Output current drift in VI converter using AD8276 and ADA4610-2

Hello,

I designed a VI converter using AD8276 difference amplifier and ADA4610-2 operational amplifier as shown on the schematic attached.

The circuit was designed with reference to CN0099 current source reference design.

During the measurement, the input VIN is connected to AGND and the output is monitored at IOUT pin. The power supplies are AVDD=+15V, AVSS=-15V.

But unfortunately, the circuit generates a big drift about 16 pA range as shown on the plot but I expected sub-pico ampere drift.

Please suggest any comments on the schematic, additional circuits, tests and even layout to reduce the current drift.

Thanks in advance.

Choon

attachments.zip