LTC1569-7
Linear Phase, DC Accurate,
Tunable, 10th Order Lowpass Filter
FEATURES
s
s
s
s
s
s
s
s
s
s
s
One External R Sets Cutoff Frequency
Root Raised Cosine Response
Up to 300kHz Cutoff on a Single 5V Supply
Up to 150kHz Cutoff on a Single 3V Supply
10th Order, Linear Phase Filter in an SO-8
DC Accurate, V
OS(MAX)
= 5mV
Low Power Modes
Differential or Single-Ended Inputs
80dB CMRR (DC)
80dB Signal-to-Noise Ratio, V
S
= 5V
Operates from 3V to
±5V
Supplies
Furthermore, its root raised cosine response offers the
optimum pulse shaping for PAM data communications.
The filter attenuation is 57dB at 1.5 • f
CUTOFF
, 60dB at 2 •
f
CUTOFF
, and in excess of 80dB at 6 • f
CUTOFF
. DC-accuracy-
sensitive applications benefit from the 5mV maximum DC
offset.
The LTC1569-7 is the first sampled data filter which does
not require an external clock yet its cutoff frequency can be
set with a single external resistor with a typical accuracy
of 3.5% or better.
The external resistor programs an
internal oscillator whose frequency is divided by either 1,
4 or 16 prior to being applied to the filter network. Pin 5
determines the divider setting. Thus, up to three cutoff
frequencies can be obtained for each external resistor
value. Using various resistor values and divider settings,
the cutoff frequency can be programmed over a range of
seven octaves. Alternatively, the cutoff frequency can be
set with an external clock and the clock-to-cutoff fre-
quency ratio is 32:1. The ratio of the internal sampling rate
to the filter cutoff frequency is 64:1.
The LTC1569-7 is fully tested for a cutoff frequency of
256kHz/128kHz with single 5V/3V supply although up to
300kHz cutoff frequencies can be obtained.
The LTC1569-7 features power savings modes and it is
available in an SO-8 surface mount package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
Data Communication Filters for 3V Operation
Linear Phase and Phase Matched Filters for I/Q
Signal Processing
Pin Programmable Cutoff Frequency Lowpass Filters
DESCRIPTIO
®
The LTC 1569-7 is a 10th order lowpass filter featuring
linear phase and a root raised cosine amplitude response.
The high selectivity of the LTC1569-7 combined with its
linear phase in the passband makes it suitable for filtering
both in data communications and data acquisition sytems.
TYPICAL APPLICATION
Frequency Response, f
CUTOFF
= 128kHz/32kHz/8kHz
Single 3V Supply, 128kHz/32kHz/8kHz Lowpass Filter
V
IN
3V
3.48k
3
2k
1µF
4
V
–
DIV/CLK
5
1/1
1
IN
+
IN
–
OUT
V
+
8
V
OUT
R
EXT
= 10k
1µF
6
1/16
1/4
–80
0
2
7
LTC1569-7
GND
R
X
GAIN (dB)
EASY TO SET f
CUTOFF
:
f
CUTOFF
=
1, 4 OR 16
128kHz (10k/R
EXT
)
1569-7 TA01
U
U
U
–20
3V
–40
–60
3V
100pF
–100
1
10
100
FREQUENCY (kHz)
1000
1569-7 TA01a
1
LTC1569-7
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
IN
+
1
IN
–
2
GND 3
V
–
4
8
7
6
5
OUT
V
+
R
X
DIV/CLK
Total Supply Voltage ................................................ 11V
Power Dissipation .............................................. 500mW
Operating Temperature
LTC1569C ............................................... 0°C to 70°C
LTC1569I ............................................ – 40°C to 85°C
Storage Temperature ............................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1569CS8-7
LTC1569IS8-7
S8 PART
MARKING
15697
1569I7
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 80°C/W (Note 6)
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
S
= 3V (V
+
= 3V, V
–
= 0V), f
CUTOFF
= 128kHz, R
LOAD
= 10k unless otherwise specified.
