The Reference Rx (Receiver) operator allows you to create a reference receiver for use when testing transmitters. After dragging the Reference Rx to the Waveform Signal Processing Setup window, click on the Reference Rx operator to open the setup dialog as shown in the following figure. The dialog allows you to cascade a CTLE equalizer, Linear Equalizer (FFE, or TDECQ), and a Non-Linear Equalizer (DFE) secondary operators. You are not required to assign all three equalizer blocks. When you click on a secondary operator block (or click Setup), the setup dialog for the associated equalizer is opened.

Advantages of Reference Rx

• Reference Rx is the only way to perform joint FFE and DFE optimization in FlexDCA. If the equalizers are chained together outside of the Reference Rx operator, they will not be jointly optimized.
• Reference Rx makes it easier to define points in the system which can be selected as the reference point for TDECQ measurements (where the reference OMA is measured and noise is conceptually added for TDECQ measurements).
• Reference Rx groups all the setup for the reference receiver in one place.
• Reference Rx allows presets to define an entire reference receiver configuration that involves multiple equalizers.

Default Configuration Upon Installation

When the operator is first installed on the Waveform Signal Processing dialog, the following defaults exist as shown in the following picture. The Show Intermediate Functions setting is off. Also, the first secondary function (CTLE) is not loaded, but the TDECQ and DFE functions are loaded. Function numbers are not assigned to the secondary functions, so no inner waveforms can be displayed. If you turn the Show Intermediate Functions setting on, the secondary function numbers will be assigned.

Assigned Function Numbers

The following diagram shows the Reference Rx operator with its associated waveforms. On the Waveform Signal Processing Setup window, the Reference Rx operator's assigned function number automatically determines function numbers of the secondary operators. For example, in the figure the Reference Rx operator's function number is F2 and its secondary functions are:

• CTLE: F3
• Linear Equalizer:F4
• DFB Equalizer: F5

Show Intermediate Functions

Use the Show Intermediate Functions setting to show or hide the operator's secondary functions. This setting is persistent, is not saved in a function preset, and has a default setting of on. When the setting is turned off:

• Existing secondary function numbers are removed. For new instances of the operator, the function numbers are not assigned until the setting is turned on.
• Secondary Function waveforms cannot be displayed.
• The TDECQ Reference Point can still be placed on the reference points. Refer to the following section for information on reference points.
• The output of the Reference Rx operator is not affected.

Show Intermediate Functions Setting

ON	OFF (Default Setting)

TDECQ Reference Point

In the dialog, the REF symbol identifies the reference point. The reference point changes the information used to measure TDECQ on the output signal. The OMA value used in calculating TDECQ is made at the reference point and the noise gain is calculated between the reference point and the output of the operator. By default, the reference point is set at the Reference Rx operator's input waveform. You can drag the reference point to the output of any secondary function. For example, from 1A to F4 as seen in the following figure.

Equalizer Assignments

The following table shows the possible equalizer assignments for each of the three equalizers. After selecting your equalizers, click Setup to configure each equalizer.

Possible Equalizer Selections

Equalizer Selections	Equalizers in Reference Receiver Operator			Aliased Noise Processing Available
	CTLE	Linear Equalizer	Non-Linear Equalizer
Not Specified	■	■	■	—
CTLE equalizer	■			Yes
Linear equalizer (FFE)		■		Yes
TDECQ equalizer		■		Yes
DFE equalizer			■	No

Automatic Taps

The Linear (FFE or TDECQ) and DFE operators include taps which can be automatically set (default) or manually entered. The taps setting is not linked and can be different for each operator. Click Recalculate and, if any of these operators has Automatic Taps selected, its tap values will be recalculated. The calculation will take a few moments to complete.

Aliased Noise Processing

Aliased noise processing is a filter that is applied to the power spectrum of the noise to calculate the appropriate magnitude of the noise on the output. The availability of the aliased noise processing options is based on the type Linear Equalizer selected:

• If a TDECQ Equalizer is selected, the Receiver Rx operator forces the use of Process Spectrum noise processing and you do not need to make a selection.
• If a Linear Equalizer (FFE) is selected, you can select noise processing to be either:
• Process Spectrum. By default, the Input Noise Bandwidth tracks the input response. In the secondary operator, you can manually set the bandwidth. This setting is linked between the CTLE, Linear and TDECQ secondary operators.
• Preserve RMS.
• Turn off noise processing.

The aliased noise processing and equalizer bandwidth settings are configured in the secondary operator's Setup dialog.