TDECQ Operator (Advanced)

Low-SNR Measurement Mode

Enable Low-SNR to allow the TDECQ operator to operate when large amounts of noise is present on the signal. The default state of this setting is enabled. This capability is activated by the L-RND or L-MFG package licenses.

Specify Pattern Symbol Sequence

Use these settings to specify input waveform's pattern symbol sequence (NRZ or PAM4). You can select to have the pattern automatically detected (default), select from a know standard Known Pattern, or a BERT Pattern File (*.ptrn). Available known patterns are listed in the following table. If you select to import a Pattern File, you can specify if the pattern uses Gray Coding. Gray coding, or reflected binary code, is a coding pattern where successive symbols differ by one binary bit. For example in the case of PAM4, binary bit sequences 00, 01,10, and 11 represent levels 0, 1, 2, and 3.

Standard Pattern Selections

Selection	Format		Command Argument	Description
	NRZ	PAM4
PRBS 7 (127 symbols)	♦	♦	PRBS7	27−1 pseudo-random symbol sequence (127 symbols).
PRBS 7 (128 symbols)	♦	♦	EPRBs7	27 pseudo-random symbol sequence (128 symbols).
PRBS 9 (511 symbols)	♦	♦	PRBS9	29−1 pseudo-random symbol sequence (511 symbols).
PRBS 9 (512 symbols)	♦	♦	EPRBs9	29 pseudo-random symbol sequence (512 symbols).
PRBS 11 (2047 symbols)	♦	♦	PRBS11	211−1 pseudo-random symbol sequence (2,047 symbols).
PRBS 11 (2048 symbols)	♦	♦	EPRBs11	211 pseudo-random symbol sequence (2,048 symbols).
PRBS 13 (8191 symbols)	♦	♦	PRBS13	213−1 pseudo-random symbol sequence (8,191 symbols).
PRBS 13 (8192 symbols)	♦	♦	EPRBs13	213 pseudo-random symbol sequence (8,192 symbols).
PRBS 15 (32767 symbols)	♦	♦	PRBS15	215−1 pseudo-random symbol sequence (32,767 symbols).
PRBS 15 (32768 symbols)	♦	♦	EPRBs15	215 pseudo-random symbol sequence (32,768 symbols).
Linearity (160 symbols)		♦	LPAM4
K28.5 (20 symbols)	♦		K28P5
PRBS9Q (511 symbols)		♦	PRBQ9	PRBS9Q (511 symbols).
PRBS13Q (8191 symbols)		♦	PRBQ13	PRBS13Q (8,191 symbols).
CEI SSPR (32762 symbols)	♦		SSPR
SSPRQ (65535 symbols)		♦	QSSPr	SSPRQ (65,535 symbols).

Aliased Noise Processing

With the TDECQ operator, the Process Spectrum selection is the only option and is always selected. Although the other Noise Processing setting are unavailable, the following paragraphs describe the way FlexDCA generally handles noise processing with other operators.

None Selection

The option None does not make any special considerations for aliased noise. This is an appropriate choice when the waveform is known to have no aliased components, such as from a real-time or simulated source. This also is the preferred choice when dealing with averaged waveforms where the desired outcome is to remove noise and interference components that are not correlated to the trigger signal.

Process Spectrum Selection

The option Process Spectrum works by applying the transfer function of the filter to the power spectrum of the noise to determine the appropriate magnitude of the noise on the output signal.

By tracking the accumulated effects of the filtering operations, accurate noise processing can be done even when chaining operations as illustrated in the following figure. In addition to the sampled waveform, information about the acquisition channel and noise power spectrum are maintained in each signal and appropriately processed by each filter. The complete set of auxiliary information is also included when storing FlexDCA waveforms in the *.wfmx file format.

The default behavior of the Process Spectrum noise processing option is to use the noise power spectrum of the input signal. If the input signal is a sampling scope channel with SIRC active, this spectrum will be established by the measured hardware response of the channel. For other channels, the response will be assumed Gaussian with a 3 dB frequency corresponding to the nominal channel bandwidth. This behavior can be overridden by clearing the Track Input Response checkbox and manually entering a bandwidth. If this option is utilized the response will be presumed Gaussian with the selected 3 dB bandwidth.

Preserve RMS Selection

The option Preserve RMS is appropriate when the noise bandwidth is very low relative to the channel and filter bandwidth. It is also appropriate when the aliased components are known to have most of the power within a range of in-band frequencies. This could be from laser RIN, for example, or from intentionally modulated interference/crosstalk. When Preserve RMS is selected, the RMS magnitude of the aliased components will be scaled by the DC gain (the sum of the taps) of the filter. For the low-pass filters (Bessel, Butterworth, Gaussian, Sinc), the DC gain is unity. For the equalizers and embedding/de-embedding operators, the DC gain depends upon the settings of the operator.