Ansys “Designer RF” Training Lecture 3: “Nexxim” Circuit ... · Ansys “Designer RF”...

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Ansys “Designer RF” Training Lecture 3: “Nexxim” Circuit Analysis for RF

Ansys “Designer RF”Solutions for RF/Microwave Component and System Design

1-2ANSYS, Inc. Proprietary© 2009 ANSYS, Inc. All rights reserved.

February 23, 2009Inventory #002593

© 2012 ANSYS, Inc. March 6, 20123.0-2 Release 7.0

• Ansoft Designer– Advanced Design Environment – Integrated Layout/Schematic– Co-Simulation– Dynamic Link to HFSS– Optimetrics

Ansoft DesignerLinear/Nonlinear Circuit Simulation

Frequency/TransientActive & Passive Physical Device Modeling

Method of MomentsFinite Element Method

Mixed Mode AnalysisFrequency/Time/Digital Waveforms

Baseband-through-RF3G Design Kits

Circuit/Nexxim System

EM Modeling

Designer Overview

HFSS, Q3D, SIWave




Welcome to Ansoft Designer

• The Nexxim Simulator– Nexxim® is Ansoft’s state-of-the-art circuit simulator for RF, analog, and mixed-signal designs. Nexxim combines

transistor-level simulation accuracy, high execution speed, and robust capability to handle circuits with thousands of active and passive elements. Nexxim simulates in all three domains — DC, time, and frequency — from the same set of device models. Nexxim offers the following simulation tools:

• DC analysis calculates the circuit’s DC operating point and is the basis for other analyses.• Transient analysis calculates the time-domain behavior of the circuit. Nexxim transient analysis incorporates a

new, Ansoft-proprietary variable time-step integration formula and advanced error estimation and control. The analysis can include S-parameter input data files for accurate analysis in the time domain.

• Harmonic balance analysis calculates the frequency-domain responses of the circuit. Nexxim harmonic balance performs single-tone and multi-tone analysis that combines Krylov subspace methods with Ansoft-proprietary preconditioning algorithms to achieve fast convergence.

• Small-signal analyses (AC, linear network, DC noise) are based on the DC solution. Nexxim’s proprietary linear system solver is optimized for circuit simulation, and produces accurate answers without compromising speed. Nexxim also supports small-signal frequency analysis based on harmonic balance.

• Nexxim provides a wide range of active, passive, and distributed device models. In addition to the classic variable sweeps of temperature, voltage, and current, Nexxim allows you to perform sweeps of any model or parameter in a circuit. Nexxim also supports both schematic and netlist circuit implementations. In addition, the Nexxim netlist format is HSPICE™-compatible, so any industry standard system-design netlist can be easily imported for analysis.




• Linear Network Analysis (LNA): – Computes the frequency-dependent scattering, impedance, and admittance parameters for a linear circuit. This is a

linear frequency-domain analysis. Circuit components are analyzed using Y-matrix analysis, and any nonlinear devices are linearized around their bias points when computing the bias values.

• Passive or active models, lumped, distributed, S parameter components can be inserted in the schematic. Ports must be added. Frequency or any other parameter can be swept.

Small-Signal Analysis

Frequency Sweep





• Group Delay and Noise Calculation– Can be performed by checking the appropriate box in the analysis window.– Available quantities include S, Y, Z parameter, Noise, Gain and Return Loss.





Rectangular plot for S11 & S22 in dB

Smith chart plot for S11




• DC Analysis (direct current) – Initializes the circuit, then solves the circuit equations to derive the DC operating point. The DC operating point consists

of the voltages at all nodes and currents through all branches, and includes the DC bias voltage applied to semiconductor devices.

– DC operating point analysis also provides the initial values used as the starting point for DC sweep analysis, harmonic balance analysis, and transient analysis, unless these are set by the user. It also provides the large-signal bias operating point for small-signal AC analysis, noise analysis, and linear network analysis. Successful and accurate calculation of the DC operating point is essential for these simulations.

– The default dc analysis does not employ the addition of components (such as resistors) to ground to aid convergence. If convergence is not achieved, five different continuation schemes are available to obtain the DC operating point.

DC Analysis




DCIV Curves

Viewing Nexxim DC Bias Voltages and Currents in a Schematic

DC AnalysisDC Analysis




• Harmonic Balance Analysis – Calculates the periodic or quasi-periodic steady-state response of a circuit to periodic inputs by solving the circuit

equations in the frequency domain. Time domain equations are represented by their Fourier series equivalents. In a one-tone analysis, the input is a sine wave at a specified frequency f, and the response is usually measured over a specified range of multiples or submultiples of that frequency. In a multi-tone analysis, the inputs are at two or more frequencies (f1, f2, ...). The response is a spectrum containing the DC response, the harmonics of the input frequencies, and the sums and differences of the harmonic frequencies. An optional Load-Pull analysis is available for schematic designs.

