# Thread: exponential delay generation in vhdl

1. Altera Beginner
Join Date
Nov 2010
Posts
2
Rep Power
1

## exponential delay generation in vhdl

hi all,
I am new to this forum. My project is Digital Beam Forming for phased antenna array. for testing purpose of algorithm i developed in vhdl, I have to generate different delayed version of input signal. input signal is AM signal from function generator. delay is exp(j*2*pi*d*n*sin(theta)),where (theta:angle in degree, d: constant and n:1,2,...).
i hv to generate this delay in vhdl. can any one please tell me how to implement this?

2. Altera Teacher
Join Date
Jul 2010
Posts
56
Rep Power
1

## Re: exponential delay generation in vhdl

If I understand you right, you want to generate a series of sine waves with different delay. The best way is to create a look-up table.

3. Altera Guru
Join Date
Aug 2005
Location
California
Posts
3,845
Rep Power
1

## Re: exponential delay generation in vhdl

My project is Digital Beam Forming for phased antenna array. for testing purpose of algorithm i developed in vhdl, I have to generate different delayed version of input signal. input signal is AM signal from function generator. delay is exp(j*2*pi*d*n*sin(theta)),where (theta:angle in degree, d: constant and n:1,2,...).
You have not quite understood your problem just yet.

A beam-former performs delay-and-sum of the input signals, so that they coherently construct in the direction of the focused beam.

You can implement a beamformer by having a fractional delay line on each input signal, program them to the appropriate delay, and sum the delay line output. Or you can take the frequency-based equivalent approach, where you essentially Fourier transform the input signals, apply a complex phase-slope (delay) and then sum.

Before you start on the VHDL, get something working in MATLAB first. It'll help clarify your understanding of the requirements.

Cheers,
Dave

4. FvM
Altera Guru
Join Date
Dec 2007
Location
Bochum Germany
Posts
5,820
Rep Power
1

## Re: exponential delay generation in vhdl

I agree about the necessity of understanding the problem.

Dave, just a minor correctiion. You are discussing beamforming for a receiver. The said project is dealing with beamforming for a transmitter. Although the methods are closely related, the signal path is different. In this case one input signal is transformed to N output signals.

Besides understanding the theory, sketching a hardware scheme would be a useful step to proceed with the project. You imagine an analog input signal, so you need an ADC front end. To generate N phase shifted output signals, the system needs N DAC channels. Front- and back-end should be specified in terms of resolution, sampling rate and carrier frequency respectively frequency range.

To implement the delay/phase shift as a rotation in the complex plane as multiply with exp(j dphi), you need to transform the real input signal to an analytical (complex) signal, e.g. by a Hilbert transformation.

Frank

5. Altera Guru
Join Date
Aug 2005
Location
California
Posts
3,845
Rep Power
1

## Re: exponential delay generation in vhdl

Dave, just a minor correctiion. You are discussing beamforming for a receiver. The said project is dealing with beamforming for a transmitter. Although the methods are closely related, the signal path is different. In this case one input signal is transformed to N output signals.
Thanks for the correction

souv1101: see how easy it is to misinterpret a poorly explained description.

Cheers,
Dave

6. Altera Beginner
Join Date
Nov 2010
Posts
2
Rep Power
1

## Re: exponential delay generation in vhdl

Sorry for delay. thank you for your valuable suggestion. I am concentrating on the basic understanding. Thank you once again

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•