New Details About the Frequency Behavior of Irradiated Bipolar Operational Amplifiers

The frequency behavior of a bipolar operational amplifier (op amp) is always expected to worsen when the device is irradiated. In other words, parameters like the slew rate and the gain-bandwidth product are to decrease after either neutron or gamma tests. However, some neutron and TID tests performed on a large variety of bipolar op amps have shown that the evolution of the frequency behavior is not as simple as it is usually believed. In fact, there is evidence of an increasing influence of the power supply values on the former parameters, which can be extremely important in some devices. Also, the relationship among different frequency parameters has been investigated and, finally, an interesting and scarcely reported phenomenon is depicted. This phenomenon is the appearance of spontaneous oscillations in fed-back op amps, without doubt related to the modification of the gain and phase margins of the devices