Ladder signal", My own signal"

The easiest way to do this is to create a Verilog A view. For example, this code:

`include "disciplines.vams"

module ladder (outp,outm);
electrical outp,outm;

// extent of the signal output
parameter real vmin=0;
parameter real vmax=2.56;
// number of steps in the "ladder"
parameter integer maxcount=256;
// is it periodic? Set to 0 if you want it to be one shot
parameter integer periodic=1;
// period of time between steps in the ladder
parameter real period=10n;
// rise, fall, and delay of each step
parameter real tr=0.1n;
parameter real tf=0.1n;
parameter real td=0;

// internal variables
real scale;
integer count;

analog begin
    @(initial_step) begin
	count=0;
	scale=(vmax-vmin)/(maxcount-1);
    end

    @(timer(period,period)) 
	if(periodic) count=(count+1)%maxcount;
	else count=min(count+1,maxcount-1);

    V(outp,outm) <+ transition(count*scale,td,tr,tf);
end

endmodule
 

Then on the instance of ladder specify vmax=-2.04 . There's a parameter in this code called periodic, which allows you to specify whether the ladder repeats.

Attached are some pictures (one zoomed out, one zoomed in). This was with periodic=0.

Regards,

Andrew.

 Couldn't add two pictures at once. Here's the zoomed in file..

 Andrew.

Andrew Beckett ,thanks.

How to add this signal to input pin of analog scheme?

How to add this Verilog A instance "lader" to schematic? Does Cadence 5 have verilog A?

Can I attache this code to symbol from Cadence schematic library such as vpwl?

I must use this signal in schematic analog scheme (ADC)

VerilogA has been supported in spectre for 10-15 years (I forget when) and is certainly supported in IC5X.

You do not attach it to a vpwl or any other source. The code itself is a new source.

To use it, do File->New->Cellview (in the CIW). Set the Tool to "VerilogA-Editor" and fill in the library name as whatever you want, and call the cell name "ladder" (you could call it something different if you like). OK this form.

Then in the resulting editor, paste in the behavioural model code I provided. Change the module name from ladder if you called the cell something other than ladder. Save and exit the editor. It should syntax check the file, and then prompt you to create a symbol. You can then place this component in your testbench, and it will generate the ladder waveform (set vmax=-2.04 when you place it).

I just noticed that my code omitted a line specifying the direction of the pins. Here's the corrected code:

`include "disciplines.vams"

module ladder (outp,outm);
output outp,outm;
electrical outp,outm;

// extent of the signal output
parameter real vmin=0;
parameter real vmax=2.56;
// number of steps in the "ladder"
parameter integer maxcount=256;
// is it periodic? Set to 0 if you want it to be one shot
parameter integer periodic=1;
// period of time between steps in the ladder
parameter real period=10n;
// rise, fall, and delay of each step
parameter real tr=0.1n;
parameter real tf=0.1n;
parameter real td=0;

// internal variables
real scale;
integer count;

analog begin
    @(initial_step) begin
	count=0;
	scale=(vmax-vmin)/(maxcount-1);
    end

    @(timer(period,period)) 
	if(periodic) count=(count+1)%maxcount;
	else count=min(count+1,maxcount-1);

    V(outp,outm) <+ transition(count*scale,td,tr,tf);
end

endmodule

Regards,

Andrew. 

 Thanks.

I am having some problems in implementation of the ladder using the code you provided. I can create the signal attached in figure, but i am not able to create a ladder that starts for example in -60mV and has the final value of 60mV (vmin = -60mV and vmax = 60mV)

Can you help me please.

Regards,

Ricardo 

Ricardo,

There's a deliberate mistake in the transition statement in the code - I forgot to add vmin to the signal, so it's always referred to 0. I ran it with this netlist:

//
V1 (lad 0) ladder vmin=-60m vmax=60m maxcount=32 periodic=0 period=80n
R1 (lad 0) resistor r=1k

ahdl_include "ladder.va"
tran tran stop=5u

And it produces the attached picture (I set it to have 32 steps to make the steps more obvious).

Here's the fixed code:

`include "disciplines.vams"

module ladder (outp,outm);
output outp,outm;
electrical outp,outm;

// extent of the signal output
parameter real vmin=0;
parameter real vmax=2.56;
// number of steps in the "ladder"
parameter integer maxcount=256;
// is it periodic? Set to 0 if you want it to be one shot
parameter integer periodic=1;
// period of time between steps in the ladder
parameter real period=10n;
// rise, fall, and delay of each step
parameter real tr=0.1n;
parameter real tf=0.1n;
parameter real td=0;

// internal variables
real scale;
integer count;

analog begin
    @(initial_step) begin
	count=0;
	scale=(vmax-vmin)/(maxcount-1);
    end

    @(timer(period,period)) 
	if(periodic) count=(count+1)%maxcount;
	else count=min(count+1,maxcount-1);

    V(outp,outm) <+ transition(count*scale+vmin,td,tr,tf);
end

endmodule

Regards,

Andrew.