www.fairchildsemi.com
TMC2242A/TMC2242B
Digital Half-Band Interpolating/Decimating Filter
12-bit In/16-bit Out, 60 MHz
Features
• TMC2242A and TMC2242B are pin-compatible with
TMC2242
• User selectable interpolate gain, -6 dB or 0 dB (2242B)
• 30, 40 and 60 MHz speed grades
• User selectable 2:1 decimation, 1:2 interpolation, and
equal-rate filter modes
• Passband ripple <
±
0.01 dB
• Stopband rejection 59.4 dB from 0.28 to 0.50 x f
s
• Cascading two TMC2242A or TMC2242B meets
CCIR 601 low-pass filter requirement
• Dedicated 12-bit 2's complement input data port and
16-bit output data port with user-selectable rounding from
9 to 16 bits
• Two's complement or offset binary output format
• Built-in limiter prevents overflow
• Single +5 Volt power supply operation
• Small 44-Lead PLCC and 44-Lead MQFP
Applications
•
•
•
•
•
•
•
•
•
Low-cost video filtering
Chrominance bandwidth limiter
Simple, inexpensive video D/A post-filters
Reduced cost and complexity for A/D anti-aliasing filters
High-performance digital low-pass filters
Digital waveform reconstruction post-filtering
Telecommunications
Direct digital synthesis
Radar
Description
The TMC2242A and TMC2242B are fixed-coefficient lin-
ear-phase half-band (low-pass) digital filters. They can be
used to halve or double the sampling rate of a digital signal.
When used as a decimating post-filter with a double-speed
oversampling A/D converter, they greatly reduce the cost and
complexity of anti-aliasing filters required ahead of the A/D
converter. When used as an interpolating pre-filter with a
double-speed oversampling D/A converter, the TMC2242A
and TMC2242B significantly reduce the design complexity
and production cost of reconstruction filters used on D/A
outputs.
The TMC2242A and TMC2242B user selects the mode of
operation (decimate, interpolate, or equal-rate) and round-
ing. The TMC2242A and TMC2242B accept 12-bit 2's com-
plement data at up to 60 MHz and output saturated
(overflow-protected) 2's complement or offset binary data
rounded to from 9 to 16 bits. Within the speed grade I/O
limit, the output sample rate may be 1/2, 1, or 2 times the
input sample rate.
Block Diagram
12
SI
11-0
12
12
12
55 Tap
FIR
Filter
Round
and
Limit
16
16
16
SO
15-0
OE
CLK
DEC
INT
SYNC
Control
Interpolate 0-1-0-1
Decimate, Equal Rate 1-1-1-1
3
TCO
RND
2-0
65-2242A-01
Rev. 1.2.0
PRODUCT SPECIFICATION
TMC2242A/TMC2242B
Description
(continued)
The filter response is flat to within
±
0.01 dB from 0.00 to
0.22 x f
s
, with stopband attenuation greater than 59.4 dB
from 0.28 x f
s
to the Nyquist frequency. The response is 6 dB
down at 0.25 x f
s
. Symmetric-coefficient filters such as the
TMC2242A and TMC2242B have linear phase response.
Full compliance with the CCIR-601 standard of 12 dB atten-
uation at 0.25 x f
s
is achieved by cascading two parts.
The TMC2242A and TMC2242B are fabricated on an
advanced submicron CMOS process. They are available in a
44-lead J-lead PLCC package. Performance is guaranteed
from 0
°
C to 70
°
C.
To perform decimation, the chip sets the output register
clock rate to half of the input rate. One output is then
obtained for every two inputs.
For interpolation, the user should bring SYNC HIGH for at
least one clock cycle, returning it LOW with the first desired
input data value. When interpolating, the chip will then con-
tinue to accept a new data input on each alternate rising edge
of the clock. When decimating, the chip will present one out-
put value for every two clock cycles. The user may leave
SYNC LOW or toggle it once per rising clock edge, with
equivalent performance.
The output data format is two's complement if TCO is
HIGH, inverted offset binary if LOW. The user can tailor the
output data word width to his/her system requirements using
the Rounding control. As shown in Table 4, the output is
half-LSB rounded to the resolution selected by the value of
RND
2-0
. The asynchronous three-state output enable control
simplifies connection to a data bus with other drivers.
Functional Description
The TMC2242A and TMC2242B implement a fixed-coeffi-
cient linear-phase Finite Impulse Response (FIR) filter of 55
effective taps, with special rate-matching input and output
structures to facilitate 2:1 decimation and 1:2 interpolation.
The faster of either the input or output registers will operate
at the guaranteed maximum clock rate (speed grade). The
total internal pipeline latency from the input of an impulse to
the corresponding output peak (digital group delay) is 34
cycles; the 55-value output response begins after 7 clock
cycles and ends after 61 cycles.
