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3/6/2015
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Fundamentals of RF DesignRF Back to Basics 2015
Keysight EEsof EDA
Updated January 1, 2015
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Objectives
–Review Simulation Types
–Understand fundamentals on
S-Parameter Simulation
–Additional Linear and
Non-Linear Simulators
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Electronic Design Automation (EDA)
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IDEA
CONCEPT | DESIGN
PRODUCT
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We Are Focusing On The Idea to Concept / Design
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– Simulations Only Consider Effects in the Model
– Reality Considers Everything
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RF Calculations
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S22 = Reflected
Incident=
b2
a 2 a1 =0
S12 =
Transmitted
Incident=
b1
a 2 a1 =0
S11 = Reflected
Incident=
b1
a 1 a2 =0
S21 =
Transmitted
Incident=
b2
a 1 a2 =0
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Cascading S-Parameters
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|S| |S’|
a1
b1
a2
b2
a1’
b1’
a2’
b2’
For Cascaded S Matrix a1’=b2 and a2=b1’
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Cascading S-Parameters
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b1=S11*a1+S12*a2=S11a1+S12*b1’ where b1’=S11’*a1’+S12’*a2’
substituting yields, b1=S11*a1+S12*S11’*a1’+S12*S12’*a2’ eq 1
a1’=b2=S21*a1+s22*a2 where a2=b1’substituting and rearranging yields,
a1’=(S21**a1+S22*S12’*a2’)/1-S22*S11 eq 2 then eq 2 into eq 1,
Repeating for b2’ results in cascaded S-Parameterw
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Advanced Design System Lineage
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Touchstone
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Touchstone Netlist
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Simulation Types
• DC, AC, Linear (S-Parameter)
• Transient (High Frequency Spice)
• Harmonic Balance
• Circuit Envelope
• EM Simulation
• MoM, FEM, FDTD
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S-Parameter Simulation
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S-Parameter Termination
– Termination can be any impedance value
– Port Count is not limited
– No Calibration needed
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S-Parameter Simulation (Frequency-domain)
– DC analysis is performed to find the bias point
– Nonlinear devices linearized at the bias point
– Assumes signal does not perturb the bias
– S-parameter sources are ports
– Components characterized by I and their small-signal [S] or [Y]
– Finds solution such that sum of all AC currents into each circuit node is zero (not iterative)
• Computes [S] and [Y] of the overall circuit at external ports
• Calculates response to small sinusoidal signals
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S-Parameter Simulation
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Instead of Take a Measurement
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We Run a Simulation
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ADS Netlist
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S-Parameter Controller Options/Sweep
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Plans
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S-Parameter Controller Options/Sweep
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Plans
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Tune
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Transmission Lines
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Ideal Transmission Line
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Microstrip Transmission Lines
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– Surface Roughness Option
– Frequency Dependent Dielectric Model
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Multilayer Transmission Lines
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Integration of EM Solvers
–Method of Moments
–Finite Elements Method
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Power Transfer Efficiency
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RS
RL
For complex impedances, maximum
power transfer occurs when ZL = ZS*
(conjugate match)
Maximum power is transferred when RL = RS
RL / RS
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6 7 8 9 10
Lo
ad
Po
wer
(no
rmalized
)
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Power Transfer Efficiency
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AC Analysis
– DC Analysis is performed to find the bias point
– Nonlinear devices linearized at the bias point
– Assumes signal does not perturb the bias
– Sources are voltage and current sine waves
– Superposition is allowed and encouraged
– Outputs are voltage and current
– Sums all AC currents into each circuit node (not iterative)
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(Frequency-domain simulator)
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Power Transfer Efficiency
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Power Transfer Efficiency
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Power Transfer Efficiency
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Smith Chart Review
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∞ →∞ →∞ →∞ →
Smith Chart maps
rectilinear impedance
plane onto polar plane
0 +R
+jX
-jX
Rectilinear impedance plane-90o
0o180
o+-
.2
.4
.6
.8
1.0
90o
∞∞∞∞0000
Polar plane
Z = ZoL
= 0Γ
Constant X
Constant R
Smith Chart
Γ
LZ = 0
= ±180 O
1
(short) Z = L
= 0 O
1Γ
(open)
Inductive
Capacitive
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Series Capacitance
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Series Inductance
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Series Resonance
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Separating Resonant Elements
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Example of Matching Elements
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Example of Matching Elements
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Smith Chart Characteristics
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Modeling Linear Behavior In ADS
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S-Parameters
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Using Optimization to Develop Models
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AmodelB Optimization Setup
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S-Parameters Before and After Optimization
Before Optimization After Optimization
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SP_Probe
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Starting LineCalc
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LineCalc Tool
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Transient Analysis
– Kirchoff’s current equations are derived at each node in differential
form
– The time derivatives are replaced with discrete-time approximations (integration)
– The solution, in the case of a complex circuit, will consist of a system of nonlinear equations which is solved using the Newton-Raphson method
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Just like SPICE
v(t)
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Convolution Analysis
– Convolution calculates the response of distributed and dispersive
network, to an arbitrary transient time-domain waveform.
