LF2272
DEVICES INCORPORATED
Colorspace Converter/
Corrector (3 x 12-bits)
T
ABLE
1.
L
ATENCY
E
QUATIONS
X(n+4) = A(n)KA1(n) + B(n)KB1(n)
Y(n+4) = A(n)KA2(n) + B(n)KB2(n)
Z(n+4)
= A(n)KA3(n) + B(n)KB3(n)
+ C(n)KC1(n)
+ C(n)KC2(n)
+ C(n)KC3(n)
products will be output five clock
cycles after the input data has been
registered. New output data is
subsequently available every clock
cycle thereafter.
DATA FORMATTING
The data input ports (A, B, C) and
data output ports (X, Y, Z) are 12-bit
integer two’s complement format.
The coefficient input ports (KA, KB,
KC) are 10-bit fractional two’s
complement format. Refer to
Figures 1a and 1b.
BIT WEIGHTING
The internal sum of products of the
LF2272 can grow to 23 bits. However,
in order to keep the output format
identical to the input format, the X, Y,
and Z outputs are rounded to 12-bit
integer words. The rounding is done
only at the final output stage to allow
accuracy, with correct rounding and
overflow, for applications requiring
less than 12-bit integer words. The
user may adjust the bit weighting by
applying an identical scaling correc-
tion factor to both the input and
output data streams.
DATA OVERFLOW
Because the LF2272’s matched input
and output data formats accommo-
date unity gain (0 dB), input condi-
tions that could lead to numeric
overflow may exist. To ensure that no
overflow conditions occur, the user
must be aware of the maximum input
data and coefficient word sizes
allowable for each specific algorithm
being performed.
SYSTEMS SMALLER THAN 12-BITS
Using a data path less than 12-bits
requires the input data to be right
justified and sign extended to 12-bits
because the LF2272 carries out all
calculations to full precision. Since all
least-significant bits are used, the
desired X, Y, and Z outputs are
rounded correctly and upper-order
output bits are used for overflow.
F
IGURE
1
A
.
I
NPUT
F
ORMATS
Data Input
11 10 9 8 7
–2
11
2
10
2
9
2
8
2
7
(Sign)
6 5 4 3 2 1 0
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Coefficient Input
9 8 7 6 5 4 3 2 1 0
–2
0
2
–1
2
–2
2
–3
2
–4
2
–5
2
–6
2
–7
2
–8
2
–9
(Sign)
Internal Sum
20 19 18 17
–2
11
2
10
2
9
2
8
(Sign)
3 2 1 0
2
–6
2
–7
2
–8
2
–9
F
IGURE
1
B
.
O
UTPUT
F
ORMAT
Result
11 10 9 8 7
–2
11
2
10
2
9
2
8
2
7
(Sign)
6 5 4 3 2 1 0
2
6
2
5
2
4
2
3
2
2
2
1
2
0
Video Imaging Products
2
08/16/2000–LDS.2272-I
LOGIC [ LOGIC DEVICES INCORPORATED ]
