Each signal integrity engineers know, eyes closed diagram analysis is never an easy task. Frequency response (or lack of bandwidth) of the transmission channel leads to inter-symbol interference (ISI), which is the culprit of causing problems with eyes closed. I've written about before eyes closed analytical techniques, this time we will discuss how to measure equilibrium aftermath of ISI, the so-called resident ISI. In this process, we will realize that the decision feedback equalization (DFE) is actually very simple.
In the definition of the impulse response increasingly popular high-speed serial bus standard in the art. You can be sent through a long string of 0 pattern generator, followed by a 1, a long string of 0 and the other to generate a pulse. That is, the pulse does not return to zero (NRZ) bit, and the impulse response of the SBR (single bit in response to) the same.
Narrow peak response (impulse response), as the impulse response and also include information track circuits, connectors, cables, pins, solder balls impedance. Whether amplitude or phase, they are built. You may even be in the intrusion device (Aggressor) transfer pulse generating crosstalk impulse responses, and measuring SBRx (t) on the receptors.
Figure 1 shows (a) narrow peak, and (b) is equivalent to the impulse response.
Figure 1: The limited bandwidth of the transport channel extends (a) narrow peak, h (t); (b) a single bit, SBR (T). (Source: ANRITSU).
Impulse response SBR (t) and the narrow peak response h (t) has the following relationship:
Wherein the pulse (t) is a long string of 0, a 1 (for the PAM4, a 3), and another long list 0.
May be a vector network analyzer (the VNA) to measure the frequency domain impulse response SBR (t), and by time domain reflectometry / transmittance time domain method (TDR / TDT), or by using an oscilloscope. Also is easily extracted from the simulation.
Because the impulse response measurement provides all the information about the channel - all of Linear and time of a channel change information, which should be all we need to consider, for measuring and calculating metrics specific performance variables include channel operation margin ( COM) and signal to noise ratio distortion ratio (SNDR).
In practical systems, the receiver at the baud rate (i.e. the bit rate of the NRZ bit rate and the half PAM4) discretely sampled once for each symbol waveform.
Wherein the sum is accumulated over the duration of the impulse response. SBR (t) of the particle size and h (t) per unit interval is typically (UI) M = 32 samples, as shown in FIG.
Figure 2: each UI sampling M times SBR (t), generating a sample waveform ratio greater detail each UI. (Source: Anritsu)
UI is a sampling point located tsp SBR (t) after the initial rise.
ISI reside, may be referred ResISI (n), the ISI equalization is reserved each UI. To calculate ResISI (n), we need to balance comprising a transmitter emitting pulses - feed forward equalizer or de-emphasis (the FFE) before the transmitter. We also need to influence the receiver continuous time linear equalizer (CTLE) is included, which is very easy to implement ADS (Keysight Advanced Design System) and other IBIS simulator. Decision feedback equalization (DFE) can be entered manually:
ResISI (n) is the difference between a pre-equalizer and post-equalizer impulse response of the impulse response, means that perfect balance for all n, ResISI (n) = 0. One of the coolest part (I think it's cool) is how to tap its b (n) the DFE explicitly included. This is obvious, right? But still incredible.
In order to obtain a single parameter measurements resident ISI, just add its components, i.e., square root and, as a right triangle is added as an edge.
As you can see in Figure 3 how the three equalizers affect pulse.
Figure 3: ADS IBIS with and without equalization simulation of the impulse response. (Source: Wild River and Keysight)
Can use the same method, using SBRx (t) is calculated how crosstalk equalization scheme. With an infestation of SBR and SBRx, can (we have done just as ResISI) to calculate the shape of any waveform equalized by the DFE expressly included. In other words, you can see the waveform in the deeply rooted into the interior of the receiver chopper (slicer) on what it looks like.
Editor in charge: GT, read full text
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