OPA1622 Datasheet, PDF (19/36 Pages) Texas Instruments – OPA1622 SoundPlus™ High-Fidelity, Bipolar-Input, Audio Operational Amplifier

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8 Application and Implementation
OPA1622
SBOS727A – NOVEMBER 2015 – REVISED NOVEMBER 2015
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The low noise and distortion of the OPA1622 make it well suited for a variety of applications in professional and
consumer audio products. However, these same performance metrics also make the OPA1622 useful for
industrial, test-and-measurement, and data-acquisition applications. The example shown here is only one
possible application where the OPA1622 provides exceptional performance.
8.1.1 Noise Performance
Figure 49 shows the total circuit noise for varying source impedances with the op amp in a unity-gain
configuration (no feedback resistor network, and therefore no additional noise contributions).
The OPA1622 is shown with total circuit noise calculated. The op amp contributes both a voltage noise
component and a current noise component. The voltage noise is commonly modeled as a time-varying
component of the offset voltage. The current noise is modeled as the time-varying component of the input bias
current, and reacts with the source resistance to create a voltage component of noise. Therefore, the lowest
noise op amp for a given application depends on the source impedance. For low source impedance, current
noise is negligible, and voltage noise generally dominates. The low voltage and current noise of the OPA1622 op
amp make it a excellent choice for use in applications where the source impedance is less than 10 kΩ.
8.1.1.1 Noise Calculations
The equations in Figure 50 show the calculation of the total circuit noise using these parameters:
• e_n = voltage noise
• I_n = current noise
• R_S = source impedance
• k = Boltzmann’s constant = 1.38 × 10^–23 J/K
• T = temperature in kelvins (K)
8.1.1.2 Application Curve
1000
Source Resistor Noise Contribution
100
10
Total Noise
1
Voltage Noise Contribution
Current Noise Contribution
0.1
10
100
1k
10k
100k
1M
Source Resistance ( )
C302
Figure 49. Noise Performance of the OPA1622 in a Unity-Gain Buffer Configuration
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