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Hi all,
i am building an input stage design with OPA1612 with TINA for TPA3255 (PFFB) and quite surprised by somme results in terms of THD.
Fourrier analysis show a very high THD calculation of 0.11163% !
Several calculation shows that THD depends of R*C products.
Better values in terms of output noise for bipolar AOP should be 1K/1K. With 330pF, the THD calculation shows 0.008531%.
Following to what i am seeing, i tried with 22pF. In this case, gain pole fequency is quite high and the signal integrity should not be modified (gain/phase), then i do not understand why the THD calculation shows a better result (0.00075097%).
Then, my question is : is OPA1612 TINA model be accurate for THD calculations ?
Second question. we often see schematic with a R3 bias resistor (with value = R1//R4) on positive input to reduce/cancel output offset voltage. Since long years, i thought that the goal is to low the THD but TINA does not show that. Moreover, it ups the total noise (about 3dB in my case).
Do i forget something ?
Thank you in advance for your help and best regards.
[quote user="Remy HOFF"]
Part Number: OPA1612
Hi all,
i am building an input stage design with OPA1612 with TINA for TPA3255 (PFFB) and quite surprised by somme results in terms of THD.
Fourrier analysis show a very high THD calculation of 0.11163% !
Several calculation shows that THD depends of R*C products.
Better values in terms of output noise for bipolar AOP should be 1K/1K. With 330pF, the THD calculation shows 0.008531%.
Following to what i am seeing, i tried with 22pF. In this case, gain pole fequency is quite high and the signal integrity should not be modified (gain/phase), then i do not understand why the THD calculation shows a better result (0.00075097%).
Then, my question is : is OPA1612 TINA model be accurate for THD calculations ?
Second question. we often see schematic with a R3 bias resistor (with value = R1//R4) on positive input to reduce/cancel output offset voltage. Since long years, i thought that the goal is to low the THD but TINA does not show that. Moreover, it ups the total noise (about 3dB in my case).
Do i forget something ?
Thank you in advance for your help and best regards.
Hello Remy,
Regarding your questions:
Then, my question is : is OPA1612 TINA model be accurate for THD calculations ?
Second question. we often see schematic with a R3 bias resistor (with value = R1//R4) on positive input to reduce/cancel output offset voltage. Since long years, i thought that the goal is to low the THD but TINA does not show that. Moreover, it ups the total noise (about 3dB in my case).
I hope this helps.
Regards, Thomas
Precision Amplifiers Applications Engineering