DC compensation
View Patent ↗An apparatus comprising an analog filter, an analog to digital converter coupled to said analog filter; and a digital filter coupled to said analog to digital converter; wherein the apparatus is configured such that distortion introduced into a filtered signal by said analog filter is substantially compensated by said digital filter.
1. An apparatus comprising: an analog filter; an analog to digital converter coupled to said analog filter; and a digital filter coupled to said analog to digital converter; wherein the apparatus is configured such that distortion introduced into a filtered signal by said analog filter is substantially compensated by said digital filter, wherein the apparatus is configured to reset a memory of the digital filter during a guard period of an orthogonal frequency division modulation (OFDM) symbol before a data symbol is received, the apparatus further comprising a low pass filter coupled between said analog filter and said analog to digital converter.
2. The apparatus of claim 1 wherein a frequency response of one of the analog filter and the digital filter is substantially an inverse of the other of said analog filter and said digital filter.
3. The apparatus of claim 1 , wherein said analog filter has a frequency response determined by the equation:
A
(
s
)
=
s
s
+
1
τ
where τ is a time constant associated with the analog filter.
4. The apparatus of claim 1 , wherein said digital filter has a frequency response determined by the equation:
D
(
z
)
=
1
-
a
·
z
-
1
1
-
z
-
1
where a is a filter coefficient.
5. The apparatus of claim 4 , wherein said filter coefficient is determined by the equation:
a
=
ⅇ
-
1
τ
·
fs
where fs is a sample frequency.
6. The apparatus of claim 1 , wherein the apparatus is configured to periodically reset the memory.
7. The apparatus of claim 1 , further comprising a base band amplifier coupled between said low pass filter and said analog to digital converter.
8. The apparatus of claim 1 , further comprising a channel filter coupled between said analog to digital converter and said digital filter.
9. The apparatus of claim 1 , further comprising a mixer coupled to an input of said analog filter, wherein said mixer is configured to mix a received signal with a mixing frequency.
10. A method comprising: filtering an analog signal with a first filter; converting the filtered analog signal in an analog to digital converter; and filtering saig-samples from the analog to digital converter with a second filter; wherein distortion introduced into said filtered analog signal by said first filter is substantially compensated by said second filter, wherein the method further comprises resetting a memory of the second filter during a guard period of an orthogonal frequency division modulation (OFDM) symbol before a data symbol is received; and low pass filtering said filtered analog signal prior to said converting.
11. The method of claim 10 , wherein a frequency response of one of the first filter and the second filter is substantially an inverse of the other of said first and second filters.
12. The method of claim 10 , wherein said first filter has a frequency response determined by the equation:
A
(
s
)
=
s
s
+
1
τ
where τ is a time constant associated with the analog filter.
13. The method of claim 10 , wherein said second filter has a frequency response determined by the equation:
D
(
z
)
=
1
-
a
·
z
-
1
1
-
z
-
1
where a is a filter coefficient.
14. The method of claim 13 , wherein said filter coefficient is determined by the equation:
a
=
ⅇ
-
1
τ
·
fs
where fs is a sample frequency.
15. The method of claim 10 , further comprising mixing a received signal with a mixing frequency to generate said analog signal.
16. A non-transitory computer-readable medium encoded with instructions that, when executed by a computer, perform: filtering an analog signal with a first filter; converting the filtered analog signal in an analog to digital converter; filtering samples from the analog to digital converter with a second filter; and resetting a memory of the second filter during a guard period of an orthogonal frequency division modulation (OFDM) symbol before a data symbol is received; and low pass filtering said filtered analog signal prior to said converting, wherein distortion introduced into said filtered analog signal by said first filter is substantially compensated by said second filter.