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VCO based ADC frequency domain behaviour (Read 455 times)
polyam
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VCO based ADC frequency domain behaviour
Apr 18th, 2018, 3:50pm
 
Hi,

I am interested in doing a proper simulation in Spectre to extract the frequency response of a VCO-based ADC. Please check the following figures. A VCO based ADC can be modeled as an integrator followed by a sampler and a differentiator. Can anyone help me to do a simulation in order to get the following curves?  It is expected to have a low pass behavior at the output of VCO (let's say ring oscillator). Such a low-pass behavior must be canceled by the frequency response of the differentiator resulting in a flat frequency response. my target is to reproduce such a figure in Spectre.
BTW these figures come from "Design of a 5bit 1GSps VCO Quantizer for a CT Delta Sigma Modulator"

https://ieeexplore.ieee.org/document/6226117/

tnx  :)
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polyam
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Re: VCO based ADC frequency domain behaviour
Reply #1 - Apr 18th, 2018, 3:50pm
 
Freq. res. of VCO-ADC
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polyam
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Re: VCO based ADC frequency domain behaviour
Reply #2 - Apr 21st, 2018, 7:52am
 
Any clue for this problem? Can something be done with Spectre-RF?
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Re: VCO based ADC frequency domain behaviour
Reply #3 - May 15th, 2018, 10:31pm
 
VCO counter ADC BW is a function of the count period. Typically you do a VCO count for a fixed period of time based upon the sample input voltage, and then do the same time period and get the count when connected to a reference voltage (typically the V bandgap) and then you take the ratio of the two numbers.

It is not a linear system simulation, and you generally run the count out to some large numbers in order to average out the inherent (flicker and thermal) noise of the system.

I designed one of these for Intel back in the Pentium 1 era for their thermal monitor. These devices are very slow, generally with update rates multiple seconds apart, and the BW approximation can be crudely approximated by the update rate.
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Jerry Twomey
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Contract IC-PCB-System Design - Analog, Mixed Signal, RF & Medical
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