ROM-based finite impulse response filter for use in mobile telephone
First Claim
1. A finite impulse response (FIR) filter apparatus comprising:
- means for receiving an input signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals;
means for storing FIR filter output values, wherein the means for storing stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; and
means for successively applying sequences of consecutive signals from the input signal stream to the means for storing to read out a sequence of output values corresponding to a filtered version of at least a portion of the input stream.
1 Assignment
0 Petitions
Accused Products
Abstract
The finite impulse response (FIR) filter is implemented as a table using read-only memory (ROM). The FIR filter table stores a pre-calculated output filter value for each permissible combination of input values to be filtered. Streams of input values are successively shifted into the table and corresponding output values are successively output. In an exemplary implementation, the FIR filter is employed within a digital cellular telephone for use in smoothing a digital signal to be transmitted. The size of the required FIR filter table is minimized by exploiting constraints imposed upon the signal to be filtered and by exploiting linearity and symmetry within the filter itself. More specifically, the telephone employs a data burst randomizer to provide a data signal composed of sequences of null or 0 values and sequences of antipodal values (+1'"'"'s and -1'"'"'s). Hence, the permissible input combinations for the FIR filter include only patterns containing either all antipodal signals, all null signals, leading antipodal signals followed by trailing null signals, or leading null signals followed by trailing antipodal signals. The FIR filter look up is configured to exploit these limitations on the input streams yielding a look up table having relatively few entries. Method and apparatus implementations are disclosed.
-
Citations
39 Claims
-
1. A finite impulse response (FIR) filter apparatus comprising:
-
means for receiving an input signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; means for storing FIR filter output values, wherein the means for storing stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; and means for successively applying sequences of consecutive signals from the input signal stream to the means for storing to read out a sequence of output values corresponding to a filtered version of at least a portion of the input stream. - View Dependent Claims (2, 3, 4, 5)
-
-
6. A finite impulse response (FIR) filter apparatus for use in filtering an input signal stream, said filter apparatus comprising:
-
a receiver receiving an input signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; a memory unit containing FIR filter output values, wherein the memory unit stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; and an input control unit for successively applying sequences of consecutive signals from the input signal stream to memory unit to read out a sequence of output values corresponding to a filtered version of at least a portion of the input stream. - View Dependent Claims (7, 8, 9, 10)
-
-
11. A method for filtering an input signal stream, said method comprising the steps of:
-
receiving an input signal stream to be filtered, said input signals stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; and successively applying sequences of consecutive signals from the input signal stream to a memory unit containing FIR filter output values to output a sequence of output values corresponding to a filtered version of at least a portion of the input stream, wherein the memory unit stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals. - View Dependent Claims (12)
-
-
13. An apparatus for converting a digital signal into an analog signal, said apparatus comprising:
-
means for receiving an input digital signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; means for storing digital FIR filter output values, wherein the means for storing stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; means for successively applying sequences of consecutive signals from the input digital signal stream to the means for storing to read out a sequence of digital FIR filter values corresponding to the input stream patterns; and digital to analog conversion means for converting the sequence of digital FIR filter values into an analog signal. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
-
-
29. A method for converting a digital signal into an analog signal, said method comprising the steps of:
-
receiving an input digital signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; successively applying sequences of consecutive signals from the input digital signal stream to a memory unit containing digital FIR filter output values to read out a sequence of digital FIR filter values corresponding to the input stream patterns, wherein the memory unit contains only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; and converting the sequence of digital values into an analog signal. - View Dependent Claims (30, 31, 32, 33, 34)
-
-
35. An apparatus for converting a digital signal into an analog signal, said apparatus comprising:
-
a receiver unit connected to an input line providing an input digital signal stream having groups of consecutive non-null signals bracketed by groups of consecutive null signals; a memory unit storing a table containing digital FIR filter output values, wherein the memory unit stores only FIR filter output values for each of a predetermined set of unique permissible input stream patterns, with the set of permissible input stream patterns including only patterns containing either leading non-null signals followed by trailing null signals, leading null signals followed by trailing non-null signals, all non-null signals or all null signals; a shift register, connected between the receiver unit and the memory unit, said shift register successively applying sequences of consecutive signals from the input digital signal stream to the memory unit to cause the memory unit to read out a sequence of digital FIR filter values corresponding to the input stream patterns; and a digital to analog converter connected to the memory unit, said digital to analog converter operating to convert the sequence of digital FIR filter values into an analog signal. - View Dependent Claims (36, 37, 38, 39)
-
Specification