SBOA590 November   2024 OPA186 , OPA206 , OPA328 , OPA391 , OPA928

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Input Offset Voltage (VOS) Definition
    1. 1.1 Input Offset Voltage Drift (dVOS/dT) Definition
    2. 1.2 VOS and VOS Temperature Drift Inside the Amplifier
    3. 1.3 Laser Trim to Adjust Performance
    4. 1.4 Package Trim (e-Trim™) to Adjust Performance
  5. 2Input bias current (IB) definition
    1. 2.1 Input Bias Current (IB) and IB Temperature Drift Inside the Amplifier
    2. 2.2 Derivation of IB Conversion to VOS
    3. 2.3 Internal Bias Current Cancelation
    4. 2.4 Super Beta Input Transistors
  6. 3Other Factors Influencing Offset
    1. 3.1 Finite Open Loop Gain (AOL)
    2. 3.2 Common Mode Rejection Ratio (CMRR)
    3. 3.3 Power Supply Rejection Ratio (PSRR)
    4. 3.4 AOL, CMRR, and PSRR Over Frequency
    5. 3.5 Electromagnetic Interference Ratio (EMIRR)
    6. 3.6 Mechanical Stress Induced Offset Shift
    7. 3.7 Parasitic Thermocouples
    8. 3.8 Flux Residue and Cleanliness
  7. 4Zero-drift Amplifiers to Minimize VOS and VOS Drift
  8. 5Calibration of VOS, IB, and Gain Error
  9. 6References
  10. 7Revision History

Electromagnetic Interference Ratio (EMIRR)

Electromagnetic interference rejection ratio (EMIRR) is a measure of how high frequency signals that are outside of the op amps bandwidth can impact VOS. Specifically, the EMIRR test directly couples a sinusoidal waveform with frequency ranging from 10 MHz to 10 GHz and looks at the shift in VOS. It may seem unusual that a DC parameter such as offset is affected by signals outside the bandwidth of the amplifier. However, this high-frequency AC input signal undergoes a rectification by internal diodes and is converted from a high frequency AC signal to a change in DC operation of the amplifier (VOS). This test can be thought of as a conducted immunity test. The details of how the EMIRR is tested is covered in EMI Rejection Ratio of Operational Amplifiers.

Figure 3-10 shows the graph of EMIRR for OPA206. As an example, assume a 40 mVpk, 100 MHz noise signal is applied to the noninverting input of the amplifier. The shift in VOS can be calculated to be 90 µV using Equation 35.

Equation 35. ΔVOS=VRF_PEAK2100mVpk10 - EMIRR/20=40mVpk2100mVpk10-45dB/20=90μV
OPA206 EMIRR vs Frequency for
                    OPA206 Figure 3-10 EMIRR vs Frequency for OPA206