Digital Signal Processing - IP and Algorithms

[falconbombay]

Hi,

I am implementing GMSK modulator using FPGA(spartan 3), using below block diagram.

                                                                                                   

Fig.(a) :  Block Diagram Of GMSK Modulator

I am describing the block diagram as I have implemented it.

NRZ signal : To generate serial data  from parallel data I did use Parallel In Serial Out shift register. Parallel data is 16 bit and the data pettern is “0001101111010100”.

Integrator :  To generate phase trajectory I have used 8 bit up - down counter.

Gaussian Filter : To implement Gaussian Filter, I have used the FIR filter and the required coefficients are generated in MATLAB. Input to the FIR filter is from Integrator.

SIN COS LUT / I Q Generator : To generate I/Q component I have used the CORDIC IP. The phase_in to the CORDIC is the output of Gaussian Filter. The expected output of CORDIC is as shown in the attachment, but I am not getting the expected output form my design.

The parameters of CORDIC IP which I had set as below:

Functional Selection: SIN COS.

Archeitectural Configuration : Parallel.

Pipelining Mode : Optimal.

Phase format : Scaled Radians.

Input Width : 10 bit.

Output Width : 10 bit.

Round Mode : Truncate.

Iteration and Precision : 0.

Coarse Rotation : ON.

I am getting the expected output upto the Gaussian Filter, but after that when I am using CORDIC IP to generate I/Q component I am not getting the expected output. Is there any problem in implementation of CORDIC IP or  am I fail to interpreat the output of CORDIC?.

I have attached the file which shows the waveform of expected output and the output which I am getting.

Please help me regarding the same.

[thomas1974]

I am using CORDIC and did not find a general problem so far.

I do not understand your design in detail, but do you wand to control der cordic's phase by the gaussian output?

I expected to gaussian output to be distinguished in IQ by multiplication wiith both Sin/Cos. In Other words, where do the signals mixed with Sin/Cos come from?

If the circuit is right, then you maybe did no scale the phase correctly. The phase rund fomr -PI ... PI and for Matlab Simulink, I remember it is scaled from 0....1.