Input bias current (I_B) for the OPA4H014-SEP is specified as ±0.5 pA typical and ±10 pA maximum at T_A = 25°C. The input bias current was measured at V_S = ±9 V, with test limits of ±6 pA for guardbanding purposes.

All of the devices exposed to neutron irradiation were found to have a measured input bias current outside of the specified data sheet limits, for both the inverting and noninverting input terminals and across all four device amplifier channels.

• Of the three samples tested to 1 × 10¹² n/cm², a mean post-irradiation I_B value of 12.80 pA and maximum post-irradiation I_B value of 14.24 pA were recorded for the inverting inputs. A mean post-irradiation I_B value of 16.07 pA and maximum post-irradiation I_B value of 17.79 pA were recorded for the noninverting inputs.
• Of the three samples tested to 5 × 10¹² n/cm², a mean post-irradiation I_B value of 73.24 pA and maximum post-irradiation I_B value of 74.87 pA were recorded for the inverting inputs. A mean post-irradiation I_B value of 90.04 pA and maximum post-irradiation I_B value of 91.92 pA were recorded for the noninverting inputs.
• Of the three samples tested to 1 × 10¹³ n/cm², a mean post-irradiation I_B value of 145.54 pA and maximum post-irradiation I_B value of 162.34 pA were recorded for the inverting inputs. A mean post-irradiation I_B value of 177.73 pA and maximum post-irradiation I_B value of 198.79 pA were recorded for the noninverting inputs.

Input offset current (I_OS) was found to remain within the data sheet specifications for the devices tested to 1 × 10¹² n/cm², which suggests that the neutron displacement damage mechanism can affect both the inverting and noninverting inputs in a comparable manner. For samples dosed to 5 × 10¹² n/cm² and 1 × 10¹³ n/cm², while offset current exceeded the data sheet limits, the offset current remained within approximately 10% of the mean measured input bias current.

Figure 4-1 Sample Inverting Input Bias Current NDD Graph