Likely pole locations for AD713, and reasons to use AD713 as unity gain amplifier?

Hi Sathyadev, 

The frequency plot will start to roll-off at a rate of 20dB/decade once it hits a pole. So for the same graph that you indicate, it does look like there's a pole that occurs at a frequency before 50Hz. Outside of this graph, there is not much more we can conclude regarding pole locations. 

I would say that your assumptions are correct. In general, a circuit is considered stable when the phase margin is greater than 35 degrees, so for this case where the phase margin is about 50 degrees, as you say, this is stable. 

We also have a rule of thumb to use an amplifier with 10 times the bandwidth of your circuit's frequency requirement to ensure stability. Given the frequency of operation of 1kHz, the 4Mhz of the AD713 is more than enough.

The choice of amplifier is really determined by the application. It can be determined by the input source and what is expected at the output, basically what the application requirements are. The AD713 has relatively good DC characteristics, fast settling time and relatively high slew rate, though, and these may have been factors in the choice of this amplifier.

Thanks!

Kris

Hi Sathyadev, 

The frequency plot will start to roll-off at a rate of 20dB/decade once it hits a pole. So for the same graph that you indicate, it does look like there's a pole that occurs at a frequency before 50Hz. Outside of this graph, there is not much more we can conclude regarding pole locations. 

I would say that your assumptions are correct. In general, a circuit is considered stable when the phase margin is greater than 35 degrees, so for this case where the phase margin is about 50 degrees, as you say, this is stable. 

We also have a rule of thumb to use an amplifier with 10 times the bandwidth of your circuit's frequency requirement to ensure stability. Given the frequency of operation of 1kHz, the 4Mhz of the AD713 is more than enough.

The choice of amplifier is really determined by the application. It can be determined by the input source and what is expected at the output, basically what the application requirements are. The AD713 has relatively good DC characteristics, fast settling time and relatively high slew rate, though, and these may have been factors in the choice of this amplifier.

Thanks!

Kris