Hello, i need to select relatively cheap operational amplifier for PH measurement circuit (2-3 Euros buying in low quantities). Circuit measures PH level with 0.01pH level of precision. Because PH sensor produces approximately 68mV per pH unit so 0.01pH difference gives 0.68mV in the pH sensor output.
I have used AD8617 opamp previously, but now it is discontinued. Now i am searching for replacement. The PCBs are already manufactured so i need direct replacement (pins must fit). I am trying to figure out which amplifier IC parameters are most important. So we have:
Offset voltage (mV);
Noise: (nV/√Hz);
Bandwidth;
Slew rate (V/us);
No phase reversal (not sure what it means??)
Low input bias current (pA);
Unity-gain stable.
I think the most important parameter is input bias current - i am searching with 1pA or less. How about other parameters mentioned above (or not mentioned)?
Found cheap Microchip opamps MCP6007 and MCP6477, both costs about 0.60 Euro. Also have found AD8646 - 3.45 Euro, AD8692 - 2.76Eur.
What you think?
I have used AD8617 opamp previously, but now it is discontinued. Now i am searching for replacement. The PCBs are already manufactured so i need direct replacement (pins must fit). I am trying to figure out which amplifier IC parameters are most important. So we have:
Offset voltage (mV);
Noise: (nV/√Hz);
Bandwidth;
Slew rate (V/us);
No phase reversal (not sure what it means??)
Low input bias current (pA);
Unity-gain stable.
I think the most important parameter is input bias current - i am searching with 1pA or less. How about other parameters mentioned above (or not mentioned)?
Found cheap Microchip opamps MCP6007 and MCP6477, both costs about 0.60 Euro. Also have found AD8646 - 3.45 Euro, AD8692 - 2.76Eur.
What you think?