PARAMETER
Filter Gain
CONDITIONS
V
S
= 5V, f
CLK
= 8.192MHz,
f
CUTOFF
= 256kHz, V
IN
= 2.5V
P-P
,
R
EXT
= 5k, Pin 5 Shorted to Pin 4
f
IN
= 5120Hz = 0.02 • f
CUTOFF
f
IN
= 51.2kHz = 0.2 • f
CUTOFF
f
IN
= 128kHz = 0.5 • f
CUTOFF
f
IN
= 204.8kHz = 0.8 • f
CUTOFF
f
IN
= 256kHz = f
CUTOFF
, LTC1569C
f
IN
= 256kHz = f
CUTOFF
, LTC1569I
f
IN
= 384kHz = 1.5 • f
CUTOFF
f
IN
= 512kHz = 2 • f
CUTOFF
f
IN
= 768kHz = 3 • f
CUTOFF
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
q
MIN
– 0.10
– 0.25
– 0.50
– 1.1
– 5.7
– 6.2
TYP
0.00
– 0.15
– 0.41
– 0.65
– 3.8
– 3.8
– 58
– 62
– 67
0.00
– 0.15
– 0.40
– 0.65
– 3.15
– 57
– 60
– 66
–11
–112
80
– 83
158
– 95
125kHz
±1%
2.1
MAX
0.10
– 0.05
– 0.25
– 0.40
– 2.3
– 2.0
– 48
– 54
– 64
0.12
– 0.05
– 0.30
– 0.50
– 3.0
– 52
– 54
– 58
–110
82
– 81
161
UNITS
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
Deg
Deg
Deg
Deg
Deg
Deg
V
S
= 2.7V, f
CLK
= 1MHz,
f
IN
= 625Hz = 0.02 • f
CUTOFF
f
IN
= 6.25kHz = 0.2 • f
CUTOFF
f
CUTOFF
= 31.25kHz, V
IN
= 1V
P-P
,
Pin 6 Shorted to Pin 4, External Clock f
IN
= 15.625kHz = 0.5 • f
CUTOFF
f
IN
= 25kHz = 0.8 • f
CUTOFF
f
IN
= 31.25kHz = f
CUTOFF
f
IN
= 46.875kHz = 1.5 • f
CUTOFF
f
IN
= 62.5kHz = 2 • f
CUTOFF
f
IN
= 93.75kHz = 3 • f
CUTOFF
Filter Phase
V
S
= 2.7V, f
CLK
= 4MHz,
f
CUTOFF
= 125kHz, Pin 6 Shorted to
Pin 4, External Clock
f
IN
= 2500Hz = 0.02 • f
CUTOFF
f
IN
= 25kHz = 0.2 • f
CUTOFF
f
IN
= 62.5kHz = 0.5 • f
CUTOFF
f
IN
= 100kHz = 0.8 • f
CUTOFF
f
IN
= 125kHz = f
CUTOFF
f
IN
= 187.5kHz = 1.5 • f
CUTOFF
– 0.08
– 0.25
– 0.50
– 0.75
– 3.3
– 114
78
– 85
155
Filter Cutoff Accuracy
when Self-Clocked
Filter Output DC Swing
R
EXT
= 10.24k from Pin 6 to Pin 7,
V
S
= 3V, Pin 5 Shorted to Pin 4
V
S
= 3V, Pin 3 = 1.11V
q
1.9
3.9
3.7
8.6
8.4
8.0
V
S
= 5V, Pin 3 = 2V
q
V
S
=
±5V
LTC1569C
LTC1569I
q
q
2
U
V
P-P
V
P-P
V
P-P
V
P-P
V
P-P
V
P-P
V
P-P
W
U
U
W W
W
LTC1569-7
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
S
= 3V (V
+
= 3V, V
–
= 0V), f
CLK
= 4.096MHz, f
CUTOFF
= 128kHz, R
LOAD
= 10k unless otherwise specified.
