The purpose of the TB_SIM_DRU_JITTER test bench is to simulate the ability of the NIDRU to operate at several popular data rates (see the following table) with synchronous and plesiochronous serial inputs. The simulation covers the nine cases shown in the following table in sequence. Any data rate can be added as an additional case. The cases show the ability of the NIDRU to operate at both fractional and integer oversampling rates.
| Protocol (Case #) | Data Rate | Ref Clock (Oversampling Rate) | Oversampling Rate | Minimum Width Supported |
|---|---|---|---|---|
| Proprietary (1) | 250 Mbit/s | 125 MHz | 10 | 20 |
| OC3 (2) | 155.52 Mbit/s | 125 MHz | 16.075 | 4 |
| SDI (3) | 270 Mbit/s (+100 ppm) | 148.5 MHz | 11 | 20 |
| OC3 (4) | 155.52 Mbit/s | 155.52 MHz | 20 | 4 |
| OC12 (5) | 622.08 Mbit/s | 125 MHz | 4.019 | 20 |
| FE (6) | 125 Mbit/s | 155.52 MHz | 24.8832 | 4 |
| Proprietary (7) | 8 Gbit/s | 229 MHz | 3.664 | 128 |
| Proprietary (8) | 4 Gbit/s | 229 MHz | 7.328 | 64 |
| Proprietary (9) | 10 Gbit/s | 229 MHz | 2.9312 | 128 |
To run the simulation script:
- Open a DOS command window.
- Change to the /scripts directory.
- Open the Mentor Graphics Questa Advanced Simulator.
- In the simulator, run the run_sim_do script.
Although the test bench has been designed for the Questa Advanced Simulator only, the NIDRU core is expected to operate with the following broader set of simulation tools.
- Vivado® Simulator
- ModelSim
- Synopsys VCS
The architecture implemented in the tb_sim_nidru_v_3_0.vhd test bench is shown in the following figure. An ideal deserializer and serializer are used instead of a full transceiver to minimize the simulation time. The serializer and deserializer datapath is 4, 20, 32, 64, or 128, programmable through the DTIN_WIDTH attribute.
The test bench contains two clock domains:
- The clock domain of the line, synchronized to CLK_DT.
- The clock domain of the DRU, synchronized to REFCLK and to HF_CLK.
The pseudo-random binary sequence (PRBS) generator works at full speed on CLK_DT and can generate any kind of industry standard PRBS (see An Attribute-Programmable PRBS Generator and Checker (XAPP884)). The ideal deserializer, the NIDRU, and the PRBS checker all work on the local REFCLK domain, a divided version of HF_CLK.
During test case 1, a 1 ns phase step datastream is applied to the input (see the following figure). The purpose of this is to show the ability of the NIDRU to respond with an exponential locking process to an input phase step and to prove the stability of the loop.
During test case 2 and 5, the eye scan is plotted with PH_NUM=1 (see the following figure). The eye is scanned with one single phase from left to right.
An example of an eye scan with 2 phases (PH_NUM=2) is shown in the following figure. The left and right half of the eye are scanned at the same time.
