The Designer's Guide Community Forum https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> VCO based ADC frequency domain behaviour https://designers-guide.org/forum/YaBB.pl?num=1524091816 Message started by polyam on Apr 18th, 2018, 3:50pm

 Title: VCO based ADC frequency domain behaviour Post by polyam on 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  :)

 Title: Re: VCO based ADC frequency domain behaviour Post by polyam on Apr 18th, 2018, 3:50pm Freq. res. of VCO-ADC

 Title: Re: VCO based ADC frequency domain behaviour Post by polyam on Apr 21st, 2018, 7:52am Any clue for this problem? Can something be done with Spectre-RF?

 Title: Re: VCO based ADC frequency domain behaviour Post by loose-electron on 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.