How to Build AMI Models for DDR5 Memory Interfaces
2021-06-03 | 5 min read
Traditionally, double data rate (DDR) technologies have relied on timing measurements, such as setup and hold times. As the standard evolves and the transfer rate increases, signal integrity becomes a lot more challenging.
For DDR5, timing measurements have been replaced with eye mask measurements for both data and command address signals. SPICE transient simulators are no longer the right approach for the latest DDR5 and LPDDR5 memory standards.
The new standards add equalization (EQ) on both the memory controller and the DRAM, and traditional simulation tools can’t model at that complexity.
Figure 1. DDR5 standards add equalization (EQ) on both the memory controller and the DRAM.
Input/Output Buffer Information Specification (IBIS) Algorithmic Modeling Interface (AMI) – or IBIS-AMI – models support statistical and time-domain channel simulations and represent the processing behavior inside the chip accurately and efficiently. However, access to models can be a bottleneck for new design work.
To create fast and accurate models that can predict eye closure, here are three ways that an AMI model builder can help you with your DDR5 and LPDDR5 modeling.
1. Generate Models Based on Industry Standards
Advanced AMI model builder software helps you create a new AMI model or edit a pre-existing model using an intuitive, wizard-style interface built to meet JEDEC specifications for DDR5 and LPDDR5. This allows you to select the modeling options you need.
Figure 2. AMI model builder software with an intuitive, wizard-style interface built to meet JEDEC specifications for DDR5.
How are these models configured? This video will walk you through the process of entering corner cases, individual pole-zero values, and input a step response file.
2. Predict Eye Opening with Confidence
To ensure the signal’s eye opens up, it is crucial that you apply the proper equalization. This includes finding the optimum decision feedback equalization (DFE) taps for your receiver equalization.
Figure 3. IBIS-AMI models with forwarded clocking capabilities better predict eye opening measurement with simulation.
At DDR5 speeds, the data eye is expected to close. AMI model builder software can generate AMI models with forwarded clocking. This means it takes in both data and data strobe waveforms as input to the model.
This advanced modeling capability ensures that your simulations will handle both jitter tracking and skew adjustment, also known as unmatched IO.
If your model has to support simulation environments other than PathWave ADS, you can turn off the dual waveform input and utilize a more traditional model with imaginary CDR instead. This video shows you how.
3. Streamline Your AMI Workflow
Once you’ve completed setting up your IBIS-AMI model, you’re now ready to send off your files. If you’re using PathWave ADS Memory Designer, the AMI builder quickly generates 4 file types: .ami, .dll, .cfg., and .ibs, making the models easy to consume and use in your simulations.
Figure 4. PathWave ADS Memory Designer layout with the memory controller and DRAM.
If you are a memory system engineer or a silicon modeling engineer, you can quickly and easily generate IBIS-AMI models using the latest version of PathWave ADS.
For a more detailed overview and to see the software in action, watch this short video: Build AMI Models Faster for DDR5/LPDDR5.
Download the free workspace to get started: PathWave ADS Memory Designer Workspace.