jebaspaul
Junior Member level 3
Qns: Assume Vdd : 0 to 3.3V
opamp DC gain : 60db
opamp is connected in unity feedback.
positive terminal is connected to 2.15 V.
Upto which precision my opamp will settle? (take settling time as infinity)
Ans:
since my supply is 0 to 3.3 V. we can assume 1.65 as reference voltage.
now at worst case;
compute 2.15 - 1.65 ==> 0.5 V
worst opamp error is : 0.5 / (DC gain) ==> 500uV
What is important in this to note??
in all text books they will assume this reference as 0 V. so they will simply tell that opamp gain error is given by;
% error = Adc /(1 + Adc*B) ; B - feedback factor.
using the above formula; % error = 999.0 uV ==> not exactly correct.
We can't use this formula blindly. We need to know initial operating point of opamp. worst case we will assume mid of supply voltage as reference voltage.
If there is any misunderstanding correct me.
opamp DC gain : 60db
opamp is connected in unity feedback.
positive terminal is connected to 2.15 V.
Upto which precision my opamp will settle? (take settling time as infinity)
Ans:
since my supply is 0 to 3.3 V. we can assume 1.65 as reference voltage.
now at worst case;
compute 2.15 - 1.65 ==> 0.5 V
worst opamp error is : 0.5 / (DC gain) ==> 500uV
What is important in this to note??
in all text books they will assume this reference as 0 V. so they will simply tell that opamp gain error is given by;
% error = Adc /(1 + Adc*B) ; B - feedback factor.
using the above formula; % error = 999.0 uV ==> not exactly correct.
We can't use this formula blindly. We need to know initial operating point of opamp. worst case we will assume mid of supply voltage as reference voltage.
If there is any misunderstanding correct me.