leon30
Junior Member level 1
Hello everybody, I'm designing a fully differential switched capacitor biquad filter with switching frequency of 1.33 MHz (actually two non-overlapping clocks). When analyzing the ideal circuit (constructed with ideal switches from analogLib and all others elements plus ideal fully differential opamp model constructed from me with vcvs) I should do the following steps(I've read many papers on the subject and I think I get the pss pretty clear, but the other (pac, pnoise) were explained for the oscillators and mixers mostly and I'm finding myself little lost there):
1) I put for input source of the circuit - one vdc with 0V dc voltage and pac magnitude of 100mv with pac phase 0, only for the one input, the other is set to ground;
(Is this is correct ?)
2) I'm setting the pss analysis as follows:
2.1) In the "Engine" section I choose the shooting method;
2.2) In the "Fundamental tones" section there are the two clock signals with the same frequency of 1.33 MHz, so as "Beat frequency" I have also 1.33 MHz;
2.3) In the "Output harmonics" section for "Number of harmonics" I write 0, because I need the pss only for determining the periodic operating point of the circuit, and because I'm interested in the circuit behavior from the range of 0 Hz to 1.33 MHz.
(First question should I entered 0 harmonics here, or I will need more in order to completely characterize an SC filter ?)
2.4) In the "Options..." section for "Integration method" I choose "gear2only" for better convergence;
2.5) When I run the analysis I check the SpectreRF log to see the "Conv. norm" value if it is less then 1 and if I have "pss: The steady-state solution was achieved in X iterations." everything is OK with this;
2.6) If not, I'm having convergence problems and I should change the initial condition (IC) parameter for all the capacitors in the circuit to 0, or to do step response of the circuit and see after witch moment of time it's become stable (let's call this moment ST) and then set the "tstab" parameter in the pss analysis form to a multiple of the clock period greater than ST.
(Second question - are these procedures correct ? Am I doing good and sufficient pss analysis of SC filter ?)
After that I'm staring to fill the form of the pac:
3) What should I choose for "Sweeptype" ? I need the behavior of the circuit from 0 Hz to the "Beat frequency" in this case 1.33 MHz, I mean that I need the AC transfer characteristic of the filter.
3.1) "Input frequency range" I think this is in strong relationship with the above parameter - I think I should choose for the above "absolute" and for that one - from 0.1 to 1.33 MHz, but I'm not sure ?
3.2) This "Sweep type" will be logarithmic with ten points per decade...
3.3) What is this parameter "Maximum sideband", what should I choose here ?
What are the other analysis I need, except Pnoise ? Do I need "Quasi periodic analysis" or others ?
Thanks in advance for your help.
1) I put for input source of the circuit - one vdc with 0V dc voltage and pac magnitude of 100mv with pac phase 0, only for the one input, the other is set to ground;
(Is this is correct ?)
2) I'm setting the pss analysis as follows:
2.1) In the "Engine" section I choose the shooting method;
2.2) In the "Fundamental tones" section there are the two clock signals with the same frequency of 1.33 MHz, so as "Beat frequency" I have also 1.33 MHz;
2.3) In the "Output harmonics" section for "Number of harmonics" I write 0, because I need the pss only for determining the periodic operating point of the circuit, and because I'm interested in the circuit behavior from the range of 0 Hz to 1.33 MHz.
(First question should I entered 0 harmonics here, or I will need more in order to completely characterize an SC filter ?)
2.4) In the "Options..." section for "Integration method" I choose "gear2only" for better convergence;
2.5) When I run the analysis I check the SpectreRF log to see the "Conv. norm" value if it is less then 1 and if I have "pss: The steady-state solution was achieved in X iterations." everything is OK with this;
2.6) If not, I'm having convergence problems and I should change the initial condition (IC) parameter for all the capacitors in the circuit to 0, or to do step response of the circuit and see after witch moment of time it's become stable (let's call this moment ST) and then set the "tstab" parameter in the pss analysis form to a multiple of the clock period greater than ST.
(Second question - are these procedures correct ? Am I doing good and sufficient pss analysis of SC filter ?)
After that I'm staring to fill the form of the pac:
3) What should I choose for "Sweeptype" ? I need the behavior of the circuit from 0 Hz to the "Beat frequency" in this case 1.33 MHz, I mean that I need the AC transfer characteristic of the filter.
3.1) "Input frequency range" I think this is in strong relationship with the above parameter - I think I should choose for the above "absolute" and for that one - from 0.1 to 1.33 MHz, but I'm not sure ?
3.2) This "Sweep type" will be logarithmic with ten points per decade...
3.3) What is this parameter "Maximum sideband", what should I choose here ?
What are the other analysis I need, except Pnoise ? Do I need "Quasi periodic analysis" or others ?
Thanks in advance for your help.
