DDS Compiler 6.0 - 2022.1 English

The Xilinx DDS (Direct Digital Synthesizer) Compiler block implements high performance, optimized Phase Generation and Phase to Sinusoid circuits with AXI4-Stream compliant interfaces for supported devices.

The core sources sinusoidal waveforms for use in many applications. A DDS consists of a Phase Generator and a SIN/COS Lookup Table (phase to sinusoid conversion). These parts are available individually or combined using this core.

Architecture Overview

To understand the DDS Compiler, it is necessary to know how the block is implemented in FPGA hardware. The following is a block diagram of the DDS Compiler core. The core consist of two main parts, a Phase Generator part and a SIN/COS LUT part. These parts can be used independently or together with an optional dither generator to create a DDS capability. A time-division multi-channel capability is supported with independently configurable phase increment and offset parameters.

Figure 1. DDS Compiler Block Diagram

Phase Generator

The Phase Generator consists of an accumulator followed by an optional adder to provide addition of phase offset. When the core is customized the phase increment and offset can be independently configured to be either fixed, programmable (using the CONFIG channel) or dynamic (using the input PHASE channel).

When set to fixed the DDS output frequency is set when the core is customized and cannot be adjusted once the core is embedded in a design.

When set to programmable, the CONFIG channel TDATA field will have a subfield for the input in question (PINC or POFF) or both if both have been selected to be programmable. If neither PINC nor POFF is set to programmable, there is no CONFIG channel.

When set to streaming, the input PHASE channel TDATA port (s_axis_phase_tdata) will have a subfield for the input in question (PINC or POFF) or both if both have been selected to be streaming. If neither PINC nor POFF is set to streaming, and the DDS is configured to have a Phase Generator then there is no input PHASE channel. Note that when the DDS is configured to be a SIN/COS Lookup only, the PHASE_IN field is input using the input PHASE channel TDATA port.

SIN/COS LUT

When configured as a SIN/COS Lookup only, the Phase Generator is not implemented, and the PHASE_IN signal is input using the input PHASE channel, and transformed into the SINE and COSINE outputs using a look-up table.

Efficient memory usage is achieved by exploiting the symmetry of sinusoid waveforms. The core can be configured for SINE only output, COSINE only output or both (quadrature) output. Each output can be configured independently to be negated. Precision can be increased using optional Taylor Series Correction. This exploits XtremeDSP slices on FPGA families that support them to achieve high SFDR with high speed operation.

AXI Ports that are Unique to this Block

Depending on the Configuration Options and Phase Increment/Offset Programmability options selected, different subfield-ports for the PHASE channel or the CONFIG channel (or both channels) are available on the block, as described in the table below.

Block Parameters

The block parameters dialog box can be invoked by double-clicking the icon in your Simulink® model.

Basic tab

Parameters specific to the Basic tab are as follows.

Configuration Options

This parameter allows for two parts of the DDS to be instantiated separately or instantiated together. Select one of the following.

• Phase_Generator_and_SIN_COS_LUT
• Phase_Generator_only
• SIN_COS_LUT_only

System Requirements

System Clock (MHz)

Specifies the frequency at which the block is clocked for the purposes of making architectural decisions and calculating phase increment from the specified output frequency. This is a fixed ratio off the System Clock.

Number of Channels

The channels are time-multiplexed in the DDS which affects the effective clock per channel. The DDS can support 1 to 16 time-multiplexed channels.

Mode of Operation

Standard

The output frequency of the DDS waveform is a function of the system clock frequency, the phase width in the phase accumulator and the phase increment value.

Rasterized

The DDS does not truncate the accumulated phase. Rasterized operation is intended for configurations where the desired frequency is a rational fraction of the system clock (output frequency = system frequency * N/M, where 0 < N < M). Values of M from 9 to 16384 are supported.

Note: Refer to the document DDS Compiler LogiCORE IP Product Guide (PG141) for a detailed explanation of these modes.

Parameter Selection

Select System_Parameters or Hardware_Parameters

System Parameters

Spurious Free Dynamic Range (dB)

The targeted purity of the tone produced by the DDS. This sets the output width as well as internal bus widths and various implementation decisions.

Frequency Resolution (Hz)

This sets the precision of the PINC and POFF values. Very precise values will require larger accumulators. Less precise values will cost less in hardware resource.

Noise Shaping

Select one: None, Phase_Dithering, Taylor_Series_Corrected, or Auto.

If the Configuration Options selection is SIN_COS_LUT_only, then None and Taylor_Series_Corrected are the only valid options for Noise Shaping. If Phase_Generator_Only is selected, then None is the only valid choice for Noise Shaping.

Hardware Parameters

Phase Width

Equivalent to frequency resolution, this sets the width of the internal phase calculations.

Output Width

Broadly equivalent to SFDR, this sets the output precision and the minimum Phase Width allowable. However, the output accuracy is also affected by the choice of Noise Shaping.

Output Selection

Sine_and_Cosine

Place both a Sine and Cosine output port on the block.

Sine

Place only a Sine output port on the block.

Cosine

Place only a Cosine output port on the block.

Polarity

Negative Sine

Negates the sine output.

Negative Cosine

Negates the cosine output.

Amplitude Mode

Full_Range

Selects the maximum possible amplitude.

Unit_Circle

Selects an exact power-of-two amplitude, which is about one half the Full_Range amplitude.

Implementation tab

Implementation Options

Memory Type

Select between Auto, Distributed_ROM, or Block_ROM.

Optimization Goal

Select between Auto, Area, or Speed.