Harmonic Balance Analysis

Non linear transistor model

Bias source

RF source specified at

port




• Single Tone– For single tone analysis one can select between HB, standard harmonic balance or Shooting, where harmonic balance

uses a time-domain method that can be efficient for strongly nonlinear circuits.

Single Tone





• Multi Tone– Shooting method not available for multitone

Multi Tone





Sweep, Spectral and Time Domain allows to plot Voltage, Current, Power, Gain …

TG21 in dB & output power in dBm @fundamental vs.. input power





Constant power contour from Load Pull analysis

Output Spectrum @10 dBm input power





• HB vs Transient– Comparison of transient and harmonic balance analyses results with number of harmonic set to 15 and 127 on strongly

non linear signal using shooting method

15 Harmonics 127 Harmonics





• Oscillator Analysis – Uses harmonic balance analyses to find the oscillating frequency of a resonant circuit. The process of finding the

unknown resonant frequency can be aided by providing an estimate that is close to the true value. Oscillator analysis uses an oscillator probe element to provide a range of test voltages and frequencies. The analysis has two phases. First, initial estimates of the oscillating frequency and test voltage are made, either from user input or as directed by simulator options, and those estimates are assigned to the probe. Second, multiple harmonic balance analyses are performed while adjusting the probe frequency and voltage, until the resonant frequency is found. Oscillator analysis can be set up for single-tone or multi-tone calculations. Optionally, you can run a phase noise analysis as part of the oscillator analysis.

Oscillator Analysis

Oscillator probe




Oscillator Resonant Frequency Search to identify resonant frequency

Looking at real & imaginary part of the probe current aids oscillator design

Oscillator Analysis




Oscillator Analysis setup sets harmonic number and initial guess frequency for the simulation.

Solution Options window allows to select from different strategies freq_sweep, transient, dc to search the oscillating frequency

Oscillator Analysis




Spectral Time and Sweep Domain to plot Voltage, current, Power …

Current at port 1

Spectrum in dBm at port 1 Phase Noise at port 1

Oscillator Analysis




• Envelope Analysis – Is commonly used to analyze systems where harmonic balance or transient analysis alone is not adequate. Such

systems include circuits with two inputs, where one input is a fast-changing periodic or quasi-periodic source such as a clock or Local Oscillator (LO) and the other input is a nonperiodic source such as a baseband RF modulator that changes on a timescale that is orders of magnitude slower than the timescale of the fast-changing input. Transient analysis would require a small time-step to capture the fast-changing input, but then would require a very large number of time-steps to simulate the slowly-changing non-periodic input. Harmonic balance would fail to analyze the non-periodic input.

IQ Modulated Voltage Signal Generator

0

0

0

inp

inm

outmoutpQ62

AQ63

A

1000

R64

1000

R65

7200

R66

1000

R67

1000

R68

1000

R69

1000

R70

V71

DC=VBB

V72

DC=VBB

V73

DC=VCC

V74

DC=VDD

Model A

Harmonic Balance Envelope Analysis




• Envelope Analysis (Continued)– Envelope analysis uses transient analysis to simulate the slowly-moving signal in the time domain, plus harmonic

balance to analyze the fast-moving signal in the frequency domain . At each time-step of the transient analysis, an HB analysis is run. The frequency coefficients at each time step are stored and returned as the result. From these coefficients, you can obtain a variety of results including a transient-like time-domain result.

Eye diagram at I channel output from Envelope Analysis





IQ Constellation Plot for output and input

Output Spectrum for 1st and 2nd Harmonic





Periodic Time-varying Noise Analysis (TV Noise)

• Time-Varying noise analysis (TV Noise)– Calculates the response of a circuit to thermal, shot, and flicker noise sources analyzed as small-signal AC

perturbations around the periodic steady-state operating point calculated by harmonic balance or oscillator analysis. – The circuit elements are linearized by a DC operating point calculation prior to the steady-state analysis.