PARAMETER
Output DC Offset
(Note 2)
Output DC Offset Drift
CONDITIONS
R
EXT
= 10k, Pin 5 Shorted to Pin 4
MIN
V
S
= 3V
V
S
= 5V
V
S
=
±5V
V
S
= 3V
V
S
= 5V
V
S
=
±5V
Min Logical “1”
Max Logical “0”
Min Logical “1”
Max Logical “0”
Min Logical “1”
Max Logical “0”
V
S
= 3V
q
TYP
±2
±6
±15
– 25
– 25
±25
2.6
0.5
4.0
0.5
4.0
0.5
6
7
MAX
±5
±12
UNITS
mV
mV
mV
µV/°C
µV/°C
µV/°C
V
V
V
V
V
V
R
EXT
= 10k, Pin 5 Shorted to Pin 4
Clock Pin Logic Thresholds
when Clocked Externally
V
S
= 3V
V
S
= 5V
V
S
=
±5V
Power Supply Current
(Note 3)
f
CLK
= 1.028MHz (10k from Pin 6 to Pin 7,
Pin 5 Open,
÷
4), f
CUTOFF
= 32kHz
8
9
9
10
13
14
14
mA
mA
mA
mA
mA
mA
mA
mA
mA
mA
mA
mA
V
mV
RMS
µV
RMS
dB
V
S
= 5V
q
V
S
= 10V
q
9
9.5
q
f
CLK
= 4.096MHz (10k from Pin 6 to Pin 7,
Pin 5 Shorted to Pin 4,
÷
1), f
CUTOFF
= 128kHz
f
CLK
= 8.192MHz (5k from Pin 6 to Pin 7,
Pin 5 Shorted to Pin 4,
÷
1), f
CUTOFF
= 256kHz
V
S
= 3V
V
S
= 5V
q
20
30
27
q
V
S
= 10V
Power Supply Voltage where
Low Power Mode is Enabled
Clock Feedthrough
Wideband Noise
THD
Clock-to-Cutoff
Frequency Ratio
Max Clock Frequency
(Note 4)
Min Clock Frequency
(Note 5)
Input Frequency Range
V
S
= 3V
V
S
= 5V
V
S
=
±5V
3V to
±5V,
T
A
< 85°C
Aliased Components <–65dB
Pin 5 Shorted to Pin 4, Note 3
R
EXT
= 10k, Pin 5 Open
Noise BW = DC to 2 • f
CUTOFF
f
IN
= 10kHz, 1.5V
P-P
q
37
3.7
4.2
0.4
125
74
32
5
9.6
13
3
0.9 • f
CLK
4.6
MHz
MHz
MHz
kHz
Hz
Note 1:
Absolute maximum ratings are those values beyond which the life
of a device may be impaired.
Note 2:
DC offset is measured with respect to Pin 3.
Note 3:
There are several operating modes which reduce the supply
current. For V
S
< 4V, relative to divide-by-1 mode, the current is typically
reduced by 50% relative to V
S
= 5V. If the internal oscillator is used as the
clock source and the divide-by-4 or divide-by-16 mode is enabled, the
supply current is typically reduced by 60%,relative to divide-by-1 mode,
independent of the value of V
S
.
Note 4:
The maximum clock frequency is arbitrarily defined as the
frequency at which the filter AC response exhibits >1dB of gain peaking.
Note 5:
The minimum clock frequency is arbitrarily defined as the frequecy
at which the filter DC offset changes by more than 5mV.
Note 6:
Thermal resistance varies depending upon the amount of PC board
metal attached to the device.
θ
JA
is specified for a 2500mm
2
test board
covered with 2oz copper on both sides.
3
LTC1569-7
TYPICAL PERFOR A CE CHARACTERISTICS
Gain vs Frequency
10
V
S
= 3V
f
C
= 128kHz
R
EXT
= 10k
PIN 5 AT V
–
LOG MAG (10dB/DIV)
GAIN (dB)
–90
5
10
100
FREQUENCY (kHz)
THD vs Input Frequency
–68
–50
–70
V
S
= 5V
PIN 3 = 2V
THD (dB)
THD (dB)
–72
–70
f
IN
= 10kHz
f
CUTOFF
= 128kHz
IN
+
TO OUT
R
EXT
= 10k
PIN 5 AT V
–
0
1
2
3
4
INPUT VOLTAGE (V
P-P
)
5
1569-7 G02
I
SUPPLY
(mA)
–74
V
IN
= 1.5V
P-P
f
CUTOFF
= 128kHz
IN
+
TO OUT
R
EXT
= 10k
PIN 5 AT V
–
0
10 20 30 40 50 60 70 80 90 100
INPUT FREQUENCY (kHz)
1569-7 G01
–76
–78
5V Supply Current
23
21
19
I
SUPPLY
(mA)
I
SUPPLY
(mA)
17
15
13
11
9
7
5
1
10
100
f
CUTOFF
(kHz)
DIV-BY-16
4
U W
Passband Gain and Group Delay
vs Frequency
1
20
V
S
= 3V
f
C
= 128kHz 19
R
EXT
= 10k
PIN 5 AT V
–
18
17
0
DELAY (µs)
–1
16
15
–2
14
13
–3
12
11
1000
1569-7 G03
–4
1
10
FREQUENCY (kHz)
100
1569-7 G04
10
THD vs Input Voltage
12
V
S
= 3V
PIN 3 = 1.11V
–60
11
V
S
= 5V
PIN 3 = 2V
10
9
8
7
3V Supply Current
DIV-BY-1
EXT CLK
DIV-BY-16
–80
6
DIV-BY-4
5
4
1
10
100
f
CUTOFF
(kHz)
1000
1569-7 G05
–90
±
5V Supply Current
35
32
DIV-BY-1
DIV-BY-1
EXT CLK
29
26
23
20
17
14
11
DIV-BY-16
EXT CLK
DIV-BY-4
1000
1569-7 G06
8
5
1
DIV-BY-4
10
100
f
CUTOFF
(kHz)
1000
1569-7 G07
LTC1569-7
PIN FUNCTIONS
IN
+
/IN
–
(Pins 1, 2):
Signals can be applied to either or
both input pins. The DC gain from IN
+
(Pin 1) to OUT
(Pin 8) is 1.0, and the DC gain from Pin 2 to Pin 8 is –1. The
input range, input resistance and output range are de-
scribed in the Applications Information section. Input
voltages which exceed the power supply voltages should
be avoided. Transients will not cause latchup if the current
into/out of the input pins is limited to 20mA.
