Simulation of I/U (I/V) converter versions for TI PCM R2R DAC's (e.g. PCM1704) ?"
For check out and compare of different I/U circuit topologies by simulation I cannot use the generator with internal resistance of 0 ohms. What I must do for prepare to get exactly simulation results ?
Best thanks for your advices.
For check out and compare of different I/U circuit topologies by simulation I cannot use the generator with internal resistance of 0 ohms. What I must do for prepare to get exactly simulation results ?
Best thanks for your advices.
Use a current source, it should be there in the simulator.
I use LT spice and it is called Current
I use LT spice and it is called Current
Sorry to correct you Sonnya, but using a current source will NOT simulate a true PCM1704 or similiar output.
Check page 2 in the PCM1704 datasheet: PCM1704 Datasheet
Find the "Analog Output" section... Here it says that the output current is 1.2mA and the output impedance is 1kohm. Since this is a "current generator", the output impedance should med simulated by using a 1.2mA current source in parallel with a 1kohm resistor.
By doing this, you will notice why the input impedance of the I/V converter is so critical. If you have a 1kohm input impedance, only half of the signal strength will go into the I/V converter, while the rest is blown away inside the PCM1704.
But it gets worse. Since the input impedance will most likely be non-linear, you will have a non-linear transfer between the PCM1704 and the I/V converter. The lower the input impedance, the less critical the non-linarities of the impedance will be. The difference in signal-energy transferred will be less, since almost all the energy is transferred at low impedances.
This really is one of the main reasons why you must ALWAYS use a low impedance I/V converter for critical applications.
The other reason is, that a high impedance input will result in voltage changes along with the music signal. And that will cause non-linarities inside the DAC-circuit.
So again! Use a low impedance input I/V-converter, and remember the paralell resistor at the current source when simulating.
Check page 2 in the PCM1704 datasheet: PCM1704 Datasheet
Find the "Analog Output" section... Here it says that the output current is 1.2mA and the output impedance is 1kohm. Since this is a "current generator", the output impedance should med simulated by using a 1.2mA current source in parallel with a 1kohm resistor.
By doing this, you will notice why the input impedance of the I/V converter is so critical. If you have a 1kohm input impedance, only half of the signal strength will go into the I/V converter, while the rest is blown away inside the PCM1704.
But it gets worse. Since the input impedance will most likely be non-linear, you will have a non-linear transfer between the PCM1704 and the I/V converter. The lower the input impedance, the less critical the non-linarities of the impedance will be. The difference in signal-energy transferred will be less, since almost all the energy is transferred at low impedances.
This really is one of the main reasons why you must ALWAYS use a low impedance I/V converter for critical applications.
The other reason is, that a high impedance input will result in voltage changes along with the music signal. And that will cause non-linarities inside the DAC-circuit.
So again! Use a low impedance input I/V-converter, and remember the paralell resistor at the current source when simulating.
😎 well. If you have read the original thread. You would have seen that i already have addressed the non lin. problem. Once again too hurtig
Sorry it is my fault.🙁 I thought i have seen the link in the top of this thread.
Here is the link
http://www.diyaudio.com/forums/showthread.php?postid=1882633#post1882633
Here is the link
http://www.diyaudio.com/forums/showthread.php?postid=1882633#post1882633
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