• Models can includes conductor loss, dielectric loss, self-and coupled inductance and capacitance, as functions of frequency, and multi-ports-parameter data sets from measurements and field solvers.
• Impulse response for all distributed components is calculated, then convolved with input signal to yield output
• Results can be transformed to the frequency domain.
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Transient Simulation with Convolution
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Harmonic Balance (Steady State Analysis)
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Measure Linear
Circuit Currents
in the Frequency-Domain
Start Simulation Frequencies
Number of Harmonics
Number of Mixing Products
• Inverse Fourier Transform: Nonlinear Voltage
Now in the Time Domain
• Calculate Nonlinear Currents
• Fourier Transform: Nonlinear Currents
Now back in the Frequency Domain
Measure Nonlinear
Circuit Voltages
in the Frequency-Domain
DC analysis
always done
Linear Components
Test: Error > Tolerance: if yes, modify & recalculate
if no, then Stop= correct answer.
Nonlinear Components
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Example Circuit: First and Last Iterations
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IDIR IC IL IY
IRIC IL ID IY-port
Initial Estimate:
spectral voltage
V Final
Solution
If within
tolerance
IR IC IL ID IY
Start in theFrequency Domain Convert: ts -> fs
Last Estimate
with least error
Calculate currents
the
n
(Momentum file)
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Harmonic Balance Setup
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Harmonic Balance Results
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Modulated Sources
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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 Simulations & Keysight’s Ptolemy
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Next, what tests can it perform?
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Test Circuits with Realistic Signals
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– Adjacent Channel Power Ratio
– Noise Power Ratio
– Error Vector Magnitude
– Power Added Efficiency
– Bit Error Rate
2-tone tests and linearized models do not predict this behavior as easily!
GSM, CDMA, GMSK, pi/4DQPSK, QPSK, etc.32.8 kHz BW
for NADC
890 MHz
carrier
Simulations can include:
Example CE results:
Also, Envelope can be used for PLL simulations:
lock time, spurious signals, modulation in the loop.
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Circuit Envelope Technology
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Time sample the
envelope and then
perform Harmonic
Balance on the
samples!
V(t) * e j2π fot
t1t4
t2
t3
ModulationCarrier
Periodic input signal
NOTE: V(t) can be complex - am or fm or pm
Circuit Vout
More...
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More on CE Technology
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Captures time and frequency characteristics:
dBm (fs (Vout[1]))
Next, an example...
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IS-95 Forward Link Modulated Signal Generation
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IS-95 Forward Link Modulated Signal Generation
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What are X-Parameters?
– X-parameters are the mathematically correct superset of S-
parameters, applicable to both large-signal and small-signal
conditions, for linear and nonlinear components. The math exists!
– We can measure, model, & simulate with X-parameters
– Each part of the puzzle has been created
– The pieces now fit together seamlessly
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Interoperable Nonlinear Measurement, Modeling & Simulation with X-parameters
“X-parameters have the potential to do for characterization, modeling, and design of nonlinear
components and systems what linear S-parameters do for linear components & systems”
NVNA: Measure X-parameters PHD: X-parameter block ADS: Simulate X-parameters
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X-parameters – From Poly-Harmonic Distortion (PHD)
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Experiment Setup and Simulation Schematic
– Objective: Design nonlinear circuits in ADS from NVNA-measured
X-parameters of individual components
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Cascaded Simulation vs. Measurement
Red: Cascade Measurement
Blue: Simulation of Cascaded Models
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“X-parameters enable predictive nonlinear design from NL data”
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Thank you!
– For More Information www.keysight.com/find/eesof-ads-info
– ADS on www.keysight.com/find/eesof-ads-videos
– Evaluate ADS www.keysight.com/find/eesof-ads-evaluation
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