Analog Channel

R2026b

Construct loss model from channel loss metric or impulse response

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Analog Channel block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
SerDes Toolbox / Utilities

Description

The Analog Channel block constructs a loss model using a channel loss metric or an impulse response from another source in a SerDes Toolbox™ model. Analog model inputs are only used for IBIS file construction when using impulse response. For more information, see Analog Channel Loss in SerDes System.

Ports

Input

WaveIn — Input signal

scalar | vector

Input signal, specified as a waveform.

Data Types: double

Output

WaveOut — Modified output data

scalar | vector

Modified output data that includes the effect of a lossy printed circuit board transmission line model according to the method outlined in [1].

Data Types: double

Parameters

Channel Model

Channel model — Source of channel model

Loss model (default) | Impulse response

Source of channel model.

• Select Loss model to model the analog channel from a loss model.

• Select Impulse response to model the analog channel from an impulse response.

Programmatic Use

Block parameter: ChannelType

Type: character vector

Values: Loss model | Impulse response

Default: Loss model

Target frequency (Hz) — Frequency for desired channel loss

20e9 (default) | positive real scalar

Frequency for the desired channel loss, specified as a positive real scalar in hertz. It corresponds to the Nyquist frequency of the system.

Dependencies

This parameter is only available when Loss model is selected as Channel model.

Programmatic Use

Block parameter: TargetFrequency

Type: character vector

Values: positive real scalar

Default: 20e9

Data Types: double

Loss (dB) — Channel loss at target frequency

8 (default) | nonnegative real scalar

Channel loss at the target frequency, specified as a nonnegative real scalar in dB.

Dependencies

This parameter is only available when Loss model is selected as Channel model.

Programmatic Use

Block parameter: Loss

Type: character vector

Values: nonnegative real scalar

Default: 8

Data Types: double

Impedance (Ohms) — Channel characteristic impedance

positive real scalar

Characteristic impedance of the channel, specified as a positive real scalar in ohms. Impedance (Ohms) depends on the setting of Signaling in the Configuration tab in the SerDes Designer app or in the Configuration block.

• If Signaling is set to Differential, the default value of Impedance (Ohms) is 100.

• If Signaling is set to Single-ended, the default value of Impedance (Ohms) is 50.

Dependencies

This parameter is only available when Loss model is selected as Channel model.

Programmatic Use

Block parameter: Zc

Type: character vector

Values: positive real scalar

Default: 100

Data Types: double

Impulse response — User provided impulse response

[zeros(1,63),1/SampleInterval,zeros(1,192)] (default) | matrix

User provided impulse response, specified as a unitless matrix. Impulse response is used to construct a channel loss model from the user-defined impulse response of the system.

You can use user specified impulse response to define your own crosstalk. If you decide to include crosstalk from your custom impulse response, you can specify up to six crosstalk stimuli as new columns in the impulse response.

Dependencies

This parameter is only available when Impulse response is selected as Channel model

Programmatic Use

Block parameter: ImpulseResponse

Type: character vector

Values: matrix

Default: [zeros(1,63),1/SampleInterval,zeros(1,192)]

Data Types: double

Impulse sample interval — Sample interval of user provided impulse response

6.25e-12 (default) | positive real scalar

Sample interval of the user provided impulse response, specified as a positive real scalar in seconds.

Programmatic Use

Block parameter: ImpulseSampleInterval

Type: character vector

Values: positive real scalar

Default: 6.25e-12

Data Types: double

Plot Channel Responses — Plot channel impulse, step, and pulse responses

button

Click to plot the impulse, step, and pulse responses of the analog channel. You must apply any changes you made to the analog channel before plotting the responses.

Import S-Parameter Touchstone File — Generate channel impulse response by combining S-parameter model with characteristics impedance of transmitter and receiver

button

Click to generate the channel impulse response by combining an S-parameter model with the characteristics impedance of transmitter and receiver. This opens the S-Parameter Fitter app where you can import the S-parameter Touchstone file.

Analog Model

Tx R (Ohms) — Single-ended impedance of transmitter analog model

50 (default) | nonnegative real scalar

Single-ended impedance of the transmitter analog model, specified as a nonnegative real scalar in ohms.

Programmatic Use

Block parameter: TxR

Type: character vector

Values: nonnegative real scalar

Default: 50

Data Types: double

Tx C (F) — Capacitance of transmitter analog model

100e-15 (default) | nonnegative real scalar

Capacitance of the transmitter analog model, specified as a nonnegative real scalar in farads.

Programmatic Use

Block parameter: TxC

Type: character vector

Values: nonnegative real scalar

Default: 100e-15

Data Types: double

Rx R (Ohms) — Single-ended impedance of receiver analog model

50 (default) | nonnegative real scalar

Single-ended impedance of the receiver analog model, specified as a nonnegative real scalar in ohms.

Programmatic Use

Block parameter: RxR

Type: character vector

Values: nonnegative real scalar

Default: 50

Data Types: double

Rx C (F) — Capacitance of receiver analog model

200e-15 (default) | nonnegative real scalar

Capacitance of the receiver analog model, specified as a nonnegative real scalar in farads.

Programmatic Use

Block parameter: RxC

Type: character vector

Values: nonnegative real scalar

Default: 200e-15

Data Types: double

Rise time (s) — 20%−80% rise time of stimulus input

10e-12 (default) | positive real scalar

20%−80% rise time of the stimulus input to transmitter analog model, specified as a positive real scalar in seconds.

Programmatic Use

Block parameter: RiseTime

Type: character vector

Values: positive real scalar

Default: 10e-12

Data Types: double

Voltage (V) — Peak-to-peak voltage at input of transmitter analog model

1 (default) | positive real scalar

Peak-to-peak voltage at the input of transmitter analog model, specified as a positive real scalar in volts.

