0.1hz to 1mhz signal generator

hi every one. i want to build a 0.1 hz to 1mhz sin, triangular, pulse generator with 10vpp adjustable amplitude.
for the first design i used a DAC for generating signal and then used a amplifier for signal conditioning.
the problem is when generating low frequency signal, the signal is corrupted due to the DAC nature.
can i use LPF filter bank for specified frequency range?
for example using 100hz LPF for 0.1hz to 100 hz signal's
1k LPF for 100hz to 1K siganl's
10k LPF for 10hz to 10K siganl's
and ....
or is there simpler way to do that?
i searched foe some dds ic's for the job but this ic's are expensive.
if u know a good/easy to use ic please suggest..

the cost is an important factor to me.

any idea would be appreciated..
thanks

Hi,

. i want to build a 0.1 hz to 1mhz

Click to expand...

1mHz or 1MHz? It makes a big difference.

Klaus

- - - Updated - - -

Hi,

There is a problem.
A sine is a single frequency, but triangle and square are signals with fundamental frequency plus their overtones.
The overtones i frequency at both waveforms are infinite. As soon as you use a LPF you create errors on the waveform.
If you use an LPF it is always a compromise between "reducing steps" and "modify the ideal waveform"

Any signal forming DAC should have it's LPF, it is called "reconstruction filter" and ideally it is an sin(x)/x function.

0.1Hz to 100Hz are 3 decades. This is huge.
100Hz to 1kHz is just one decade
10Hz to 10kH is again 3 decades.

Conclusion:
Use a high resolution DAC and high sampling rate
Sine: use (different) LPF
Square: don't use an LPF
Triangle: compromise. No ideal solution.

Klaus

I presume MHz.

If not using digital synthesis, how are you generating sine or triangular waveforms? Most today's function generators are DAC based, updating the DAC at a constant high rate (e.g. some 10 to 100 MS/s) and interpolating the output with a low pass.

hi

A sine is a single frequency, but triangle and square are signals with fundamental frequency plus their overtones

Click to expand...

you're right.

If not using digital synthesis, how are you generating sine or triangular waveforms? Most today's function generators are DAC based, updating the DAC at a constant high rate (e.g. some 10 to 100 MS/s) and interpolating the output with a low pass.

Click to expand...

so far i know =>for example, for generating 0.1 HZ sine wave via DAC do i have to use different reconstruction filter in compare with 1MHz sine. right?
and if i just use fixed reconstruction filter(1Mhz LPF Filter) do i have to increase DAC's resolution for low frequency signal?

so far i know =>for example, for generating 0.1 HZ sine wave via DAC do i have to use different reconstruction filter in compare with 1MHz sine. right?
and if i just use fixed reconstruction filter(1Mhz LPF Filter) do i have to increase DAC's resolution for low frequency signal?

Click to expand...

Neither. You only change the phase accumulator increment.

FvM said:

Neither. You only change the phase accumulator increment.

Click to expand...

Well of course with limited vertical resolution the dac steps will start coming at a slower rate at slower frequencies and may fall substantially below a filter appropriate for 1Mhz sin waves.


Though this depends on the dac resolution. All the problems here go away with a fast DAC that has high resolution. Of course those are the things that cost money.

Post #1 demands a frequency range of 7 decades, thus it should be crystal clear that low distortion, spurious and noise has to be achieved by sufficient DAC resolution rather than filters. In a DDS topology you can still reduce quantisation error by applying dither, if DAC DNL allows it.