SBOS035C December   1995  – January 2026 INA2128

PRODUCTION DATA  

  1.   1
  2. 1Features
  3. 2Applications
  4. 3Description
  5. 4Pin Configuration and Functions
  6. 5Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6Application and Implementation
    1. 6.1 Application Information
    2. 6.2 Typical Application
      1. 6.2.1 Setting The Gain
      2. 6.2.2 Dynamic Performance
      3. 6.2.3 Noise Performance
      4. 6.2.4 Offset Trimming
      5. 6.2.5 Input Bias Current Return Path
      6. 6.2.6 Input Common-Mode Range
      7. 6.2.7 Low-Voltage Operation
      8. 6.2.8 Input Protection
      9. 6.2.9 Channel Crosstalk
  8. 7Device and Documentation Support
    1. 7.1 Device Nomenclature
    2. 7.2 Receiving Notification of Documentation Updates
    3. 7.3 Support Resources
    4. 7.4 Trademarks
    5. 7.5 Electrostatic Discharge Caution
    6. 7.6 Glossary
  9. 8Revision History
  10. 9Mechanical, Packaging, and Orderable Information

6.2.5 Input Bias Current Return Path

The input impedance of the INA2128 is extremely high—approximately 1010 Ω. However, a path must be provided for the input bias current of both inputs. This input bias current is approximately ±2 nA. High input impedance means that this input bias current changes very little with varying input voltage.

Input circuitry must provide a path for this input bias current for proper operation. Figure 6-3 shows various provisions for an input bias current path. Without a bias current path, the inputs float to a potential that exceeds the common-mode range of the INA2128 and the input amplifiers saturate.

If the differential source resistance is low, the bias current return path can be connected to one input (see the thermocouple example in Figure 6-3). With higher source impedance, using two equal resistors provides a balanced input with possible advantages of lower input offset voltage due to bias current and better high-frequency common-mode rejection.