Advanced Design System - Fundamentals. Mao Wenjie

Transcription

1 Advanced Design System - Fundamentals Mao Wenjie wjmao@263.net

2 Main Topics in This Class Topic 1: ADS and Circuit Simulation Introduction Topic 2: DC and AC Simulations Topic 3: S-parameter Simulation Topic 4: E-Syn, Momentum and Transient Simulation Topic 5: Harmonic Balance Topic 6: Circuit Envelope Simulation Topic 7: Circuit and System Co-Simulation

3 Topic 1: ADS and Circuit Simulation Introduction

4 Integrated Design Environment Receiver Block AGC D/A 90 Frequency Synthesizer A/D I Baseband DSP From Synthesizer A/D Q Circuit Envelope Simulation Transient Simulation HP Ptolemy Simulation

5 Here is ADS Simplified: 3 steps STEP 1: design capture Insert circuit & system components and set up the simulation. STEP 3: display the results Plot or list data & write equations. STEP 2: Simulate Netlist is automatically sent to the simulator. Simulation results (data) are written to a dataset. Layout / Momentum.

6 ADS Windows: Main, Schematic, Status, Data Display Main window: manage projects and open other windows... Schematic window: create / refine circuits & run simulations... Open a schematic Simulation Controller Project Directory Data Display window: plots, lists, equations Simulate Display opens Default Dataset

7 Main window: File, View, and more... Use icons or commands. However, not all commands have icons. But all icons have commands. File commands: Examples directory Zap projects View commands: Spice or IFF Click + box to expand or - box to collapse.

8 Schematic window Save your work often... All icons have labels (balloon help). A new schematic becomes a.dsn file in the networks directory only after you save it. Also use Window > Open Designs

9 Data Displays are powerful... Insert Templates. Scroll through lists. View and zoom data. Write equations to manipulate data to be listed or plotted. Markers have readout properties you can edit. Use cursor or arrow keys to move a marker. Traces can be edited for color and thickness. Explicit dataset..path if not default.

10 Topic 2: DC and AC Simulations

11 DC Simulation You get steady-state DC voltages and currents according to Ohm s Law: V= IR Capacitors = treated as ideal open circuits Inductors = treated as ideal short circuits Topology check: dc path to ground (if not => error message) Kirchoff s Law satisfied: sum of node current = 0 Convergence simulator algorithms (modes) can be set

12 DC simulation controller Simulation Controller and Editor (dialog box) Sweep: allows you to sweep a parameter but it must be defined as a variable. Note the dialog entry automatically puts quotes on the controller (screen) entry. VAR

13 AC Simulation You get linear small-signal response and you get Noise values: DC analysis performed (unseen) Nonlinear devices are linearized Kirchoff s Law satisfied: sum of node current = 0 Noise contributors defined and listed Budget analysis available (for named nodes) Signal voltages are peak - noise voltages are RMS

14 AC Simulation Controller Turn Noise on/off: yes / no. Set on-screen parameters in the Display tab. AC is a linear or small signal simulation and freq is usually set in the controller not the source.

15 Set up the circuit & simulate with Noise Use ideal DC blockers. Vcc is a node name. Vin and Vout nodes provide data (noise and voltage) for equations. V_AC source voltage = 1 V, cosine wave. MeasEqn: NOTE: Freq is a global variable. Here, Freq is controlled by the source. Use freq=freq, freq=10 MHz, or a variable: freq=f_rf.

16 Simulation results... Two schematic MeasEqns: One Data Display eqn: Write the same equation in Data Display as you did in schematic. Then put it in a list. Edit the traces onscreen: all are equal.

17 Topic 3: S-parameter Simulation

18 S-parameters are Ratios Usually given in db as 20 log of the voltage ratios of the waves at the ports: incident, reflected, or transmitted. S-parameter ratios: S out / S in S11 - Forward Reflection (input match - impedance) S22 - Reverse Reflection (output match - impedance) S21 - Forward Transmission (gain or loss) S12 - Reverse Transmission (isolation) Results of an S-Parameter Simulation in ADS These are easier to understand and simply plotted. Read the complex reflection coefficient (Gamma) Change the marker readout for Zo Read all four S-parameters Smith chart plot: use for impedance matching (S11 and S22) Similar to Network Analyzer measurements These are best viewed on a Smith chart (next slides).

