Generating an input signal which changes frequency at a given rate

Dear DenisJos,

DenisJos said:

Is there a way to generate an input voltage stimuli which works at a certain frequency freq1 and after time t ramps to freq2 with a given rate of change like 150MHz/5ns.

I would consider using a verilog-A block with an input that allows you to change the frequency. There is an example of some code that Ken Kundert assembled in response to a question that you might use. In this fashion, you can set the frequency input to a value corresponding to freq1 until time t and then change it using a ramp to an input corresponding to freq2 at a rate corresponding to 150 MHz/5 ns.

The relevant code from Mr. Kundert is at

designers-guide.org/forum/YaBB.pl?num=1642147821

and shown below for your convenience.

    module sinegen(out, freq, ampl, phase, offset);
    output electrical out;
    input wreal freq, ampl, phase, offset;
    parameter tt=1u from [0:inf);
    reg break = 0;

    always @(freq or ampl or phase or offset) break <= !break;

    analog begin
	  @(posedge break or negedge break)
		;
	  V(out) <+ transition(ampl, 0, tt)*sin(transition(freq, 0, tt)*$abstime + transition(phase, 0, tt)) + transition(offset, 0, tt);
	  $bound_step(10/freq);
    endmodule

Shawn

I had thought of an even simpler idea (just been busy yesterday and today and so didn't have a chance to post it). Use a Verilog-A model of a VCO (e.g. the "vco" component from ahdlLib) and then have a PWL voltage source setting the initial input frequency and then ramp up at the rate you want to the second frequency. That way you don't need anything other than the existing VCO model and a standard PWL voltage source.

Regards,

Andrew