jackeeer
Newbie level 6
Hello everyone,
i am working on sigma delta modulator that I need to use in the fractional divider. Like for now I am facing the noise shaping phenomena and I do not understand one thing... Let me describe the problem:
I know why the noise shaping occurs in sigma delta and can see it in the simulation of 2 nd order sigma delta (verilog model). I am applying 1 kHz sine wave at modulator input and using sampling clock of 1Meg. The noise shaping is present around the frequency of 1kHz, at modulator output hovewer when I use this modulator to control the divider (changing the dividing factor) I can't see the noise shaping around the output signal of divider. For instance I have 10Meg divider input, I am dividing it by 7 or 8 depending on sigma delta output - 0 or 1 and I can't see the noise shaping around 1.4 Meg that I have got at divider output. What I expect is that I will have the same noise shaping around the output fequency as I got around sigma delta output.
My question is...should I expect the noise shaping around output of divider ? How does the sigma delta controling cause the noise around the divider output to be shaped ? I know why I see it at the modulator outptut but I am not sure why should I see it at the divider output also.
Modulator output:
Divider output(i do not why I the output frequency look like this - there is a lot of distortions near the output frequency):
I do not now whether I have presented it clearly...In case of question please ask.
I will provide more data like schematic, simulation results if needed.
Thanks & Regards,
jack
i am working on sigma delta modulator that I need to use in the fractional divider. Like for now I am facing the noise shaping phenomena and I do not understand one thing... Let me describe the problem:
I know why the noise shaping occurs in sigma delta and can see it in the simulation of 2 nd order sigma delta (verilog model). I am applying 1 kHz sine wave at modulator input and using sampling clock of 1Meg. The noise shaping is present around the frequency of 1kHz, at modulator output hovewer when I use this modulator to control the divider (changing the dividing factor) I can't see the noise shaping around the output signal of divider. For instance I have 10Meg divider input, I am dividing it by 7 or 8 depending on sigma delta output - 0 or 1 and I can't see the noise shaping around 1.4 Meg that I have got at divider output. What I expect is that I will have the same noise shaping around the output fequency as I got around sigma delta output.
My question is...should I expect the noise shaping around output of divider ? How does the sigma delta controling cause the noise around the divider output to be shaped ? I know why I see it at the modulator outptut but I am not sure why should I see it at the divider output also.
Modulator output:
Divider output(i do not why I the output frequency look like this - there is a lot of distortions near the output frequency):
I do not now whether I have presented it clearly...In case of question please ask.
I will provide more data like schematic, simulation results if needed.
Thanks & Regards,
jack