1、1-1 1. SpectreRF Overview SpectreRF is an optional feature added to Spectre ,and is represented by 6 analyses: 1. PSS: Periodic Steady State Analysis 2. PAC: Periodic AC Analysis 3. PXF: Periodic Transfer Function Analysis 4. PNOISE: Periodic Noise Analysis Tdnoise: Time Domain Noise QPNOISE: Quasi-
2、Periodic Noise (not discuss here) 5. PDISTO: Periodic Distortion Analysis QPSS: Quasi-Periodic Steady State (not discuss here) 6. Envelope Analysis (not discuss here) PAC, PXF, and PNOISE are similar in concept to AC, XF, and Noise. However, they are applied to periodically-driven circuits such as m
3、ixers and oscillators.1-2 SpectreRF in a Design Flow Design Analog Artist Environment Netlist SPECTRE Engine Spectre RF Control Analog Artist Plot Results Schematic Models The netlists include all components along with an analysis selection, simulation controls and statements to save, plot nodes or
4、currents. Use Direct plot or the Calculator plot capabilities.1-3 SpectreRF Tool Flow Spectre Engine -PAC Analysis -PXF Analysis -PNOISE Analysis SpectreRF PSS setup Spectre Engine PSS Analysis PSS Results Report Results PDISTO Setup Spectre Engine PDISTO Analysis PDISTO Results PSS is a large-signa
5、l analysis and determines the period of the small-signal analyses. PSS requires that multiple periodic stimuli be coperiodic. PDISTO is also a large- signal analysis, and need not to be run after a PSS analysis. PDISTO does not require multiple periodic stimuli to be coperiodic.1-4 SpectreRF Feature
6、s Compute a steady-state solution efficiently and directly Handles very large circuits ( 10,000 transistors) Displays results in both time and frequency domains Use Discrete Fourier Transform (DFT) for better accuracy Displays standard RF measurements, such as s-parameter in Smith chart, NF, IP3, an
7、d 1dB compression point in the Analog Artist design environment. Performs oscillator analysis.1-5 2. S-Parameter Analysis Linear Simulation: Entirely in the frequency domain A basic RF feature of the Spectre simulator Ports: Specify the port number on the psin ( or port); psin (or port) can act as a
8、 source port or a load. Required properties for linear analysis: Resistance the window “Parametric Analysis” appears, then key in the values as below . In the window “Parametric Analysis” select Analysis Start to start the simulation.1-19 The Results Select Results Direct Plot DC and select the term
9、inal “Drain” of the nmos in the schematic window; then push ESC, and the results will be showed.1-20 4. Periodic Steady State Analysis Directly computes the periodic steady-state response of a circuit in the time domain. Iterative Shooting Newton method is employed. Calculate frequency translations
10、using the saved matrices at every time point. The fundamental frequency of the circuit or system is determined, based on integer multiples of all source frequencies. The circuit is evaluated for one period of the common frequency, and the period is adjusted until all node voltages and all branch cur
11、rents fall within a specified tolerance.1-21 Shooting Newton Method PSS operates by efficiently finding an initial condition that results in steady state. The first iteration is transient simulation from t=0 to t=1/PSS fund by default. The tstab parameter can be adjusted to facilitate convergence. T
12、he second iteration is PSS analysis between t=tstab to t=(tsatb+1/PSS fund ) and compares all voltage and currents at the start and end of the shooting interval. Set the value of tstab to keep “start-up behavior” away. The starting point is adjusted by the shooting method to result in periodic stead
13、y state. The signal starts at a point v i doesnt result in periodicity. v i v f Dv tstab t=0s t=1/PSS fund t=2/PSS fund Transient Analysis PSS Analysis All node voltages and Admittance Matrices are saved Shooting Interval1-22 Shooting Newton Method(continued) fund PSS 1 t = fund PSS 1 t = Transient
14、Analysis PSS Analysis RF 2.4GHz LO 2.3GHz IF 100MHz PSS fund =100MHz Shooting method takes the last few point data at the end of the shooting interval to adjust the slopes of the waveform at the beginning of the next iteration. If 20 iterations do not yield a solution, this might indicate the circui
15、t won t converge to a PSS solution.1-23 PSS Analysis Assumptions 1st Assumption : Periodicity All stimuli are periodic and coperiodic with the PSS fund ; All responses are periodic. PSSfund can be set to includes the subharmonics. If periodicity assumptions fail, PSS analysis will not converge. 2 nd
16、 Assumption : Linearity A near-linear relationship need to exist between initial and final points of the shooting interval.1-24 The PSS Fundamental 150 MHz RF Input 900 MHz Local Osc. Local Osc. 1050 MHz 160 MHz 10 MHz IF1 IF2 Mixer BPF Mixer BPF Output PSS fund = 10 MHz1-25 PSS Operation Start PSS
17、Periodicity Meet? Initial Transient (1 period or tstab) 1 Period of PSS Analysis Final State = Initial State Exit Refine Initial Guess Yes Yes No No1-26 Simulator Accuracy Suggestions Do not set “conservative”. This will dramatically extend the simulation time. The suggested settings are recommended
18、 for IP3 Analysis, Noise Analysis, or wherever high accuracy is needed. Choose the gear2only integration method. The default trap integration gear2only trap Method 1e-13 1e-12 iabstol 3e-8 1e-6 vabstol 1e-5 1e-3 reltol Suggested Settings Defaults Parameter 10.0 0.00001 0.1/maxacfreq gear2only allloc
