Hi Everyone,

I am making a GMSK TX thru directly modulating the delta-sigma fractional-N PLL, but no numeric gaussian filter is found.

What I found is only numeric raised-cosine filter or timed gaussian filter. :-/

Does anyone know where this filter is or know how to make it?

Thanks a lot!!

I am making a GMSK TX thru directly modulating the delta-sigma fractional-N PLL, but no numeric gaussian filter is found.

What I found is only numeric raised-cosine filter or timed gaussian filter. :-/

Does anyone know where this filter is or know how to make it?

Thanks a lot!!

You can generate coeffients for FIR filter.

Then use "FIR" component.

Here you have to consider the following issues.

Â (1) Input samples per symbol(UpSample), N

Â (2) Length of the filter's impulse response, which is 2*N*Group_delay+1.

Â (3) BT product

Â (4) Filter coefficient normalization(Generally the sum of the coefficients should equal 1.)

double ht_gmsk_lpf(double Â t, bt, tsymb)

{

Â Â double Â ht, x, sigma;

Â Â sigma = sqrt(log(2.0)) / (2 * M_PI * bt);

Â Â x = t / (sqrt(2.0) * sigma * tsymb);

Â Â ht = exp(-x * x) / (sqrt(2 * M_PI) * sigma * tsymb);

Â Â return (ht);

}

# Tue Feb 21 15:28:20 2006

# LPF_GMSK_FIR

# FIR_Length=17

# BT=0.55, Delay_Nsymb=1, Up_Samples=8

# Rectangular window

# Normalized by Sum of Coefficients

3.755980849014431e-05

2.828640100738817e-04

1.627472423660382e-03

7.153803648994064e-03

2.402408879464853e-02

6.163729240501887e-02

1.208166661815747e-01

1.809242702077309e-01

2.069919650396171e-01

1.809242702077309e-01

1.208166661815747e-01

6.163729240501881e-02

2.402408879464852e-02

7.153803648994044e-03

1.627472423660377e-03

2.828640100738970e-04

3.755980849014430e-05

# Summation_of_h[i]=1, (wacc-dacc)>=2

# Summation_of_abs(h[i])=1, (wacc-dacc)>=2