Altera FIR Compiler II MegaCore Function - Manual (Page 30)

Parameter Value Description
Output Data Type Signed Binary
Signed Fractional
Binary
Specifies whether the output data is in a signed
binary or a signed fractional binary format. Select
Signed Fractional Binary to monitor which bits
the IP core preserves and which bits it removes
during the filtering process.
Output Bit Width 0–32 Specifies the width of the output data (with limited
precision) from the filter.
Output Fractional Bit
Width
0–32 Specifies the width of the output data (with limited
precision) from the filter when you select Signed
Fractional Binary as your output data.
Output MSB rounding Truncation/
Saturating
Specifies whether to truncate or saturate the most
significant bit (MSB).
MSB Bits to Remove 0–32 Specifies the number of MSB bits to truncate or
saturate. The value must not be greater than its
corresponding integer bits or fractional bits.
Output LSB rounding Truncation/ Rounding Specifies whether to truncate or round the least
significant bit (LSB).
LSB Bits to Remove 0–32 Specifies the number of LSB bits to truncate or
round. The value must not be greater than its
corresponding integer bits or fractional bits.
Signed Fractional Binary
The FIR II IP core supports two’s complement, signed fractional binary notation, which allows you to
monitor which bits the IP core preserves and which bits it removes during filtering. A signed binary
fractional number has the format:
<sign> <integer bits>.<fractional bits>
A signed binary fractional number is interpreted as shown below:
<sign> <x
1
integer bits>.<y
1
fractional bits> Original input data
<sign> <x
2
integer bits>.<y
2
fractional bits> Original coefficient data
<sign> <i integer bits>.<y
1
+ y
2
fractional bits> Full precision after FIR calculation
<sign> <x
3
integer bits>.<y
3
fractional bits> Output data after limiting precision
where i = ceil(log
2
(number of coefficients)) + x
1
+ x
2
For example, if the number has 3 fractional bits and 4 integer bits plus a sign bit, the entire 8-bit integer
number is divided by 8, which gives a number with a binary fractional component.
The total number of bits equals to the sign bits + integer bits + fractional bits. The sign + integer bits is
equal to Input Bit Width – Input Fractional Bit Width with a constraint that at least 1 bit must be
specified for the sign.
UG-01072
2014.12.15
Signed Fractional Binary 3-5
FIR II IP Core Parameters Altera Corporation
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