier circuit. At higher closed-loop gains, the loop gain of the circuit
reduces, which increases the harmonic distortion. The relationship between distortion and closed-loop gain at a
fixed input frequency is shown in Figure 36 in Typical Performance Graphs: VS = 5 V. The test was performed
under using resistive loads of 300 Ω and 100 KΩ. Figure 34 shows the distortion performance of the amplifier
versus the resistive load. Output loading, output swing, and closed-loop gain play a key role in determining the
distortion performance of the amplifier.
The 100-pF capacitor to ground on the input helped to decouple noise pickup in the lab
and improved noise performance.
The Audio Precision was configured as a single-ended output in this application circuit. In applications where a
differential output is available, the OPA836 device can be configured as a differential-to-single-ended amplifier as
shown in Figure 67. Power-supply bypassing is critical to reject noise from the power supplies. A 2.2-μF supply
decoupling capacitor must be placed within 2 inches of the device and can be shared with other operational
amplifiers on the same board. A 0.1-μF supply decoupling capacitor must be placed as close to the supply pins
as possible, preferably within 0.1 inch. For a split supply, a capacitor is required for both supplies. A 0.1-µF
capacitor placed directly between the supplies is also beneficial for improving system noise performance. If the
output load is heavy, such as 16 Ω to 32 Ω, performance of the amplifier could begin to degrade. To drive such
heavy loads, both channels of the OPA2836 device can be paralleled with their outputs isolated with 1-Ω
resistors to reduce the loading effects.
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