I have written a process to generate sine wave. I am getting a distorted wave and not a pure sine wave. I am not sure if this has anything to do with the simulator. two : process variable phase_temp,result : real; constant scale : real := 2.0*real(bw); begin phase_temp := phase_sin; --phase_sin; l1 : for i in 1 to samples_sin loop --number_of_samples loop result := scale*(amp_sin*(sin(frq_sin + phase_temp))); sine_real <= (amp_sin*(sin(frq_sin + phase_temp))); sinWave <= toSigned(result,bw); phase_temp := phase_temp+incr_sin; wait for 5 ns; end loop l1; end process two; generic value : phase_sin : real := 0.0; samples_sin : integer := 1000; incr_sin : real := 1.0; frq_sin : real := 1000.0; I dont see the frequency of the wave change if the frq_sin is changed. Same happens when samples_sin is changed. I am not sure what is going wrong. Please help

Your frq_sin value is actually just a phase offset. There is no time associated with this constant to feed the sin(). The phase_temp, on the other hand, is effectively t*incr_sin where t is a cycle count. To see the frequency change, change the incr_sin value instead. In what way is your sine distorted? - John_H

How can I pass time parameter to the sineWave? I was able to remove the distortion by reducing the incr_sin value. Still not clear on the frequency and time parameter that you are talking about.

Change incr_sin to .1 and look at the difference in the waveform. You are stepping through the sine wave in 6 steps so you will not see what you expect. The wave will look a lot prettier with more steps.

Time is being implied in your phase assignment. But you are not coding the frequency generation correctly. You code mathematiclly is saying the following y=A*sin(fq+x) x=x+c Where fq is frq_sin, and c is incr_sin the sin wave cycle lasts from 0 to 2PI. There is no time or frequency associated with it. Your fq is just offseting the start point not seting a period. What you want to do is the following. x=x+c y=A*sin(2*PI*fq*x) now remember that x is being incremented in time. fq is in hz. You need to inverse fq to get your period time. which yeilds. x=x+c; y=A*sin(2*PI*x/tp) where tp is the cycle length. Your code should look like so: for i in 1 to samples_sin loop result:= scale*(amp_sin*(sin(2.0*PI*frq_sin*phase_temp); sine_real<=(amp_sin*(sin(2.0*MATH_PI*frq_sin*phase_temp); sineWave<=toSigned(result,bw) phase_temp:= phase_temp+incr_sin; wait for 5 ns; ---Note: This 5ns is not setting the actual frequncy result with this code end loop; --to see a full sine wave cycle set the following: phase_sin=0.0; frq_sin=1000; --(1khz) samples_sin=1000; incr_sin=0.000001--(1ms/1000 samples) With this code the "5ns" doesn't do anything constructive. But you could change the code to make it useful If you want the time display of the code to match the values that are given in my comments use "wait for 1us" Just looking at the time display based on the above code would apear to have a 200MHZ sign wave. (1us/5ns)=200, 200*(1 khz)=200Mhz How can I pass time parameter to the sineWave? I was able to remove the distortion by reducing the incr_sin value. Still not clear on the frequency and time parameter that you are talking about.

Phase accumulators are used to mark the prograssion of time. You want sin(f*T) which is sin(f*n*deltaT) where deltaT is your clock period. f*n*deltaT is the same as sum from 1 to n of f*deltaT, this last item being a constant. That's what you're doing with the incr_sin, isn't it? If you have an increment of 1/100 of a sinusoidal period, the sum of 100 increments will be one sinusoidal period bringing you right back to the beginning. You *are* doing this for simulation only, aren't you? - John_H

This is for simulation only. Thanks for all your comments. I will make the suggested changes and let you guys know how it went.