DSP48 Use

Select between Minimal, or Maximal. When set to Maximal, XtremeDSP slices are used to achieve to maximum performance.

Latency Options

Auto

The DDS is fully pipelined for optimal performance.

Configurable

Allows you to select less pipeline stages in the Latency pulldown menu below. This generally results in less resources consumed.

Control Signals

Has phase out

When checked the DDS will have the phase_output port. This is an output of the Phase_Generator half of the DDS, so it precedes the sine and cosine outputs by the latency of the sine/cosine lookup table.

ACLKEN

Enables the clock enable (aclken) pin on the core. All registers in the core are enabled by this control signal.

ARESETn

Active-low synchronous clear input that always takes priority over ACLKEN. A minimum ARESETn active pulse of two cycles is required, since the signal is internally registered for performance. A pulse of one cycle resets the core, but the response to the pulse is not in the cycle immediately following.

Explicit Sample Period

Use explicit period

When checked, the DDS Compiler block uses the explicit sample period that is specified in the dialog entry box below.

AXI Channel Options tab

AXI Channel Options

TLAST

Enabled when there is more than one DDS channel (as opposed to AXI channel), as TLAST is used to denote the transfer of the last time-division multiplied channel of the DDS. Options are as follows.

Not_Required

In this mode, no TLAST appears on the input PHASE channel nor on the output channels.

Vector_Framing

In this mode, TLAST on the input PHASE channel and output channels denotes the last.

Packet_Framing

In this mode, TLAST is conveyed from the input PHASE channel to the output channels with the same latency as TDATA. The DDS does not use or interpret the TLAST signal in this mode.This mode is intended as a service to ease system design for cases where signals must accompany the datastream, but which have no application in the DDS.

Config_Triggered

This is an enhanced variant of the Vector Framing option. In this option, the TLAST on the input PHASE channel can trigger the adoption of new configuration data from the CONFIG channel when there is new configuration data available. This allows the re-configuration to be synchronized with the cycle of time-division-multiplexed DDS channels.

TREADY

Output TREADY

When selected, the output channels will have a TREADY and hence support the full AXI handshake protocol with inherent back-pressure. If there is an input PHASE channel, its TREADY is also determined by this control, so that the datapath from input PHASE channel to output channels as a whole supports backpressure or not.

TUSER Options

Select one of the following options for the Input, DATA Output, and PHASE Output.

Not_Required

Neither of the above uses is required; the channel in question will not have a TUSER field.

Chan_ID_Field

In this mode, the TUSER field identifies the time-division-multiplexed channel for the transfer.

User_Field

In this mode, the block ignores the content of the TUSER field, but passes the content untouched from the input PHASE channel to the output channels.

User and Chan_ID_Field

In this mode, the TUSER field has both a user field and a chan_id field, with the chan_id field in the least significant bits. The minimal number of bits required to describe the channel will determine the width of the chan_id field. For example, 7 channels will require 3 bits.

User Field Width

This field determines the width of the bit field which is conveyed from input to output untouched by the DDS.

Config Channel Options

Synchronization Mode

On_Vector

In this mode, the re-configuration data is applied when the channel starts a new cycle of time-division-multiplexed channels.

On_Packet

In this mode, available when TLAST is set to packet framing, the TLAST channel will trigger the re-configuration. This mode is targeted at the case where it is to be associated with the packets implied by the input TLAST indicator.

Output Frequency tab

Phase Increment Programmability

Specifies the phase increment to be Fixed, Programmable or Streaming. The choice of Programmable adds channel, data, and we input ports to the block.

The following fields are activated when Phase_Generator_and_SIN_COS_LUT is selected as the Configuration Options field on the Basic tab, the Parameter Selection on the Basic tab is set to Hardware Parameters and Phase Increment Programmability field on the Phase Offset Angles tab is set to Fixed or Programmable.

Output frequencies (MHz)

For each channel, an independent frequency can be entered into an array. This field is activated when Parameter Selection on the Basic tab is set to System Parameters and Phase Increment Programmability is Fixed or Programmable.

Phase Angle Increment Values

This field is activated when Phase_Generator_and_SIN_COS_LUT is selected as the Configuration Options field on the Basic tab, the Parameter Selection on the Basic tab is set to Hardware Parameters and Phase Increment Programmability field on the Phase Offset Angles tab is set to Fixed or Programmable. Values must be entered in binary. The range is 0 to the weight of the accumulator, for example, 2Phase_Width-1.

Phase Offset Angles tab

Phase Offset Programmability

Specifies the phase offset to be None, Fixed, Programmable or Streaming. The choice of Fixed or Programmable adds the channel, data, and we input ports to the block.

Phase Offset Angles (x2pi radians)

For each channel, an independent offset can be entered into an array. The entered values are multiplied by 2π radians. This field is activated when Parameter Selection on the Basic tab is set to System Parameters and Phase Increment Programmability is Fixed or Programmable.

Phase Angle Offset Values

For each channel, an independent offset can be entered into an array. The entered values are multiplied by 2π radians. This field is activated when Parameter Selection on the Basic tab is set to Hardware Parameters and Phase Increment Programmability is Fixed or Programmable.

Advanced tab

Block Icon Display

Display shortened port names

This option is ON by default. When unselected, the full AXI name of each port is displayed on the block.

Other parameters used by this block are explained in the topic Common Options in Block Parameter Dialog Boxes.

LogiCORE™ Documentation

DDS Compiler LogiCORE IP Product Guide (PG141)