#### Junus2012

##### Advanced Member level 5

Dear Friends

couple of days gone without posting a thread , the weekend is now finished and the work time started

I have attached you the AC response from my designed OTA

the OTA is a current mirror OTA which I had some questions about it in other posts.

In the picture, I have pointed at the pole frequencies (-45, -135).

the first question is , after the second pole, the gain should drop by the rate of -40 dB/decade, but in my figure it is not like that, I have tested the drop and it is giving me 13 dB/decade rather.

the second question, the Gain bandwidth product is constant only when the roll off is constant , in my design the roll off is constant and it is 20 db/decade untill the unity gain point, which make the GBW constant........ what about the case if the second pole is before the unity gain bandwidth, I never hear about how to deal with GBW in this case (without using the compensation miller capacitor)

the third question, if you know the GBW, how you could determine the DC gain (please prove it from my graph)

the fourth question : the far distance of the second pole from the first one will improve the PM (increase it), this because it will push far the accumulation of the second pole phase when it become 180. However, what about if the distance between the poles are increase by decreasing the first pole position ????????????, for me I am thinking it must degrade the phase margin coz the phase shift will approach the 180 earlier ..... practically is the reverse I am finding

Thank you all in advance

couple of days gone without posting a thread , the weekend is now finished and the work time started

I have attached you the AC response from my designed OTA

the OTA is a current mirror OTA which I had some questions about it in other posts.

In the picture, I have pointed at the pole frequencies (-45, -135).

the first question is , after the second pole, the gain should drop by the rate of -40 dB/decade, but in my figure it is not like that, I have tested the drop and it is giving me 13 dB/decade rather.

the second question, the Gain bandwidth product is constant only when the roll off is constant , in my design the roll off is constant and it is 20 db/decade untill the unity gain point, which make the GBW constant........ what about the case if the second pole is before the unity gain bandwidth, I never hear about how to deal with GBW in this case (without using the compensation miller capacitor)

the third question, if you know the GBW, how you could determine the DC gain (please prove it from my graph)

the fourth question : the far distance of the second pole from the first one will improve the PM (increase it), this because it will push far the accumulation of the second pole phase when it become 180. However, what about if the distance between the poles are increase by decreasing the first pole position ????????????, for me I am thinking it must degrade the phase margin coz the phase shift will approach the 180 earlier ..... practically is the reverse I am finding

Thank you all in advance