Continue to Site

Sine wave generation using Direct Digital Synthesizer

Status
Not open for further replies.

Prem Nath

Newbie level 1
Please help me out in resolving the issue with sine wave generation using DDS. How to generate 4 different sinusoidal signals with phase angles 0,90,180 and 270. How phase increment values are related to frequency. am designing my QPSK modulator for a clock frequency of 100 MHz. Do help me in sorting this problem. Thanks in advance

it is some years since I used a pair of DDS devices
the application generated two sine waves freqiency between 1 and 10MHz with a phase difference of 90degrees
I seem to remember that the frequency and phase were under program control

Quadrature signals are generally generated by ROM Look-at-Table method.If the frequency is constant ( 100 MHz ) you can also obtain these quadrature signals by using Poly-Phase filter approximation.There are also DDS Generators ( and Oscillators) that supply directly quadrature signals but I'm not sure the efficiency about them..

The AD9959 is a quad DDS which can generate 4 carriers easily. But if you just want 0, 90, 270 and 180 then you really only need two channels, since the outputs are differential.

A simple D flip-flop 74AC74 will do the job, very accurate and broadband:

https://www.wb5rvz.com/sdr/g3020/04_div.htm

The only issue is that the LO input will be divided by 2.
As already was mentioned, all the latest DDS chipsets have 0, 90, 180 and 270 outputs.
If you use an FPGA DDS just use the schematic from the link above.

the ad9850 modules available cheaply will do the job
the phase output can be programmed in 11.25 deg. steps.
you will need 2 modules. you can get 2 sine wave output from
each module but they are 180 deg out of phase.
you will have to drive the modules from the same clock source.
if one module is programmed for 0 phase you will get 0-180deg
and if the other module is programmed to 90 deg phase you will get
the 90 and 270 deg. phase difference. look on the WWW.

you could also use 4 modules fed from the same clock source.
to provide 0,90,180,270,360 or what ever .
also you will have to select a working if frequency for your design.
say (12 Mhz), then using a VHF mixer circuit and a 88Mhz local oscillator
mix up to the frequency of 100Mhz.
if you use the ad9851 (CHEAP BUT NOT AS CHEAP), you could use say
40Mhz and 60Mhz local oscillator, or if you got lots of money you could
use the AD top of the range DSS which will do 100Mhz but you will need
some software to drive it.
and way its not a problem to do what you want plenty suggestions
are on the WWW.

Status
Not open for further replies.