EMI Analyst™

EMI ANALYST™ Software SuiteI n t u i ti v e A c c u r a t e E ff e c ti v e

How to use IBIS files in EMI Analyst™IBIS – Input/Output Buffer Information Specification

EMI Analyst™

What is an IBIS File?• IBIS is a standard for describing the analog behavior of digital device buffers

using plain ASCII text.• IBIS files are not really models, they contain data used for modeling. IBIS is really a

specification.• Simulation tools interpret IBIS specifications to implement their own models and

algorithms.• IBIS defines component properties in terms of behavior instead of circuitry.

• Spice models are limited to small signals.• IBIS covers entire operating range, plus clamping of over- and under voltage

transients, making it possible to model ringing that overshoots or undershoots.

• IBIS does not reflect the product’s interior logic and interactions, only the behavior of the circuits connected to the device pins.

EMI Analyst™

What Is Needed for an EMI Analyst™ Model?For example, LVDS circuit

Outputs DO+/DO-• Output Impedance

• Cpin, Rpin, Lpin• C_comp• Rout

• Rise/Fall Time Waveforms• Rising waveform• Falling waveform

Inputs RI+/RI-• Input Impedance

• Cpin, Rpin, Lpin• C_comp• Rin

EMI Analyst™

IBIS Output and Input ModelsVDD

Output +

Output -

GND

Input/Enable

Pins

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

PowerClamp(V-I)

GroundClamp(V-I)

InternalLogic

VDD

In Pin

GND

C_comp

C_comp

LpinRpinCpin

LpinRpinCpin

LpinRpinCpin

VDD

Input +

GND

OutputPin

Input -

EMI Analyst™

Pin Parasitics – Rpin, Lpin, Cpin• Outputs

• Inputs

Out PinC_comp

Lpin Rpin Cpin

C_comp

LpinRpinCpin

In Pin

EMI Analyst™

Output Model Input ModelDO+, DO- RI+, RI-

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LVDS Waveform Specs• Constant current: 4.0 mA nom.• Some mfg. use 3.5 mA

• Char. Z: 100 ohms nom.• Output voltage: ±400 mV nom.• Offset voltage: 1.2V (Vref)• VOH = 1.4V, VOL = 1.0V

• Rcvr input threshold voltage: ±100 mV nom.• Rcvr max. CM voltage: ±1V min.

EMI Analyst™

Output Impedance and Input ImpedanceOutput Z from datasheet

Rout = 58 ohms (350 mV / 6 mA)?

Input Z from datasheet

Rin = 2.4 Mohm (2.4V / 1uA)? = 240 kohm (2.4V / 10 uA)?

Input and output impedance change dynamically with signal amplitudeFrom IBIS model, output impedance is about 230 ohms in operating range

EMI Analyst™

Pullup CurveI-V curve for VOH

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

EMI Analyst™

Pulldown CurveI-V curve for VOL

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

EMI Analyst™

Output Model – Power ClampI-V curve when output pin is pulled above VCC

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

EMI Analyst™

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

Output Model – Ground ClampI-V curve when output pin is pulled below GND

EMI Analyst™

Output Model – Rising Waveform20% - 80% (1.08V – 1.32V): 700 ps

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

EMI Analyst™

Output Model – Falling Waveform80% - 20% (1.32V – 1.08V): 390 nsec

Rising Ramp(V-t)

Pullup(V-I)

PowerClamp(V-I)

GroundClamp(V-I)

Pull-Down(V-I)

FallingRamp(V-t)

InternalLogic

VDD

Out Pin

GND

C_comp

C_comp

Lpin Rpin Cpin

Lpin Rpin Cpin

Lpin Rpin Cpin

EMI Analyst™

DM Waveform from IBIS FileCreate data file from IBIS values and import into EMI Analyst™ Source form.

EMI Analyst™

Input Model – Power ClampI-V curve when input pin is pulled above VCC

EMI Analyst™

Input Model – Ground ClampI-V curve when input pin is pulled below GND

EMI Analyst™

LVDS Circuit and Equivalent ModelLVDS Circuit Model

Equivalent Circuit from IBIS File and Datasheet

DO+

DO-

RI+

RI-

100

Ω

50m1.05193n

0.16890p

58

50m1.05308n

0.16861p

58

DO+

DO-

RI+

RI-

100

Ω

50m 1.05193n

0.16890p

240k

50m 1.64135n

0.37335p

240k

4.13p

4.13p

3.56P

3.56P

Z0 = 100 Ω

1p

EMI Analyst™

Predicted Radiated Emissions for Shielded LVDS Cable with no Common Mode Voltage

EMI Analyst™

References• The IBIS model, Part 1: A conduit into signal-integrity analysis

http://www.ti.com/lit/an/slyt390/slyt390.pdf• The IBIS model, Part 2: Determining the total quality of an IBIS model

http://www.ti.com/lit/an/slyt400/slyt400.pdf• The IBIS model, Part 3: Using IBIS models to investigate signal-integrity issues

http://www.ti.com/lit/an/slyt413/slyt413.pdf• IBIS reader: https://www.mentor.com/pcb/downloads/visual_ibis_editor/