Hi Ti Team
At the output of OPA657, we are getting a second harmonic peak which is degrading our SFDR. PFB CRO observation and schematic for your reference
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Hi Ti Team
At the output of OPA657, we are getting a second harmonic peak which is degrading our SFDR. PFB CRO observation and schematic for your reference
Hi Sir
1. we are converting DAC's differential output to single-ended by Transformer. I have checked the Noise on the input side of OPA657. I am not getting any harmonic there. After OPA657 we are getting 2nd harmonic.
2. Yes sir by default it is 50-ohm termination in the spectrum analyzer. How many loads do we require? How end load will affect 2nd harmonic?
Thanks
Can you check the actual voltage swing at the output pin? Do this with a high impedance probe tacking a 100ohm R off the output pin with short leads to probe on the other side of that to isolate the probe capacitance.
50ohm is a pretty heavy load, eventually I am trying to work back to where we can compare your operating conditions to the data sheet plots. HD2 does not simulate well even in the full designer models and certainly is not in the TINA models.
Hi Balvan,
a 50R load looks like a short circuit. In order to get lower distortion you need to increase the load resistance:
Kai
Hi Sir
The voltage output swing at the output is 0.425Vpp. I have checked with other load but the issue is still there
Can you change that R144 to 49.9 ohms and try again, might be seeing some cload putting the op amp into oscillation - also, carefully check the output DC level probing through a 100ohm iso resistor