No, the .four and the spec are large signal, and there accuracy depends on the models. Transient is large-signal.
There exists an accurate THD test called Harmonic Balance, which basically is balancing the harmonic components and the carrier to get the output signal as computed. But to the best of my knowledge it is only used in some very expensive hf/vhf/uhf simulators.
Jan Didden
There exists an accurate THD test called Harmonic Balance, which basically is balancing the harmonic components and the carrier to get the output signal as computed. But to the best of my knowledge it is only used in some very expensive hf/vhf/uhf simulators.
Jan Didden
Hjelm,hjelm said:Pedja:
Which file did you run and what distortion did you get?
I tried running the circuit with the ideal models but then it was just silly i got -116dB THD.
I am using Winspice but i have a feeling that the BC850C BC860C models from Siemens, actually it should be Infineon today, seems to be better than most, at least it is hard to get good values with them. These models were posted here in a thread somewhere.
Hjelm
IIRC it was the SA970 file. IIRC something like 50dB. But again, I did not check what has left of the file finally…
If you are interested for, here is the MicroCap file I made. Philips models for BC547C/557C are embedded. Run transient & AC analysis.
Distortion measurements in SPICE are based on the transient analysis and thus are not small signal measurements.
Pedja
Thanks pedja.
Fiddled a bit with it and it was possible to remove the input dc offset some by increasing r3 to 126.
The addition of a cascode on the output didnt work as well as i had hoped for these transistors. N or was there any obvious improvement in trimming the resistor r13.
For those of you inclined to do current feedback, , it is possible to connect the resistor r7 between output and input.
This gives a bit of better performance -82dB second harmonic for the circuit pedja supplied, i have also cascoded the output and increased the r13 to 126 but i do not know if that is necessary.
To further improve the versatility of the circuit it is possible to include a lowpass filter by using the feedback, see the Hawksford IV paper for inspiration. He is keen on not using the ground for the high frequency feedback which seems like a good idea.
If you only desire a neat step response use a very small cap directly between output and input, 2p in my case. There was a bit of overshoot in the simulations without it.
Fiddled a bit with it and it was possible to remove the input dc offset some by increasing r3 to 126.
The addition of a cascode on the output didnt work as well as i had hoped for these transistors. N or was there any obvious improvement in trimming the resistor r13.
For those of you inclined to do current feedback,
, it is possible to connect the resistor r7 between output and input.This gives a bit of better performance -82dB second harmonic for the circuit pedja supplied, i have also cascoded the output and increased the r13 to 126 but i do not know if that is necessary.
To further improve the versatility of the circuit it is possible to include a lowpass filter by using the feedback, see the Hawksford IV paper for inspiration. He is keen on not using the ground for the high frequency feedback which seems like a good idea.
If you only desire a neat step response use a very small cap directly between output and input, 2p in my case. There was a bit of overshoot in the simulations without it.
And for those of you who like mosfet .
The topology works with mosfets as well. I tried it with irf230 and irf9230 and it seems to work pretty well. The step response was slower but these are power mosfets so that isn't so strange, they were in a model package from irf that i already had so that is why i used them.
The results were, in the simulations at least, better with the mosfets, isuppose the current mirrors didn't have the base current leakage as problem.
Not changing a single resistor and only replacing the transistors i got a -83dB THD and 60uV input swing.
I use a Sziklai cascode on the output which in the simulations seems to do very much for the THD, is that to be expected?
The gain from using a simple caclode is a lot less, the mosfets also seem to be coping without cascode better than the bipolars.
Does anyone have a suggestion for mosfets, including models, to try?
.The topology works with mosfets as well. I tried it with irf230 and irf9230 and it seems to work pretty well. The step response was slower but these are power mosfets so that isn't so strange, they were in a model package from irf that i already had so that is why i used them.
The results were, in the simulations at least, better with the mosfets, isuppose the current mirrors didn't have the base current leakage as problem.
Not changing a single resistor and only replacing the transistors i got a -83dB THD and 60uV input swing.
I use a Sziklai cascode on the output which in the simulations seems to do very much for the THD, is that to be expected?
The gain from using a simple caclode is a lot less, the mosfets also seem to be coping without cascode better than the bipolars.
Does anyone have a suggestion for mosfets, including models, to try?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.