9 Procedure for Selecting a Zero-Drift Amplifier

Use the following steps to select a zero-drift amplifier:

1. Does your application benefit from an amplifier with low input offset voltage, very low offset drift, or low flicker noise? If these parameters are not important in your application,look at traditional amplifiers as opposed to zero-drift amplifiers. Review columns B through E of Table 9-1 to find zero drift amplifiers that meet your requirements.
2. Compare your source impedance to column F in Table 9-1. Only use amplifiers less than or equal to this maximum source impedance (see Section 5 for details).
3. To optimize noise, the feedback network and source impedance needs to be less than column G in Table 9-1 (see Section 7 for details).
4. Check to make sure that the DC bias current does not translate into significant offset. This is most important in higher temperature applications, because the DC bias current increases over temperature. See Section 6.
5. Some applications can benefit from balancing the source impedance with the feedback impedance. This is generally useful for higher temperature applications as I_BOS at higher temperature can be significantly less than I_B. Nevertheless, this approach typically does not help for the chopping bias current transients, because these transients are generally not well balanced. For I_B cancellation, the feedback network parallel impedance is set equal to the source impedance (R_s = R_f || R_g ). See Section 6.
6. Consider the chopper noise. If your circuit is in gain, the closed-loop bandwidth generally is significantly less than the chopping frequency. Thus, the broadband noise will be gained up relative to the chopping transients. Adding an external filter can also be used to minimize the chopping noise. Chopping noise is of the greatest concern when the amplifier is in unity gain, with no external filter. Also, large source or feedback impedances increase the amplitude of the chopping noise (see Section 7 for details).
7. Finally, assuming all other criteria are acceptable, check all other amplifier specifications. For example, is bandwidth, slew rate, and output drive meeting your application specific requirements.