How to design a FM modulator using ADAU1401?

Hello Shu,

Here's one way to do FM modulation with a VCO. The VCO's output frequency vs. input "voltage" is: f = V * fs / 2. Thus, set a DC source to feed the VCO according to the desired carrier frequency: V = 2 * f / fs. For example, with a sample rate of 96 KHz, use a DC source of 0.5 to get a carrier frequency of 24 KHz.

Then add in your modulating input. Your deviation D is related to the modulating input V by the same VCO relationship:

D= V * fs

Best regards,

Bob

Hi Bob,

Thanks a lot!

I have one more question. I want to show my project to my boss. I have to connect the computer and the board together always. If I disconnect the computer and power off the board, i cannot get the design and results when i power on the board. i have to active and download my design to the board again. Is there any way i can show my design directly after i power on the board?

Thanks,

Shu

Hello Shu,

The ADAU1401's self-boot option allows it to boot its program from an external E2PROM. Your -1401A evaluation board includes this E2PROM at U14. For instructions on loading your compiled SigmaStudio project into the E2PROM and setting the eval board to self-boot, please see page 7 of the ADAU1401AEBZ User Guide:

http://www.analog.com/media/en/technical-documentation/user-guides/UG-072.pdf

Best regards,

Bob

Dear Bob,

Thanks very much for your help.

I can use the self-boot option now. But I have to use the USBi at the same time. I mean If I only use the power supply J14 and disconnect the USBi, the self-boot doesn't work. If I connect the USBi to my computer or any 5V source, the self-boot work well. Could you please tell me why i have to use the USBi for the self-boot option or what is the function of the USBi for the self-boot. I will design a circuit for the 1401A later, so I don't want the circuit does't work because i miss some necessary condition.

Thanks,

Shu

Hello Shu,

Sorry to take so long, but I had to try it myself to work the problems out. The troubles appear around LK7, the Write-Protect jumper on the -1401 Eval board:

Connect the jumper in order to write your compiled code to the E2PROM -- Jumper Off = Write Protected. This is the opposite of what UG-72, the ADAU1401AEBZ User Guide: says!

Check your E2PROM contents by selecting the option shown below:

Set your Self-boot switch S3-1 to the left to choose the self-boot option. Also disconnect the Write-Protect Jumper LK7 -- I could only get self-boot to work with this jumper Off.

Your project should now self-boot with the USBi disconnected.

The above-mentioned User Guide includes the board schematics. I also suggest you download and read the Application Note AN-923, Designing a System Using the ADAU1701/ ADAU1702 in Self-Boot Mode.

Best regards,

Bob

Hi Bob,

The self-boot option work well now. I found if I disconnect the USBi only from computer and keep another side on the board at J8, the project still cannot self-boot. But if i disconnect the USBi from the board at J8 directly, the project self-boot well. I cannot explain this, i guess the USBi mini board affect the self-boot of the main board.

Thanks a lot. I can design my circuit now!

Shu

The USBi is capable of resetting the DSP(s) on your target board. It has a 10K pullup on its BRD_RESET line, which becomes a pull-down when no longer powered by your PC. As a result, removing the USBi's power may reset your DSP. Avoid this by disconnecting the USBi's business end before unplugging its USB cable from the PC.

Bob

Hello Bob;

I'm working on this project right now. What kind of output will we see on the oscilloscope as a result of this circuit? I just want to make sure the output is correct. Thank you from now.

Good work,

Beste