op amp gain curve (frequency response )

[ali kotb]

attached below the gain curve of certain Opamp
i dont have schematic design , i want to understand how come to have -ve slope gain while phase is increasing ?
is it RHP zero ?
can any body explain to me the low freq gain effect in the graph (0- 10Hz)

thank u , ali

 

[zorro]

Hi Ali,

Looking how looks the plot increasing frequency, it seems that:

(1) at dc (freq=0) gain is quite high and phase is 180 deg (inverting amplifier)
(2) al some very very low frequency (not seen in the plot) there is a real pole; gain starts to drop at 20 dB/decade an phase decreases towards +90 deg
(3) there is a real zero at about 4 Hz (in LHP) that stops the drop of gain and raises phase up to 180 deg
(4) there is a real pole at about 70 MHz that starts a drop in amplitude and produces a total lag in phase of 90 deg
(5) there is a real zero in RHP at about 400 MHz that stops drop in amplitude and lags the phase 90 deg more

At low frequencies (between 1 and 10 Hz), the negative slope in gain is produced by the pole (2), and the increasing phase by the zero (3).
Regards

Z

 

[ali kotb]

thank u =D