GND (Pin 3):
The GND pin is the reference voltage for the
filter and should be externally biased to 2V (1.11V) to
maximize the dynamic range of the filter in applications
using a single 5V (3V) supply. For single supply operation,
the GND pin should be bypassed with a quality 1µF
ceramic capacitor to V
–
(Pin 4). The impedance of the
circuit biasing the GND pin should be less than 2kΩ as the
GND pin generates a small amount of AC and DC current.
For dual supply operation, connect Pin 3 to a high quality
DC ground. A ground plane should be used. A poor ground
will increase DC offset, clock feedthrough, noise and
distortion.
V
–
/V
+
(Pins 4, 7):
For 3V, 5V and
±5V
applications a
quality 1µF ceramic bypass capacitor is required from V
+
(Pin 7) to V
–
(Pin 4) to provide the transient energy for the
internal clock drivers. The bypass should be as close as
possible to the IC. In dual supply applications (Pin 3 is
grounded), an additional 0.1µF bypass from V
+
(Pin 7) to
GND (Pin 3) and V
–
(Pin 4) to GND (Pin 3) is recom-
mended.
The maximum voltage difference between GND (Pin 3) and
V
+
(Pin 7) should not exceed 5.5V.
DIV/CLK (Pin 5):
DIV/CLK serves two functions. When the
internal oscillator is enabled, DIV/CLK can be used to
engage an internal divider. The internal divider is set to 1:1
when DIV/CLK is shorted to V
–
(Pin 4). The internal divider
is set to 4:1 when DIV/CLK is allowed to float (a 100pF
bypass to V
–
is recommended). The internal divider is set
to 16:1 when DIV/CLK is shorted to V
+
(Pin 7). In the
divide-by-4 and divide-by-16 modes the power supply
current is reduced by typically 60%.
When the internal oscillator is disabled (R
X
shorted
to V
–
) DIV/CLK becomes an input pin for applying an
external clock signal. For proper filter operation, the clock
waveform should be a squarewave with a duty cycle as
close as possible to 50% and CMOS voltages levels (see
Electrical Characteristics section for voltage levels). DIV/
CLK pin voltages which exceed the power supply voltages
should be avoided. Transients will not cause latchup if the
fault current into/out of the DIV/CLK pin is limited to 40mA.
R
X
(Pin 6):
Connecting an external resistor between the R
X
pin and V
+
(Pin 7) enables the internal oscillator. The value
of the resistor determines the frequency of oscillation. The
maximum recommended resistor value is 40k and the
minimum is 3.8k/8k (single 5V/3V supply). The internal
oscillator is disabled by shorting the R
X
pin to V
–
(Pin 4).
(Please refer to the Applications Information section.)
OUT (Pin 8):
Filter Output. This pin can drive 10kΩ and/or
40pF loads. For larger capacitive loads, an external 100Ω
series resistor is recommended. The output pin can ex-
ceed the power supply voltages by up to
±2V
without
latchup.
BLOCK DIAGRA
W
U
U
U
IN
+
1
10TH ORDER
LINEAR PHASE
FILTER NETWORK
IN
–
2
8 OUT
7 V
+
R
EXT
GND 3
POWER
CONTROL
6 R
X
V
–
4
DIVIDER/
BUFFER
5 DIV/CLK
PRECISION
OSCILLATOR
1569-7 BD
5
嵌入式系统
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