Circuit SimulationCircuit SimulationSome humbling thoughts…Some humbling thoughts…

Manfred WendtFermilab

Manfred Wendt, Fermilab/AD-Instrumentation 2Nov. 30, 2006

Circuit Simulation: For What?Circuit Simulation: For What?Typical beam instrument, e.g. BPM, toroid, WCM, PMT, etc.

AnalogSignalProcessing

ADC

DigitalSignalProcessing

Clock & TriggerDistribution

DAQ &LANInterface

Beam

Pickup Detector

Analog Domain Digital Domain

Manfred Wendt, Fermilab/AD-Instrumentation 3Nov. 30, 2006

Circuit Simulation DomainsCircuit Simulation Domains– Digital signal simulation is mostly based on

vendor supplied simulators (e.g. Quartex II, etc.).– No model data is available for most complex

semiconductors (ADC, DAC, T&H amps, limiters, many – if not most - analog parts).

+ Circuit simulation may still be useful for critical sections and subsystems: Gain stages Passive sections (filters, diplexers, hybrids, transmission-

lines) RF- & microwave circuits Layout effects, cross-talk, reflections Noise and temperature analysis Pickup detectors (button, stripline, cavity & other monitors High-speed digital I/O (CLK distribution, PECL & LVDL circuits,

single-ended to differential transition)

Manfred Wendt, Fermilab/AD-Instrumentation 4Nov. 30, 2006

Circuit Simulator SoftwareCircuit Simulator Software “Brainware”

Pencil and paper Apply Kirchhoff and Ohm’s law for a simple, idealized

subcircuit. Analytic result! Limited to linear circuits.

Freeware Berkley SPICE and variants (google “free spice simulator”). Student versions, often limited. Simulators for special purposes.

$$$ware Schematic entry Combined with layout system, or add-on to layout system. Design suites, including various circuit and EM simulators.

Manfred Wendt, Fermilab/AD-Instrumentation 5Nov. 30, 2006

Capabilities and Capabilities and CharacteristicsCharacteristics

Circuit simulators canFully analyze the circuit (based on the models).Have sometimes (often limited) synthesis

capabilities.Numerical solution of the circuit topology

Circuit elementsLumped elements based on ideal modelsDistributed elements based on analytic solutions

or approximations of the EM problemNonlinearities, noise & temperature and other

effects may be included in some modelsUser specified (analytical) models and sources.

Manfred Wendt, Fermilab/AD-Instrumentation 6Nov. 30, 2006

Circuit Simulator TypesCircuit Simulator Types Linear Solvers:

DC, AC, S-parameter, etc. Frequency domain solution in steady state

Nonlinear Solvers (e.g. Harmonic Balance): Small signal analysis around the working point. Spectral, distortion and other characterization of the

frequency harmonics.

Transient Solvers (e.g. SPICE): Approximate solution of the system of differential

equations Time domain approach includes all transient effects and

initial values.

Special Solvers: Analytic circuit analysis, EM solvers, circuit synthesis,

etc.

Manfred Wendt, Fermilab/AD-Instrumentation 7Nov. 30, 2006

Simulation ExamplesSimulation Examples

Fermilab Main Injector BPM Upgrade Project

Manfred Wendt, Fermilab/AD-Instrumentation 8Nov. 30, 2006

Simulation Examples (cont.)Simulation Examples (cont.)

MI BPM Analog Signal Processing

2.3.

1. Entire input section2. Absorptive low-pass3. Diplexer

Manfred Wendt, Fermilab/AD-Instrumentation 9Nov. 30, 2006

Simulation Examples (cont.)Simulation Examples (cont.)

MI BPM Analog Circuit (1 ch., 2.5 & 53 MHz)