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https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> Spectre RF simulation with one or more custom command clocks with the same globa https://designers-guide.org/forum/YaBB.pl?num=1293039528 Message started by GrugetA on Dec 22nd, 2010, 9:38am |
Title: Spectre RF simulation with one or more custom command clocks with the same globa Post by GrugetA on Dec 22nd, 2010, 9:38am Hello all, I'm working on a circuit that is quite simple when studied in schematics and in transient simulation, but the difficulty comes when I want to extract its transfert function. The basis and my objectives are similar to the basic circuit described in the document "Simulating Switched-Capacitor Filters with SpectreRF" ( http://www.designers-guide.org/Analysis/sc-filters.pdf ). I have a perfect current sine signal, chopped by switches driven by clocks. This chopped current integrates into a capacitor. After a time the voltage of the signal is taken as a sample, and then the capa is reset by closing a switch on both nodes of the capacitor. The global length of this pattern is Ts. Then all this pattern restart for a new cycle. So all the behaviour is periodic of period Ts, and the output samples are taken at frequency Fs. This circuit is doing a bandpass filtering and a subsampling function. The clocks that are chopping the current are some custom clock sources with a global period Ts. (vpwlf sources) All this circuit can be called a "bandpass filtering integration subsampler" (BFIS). I want to measure the transfert function of the filtering function of my circuit, so i have the same issues as described in the aforementioned document. Spectre RF seems a good solution. But my questions are : 1) Is it possible to run a PSS and a PAC simulation with a periodic clock, but different from the standard (50% duty cycle) clock ? (For example in my case during the Ts lenght the clock is switching many times betweed Vdd and 0). If yes, which parameters do I have to set in this command clock ? 2) Is it possible to run a PSS and a PAC simulation with several command clocks driving several parts of the circuit. With the same global period Ts but with different behavours during this time ? (For example a chopping clock at hight frequency + a reset clock only at Vdd during one short time in the whole Ts time) ? In order to maybe help the understanding of my circuit I attached a capture of the simplified scheme, and here just below the corresponding netlist. Thanks in advance for your help --------------------------------------------------------------------------- // Library name: test // Cell name: lnta_ideal_cleaned // View name: schematic subckt lnta_ideal_cleaned LNTAn LNTAp RFin Vcm inh_gnd inh_gnds inh_vdds G0 (inh_gnd LNTAp RFin inh_gnd) vccs gm=80m G1 (inh_gnd LNTAn RFin inh_gnd) vccs gm=-80m R3 (Vcm LNTAp) resistor r=10G R4 (LNTAn Vcm) resistor r=10G ends lnta_ideal_cleaned // End of subcircuit definition. // Library name: test // Cell name: Simple_BFIS // View name: schematic W14 (net109 Vintp CMDcn 0) relay vt1=300.0m vt2=1 ropen=RoffC rclosed=RonC W15 (net109 Vintn CMDcp 0) relay vt1=300.0m vt2=1 ropen=RoffC rclosed=RonC W5 (Vintn Vcm CMDr 0) relay vt1=300.0m vt2=1 ropen=RoffR rclosed=RonR W13 (net110 Vintn CMDcn 0) relay vt1=300.0m vt2=1 ropen=RoffC rclosed=RonC W12 (Vcm Vintp CMDr 0) relay vt1=300.0m vt2=1 ropen=RoffR rclosed=RonR SWcp1 (net110 Vintp CMDcp 0) relay vt1=300.0m vt2=1 ropen=RoffC \ rclosed=RonC V3 (CMDr 0) vsource type=pulse val0=0 val1=1.2 period=1/Fs \ delay=1/Fs/Ndiv*(Ndiv-2) rise=1/Fs/Ndiv/10 fall=1/Fs/Ndiv/10 \ width=1/Fs/Ndiv V10 (0 gnd) vsource dc=0 type=dc V11 (vdd! gnd) vsource dc=1.2 type=dc V15 (Vcm gnd) vsource dc=600.00m type=dc C0 (Vintp Vintn) capacitor c=600f V0 (CMDcn 0) vsource file="pwlFile_CLKcn" fundname="Fs" type=pwl \ pwlperiod=1/Fs V13 (CMDcp 0) vsource file="pwlFile_CLKcp" fundname="Fs" type=pwl \ pwlperiod=1/Fs V2 (RFin gnd) vsource mag=Vin_amp type=sine ampl=Vin_amp freq=Fin I63 (net109 net110 RFin Vcm 0 gnds! vdds!) lnta_ideal_cleaned ---------------------------------------------------------------------------- |
Title: Re: Spectre RF simulation with one or more custom command clocks with the same globa Post by Ken Kundert on Dec 25th, 2010, 3:44pm Quote:
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Title: Re: Spectre RF simulation with one or more custom command clocks with the same globa Post by GrugetA on Dec 26th, 2010, 2:17pm Ok, thanks, I start the design ! Quote:
Do i need to choose the frequencies of my circuit so as the output period is a multiple of the fundamental period (sampling period) ? Or i don't care ? |
Title: Re: Spectre RF simulation with one or more custom command clocks with the same globa Post by Ken Kundert on Dec 27th, 2010, 12:03am The periodicity requirement only applies in the PSS analysis. Presumably the downcoversion is occurring in the PAC analysis, in which case the small input frequency is unconstrained. -Ken |
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