IBIS-AMI Analysis

IBIS-AMI (Algorithmic Modeling Interface) is a methodology used for high-speed serial link design, analysis, and verification.

IBIS-AMI provides an interface for the behavioral modeling of transmitters, receivers, and channels. The purpose of IBIS-AMI analysis is to predict the bit error rate (BER) of a high-speed serial link using IBIS-AMI models of the transmitter, receiver, and channel. For example, it can be used to analyze the performance of a PCI Express, USB, Ethernet interface, etc.

AMI is a widely used behavioral modeling standard for SerDes transceivers. The AMI model typically involves adaptive filtering and is comprised of two main components: an analog model and an algorithmic model. And it consists of three files: .ibs, .ami, and DLL. The analog model is specified in the .ibs file. DLL is the executable of the algorithmic model, whose parameters are specified in the .ami file.

By performing IBIS-AMI simulation, designers can evaluate different design options, such as different equalization techniques, signaling schemes, or termination strategies, and choose the optimal design that meets the required signal quality.

Figure 1.

Features and Menu Description

Through the Network Analysis menu, users can perform waveform analysis and eye diagram analysis of IBIS-AMI models. Just select the differential net you want to analyze and choose the Active Driver Pin corresponding to the Tx model. The input stimulus (e.g. a PWL source) can be set in the Transient Analysis Pattern which is one of the analysis Constraints. IBIS-AMI feature supports simulation for pin-to-pin topology, which means only one Transceiver model and one Receiver model. The simulation for pin-to-multi pins (Receivers) topology is not supported.

As IBIS-AMI models are simulated, the PollEx Spice engine calculates the impulse response of the analog channel which is engaged in buffer parasitics, PCB, connector, or cable and it computes waveforms by parsing the IBIS model and AMI model.

Multiple nets can be selected for analysis, but each net is modeled separately without coupling it to other nets. If one of the differential nets is selected, the corresponding differential pair net is automatically selected, and if multiple differential pair nets are chosen as the model, the simulation proceeds sequentially, one by one.

Figure 2.

In the IBIS Manager dialog, users can check the DLL file, AMI file, and model information of IBIS.

Figure 3.
  1. O/S type of IBIS-AMI model: The ami file has a Windows version and a Linux version, which shows its type.
  2. DLL file: The DLL executable supports a set of standard C function APIs that models Tx/Rx functionalities, and it shows the DLL files applied to the simulation.
    For example, there are three functions called by the simulator:
    • Init_Retrun_Impulse (char * params_in, …) - initialization Note despite its name, AMI_Init also deals with linear time-invariant (LTI) impulse response processing.

      GetWave_Exsists (waveform_in, waveform_out, clock_tick_array) - nonlinear time-varying (NLTV) waveform processing if needed.

      AMI_Close ( ) - memory deallocation, etc.

  3. AMI File: This is the ami file that specifies the algorithmic model parameter for the simulation. The AMI file contains information on the equalization, timing recovery, and other parameters used in the AMI model.
  4. Reserved Parameter: These are common parameters that are shared by all models. Their names, types, and meanings are defined by the AMI standard.
  5. Model specific: These are private to the model. Model makers can define any number of model specific parameters under any name and any type.

Waveform Analysis

Waveform analysis is running transient circuit simulation on the network model for user-specified simulation time to obtain time-domain voltage waveforms at the input and output nodes. Upon completion of the analysis, waveforms at all input and output nodes are displayed. If you select or deselect an input node for waveform display, the corresponding differential pair nodes are automatically selected or deselected. Many displays and measuring options are available in the waveform viewer.

The following is the waveform result of a differential line with an IBIS-AMI model applied.

Figure 4.

By selecting the submenu of the receiver (CN2_3) as shown below, you can view the calculated impulse response of the analog channel (such as buffer parasitics, PCB, connector, or cable). If connectors and cables are provided as S-parameter models, the simulation is possible. The following represents the impulse response regarding the positive net of a differential line.

Figure 5.

Eye Diagram Analysis

Eye Diagram analysis involves performing a transient circuit simulation on the network model to obtain eye diagrams at the input nodes. An eye diagram is created by overlapping multiple waveforms at the receiver node of a net generated by randomly selected high/low states of the input signals for the selected net and adjacent nets. Users can modify the analysis control parameters, such as the number of random pulses and bit pattern style, before running the analysis.

The following is the eye diagram result of a differential line with an IBIS-AMI model applied. Please note that no sub-menu is provided to view the impulse response in the eye diagram. To view the impulse response results, perform waveform analysis.

Figure 6.
Note: For simulation models with applied IBIS-AMI models, the Radiated Emission Analysis function is not supported. Kindly be aware that there is a possibility of the program not functioning correctly.