19 The Impedance Smith Chart simplified... This is an impedance chart transformed from rectangular Z. Normalized to 50 ohms, the center = R50+J0 or Zo (perfect match). For S11 or S22 (two-port), you get the complex impedance. Top Half: Inductive Reactance (+jx jx) Circles of constant Resistance SHORT OPEN Lines of constant Reactance (+jx above and -jx below) Bottom Half: Capacitive Reactance (-jx( jx) Zo (characteristic impedance) = 50 + j0

20 Matching means: Moving toward the center of the Smith Chart! Add Series or Parallel (shunt) components. Parallel L Series L Adjust the value to move toward open, short, L, C, or center of chart. Parallel C Series R Parallel R Series C

21 S-Parameter Simulation Controller Default sweep = Freq The simulator requires port termination: Num = 1 Sweep plan can also be used (see next slide). Either way, simulation data (S matrix) will be for the specified range and points.

22 Typical S-parameter plots: ADS data display Plotted S21 in db vs frequency Plotted S11 on a Smith Chart: note marker readout. Complete S-matrix with port impedance Note marker readout is x50. NOTE: For example, you can write an equation for Z at Term (port 2), as freq changes >400MHz, Z = 35 Ohms.

23 Topic 4: E-Syn, Momentum and Transient Simulation

24 Using E-Syn Quick S-parameter simulation What does E-Syn do? It makes it easy to create FILTERS and Matching Networks. E-Syn user interface is a little different than the ADS interface. Also, you could use a Filter Design Guide instead of E-Syn. This may appear in future releases of ADS! You specify the TYPE of design, the RESPONSE, and the BAND. SYNTHESIZE the design and you get a selection of topologies and values. ANALYZE the design and plot the response in the ADS data display. Optimize if desired.

25 Using Momentum MOM engine gives S-parameter results What is Momentum? E-M (electro-magnetic) solver using Method of Moments technique and Green s functions to compute the current in planar structures, including vias and the coupling between surfaces. Antenna patterns! Why use Momentum? You have no accurate model for a passive layout. You want to know the coupling effects between structures. You want to optimize the layout real-estate, performance, etc. Your other structure simulator takes too long to simulate! You want to use the results in ADS simulations. Example spiral meshed as a strip geometry. Hole in ground plane is meshed as a slot, which is more efficient than meshing the entire ground plane.

26 Transient simulation Analysis performed in the Time Domain Use any Source Solutions use Newton_Raphson iterations You get Amplitude vs. Time Time Domain data can be transformed: FS NOTE on Convolution: Frequency domain models (microstrip) can be brought into the time domain and converted to the time domain - then convolved with the time-domain input signal to obtain the time-domain output signal. The convolution tab in the transient simulator allows you to define methods and settings.

27 Transient simulation controller Integration: step control & error (default:fixed) Time Step is critical! Ignored if no TL s

28 Setting the Transient Time Step Start time: sampling begins Stop time: sampling ends Time step: sampling rate 2 x BW Use the Nyquist rule: Sample at 2 x or more the rate of the highest frequency of interest: To sample the fundamental (1900 MHz) plus harmonics, you must 2 x (rate of highest harmonic desired). 1 / (2 x 15 x 1900MHz) = picoseconds.

29 Setting the Transient Stop Time For many circuits: stop time should allow for periodic - settling. Dataset Start Time Stop Time NOTE: Transient analysis can be tricky. Sampling before a circuit reaches steady state will not give correct results when transformed into the frequency domain. Also, you must use a time step that is a multiple of the frequencies of interest or the results will not be correct.

30 Transient simulation of 1900 MHz BPF Microstrip coupled line filter with substrate and VtSine source. Also calculate delay:

31 Topic 5: Harmonic Balance

32 Harmonic Balance Simulation Analyze circuits with Linear and Non-linear components: You define the tones, harmonics, and power levels You get the spectrum: Amplitude vs. Frequency Data can be transformed to time domain (ts function) Solutions use Newton-Raphson technique Krylov subspace method also available (large circuits) Use only Frequency domain sources Similar to Spectrum Analyzer

33 Harmonic Balance Simulation Flow Chart Start Sample Points Number of Harmonics Simulation Frequency Error Tolerance DC analysis always done Linear Components Measure Linear Circuit Currents in the Frequency-Domain Nonlinear Components Measure Nonlinear Circuit Voltages in the Frequency-Domain Inverse Fourier Transform: Nonlinear Voltage Now in the Time Domain Calculate Nonlinear Currents Fourier Transform: Nonlinear Currents Now back in the Frequency Domain Test: Error > Tolerance: if yes, modify & recalculate if no, then Stop= correct answer. Kirchoff s Law satisfied!

