phase modulation

[mohannandigana]

Dear Sir

We are looking a multifunction sine wave generator two  analog out puts from few Hz to 20 KHz to drive the piezo discs through two independent amplifiers.  The two outputs will be connected to two amplifiers independent and the out put from the amplifiers will be connected to piezo discs for excitation. During our application, we would like run the sine wave generator  with the same frequency and amplitude, but we would like to vary the phase between the two out-puts from 0-360 degrees from the sine wave generator. Duringthe phase variation 0-360 degree, we need the amplitudes between the two out-puts should remain the same. Probably similar to Sine Wave Generator with two 2 Channels.  Can you provide us the technical support for such a PCI card with accessories for our application.

[Jesse_O]

Hello,

If you look at or multifunction boards such as our PCI-6251 (found here), it is capable of writing data out on two ports.  If you look at the specifications for this device it specifies the update rate for 2 channels is 2MS/s so 20KHz is not a problem.

The data the devices generates is up to you.  You simply write an array of data to the device and it will generate that data.  If you want to update the data buffer you originally wrote to the device while it is running you can do this too.  However, if you do this, you will see a discontinuity where the old buffer meets the new one.

There is no functionality built into our Multifunction IO boards to perform a phase sweep.  This is something you would have to code in software.  You might be interested in one of our function generators, however each function generator is only a single port and would require a PXI chassis.  With a PXI chassis you can synchronize the two boards.  If you have any additional questions about our function generators you can post more questions in our signal generator discussion forum page.

Regards,

Jesse O.
Applications Engineering
National Instruments

[nimic]

At some point, when shifting phases, as Jesse points out, there has to happen something to one of the output data.
Either you work 'stepwise' as he suggested, by writing new data of different phase. This will create a (small) discontinuity.
Or you set one frequency slightly off the desired freq, causing a continous phase shift with f1- f2 as the 'speed' of phase shift (aka beat frequency). Again, changing one of the freqs to change the phase shift velocity will cause a small discontinuity.
Best regards
Michael