Method and device for generating a filter coefficient in real time
View Patent ↗The present invention provides a method and device for generating a filter coefficient in real time. The method includes: looking up a converted window function value in a converted window function table based on a current coefficient index; generating a current cut-off angular frequency; generating a look-up table address based on the current coefficient index, the filter order and the current cut-off angular frequency and looking up a sine value in a sine table based on the look-up table address; and multiplying the converted window function value by the sine value to obtain the filter coefficient. The device includes a first memory, a second memory, a look-up table address generation module and a first multiplier. The present invention is easily implemented with low hardware resource consumption and high flexibility, and is particularly applicable for the hardware implementation of high-order finite impulse response filters.
1. A method for generating a filter coefficient in real time, comprising:
looking up a first intermediate value in a first memory in which a converted window function table is stored, based on a current coefficient index;
generating a look-up table address, via a look-up table address generation module, the look up table address based on the current coefficient index, a filter order and a current cut-off angular frequency;
looking up a second intermediate value in a second memory in which a sine table is stored, based on the look-up table address; and
multiplying, via a multiplier, the first intermediate value by the second intermediate value to obtain the filter coefficient.
2. The method of claim 1 , wherein generating the look-up table address comprises:
converting, via an index conversion unit, the current coefficient index to obtain a third intermediate value;
generating, via a cut-off angular frequency generation unit, the current cut-off angular frequency; and
multiplying, via a second multiplier, the third intermediate value by the current cut-off angular frequency to obtain the look-up table address.
3. The method of claim 2 , wherein generating the current cut-off angular frequency comprises:
looking up a current cut-off angular frequency change in a third memory in which a cut-off angular frequency change table is stored, based on the sequence number of a current time segment generated by a counter; and
adding, via an adder, a previous cut-off angular frequency stored in a register and the current cut-off angular frequency change to obtain the current cut-off angular frequency.
4. The method of claim 3 , wherein the filter coefficient is calculated using the following equation:
h
(
n
)
=
sin
[
(
2
n
+
1
-
N
)
*
k
*
pi
/
M
]
*
(
0.54
-
0.46
cos
(
2
*
pi
*
n
/
(
N
-
1
)
)
)
pi
*
(
n
-
(
N
-
1
)
/
2
)
wherein, h(n) is the filter coefficient; n is the current coefficient index, n=0, 1, . . . , N−1; N is the filter order; k is the current cut-off angular frequency; and M is the integral power of two.
5. The method of claim 1 , wherein the filter order corresponds to a highest exponent in a denominator of a Z-domain transfer function.
6. A device for generating a filter coefficient in real time, comprising:
a first memory for storing a converted window function table, such that a first intermediate value is looked up in the first memory using a current coefficient index;
a look-up table address generation module for generating a look-up table address based on the current coefficient index, a filter order and a current cut-off angular frequency;
a second memory for storing a sine table, such that a second intermediate value is looked up in the second memory using the look-up table address; and
a first multiplier for multiplying the first intermediate value by the second intermediate value to obtain the filter coefficient.
7. The device of claim 6 , wherein the first memory is a random access memory.
8. The device of claim 6 , wherein the second memory is a read only memory.
9. The device of claim 6 , wherein the look-up table address generation module comprises:
an index conversion unit for converting the current coefficient index to obtain a third intermediate value;
a cut-off angular frequency generation unit for generating the current cut-off angular frequency; and
a second multiplier for multiplying the third intermediate value by the current cut-off angular frequency to obtain the look-up table address.
10. The device of claim 9 , wherein the cut-off angular frequency generation unit comprises:
a counter for generating the sequence number of a current time segment;
a third memory for storing a cut-off angular frequency change table, such that a current cut-off angular frequency change is looked up in the third memory using the sequence number of the current time segment;
a register for storing a previous cut-off angular frequency; and
an adder for adding the previous cut-off angular frequency and the current cut-off angular frequency change to obtain the current cut-off angular frequency.
11. The device of claim 10 , wherein the counter is a uniform counter.
12. The device of claim 10 , wherein the third memory is a random access memory.
13. The device of claim 10 , wherein the first multiplier calculates the filter coefficient using the following equation:
h
(
n
)
=
sin
[
(
2
n
+
1
-
N
)
*
k
*
pi
/
M
]
*
(
0.54
-
0.46
cos
(
2
*
pi
*
n
/
(
N
-
1
)
)
)
pi
*
(
n
-
(
N
-
1
)
/
2
)
wherein, h(n) is the filter coefficient; N is the filter order; n is the current coefficient index, n=0, 1, . . . , N−1; k is the current cut-off angular frequency; and M is the integral power of two.