inp

inm

ou

tpo

utm

i b i a s v d d

v s s

M 2 9 0n b s i m

W = 1 0 uL = 2 5 0 nM = 1

2p

F

C2

91

1 0 k

R 2 9 2

1 7 . 5 n H

L 2 9 3

M 3 0 2n b s i m

W = 1 0 uL = 2 5 0 n

M = 1

14

.3k

R3

03

2p

F

C3

04

7.5

k

R3

07

M 3 1 0n b s i m

W = 1 0 uL = 2 5 0 nM = 1 0

M 3 1 1n b s i m

W = 1 0 uL = 2 5 0 nM = 1 0

M 3 1 4n b s i m

W = 1 0 uL = 2 5 0 n

M = 1 0

M 3 1 5n b s i m

W = 1 0 uL = 2 5 0 n

M = 1 0

50

0

R3

16 5

00

R3

17

1 7 . 5 n H

L 3 2 0

10

k

R3

23

10

k

R3

24

1 0 k

R 3 2 5

1 0 k

R 3 2 6

2p

F

C3

29

M 3 3 3n b s i m

W = 1 0 uL = 2 5 0 nM = 1 0

M 3 3 4n b s i m

W = 1 0 uL = 2 5 0 n

M = 1 0

1 n H

L 3 3 7

1 n H

L 3 3 8

70

0f

C3

41

70

0f

C3

42

M 3 4 6n b s i m

W = 1 0 uL = 2 5 0 nM = 3 0

M 3 4 7n b s i m

W = 1 0 uL = 2 5 0 n

M = 3 0A i 1 _ p r o b e

A i 2 _ p r o b ev s s v s s

v s s

v s s

v s s

v s s

v s s

3 . 2 5 m A

9 . 5 m A

0

0

in in_

outout_

lolo

_

i b i a s

v d d _ s u p

v s s _ s u p

M 3 7 3n b s i m

W = 1 0 uL = 2 5 0 n

M = 1

M 3 7 9n b s i m

W = 1 0 uL = 1 uM = 1

M 3 8 0n b s i m

W = 1 0 uL = 1 uM = 1

M 3 8 3n b s i m

W = 1 0 uL = 2 5 0 nM = 8

M 3 8 6n b s i m

W = 1 0 uL = 2 5 0 n

M = 8

10k

R38

7

10k

R38

8

2 p

C 3 8 9

2 p

C 3 9 0

M 3 9 4n b s i m

W = 1 0 uL = 2 5 0 nM = 1 2

M 3 9 5n b s i m

W = 1 0 uL = 2 5 0 n

M = 1 2

10p

C39

6

1 0 k

R 3 9 7

A

i 5 m a

1 0 k

R 3 9 9

M 4 0 3n b s i m

W = 1 0 uL = 2 5 0 nM = 3 0

M 4 0 4n b s i m

W = 1 0 uL = 2 5 0 n

M = 3 0

M 4 0 5n b s i m

W = 1 0 uL = 2 5 0 nM = 3 0

M 4 0 6n b s i m

W = 1 0 uL = 2 5 0 n

M = 3 0

150

R40

9 150

R41

0

M 4 1 3n b s i m

W = 1 0 uL = 2 5 0 nM = 2 4

M 4 1 4n b s i m

W = 1 0 uL = 2 5 0 nM = 2 4

1 0 k

R 4 1 7

1 0 k

R 4 2 0

M 4 2 3n b s i m

W = 1 0 uL = 2 5 0 nM = 8

M 4 2 4n b s i m

W = 1 0 uL = 2 5 0 nM = 8

M 4 2 7n b s i m

W = 1 0 uL = 2 5 0 nM = 2 0

M 4 2 8n b s i m

W = 1 0 uL = 2 5 0 n

M = 2 0

3p

C42

9

3p

C43

0

5 0 n

L 4 3 1

5 0 nL 4 3 2

A

i 7 m a _ 1

A

i 7 m a _ 2

1000

k

R45

8

1000

k

R45

9

v s s _ s u p

v s s _ s u p

v s s _ s u p v s s _ s u p

v s s _ s u p v s s _ s u p

v s s _ s u p

v s s _ s u p

v s s _ s u p

v s s _ s u p

TV Noise is specifically useful to analyze circuit with frequency conversion like mixer.

LNA MIXER




Conversion Gain & NF vs. IF output frequency

F specifies output frequency value (IF). The Input frequency sweep is then calculated from LO Frequency and F





Conversion Gain & NF vs. LO Power sweep

The power of the LO is swept, value of the IF frequency is 200MHz





• Periodic Transfer Function– The TV Noise analysis can be extended to include Periodic Transfer Function (PXF) Analysis. Periodic transfer

function analysis computes the small-signal transfer function from multiple input sources at multiple frequencies to one output at one frequency, or using the sweep of output frequencies from the TV noise analysis setup. A typical application for periodic transfer function analysis is to determine image rejection.

– PXF is very useful in calculating mixer properties such as image and side-band rejection, high-side and low-side conversion gain, LO feed-through, and power supply rejection, all within one simulation run.

Periodic Transfer Function (PXF)

RF input deviation frequency is defined using output frequency value, IF in this case.

High-side (blue) and low-side (red) Conversion Gain vs..IF

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