User`s guide

Understanding the IBIS Model

i.MX53 System Development User’s Guide, Rev. 1

Freescale Semiconductor 3-5

3.4.1 Ramp and Waveform Keywords

Table 3-3 defines the keywords that provide the information about an output or I/O buffer, and

Example 3-4 shows what they look like in an IBIS file.

Eqn. 3-1

NOTE

The dV value is the 20% to 80% voltage swing of the buffer when driving

into the specified load, R_load (for [Ramp], this load defaults to 50). For

CMOS drivers or I/O buffers, this load is assumed to be connected to the

voltages defined by the [Voltage Range] keyword for falling edges and to

ground for rising edges.

Example 3-4. Ramp and Waveform Keywords

An example of ramp and waveform table from MX53 IBIS:

[Ramp]

| variable typ min max

dV/dt_r 0.4717/0.2207n 0.4714/0.3252n 0.5647/0.1323n

dV/dt_f 0.4676/0.1382n 0.4749/0.2495n 0.6009/0.1270n

R_load = 50.0000

[Rising Waveform]

R_fixture= 50.0000

V_fixture= 0.0

V_fixture_min= 0.0

V_fixture_max= 0.0

|time V(typ) V(min) V(max)

0.0S 67.3645uV 17.6030uV 38.0931uV

79.7191pS 67.3645uV 17.6030uV 38.0931uV

0.3871nS 67.3645uV 17.6030uV 38.0931uV

0.4395nS 67.3645uV 17.6030uV 38.0931uV

0.5059nS 67.3645uV 17.6030uV 38.0931uV

The [Ramp] keyword is always required, even if the [Rising Waveform] and [Falling Waveform] keywords

are used. However, the VT tables under [Rising Waveform] and [Falling Waveform] are generally

preferred to [Ramp] for the following reasons:

• VT data may be provided under a variety of loads and termination voltages

• VT tables may be used to describe transition data for devices as they turn on and turn off.

Table 3-3. Ramp and Waveform Keywords

Keyword Required Comment

[Ramp] Yes Basic ramp rate information, given as a dV/dt_r for rising edges and dV/dt_f for falling

edges, see Equation 3-1.

[Rising Waveform] No The actual rising (low to high transition) waveform, provided as a VT table.

[Falling Waveform] No The actual falling (high to low transition) waveform, provided as a VT table.

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20 % to 80% voltage swing

time taken to swing above voltage

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