It is surprising, but the second graph shows the inverting gain - measured with a test signal at the inverting input (because the phase shift is -180deg for low frequencies, including DC). This is rather uncommon but creates no problem at all (normally, the non-inv. gain is given with 0 deg. for low frequencies). So - this difference does not mean anything.

More important is the phase shift at the frequency for unity gain. This value determines if resp. how far the loop gain phase will be from the critical value (for unity gain feedback). This critical value is -180deg for the 1st diagram and 0 deg for the 2nd diagram. This difference is called minimum PHASE MARGIN PM.

In the first diagram we have app. (180-100)=80 deg. and from the 2nd diagram we derive (45-0)=45 deg.

Hence, as far as the phase margin (stability margin against self-oscillations) for unity gain feedback is concerned, the first device is better (more stability margin).

It is surprising, but the second graph shows the inverting gain - measured with a test signal at the inverting input (because the phase shift is -180deg for low frequencies, including DC). This is rather uncommon but creates no problem at all (normally, the non-inv. gain is given with 0 deg. for low frequencies). So - this difference does not mean anything.

More important is the phase shift at the frequency for unity gain. This value determines the distance of the loop gain phase from the critical value (in case of unity gain feedback). This critical value is -180deg for the 1st diagram and 0 deg for the 2nd diagram. This difference is called minimum PHASE MARGIN PM. For PM=0 the circuit with unity gain feedback is unstable.

In the first diagram we have app. PM=(180-100)=80 deg. and from the 2nd diagram we derive PM=(45-0)=45 deg.

Hence, as far as the phase margin (stability margin against self-oscillations) for unity gain feedback is concerned, the first device is better (more stability margin).