Question about the negative impulse response of a lead-lag compensator

[ruwan2]

Hi,
I am studying an equalizer which uses a lead-lag compensator after a high frequency attenuated distortion. At first, it seems quite simple: The equalizer emphasizes high frequency gain to make the total response flat at the high frequency part. When I try to get the total impulse response, I find that the impulse response of the lead-lag filter (nominator:[2.5e10, 1], denominator:[1.0e10, 1]) has a negative response. This is the first time I have a negative impulse response in contrast to the normal positive impulse response. I guess that it is because the high frequency pass feature.

The further problem is that the total impulse response of the low pass channel and the equalizer is still a negative impulse response. On the other hand, I do not see the equalized result has inversed the signal in the Simulink simulation model. How to explain the contradictory?

Please help me if you have the answer.
Thanks.

 

[FvM]

A first order lead-lag compensator generates a maximum phase shift of 90°, so it can hardly have a a negative impulse response.

 

[ruwan2]

I am curious too, but it is got from Matlab for the below
lead-lag filter (nominator:[2.5e10, 1], denominator:[1.0e10, 1])

Its transfer function is:
sys0

sys0 =

2.5e-10 s + 1
-------------
1e-10 s + 1


I get the picture with Matlab code:
figure(4);
[tresp0,t0] = impulse(sys0);
subplot(211);
hold off;
plot(t0*1e9,tresp0);



I cannot find the error yet.
What impulse response can you get? Or what method you can use for that?
Thanks,

 

[FvM]

The impulse response plot is correct, but not showing the positive impulse at t=0. I think the step response shows better what happens.

 

[ruwan2]

I really need the impulse response to check for the eye diagram.
I just realize that impulse response is for transient purpose. It excludes the stable condition (which is for the low pass components), but I still do not make it out for how to get that yet.
Thanks,