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https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr https://designers-guide.org/forum/YaBB.pl?num=1454504258 Message started by Ankit Shivhare on Feb 3rd, 2016, 4:57am |
Title: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by Ankit Shivhare on Feb 3rd, 2016, 4:57am I am designing synchronous buck converter with following specifications fs=1MHz, L=1uH, C=200uF, Vin=5V, Vout=1.8V, R=3ohms, PWM Ramp VM=1V. I am trying to do PSS/PAC analysis in cadence to find uncompensated open loop gain. I am assuming control voltage vc=0.36V which is applied to a comparator +ve terminal. -ve side of comaparator is connected with sawtooth(tr=999n,period=1000n) This is transient output of vout(voltage across capacitor) This is our PAC output |
Title: Re: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by Ken Kundert on Feb 3rd, 2016, 11:36pm Do you have a question? |
Title: Re: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by saralandry on Nov 16th, 2016, 4:27am Hi Ken, I have a question and I do appreciate that if you help me. I don't know if this is Ankit Shivhare's problem or not. But regrading the figure he posted, I am guessing that he has a problem with PSS and PAC analysis. Me too. C Would you please let me know how to do PSS and PAC analysis to extract the closed loop frequency response of a PWM modulator? I attached the test bench. Two VCVS are used as comparators. (gain=1000, max=1, min=0) Triangle wave is generated by Vpulse. P-to-P is 1 V. The carier frequency is 640 MHz. Vsource is also used as an input with pac mag=1 and pac phase=0. Now I like to see the frequency response of the PWM. I think there is somthing wrong with the testbench since it is not essentially closed. Honestly speaking I have not got the concept to perform PSS and PAC analysis for this structure. Would you please post a simple tutorial to perform such analyses for this circuit? Clearly speaking, how can we extract the closed loop frequency response of the a simple standalone PWM genrator? Thank you |
Title: Re: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by sheldon on Nov 18th, 2016, 9:04am Saralandry, Not sure what this circuit does, but it does not appear to be a PWM modulator. In a DC-to-DC converter, the inputs to the PWM Modulator are the feedback output voltage and the saw tooth wave. Here your circuits converts the saw tooth waveform into a differential voltage. Sheldon |
Title: Re: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by saralandry on Nov 19th, 2016, 11:42am Sheldon, Thank you for the reply. If you are talking about the schematic posted by Ankit Shivhare, yes you're right. What I posted is a complementary PWM generator. The sin input signal is converted to the diff mode. I sued two VCVCs with the gain of 1000, max=1 and min=0 as comparators. And a triangular wave. I appreciate if you take a look at the Fig. 4 of this paper: "True Filterless Class-D Audio Amplifier". What I am looking for is to plot the frequency response of the PWM generator. Theoretically, it is supposed to be a low-pass form profile while the gain is defined by Gain=Vdd/Vtri ( Vdd, supply voltage, and Vtri is peak to peak voltage of the triangular wave. I searched for a lot of solution but none of them has not worked for me. I worked with verilog-A module of the comparator and I figured out it is not possible to do PSS/PAC analyses on verilog-A modules. Hidden state problem adds more difficulties. What I want to know is what is the proper test bench with ideal (macro) models and how to properly set the parameters in the PSS/PAC analyses to extract the Fig. 4 of the paper. Thank you |
Title: Re: Measuring uncompensated loop gain of an buck converter by PSS/PAC cadence spectr Post by deba on Nov 19th, 2016, 9:18pm Hi, Those plots in Fig. (4) are the closed loop responses of the class-D amplifier. The circuit which you posted doesn't have the filter. If you have the complete loop setup, pss/pstb or pss/pac can give the transfer function. Thanks |
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