DDSPipelined (DDS.v)

This module is a signal generator that outputs I/Q vectors with a given phase increment between samples. It is phase continuous with respect to changes of frequency and, once started, runs until it is reset. Performance information is available in the documentation of the Cordic module . This module is the pipelined version of the serial DDS module.

Ports

clk	input	The clock input.
reset	input	The reset input. Use this port to stop the DDS and output zero.
go	input	A multi-bit trigger to start conversions.
gonow	output	Pulsed when all trigger conditions have been met. It is this pulse that starts the DDS.
PhIncr	input	The phase increment per clock on a `2^wpa` phase scale per revolution.
I, Q	output	The I/Q-pair output.
busy	output	When asserted, The DDS is running and outputting I/Q pairs.

Parameters

Parameters, their defaults, and descriptions:

wd	16	The bit width of the outputs `I`, `Q`, `IN`, `QN`, and `out`.
apb	0	Extra internal bits of precision of the Cordic computation.
wpa	wd+apb+1	The width of the internal phase accumulator and phase-increment port. A phase of `2^wpa` corresponds to 360 degrees. The port `PhIncr` is added to the accumulator every clock cycle.
gb	1	The width of the `go` trigger vector.

Notes

The output frequency is
```
f = f_s × PhIncr/2^wpa
```
where f_s is the data (clock) rate. An updated I/Q pair is available at the I and Q output ports each clock. The delay between the PhIncr port and the I and Q ports is wd-1 clocks.
The output I/Q vector magnitude is shy of full scale (2^wd-1) by a few percent.

Example instantiation:

// data and phase bit widths
localparam	wd = 16, wpa = wd+1;

// start trigger input; can have multiple bits
wire				go;

// stop trigger input
wire				stop;

// dds outputs
wire	signed	[wd-1:0]	I, Q;	// I/Q vector
wire				busy;	// asserted when DDS is running

// frequency = 28.2 MHz (= -11.8 MHz) @ clk = 40 MHz
wire		[wpa-1:0]	freq = 92389;

DDSPipelined 
    #(.wd(wd), .wpa(wpa))
    instancename (
        .clk(clk),		.reset(stop),
        .go(go),		.PhIncr(freq),
        .I(I),			.Q(Q),
        .busy(busy)
    );