Hans,
The input bias current graph over temperature shown in the datasheet is typical in all versions of OPAx188. There are two distinct components to the OPAx188 input bias current:
- The first one is caused by the current leakage of the reverse-biased ESD protection diodes. At 25 deg C it is in few pA range BUT its magnitude roughly doubles for each 10 deg C rise in the ambient temperature.
- The second component is the integrated value of the input bias current spikes caused by the parasitic capacitance during opening and closing of the input chopping switches – see below.
At room temperature the second component of around 160pA dominates the total input bias current while the first component becomes dominant above 85 deg C; 3pA at 25C becomes 3pA*2^6=192pA @85C causing IB rise above 85C shown in the IB vs Temperature graph and reaching 3nA at 125C (3pA*2^10=~3nA).