19、al x0.1 conservative 3.5 0.001 0.2/maxacfreq traponly sigglobal x1.0 moderate 3.5 0.1 0.4/maxacfreq gear2 allglobal x10.0 liberal lteratio steady-ratio maxstep method relref reltol errpreset o steadyrati * lteratio * reltol ?I and ?V method yields underdamping and gearOne yields too much overdamping
20、.1-27 Normalized Convergence ratio When the Conv norm is 1(unity) or less, the simulation meets the matching criterion. The PSS messages also display the number of PSS iterations, the number of accepted timesteps, and the total time required for PSS analysis. Conv norm = Measured DV between start an
21、d end of shooting interval reltol*lteratio*steadyratio1-28 Lab3 : PSS and swept PSS Analysis Create a new schematic view and use library “analogLib” key in appropriate value for the variables in the “Design Variables” section. Analyses Choose. In the window “Choosing Analyses”, select pss.1-30 Setup
22、 up the PSS Simulation(2) The Signal field is ONLY applicable to the pdisto analysis. Beat Frequency represents the PSS Fundamental (PSS fund ) frequency. This fundamental is the highest frequency that evenly divides into all frequencies in the circuit. You may key in an appropriate value or push Au
23、to Calculate button to get an auto- responded value. Set the value for number of harmonics. The number of harmonics won t affect the simulation accuracy or time. Make sure the Enabled field is on. Click the Options button and set the integration method to gear2only.1-31 Setup up the PSS Simulation(3
24、) In the Analog Artist Simulation window, select Simulation Options Analog. Set the Tolerance Options as recommended. If it is hard to converge set the Tolerance Options looser. Finally, Select Simulation Netlst and Run to start the simulation. Note if the Conv norm is less than 1 or if the PSS simu
25、lation has a convergent result. 1-32 Display the Conversion Power Gain- method 1 In the Analog Artist Simulation Window, select Results Direct Plot PSS. Note the prompts on the bottom of the schematic and PSS Results windows. The PSS Results window MUST be on the screen when probing the nodes in the
26、 schematic. Don t push OK. In the PSS Results form, use the cursor to select the Pif net and Prf nets on the schematic. Press Esc to end this command. Click the Switch Axis Mode icon on the Waveform Window or select Axes To Strip.1-33 Display the Conversion Power Gain- method 1(continued) Click the
27、Crosshair Marker A icon and place the marker on the 2.4GHz harmonic of Prf. Click the Crosshair Marker B icon and place the marker on the 100MHz harmonic of Pif. Prf: Magnitude: 4.0085m Power: -38 dBm Pif: Magnitude: 4.08038m Power: -37.8 dBm Conversion Power Gain 0.2dB + 3 dB = 3.2 dB1-34 Display t
28、he Conversion Power Gain-method 2 Select Output Save All and the window “Save Options” appears. Set the buttons as below window in order to get the AC power! Select Outputs To Be Saved Select On Schematic. In the schematic, select the PORT1 and RL1. The terminals are circled in the schematic window
29、after you select them. Press Esc to end the selections. Double click on the name in the Outputs section or select Outputs Setup. Set the outputs Will Be Plotted and Saved.1-35 Display the Conversion Power Gain- method 2(Continued) Push Netlist and Run icon to run this simulation. Select Results Dire
30、ct Plot PSS. Set the function and modifier as right; Select instance terminal(PORT1 Designate a value to prf in the Design Variables section. In the Choosing Analyses window, turn on the Sweep button as shown here. Type in prf for the Design Variable Name, or click the Select Design Variable button,
31、 and highlight prf from a list , then click OK. Remember to check in the INTEGRATION METHOD PARAMETERS the method is gear2only. Select Netlist and Run button.1-37 P1 dB Simulation Results Use Direct Plot function to see the results. Set up PSS Results form as shown here. Then select the Pif net in t
32、he schematic. With the cursor still in the schematic window, press ESC key to end the Direct Plot command.1-38 Simulating IP3 PSS by itself is seldom used for IP3 simulation, because the separation between the 2-tone frequency is typically only a few Khz, and leads to a very long simulation time. Ed
33、it PORT1 properties as right. So The Fundamental (Beat) Frequency is now 25MHz. Set up Choosing Analysis form appears as shown below and push OK Run the simulation1-39 IP3 Results Use Direct Plot function to see the results. Set up PSS Results form as shown here. Then select the Pif net in the schem
34、atic. Press ESC key to end the Direct Plot command. 3rd order intermodulation product will occur at (2 2.4GHz 2.425GHz) 2.3GHz = 75 MHz1-40 5. PAC Analysis PAC is a small-signal analysis like AC analysis, except the circuit is first linearized around a periodically varying operating point as opposed
35、 to a simple DC operating point. Linearizing around a periodically time-varying operating point allows analyzing transfer-functions that include frequency translation. When a small sinusoid is applied to a linear circuit that is periodically time-varying, the circuit responds with harmonics. PAC computes a series of transfer functions, one for each frequency. These transfer functions are unique because the input and output frequencies are offset by the harmonics of the LO.