34 Basic 1 Tone HB simulation setup Basic HB controller and source setup gives you spectral tones: Numerous builtin sources and measurement equations. Freq[1] is the fundamental tone you want HB to calculate. Freq[1] must match a tone in the circuit or you get a warning message. Order [1] = 3 means HB calculates 3 harmonics of Freq [1] HB gives you a Mix table:

35 Topic 6: Circuit Envelope Simulation

36 What is Circuit Envelope? Time samples the modulation envelope (not carrier) Compute the spectrum at each time sample Output a time-varying spectrum Use equations on the data Faster than HB or Spice in many cases Integrates with System Simulation & HP Ptolemy

37 Circuit Envelope Technology: Circuit Vout Time sample the envelope and then Modulation t 1 t 2 V(t) * e t 3 t 4 j2π fot Carrier performs Harmonic Balance on the samples! Periodic input signal NOTE: V(t) can be complex - am or fm or pm

38 more on CE Technology Captures time and frequency impairments: dbm (fs (Vout))

39 CE example: AMP with RF pulse ONE TONE You will do this in the lab! Step time is critical for sampling the envelope: rise, fall, and modulation rate. Therefore, Step (sample time) is NOT the same as Transient. mag of Vin [1]: envelope ts of Vout: signal mag of Vout [1]: envelope...where [1] is the carrier Freq[1].

40 Env Setup tab in dialog Stop time Determines resolution bandwidth of output spectrum Large enough to resolve spectral components of interest Time step Determines bandwidth of Circuit Envelope simulation Small enough to capture highest modulation frequency (Reference slide for one tone with 3 harmonics) Stop Time Resolution BW Time step Modulation BW more

41 ENV Steup tab (continued) 7 Harmonics of Fundamental: Freq [1] 3 Harmonics of Fundamental: Freq [2] Harmonic Balance (Reference slide for multiple tones: mixer) t0 t1 t2 t3 t4 time Multiple tone simulation requires more data display

42 Topic 7: Circuit and System Co-Simulation

43 What is Co-simulation? Integrated Circuit, System Simulation & HP Ptolemy Co-simulation is simulating an A/RF schematic design with a DSP schematic design. Top Level System Design: DSP network A/RF network DSP network The simulator in the A/RF design must use either Transient or Circuit Envelope DSP Schematic Window The A/RF schematic can be any kind of design: amplifier, mixer, PLL, etc...

44 What is Ptolemy? Agilent Ptolemy is a Timed Synchronous Data Flow Simulator TSDF is a unique Agilent EEsof Innovation Agilent Ptolemy adds timed elements - parameters on signals are t, I, Q, Fc (rf carrier) Benefits: - easy to add real RF effects on signals - more efficient simulations - more accurate modeling of RF effects Agilent Ptolemy is the data flow simulator used in the DSP schematic window...

45 What is Data Flow? Tokens (like current or numbers) NODE (or component) Token arc (like a wire) NODE (or component) Tokens can also be time stamped - then they become samples. Now you can simulate time and frequency domain impairments such as multi-path and fading...

46 Co-simulation continued... Open a top level DSP network so that the Ptolemy / DSP palettes become available in schematic. Then build the system shown here: All the steps are in the lab, including the settings for the data components, filters, etc. The t_step and t_stop are now set for symbol rate and time. Bottom level system. Data flow controller runs showing filtered bits and IF signal: TkXY plots

47 Data Flow simulation - TK plots are active! Quit the DF simulation and connect a SpectrumAnalyzer sink to collect the data. Results of this co-simulation show spectrum of the behavioral system. To use amp_1900 and your filters, replace them in the system and setup a new simulation (requires more time). Spectrum Analyzer sink:

48 Thank you! 3/25/02