LF2242
DEVICES INCORPORATED
12/16-bit Half-Band Interpolating/
Decimating Digital Filter
RND2-0 — Rounding Control
FIGURE 2. INPUT AND OUTPUT FORMATS
The rounding control inputs set the posi-
tionoftheeffectiveLSBoftheoutputdata
by adding a rounding bit to the internal
bit position that is one below that speci-
fied by RND2-0. All bits below the effec-
tive LSB position are subsequently ze-
roed (Table 2).
Two’s Complement Input Format
11 10
9
8
3
2
1
0
–20 2–1 2–2 2–3
2–8 2–9 2–10 2–11
(Sign)
Two’s Complement Output Format (TCO = 1, Non-interpolate)
15 14 13 12
3
2
1
0
TCO — Two’s Complement Format
Control
–20 2–1 2–2 2–3
2–12 2–13 2–14 2–15
(Sign)
The TCO input determines the format of
theoutputdata. WhenTCOisHIGH, the
outputdataispresentedintwo’scomple-
ment format. When TCO is LOW, the
data is in inverted offset binary format
(all output bits are inverted except the
Two’s Complement Output Format (TCO = 1, Interpolate)
15 14 13 12
–21 20 2–1 2–2
3
2
1
0
2–11 2–12 2–13 2–14
(Sign)
Inverted Offset Binary Output Format (TCO = 0, Non-interpolate)
MSB — the MSB is unchanged).
15 14 13 12
20 2–1 2–2 2–3
3
2
1
0
2–12 2–13 2–14 2–15
OE — Output Enable
(Sign)
When the OE signal is LOW, the current
data in the output register is available on
the SO15-0 pins. When OE is HIGH, the
outputs are in a high-impedance state.
Inverted Offset Binary Output Format (TCO = 0, Interpolate)
15 14 13 12
3
2
1
0
21 20 2–1 2–2
2–11 2–12 2–13 2–14
(Sign)
TABLE 2. ROUNDING FORMAT
RND2-0
000
SO15
X
SO14
X
SO13
X
SO12
X
• • •
• • •
• • •
• • •
• • •
• • •
• • •
• • •
• • •
SO8
X
SO7
X
SO6
X
SO5
X
SO4
X
SO3
X
SO2
X
SO1
X
R
0
SO0
R
0
001
X
X
X
X
X
X
X
X
X
X
X
010
X
X
X
X
X
X
X
X
X
X
R
0
0
011
X
X
X
X
X
X
X
X
X
R
0
0
0
100
X
X
X
X
X
X
X
X
R
0
0
0
0
101
X
X
X
X
X
X
X
R
0
0
0
0
0
110
X
X
X
X
X
X
R
0
0
0
0
0
0
111
X
X
X
X
X
R
0
0
0
0
0
0
'R' indicates the half-LSB rounded bit (effective LSB position)
Video Imaging Products
08/16/2000–LDS.2242-K
3
LOGIC [ LOGIC DEVICES INCORPORATED ]
