SBOS931B January   2019  – August 2019 OPA1671

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Electret Microphone Preamplifier
      2.      OPA1671 Voltage Noise Density
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Operating Voltage
      2. 7.3.2 Input Bias Current
      3. 7.3.3 Common-Mode Voltage Range
      4. 7.3.4 EMI Susceptibility and Input Filtering
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Capacitive Loads
      2. 8.1.2 Noise Performance
      3. 8.1.3 Basic Noise Calculations
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 TINA-TI (Free Software Download)
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2 Detailed Design Procedure

The preamplifier circuit uses a noninverting gain configuration to allow for high input impedance, with independent gain-setting resistor values. DC bypass is accomplished with C2 and C3, with the low frequency poles set by C2, R4, C3 and R5; see Equation 1 and Equation 2.

Equation 1. OPA1671 opa1671_equation1.gif
Equation 2. OPA1671 opa1671_equation2.gif

The filter cutoff frequency is determined by a higher frequency pole, set by R5 and C4.

Equation 3. OPA1671 opa1671_equation5.gif

The gain of the circuit in the passband is set by R5 and R6.

Equation 4. OPA1671 opa1671_equation3.gif

The ouput noise of the circuit (ignoring the electret microphone intrinsic noise and impedance) is the RSS average noise contribution from R5 and the input voltage noise of OPA1671. R5 was selected for minimal noise contribution without requiring a dc blocking cap. (C3) larger than 10 µF. See Equation 5 for the output noise density calculation at 10 kHz.

Equation 5. OPA1671 opa1671_equation4.gif