Martin_Anderson
New Member
Offline
Posts: 4
Lund, Sweden.
|
Hi Ken, thanks for your quick answer. It was helpful, I think I'm starting to get a grip on how to use some of the SpectreRF tools.
I'm working with pipelined ADCs where the amplification of residue voltages are the most critical part. This residue amplification is done using one SC amplifier in every stage of the pipeline. This circuit is clocked with two phases, one sampling and one amplification phase. The output is sampled by the next pipeline stage at the end of the amplification phase of the first stage, so one can think of it as more or less a time discrete output (since the actual information is only valid at discrete time points)
I'm currently trying to analyze the contribution of the amplifier noise to the output. Thanks to the used switching scheme the amplifier DC offset is removed and also the 1/f noise should be attenuated. During the sampling phase, the input reffered noise of the amplifier is sampled onto the sampling capacitors, and in the amplification phase the low frequency noise (which has a value close to the sampled noise value) should be cancelled.
I would like to think of it like this: At the sampling instant, the instantaneous input reffered amplifier noise voltage is sampled onto the capacitors, its time discrete, simply a number (like the vs waveform on page 4). If the noise voltage at the end of the amplification phase has not moved a lot, a large part of the noise will be cancelled (like the DC offset is cancelled) and the error that is actually transferred onto the next pipeline stage is small.
I'm wondering, how can I simulate this discrete-like transfer to see this cancelling effect for low frequencies? Using another sampling circuit at the end of the SC amplifier together with the PAC does not seem correct since the PAC seems to consider the continous sampled and held signal waveform at the output, which is actually of little interest. In figure 8 you have used a PXF to see the 3dB bandwidth of the simple S/H circuit. Do you think that something similar could be used in this case? We have thought about putting the duty cycle m in the perfect sampler that samples the amplifier output very short to get a continous time output that looks like the vs waveform on page 4. What do you think about this approach? Do you have any suggestions?
Once again, we're grateful for your help. Martin.
|