# regarding Integrate and dump filter and Early-Late Gate Correlator

Discussion in 'General Electronics' started by viswanath, Jul 8, 2004.

1. ### viswanathGuest

Hi,
I wanted to know how an integrate and dump filter acted as a low pass
filter. I have come across literature where instead of a low pass
filter an accumulate and dump(integrate and dump) has been used. I was
wondering how it would result in filtering action. Could anyone throw
some light on this subject?
I had another question too: I wanted to know how exactly an early late
correlator works during pn code synchronization. Precisely how one can
change the clock rate. I wanted to know if we need to change the
frequency of the clock or keep the frequency constant and just shift
the clock when we say advance or retard the clock.
I would really appreciate if someone could help me on these two
questions.
Thanking You,
Viswanath

2. ### Tim WescottGuest

If you make a running average filter, where y_k = 1/n * sum(x_(k-n+1)
.... x_k) then it will have a lowpass response (really sinc(f), but
that's kinda lowpass).

If you only sample y_k every n points then you may as well use and
integrate and dump.

QED.

Do you want to know what the correlator does, or what you do with the
output? The correlator lets you know where the clock should be. How
you change the clock rate depends on your technology (but you would use
a VCO in an analog circuit). You want to change the clock rate so
you'll still be correlated if your signal suffers dropout.

3. ### Eric JacobsenGuest

Consider that an integrate and dump filter can be realized as a FIR
with a rectangular impulse response. The filter frequency response
is then the FT of a rectangular function, in other words a sinx/x
frequency response. That's a low-pass filter, although not a very
good one.

Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org