complex_mixer HDL Worker

Application worker HDL implementation with settable runtime configuration parameters and a numerically-controlled oscillator (NCO) that uses the coordinate rotation digital computer (CORDIC) algorithm to generate the digital sine wave for the complex multiply operation.

Detail

The following figure shows a functional representation of the HDL implementation:

Figure 2: Complex Mixer Functional Diagram

Build-time parameters can be used to control the width of the NCO data output (NCO_DATA_WIDTH_p), the width of the input data (INPUT_DATA_WIDTH_p), the number of stages in the Coordinate Rotation Digital Computer (CORDIC) used to implement the NCO (CORDIC_STAGES_p) and the amplitude of the NCO’s sine wave (mag). There are also parameters to control insertion of a peak detection circuit (PEAK_MONITOR_p) a Chipscope circuit (CHIPSCOPE_p, and a Vivado integrated logic analyzer (VIVADO_ILA_p).

The peak detector has two inputs and does not compute magnitude. The output of the the peak detector (peak) is either the peak of I or the peak of Q, whichever is greater.

The enable input is available to either enable (true) or bypass (false) the circuit. In bypass mode, the HDL worker does not use pipe-lining registers. It uses FPGA multipliers to process input data at the full clock rate. The HDL worker produces valid output two clock cycles after each valid input.

The relationship between the frequency shift magnitude and the NCO output frequency is given by the following equation:

\[nco\_output\_freq = sample\_freq*\frac{phs\_inc}{2^{phs\_acc\_width}}\]

In this equation:

• phs_inc is the NCO phase increment, which is runtime-configurable and has a data type of 16-bit signed short.

• phs_acc_width is fixed at 16.

• The input clock frequency is the sample rate of the samples.

A positive and negative phs_inc will mix up and down, respectively. Use the following equation as an aid in setting phs_inc to have the desired mixing effect:

(1)\[x_{out}[n] = x_{in}[n] * \dfrac{mag}{2^{NCO\_DATA\_WIDTH\_p-1}} * e^{\big(j2\pi\big(sample\_freq * \dfrac{phs\_inc \; * \; n}{2^{phs\_acc\_width}}\big) + phs\_init\big)} \;\; \forall \;\; n, \; n \ge 0\]

The following figure shows a block diagram representation of the HDL implementation:

Figure 3: Complex Mixer Block Diagram

Worker Properties

• VIVADO_ILA_p

  • Type: bool

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: false

• CHIPSCOPE_p

  • Type: bool

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: false

• NCO_DATA_WIDTH_p

  • Type: uchar

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 12

• INPUT_DATA_WIDTH_p

  • Type: uchar

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 12

• CORDIC_STAGES_p

  • Type: uchar

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 16

• PEAK_MONITOR_p

  • Type: bool

  • Access:

    • Parameter: True

    • Writable: False

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: true

• peak: Peak detector output. Either peak of I or peak of Q, whichever is greater.

  • Type: short

  • Access:

    • Parameter: False

    • Writable: False

    • Initial: False

    • Volatile: True

    • Read back: False

  • Default value: None

• phs_init

  • Type: ushort

  • Access:

    • Parameter: False

    • Writable: True

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 0

• mag: Must be in the range \(-2^{(NCO\_DATA\_WIDTH\_p-1)} <= mag <= 2^{(NCO\_DATA\_WIDTH\_p-1)}-1\) for the worker to operate properly.

  • Type: ushort

  • Access:

    • Parameter: False

    • Writable: True

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 1024

• messageSize

  • Type: ushort

  • Access:

    • Parameter: False

    • Writable: True

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: 8192

• data_select: 0 = input data, 1 = output of NCO.

  • Type: bool

  • Access:

    • Parameter: False

    • Writable: True

    • Initial: False

    • Volatile: False

    • Read back: False

  • Default value: false

Worker Ports

Inputs:

• in: Signed complex samples.

  • Type: streaminterface

  • Data width: 32

  • Protocol: iqstream_protocol.xml

  • Zero length messages: true

  • Optional: False

Outputs:

• out: Signed complex samples.

  • Type: streaminterface

  • Data width: 32

  • Protocol: iqstream_protocol.xml

  • Zero length messages: true

  • Optional: False

Finite State Machine

This worker implements only one finite state machine (FSM). The FSM supports zero-length messages. In future releases, this FSM will be replaced with a register delay-based mechanism currently used in the dc_offset_filter HDL implementation. The following figure illustrates this FSM:

Figure 4: Complex Mixer Finite State Machine

Control Timing and Signals

The complex mixer HDL worker uses the clock from the control plane and standard control plane signals. There is a startup delay for this worker: once the input is ready and valid and the output is ready, there is a delay of CORDIC_STAGES_p+3 before the first sample is taken. After the initial delay, valid output data is given two clock cycles after input data is taken (latency=2).

Utilization

Utilization reporting is not currently implemented.