I am trying to perform SPICE Analysis of Operational Amplifier Voltage Noise Analysis for the AD8021 Low Noise Operational Amplifier.
As per the data sheet the Voltage Noise specification is as follows :
The Flicker Noise is at about 40nV/rt.Hz at 10 Hz and tapers down to a broadband white noise of about 2.1nV/rt.Hz at about 100kHz.
I am trying to generate the same results in LTSpice using a buffer operational amplifier circuit as shown below :
The results obtained are as follows:
Now in the above Output Noise Plot, I am seeing the flicker noise start off in agreement with the datasheet noise spec of around 40nV/rt. Hz at 10Hz and tapers down to a value which is far off from the data sheet specs at 1kHz. Then proceeding further down, we are finding that the White Noise (Broadband) Component is of the order of 7.55nV /rt.Hz at 100kHz whereas the datasheet lists a 2.1nV/rt.Hz value. This reading seems to be significantly off.
I tried replicating the results with other SPICE Simulators like TINA-TI from TI. The Flicker Noise component starting point and trend seems to be matching in that case, but the White Noise Component is steady at 5.52nV/rt. Hz., which is also more than twice the figure quoted in the datasheet specs.
Am I doing something wrong or is there an accuracy limitation in the AD8021 SPICE Model provided in the Analog Devices Page for Noise Simulations ?