SBOSAI7 November   2023 OPA891

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information: OPA891
    5. 5.5 Thermal Information: OPA2891
    6. 5.6 Electrical Characteristics: RL = 150 Ω
    7. 5.7 Electrical Characteristics: RL = 1 kΩ
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Offset Nulling
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Driving a Capacitive Load
      2. 7.1.2 Low-pass Filter Configurations
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Selection of Multiplexer
        2. 7.2.2.2 Signal Source
        3. 7.2.2.3 Driving Amplifier
        4. 7.2.2.4 Driving Amplifier Bandwidth Restriction
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 General PowerPAD™ Design Considerations
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.2.2.4 Driving Amplifier Bandwidth Restriction

Restricting excess bandwidth use by including a passive RC filter before the ADC results in better SNR and THD. However, restricting the bandwidth too much results in a excessive operational amplifier settling time. If the amplifier output does not settle quick enough, some residual charges from the previous channel remain in the next sampling interval and appear as crosstalk. One approach to solve this settling issue is to reduce the throughput of the ADC. However, the high sample rate ADC is often selected to meet the need to acquire higher frequency signals, limiting the freedom to reduce the ADC throughput. Due to these tradeoffs, the choice of the filter capacitor becomes critical. Figure 7-6 and Figure 7-7 show SNR and crosstalk as a function of the filter capacitor.

Figure 7-8 shows input settling behavior with three different filter capacitor values. The value of the capacitor changes to filter bandwidth. As the filter bandwidth increases, the settling time improves as shown in Equation 4.

Equation 4. Filter Bandwidth ≅12πR1C1