LTC1569C [Linear]
Linear Phase, DC Accurate, Tunable, 10th Order Lowpass Filter; 线性相位， DC准确，可调，第10阶低通滤波器
| 型号： | LTC1569C |
| 厂家： | 
Linear |
| 描述： | Linear Phase, DC Accurate, Tunable, 10th Order Lowpass Filter |
| 文件： | 总12页 (文件大小：226K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC1569-7
Linear Phase, DC Accurate,
Tunable, 10th Order Lowpass Filter
Furthermore, its root raised cosine response offers the
optimum pulse shaping for PAM data communications.
The filter attenuation is 50dB at 1.5 • fCUTOFF, 60dB at 2 •
FEATURES
■
One External R Sets Cutoff Frequency
■
Root Raised Cosine Response
fCUTOFF, andinexcessof80dBat6•fCUTOFF. DC-accuracy-
■
Up to 300kHz Cutoff on a Single 5V Supply
sensitive applications benefit from the 5mV maximum DC
offset.
■
Up to 150kHz Cutoff on a Single 3V Supply
■
10th Order, Linear Phase Filter in an SO-8
The LTC1569-7 is the first sampled data filter which does
notrequireanexternalclockyetitscutofffrequencycanbe
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.
■
DC Accurate, VOS(MAX) = 5mV
■
Low Power Modes
■
Differential or Single-Ended Inputs
■
80dB CMRR (DC)
■
80dB Signal-to-Noise Ratio, VS = 5V
■
Operates from 3V to ±5V Supplies
U
APPLICATIO S
■
Data Communication Filters for 3V Operation
■
Linear Phase and Phase Matched Filters for I/Q
Signal Processing
Pin Programmable U Cutoff Frequency Lowpass Filters
■
DESCRIPTIO
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 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
bothindatacommunicationsanddataacquisitionsytems.
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.
U
TYPICAL APPLICATION
Frequency Response, fCUTOFF = 128kHz/32kHz/8kHz
Single 3V Supply, 128kHz/32kHz/8kHz Lowpass Filter
0
1
2
8
7
+
V
IN
OUT
V
OUT
IN
–20
–40
R
EXT
= 10k
3V
–
+
3V
1µF
IN
V
LTC1569-7
GND
3.48k
2k
3
4
6
5
R
X
–60
3V
1µF
1/16
1/1
1/4
–
V
DIV/CLK
–80
100pF
EASY TO SET f
:
CUTOFF
–100
128kHz (10k/R
1, 4 OR 16
)
EXT
1
10
100
1000
f
=
CUTOFF
1569-7 TA01
FREQUENCY (kHz)
1569-7 TA01a
1
LTC1569-7
W
U
W W W
U
/O
ABSOLUTE AXI U RATI GS
PACKAGE RDER I FOR ATIO
(Note 1)
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
TOP VIEW
NUMBER
+
IN
IN
1
2
3
4
8
7
6
5
OUT
–
+
LTC1569CS8-7
LTC1569IS8-7
V
GND
R
X
–
V
DIV/CLK
S8 PART
MARKING
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, θJA = 80°C/W (Note 6)
15697
1569I7
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VS = 3V (V+ = 3V, V– = 0V), fCUTOFF = 128kHz, RLOAD = 10k unless otherwise specified.