Programmatic Use

Block parameter: VoltageSwingIdeal

Type: character vector

Values: positive real scalar

Default: 1

Data Types: double

Crosstalk

Include Crosstalk — Include crosstalk in simulation

off (default) | on

Select to include crosstalk in the simulation. By default, this option is deselected.

You can add up to 50 crosstalk aggressors and their individual stimulus settings as additional impulse response columns to the impulse response of the Channel Model tab. The block displays the crosstalk stimulus parameters as a table in the Crosstalk tab. You can customize the symbol time, delay, modulation and PRBS order or port of individual crosstalk aggressors.

Note

Adding more than six crosstalk aggressors requires a license for Signal Integrity Toolbox™.

Include Bi-Directional — Include bidirectional links in SerDes Simulink^® models

off (default) | on

Select to include bidirectional links in SerDes Simulink models. By default, this option is deselected.

If you select the Include Bi-Directional parameter, the crosstalk aggressor table in the Crosstalk tab contains a column for S₂₂ input port with mutual exclusion to create the bidirectional link. You must provide the impulse responses for the bidirectional link using the Impulse response parameter in the Channel Model tab.

More About

Integrated Crosstalk Noise (ICN)

ICN is a frequency domain metric where the crosstalk is multiplied by a weighting function and then numerically integrated from 50 MHz to the baud rate (f_b). If there are multiple aggressors, their power are summed together before combining with the weighting function.

The time domain signal does not excite all frequencies evenly. The power spectral density (PSD) of a baseband time domain excitation follows a sinc-squared type response. The weighting function mimics the excitation of the PSD and shapes the PSD by including the effects of the receiver bandwidth and the transmitter rise time.

The total ICN is calculated by root-sum-squaring the FEXT ICN and NEXT ICN values together.

$$\begin{array}{l}{W}_{ft}(f)=\left(\frac{A_{ft}^2}{4f_b}\right){\text{sinc}}^2\left(\frac{f}{f_b}\right)\left[\frac{1}{1+{\left(f/f_{ft}\right)}^4}\right]\left[\frac{1}{1+{\left(f/f_{ft}\right)}^8}\right]\\ {\sigma }_{fx}={\left(2\Delta f{{\displaystyle \sum _n{W}_{ft}(f_n)10}}^{-MDFEX{T}_{loss}(f_n)/10}\right)}^{1/2}\\ {\sigma }_{nx}={\left(2\Delta f{{\displaystyle \sum _n{W}_{ft}(f_n)10}}^{-MDNEX{T}_{loss}(f_n)/10}\right)}^{1/2}\\ {\sigma }_x=\sqrt{{\sigma }_{fx}^2+{\sigma }_{nx}^2}\end{array}$$

Algorithms

Creating Far End Crosstalk

The impact felt on a victim line from a far end crosstalk aggressor is proportional to the rate of change of the aggressor waveform [2]. So, you can estimate the shape of a FEXT time domain signal with the derivative of the through response lossy impulse response.

$$I_{\text{FEXT}}(t)=k_{\text{FEXT}}\frac{dI(t)}{dt}$$

where, k_FEXT is a scale factor that scales the I_FEXT(t) so that it has user specified ICN value.

To calculate the ICN of the signal, transform the signal to frequency domain using Fourier transform.

$$H_{\text{FEXT}}(f)=ℱ\left[I_{\text{FEXT}}(t)\right]$$

The magnitude of the scale factor k_FEXT is: $$k_{\text{FEXT}}(f)=-\frac{IC{N}_{\text{FEXT}}}{\mathbb{I}ℂ{\mathbb{N}}_{\text{FEXT}}\left(H_{\text{FEXT}}(f)\right)}$$,

where $$\mathbb{I}ℂ\mathbb{N}$$ is the integrated crosstalk noise operator.

The sign of k_FEXT is negative since in typical transmission lines in inhomogeneous dielectrics, the inducting coupling is generally greater than capacitive coupling. As a result, the forward crosstalk pulse has the opposite magnitude from the magnitude of the aggressor signal.

Creating Near End Crosstalk

To calculate the near end crosstalk, note that the frequency domain NEXT response is similar in shape (not in magnitude) to the victim's return loss (S₁₁ or S₁₁).

$$H_{\text{NEXT}}(f)=k_{\text{NEXT}}·S_{11}(f)$$

Then the scale factor k_NEXT is: $$k_{\text{NEXT}}=-\frac{IC{N}_{\text{NEXT}}}{\mathbb{I}ℂ\mathbb{N}\left(S_{11}(f)\right)}$$

And the time domain NEXT signal is derived from the inverse Fourier transform.

$$I_{\text{NEXT}}(t)={ℱ}^{-1}\left[k_{\text{NEXT}}·S_{11}(f)\right]$$

References

[1] IEEE 802.3bj-2014. "IEEE Standard for Ethernet Amendment 2: Physical Layer Specifications and Management Parameters for 100 Gb/s Operation Over Backplanes and Copper Cables." URL: https://standards.ieee.org/standard/802_3bj-2014.html.

[2] Stephen Hall and Howard Heck. Advanced Signal Integrity for High-Speed Digital Designs. Hoboken, NJ: Wiley Press, 2009.

Version History

Introduced in R2019a

R2026b: Bidirectional Links in SerDes Simulink Model

Design bidirectional links in the SerDes Simulink models.

R2026b: Instantiate Multiple Analog Channel Blocks in Simulink

You can instantiate multiple Analog Channel blocks in a SerDes system Simulink model to design redriver workflow.