To perform interpolation, the chip slows the effective input
register clock rate to half the output rate. It internally inserts
zeroes between the incoming data samples to "pad" the input
data rate to match the output rate.
Table 1. Operating Modes
DEC
0
0
1
1
INT
0
1
0
1
TMC2242A
Equal Rate
Decimate
Equal Rate
TMC2242B
Interpolate (0 dB)
Decimate
Equal Rate
Interpolate (-6 dB) Interpolate (-6 dB)
1
Note:
1. With 15-bit overflow protection. All other modes on both
parts limit to 16 bits.
Pin Assignments
SO
13
SO
14
SO
15
OE
TCO
DEC
INT
SYNC
CLK
GND
SI
11
SO
13
SO
14
SO
15
OE
TCO
DEC
INT
SYNC
CLK
GND
SI
11
44
43
42
41
40
39
38
37
36
35
44
43
42
41
40
6
5
4
3
2
1
18
19
20
21
22
23
24
25
26
27
28
SO
12
SO
11
SO
10
SO
9
SO
8
GND
V
DD
SO
7
SO
6
SO
5
SO
4
7
8
9
10
11
12
13
14
15
16
17
39
38
37
36
35
34
33
32
31
30
29
TMC2242A
TMC2242B
GND
V
DD
SI
10
SI
9
SI
8
SI
7
SI
6
SI
5
SI
4
SI
3
V
DD
12
13
14
15
16
17
18
19
20
21
SO
3
SO
2
SO
1
SO
0
RND
2
RND
1
RND
0
SI
0
SI
1
SI
2
GND
65-2242A-02
65-2242A-02
44 Lead PLCC
2
SO
3
SO
2
SO
1
SO
0
RND
2
RND
1
RND
0
SI
0
SI
1
SI
2
GND
44 Lead MQFP
22
SO
12
SO
11
SO
10
SO
9
SO
8
GND
V
DD
SO
7
SO
6
SO
5
SO
4
34
1
2
3
4
5
6
7
8
9
10
11
33
32
31
30
29
28
27
26
25
24
23
TMC2242A
TMC2242B
GND
V
DD
SI
10
SI
9
SI
8
SI
7
SI
6
SI
5
SI
4
SI
3
V
DD
TMC2242A/TMC2242B
PRODUCT SPECIFICATION
Pin Descriptions
Pin Number
Pin Name
INT
PLCC
44
MQFP
38
Pin Function Description
Interpolate.
When INT is LOW and DEC is HIGH, the input data register runs at
1/2 the CLK rate and zeros are inserted in the data stream between valid input
values, reducing gain by 6dB. The TMC2242A and TMC2242B interpolate and
output results at the full CLK rate.
Decimate.
When DEC is LOW and INT is HIGH, the input data register runs at
the full CLK rate. In this mode, the TMC2242A and TMC2242B decimate and
output results at 1/2 the CLK rate.
When INT = DEC, the TMC2242A is in equal rate mode. When both INT and DEC
are HIGH, the TMC2242B is likewise in equal-rate mode, but when both INT and
DEC are LOW, the TMC2242B interpolates with unity gain.
In equal-rate mode, the input and output sample rates equal the chip clock rate.
SYNC
43
37
Synchronization.
Incoming data are synchronized by holding SYNC HIGH on
CLK N–1 and LOW on CLK N when the first input data word is present on SI
11-0
.
If DEC = INT=1 (equal rate mode), SYNC is inactive. SYNC may be held LOW
until resynchronization is desired, or it may be toggled at 1/2 the CLK rate.
Clock.
The TMC2242A and TMC2242B operate from a single master clock. All
internal registers, except the output register in decimation mode, are strobed on
the rising edge of CLK. All timing parameters are referenced to the rising edge of
CLK.
Input Data Port.
A 12-bit 2's-complement input word is registered by the rising
edge of CLK. In Interpolate Mode, SI
11-0
is registered on every other CLK
(synchronized by SYNC). SI
11
is the MSB.
Output Data Port.
A 16-bit 2's-complement output result is available after the
rising edge of CLK. In Decimate Mode, SO
15-0
is registered on every other CLK
(synchronized by SYNC). SO
15-0
is rounded according to the state of RND
2-0
.
SO
15
is the MSB.
The limiter circuitry ensures that for internal overflow, a valid full-scale output
(7FFF or 8000) will be generated. With the TMC2242B in interpolate mode with
-6dB gain, limits are 3FFF and C000 (TCO=1).
Output Controls
OE
TCO
RND
2-0
Power
V
DD
GND
13,29,
38
12,28,
39,41
7, 23,
32
6, 22,
33, 35
Supply Voltage.
+5 Volt power inputs. These should come from the same power
source and be decoupled to GND.
Ground.
Ground inputs should be connected to the system digital ground plane.
3
2
22-24
41
40
16-18
Output Enable.
When LOW, SO
15-0
are enabled. When HIGH, SO
15-0
are in a
high-impedance state. OE is asynchronous with respect to CLK.
Output Format.
When TCO is HIGH, output data are in signed 2's-complement
format. When LOW, the output is inverted offset binary.
Rounding Select.
These inputs set the position of the effective LSB of the output
result. Outputs below the rounding bit are zeroed (Table 4).
Timing Controls
DEC
1
39
CLK
42
36
Data Inputs
SI
11-0
40,
37-30,
27-25
4-11,
14-21
34,
31-24,
21-19
42-44,
1-5,
8-15
Data Outputs
SO
15-0
3
PRODUCT SPECIFICATION
TMC2242A/TMC2242B
Absolute Maximum Ratings
(beyond which the device may be damaged)
1
Parameter
Supply Voltage
Input Voltage
Output Applied Voltage
2
Externally Forced Current
3,4
Short Circuit Duration
Operating Temperature (Case)
Junction Temperature
Lead Soldering Temperature
Storage Temperature
10 seconds
-65
Single output in HIGH state to ground
-20
Conditions
Min
-0.5
-0.5
-0.5
-3.0
Max
7.0
V
DD
+ 0.5
V
DD
+ 0.5
+6.0
1
110
140
300
150
Units
V
V
V
mA
sec
°
C
°
C
°
C
°
C
Notes:
1. Functional operation under any of these conditions is NOT implied. Performance and reliability are guaranteed only if
Operating Conditions are not exceeded.
2. Applied voltage must be current limited to specified range.
3. Forcing voltage must be limited to specified range.
4. Current is specified as conventional current flowing into the device.
Operating Conditions
Parameter
V
DD
f
CLK
Power Supply Voltage
Clock frequency
TMC2242A, B
TMC2242A-1,B-1
TMC2242A-2,B-2
t
PWH
t
PWL
t
S
t
H
V
IH
V
IL
I
OH
I
OL
T
A
CLK pulse width, HIGH
CLK pulse width, LOW
Input Data Set-up Time
Input Data Hold Time
Input Voltage, Logic HIGH
Input Voltage, Logic LOW
Output Current, Logic HIGH
Output Current, Logic LOW
Ambient Temperature, Still Air
0
6
6
6
1
2.0
0.8
-2.0
4.0
70
Conditions
Min
4.75
Nom
5.0
Max
5.25
30
40
60
Units
V
MHz
MHz
MHz
ns
ns
ns
ns
V
V
mA
mA
°
C
4
TMC2242A/TMC2242B
PRODUCT SPECIFICATION
Electrical Characteristics
Parameter
I
DD
Total Power Supply
Current
Conditions
V
DD
= Max, C
LOAD
=25pF, f
CLK
=Max
TMC2242A,B
TMC2242A-1,B-1
TMC2242A-2,B-2
I
DDU
Power Supply Current,
Unloaded
V
DD
= Max, OE = HIGH, f
CLK
=Max
TMC2242A,B
TMC2242A-1,B-1
TMC2242A-2,B-2
I
DDQ
C
PIN
I
IH
I
IL
I
OZH
I
OZL
I
OS
V
OH
V
OL
Power Supply Current,
Quiescent
I/O Pin Capacitance
Input Current, HIGH
Input Current, LOW
Leakage Current, HIGH
Leakage Current, LOW
Short-Circuit Current
Output Voltage, HIGH
Output Voltage, LOW
V
DD
= Max, V
IN
= V
DD
V
DD
= Max, V
IN
= 0 V
OE = HIGH, V
OUT
= V
DD
OE = HIGH, V
OUT
= 0 V
V
DD
= Max, Output = HIGH, one pin to
ground, one second duration max.
SO15-0, I
OH
= Max
SO15-0, I
OL
= Max
-20
2.4
0.4
V
DD
= Max, CLK = LOW
5
±
10
±
10
±
10
±10
-80
120
155
230
5
mA
mA
mA
mA
pF
m
A
m
A
m
A
mA
mA
V
V
150
195
290
mA
mA
mA
Min
Typ
Max
Units
Switching Characteristics
Parameter
t
DO
t
HO
t
ENA
t
DIS
Output Delay Time
Output Hold Time
Output Enable Time
Output Disable Time
Conditions
C
LOAD
= 25 pF
C
LOAD
= 25 pF
C
LOAD
= 0 pF
C
LOAD
= 0 pF
2.5
12
12
Min
Typ
Max
15
Units
ns
ns
ns
ns
5
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