PARAMETER
CONDITIONS
V = 5V, f
MIN
TYP
MAX
UNITS
Filter Gain
= 8.192MHz,
f
f
f
f
f
f
f
f
f
= 5120Hz = 0.02 • f
= 51.2kHz = 0.2 • f
= 128kHz = 0.5 • f
= 204.8kHz = 0.8 • f
●
●
●
●
●
●
●
●
●
–0.10
–0.25
–0.50
–1.1
–5.7
–6.2
0.00
–0.15
–0.41
–0.65
–3.8
–3.8
–58
0.10
–0.05
–0.25
–0.40
–2.3
–2.0
–48
dB
dB
dB
dB
dB
dB
dB
dB
dB
S
CLK
IN
IN
IN
IN
IN
IN
IN
IN
IN
CUTOFF
CUTOFF
CUTOFF
f
= 256kHz, V = 2.5V ,
= 5k, Pin 5 Shorted to Pin 4
CUTOFF
IN
P-P
R
EXT
CUTOFF
= 256kHz = f
= 256kHz = f
, LTC1569C
, LTC1569I
CUTOFF
CUTOFF
= 384kHz = 1.5 • f
CUTOFF
= 512kHz = 2 • f
= 768kHz = 3 • f
–62
–67
–54
–64
CUTOFF
CUTOFF
V = 2.7V, f
= 1MHz,
f
f
f
f
f
f
f
f
= 625Hz = 0.02 • f
CUTOFF
●
●
●
●
●
●
●
●
–0.08
–0.25
–0.50
–0.75
–3.3
0.00
–0.15
–0.40
–0.65
–3.15
–57
0.12
–0.05
–0.30
–0.50
–3.0
–52
dB
dB
dB
dB
dB
dB
dB
dB
S
CLK
IN
IN
IN
IN
IN
IN
IN
IN
f
= 31.25kHz, V = 1V
Pin 6 Shorted to Pin 4, External Clock
,
= 6.25kHz = 0.2 • f
CUTOFF
IN
P-P
CUTOFF
= 15.625kHz = 0.5 • f
CUTOFF
= 25kHz = 0.8 • f
CUTOFF
= 31.25kHz = f
CUTOFF
= 46.875kHz = 1.5 • f
= 62.5kHz = 2 • f
CUTOFF
–60
–66
–54
–58
CUTOFF
= 93.75kHz = 3 • f
CUTOFF
Filter Phase
V = 2.7V, f
= 4MHz,
f
f
f
f
f
f
= 2500Hz = 0.02 • f
= 25kHz = 0.2 • f
–11
–112
80
–83
158
–95
Deg
Deg
Deg
Deg
Deg
Deg
S
CLK
IN
IN
IN
IN
IN
IN
CUTOFF
CUTOFF
f
= 125kHz, Pin 6 Shorted to
Pin 4, External Clock
●
●
●
●
–114
78
–85
155
–110
82
–81
161
CUTOFF
= 62.5kHz = 0.5 • f
CUTOFF
CUTOFF
= 100kHz = 0.8 • f
= 125kHz = f
CUTOFF
= 187.5kHz = 1.5 • f
CUTOFF
Filter Cutoff Accuracy
when Self-Clocked
R
= 10.24k from Pin 6 to Pin 7,
125kHz ±1%
EXT
V = 3V, Pin 5 Shorted to Pin 4
S
Filter Output DC Swing V = 3V, Pin 3 = 1.11V
2.1
3.9
8.6
V
V
S
P-P
P-P
●
●
1.9
3.7
V = 5V, Pin 3 = 2V
S
V
V
P-P
P-P
V = ±5V
S
V
V
P-P
P-P
LTC1569C
LTC1569I
●
●
8.4
8.0
V
P-P
2
LTC1569-7
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VS = 3V (V+ = 3V, V– = 0V), fCLK = 4.096MHz, fCUTOFF = 128kHz, RLOAD = 10k unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output DC Offset
(Note 2)
R
R
= 10k, Pin 5 Shorted to Pin 4
= 10k, Pin 5 Shorted to Pin 4
V = 3V
±2
±6
±15
±5
±12
mV
mV
mV
EXT
S
V = 5V
S
V = ±5V
S
Output DC Offset Drift
V = 3V
–25
–25
±25
µV/°C
µV/°C
µV/°C
EXT
S
V = 5V
S
V = ±5V
S
Clock Pin Logic Thresholds
when Clocked Externally
V = 3V
S
Min Logical “1”
Max Logical “0”
2.6
0.5
V
V
V = 5V
S
Min Logical “1”
Max Logical “0”
4.0
0.5
V
V
V = ±5V
S
Min Logical “1”
Max Logical “0”
4.0
0.5
V
V
Power Supply Current
(Note 3)
f
= 1.028MHz (10k from Pin 6 to Pin 7,
V = 3V
6
8
9
mA
mA
CLK
S
Pin 5 Open, ÷ 4), f
= 32kHz
●
●
●
●
●
CUTOFF
V = 5V
S
7
9
10
mA
mA
V = 10V
S
9
13
14
mA
mA
f
= 4.096MHz (10k from Pin 6 to Pin 7,
V = 3V
S
9.5
20
27
4.2
mA
mA
CLK
Pin 5 Shorted to Pin 4, ÷ 1), f
= 128kHz
14
30
CUTOFF
f
= 8.192MHz (5k from Pin 6 to Pin 7,
V = 5V
S
mA
mA
CLK
Pin 5 Shorted to Pin 4, ÷ 1), f
= 256kHz
CUTOFF
V = 10V
S
mA
mA
●
●
37
Power Supply Voltage where Pin 5 Shorted to Pin 4, Note 3
Low Power Mode is Enabled
3.7
4.6
V
Clock Feedthrough
Wideband Noise
THD
R
= 10k, Pin 5 Open
0.4
125
74
mV
RMS
EXT
Noise BW = DC to 2 • f
µV
RMS
CUTOFF
f
= 10kHz, 1.5V
dB
IN
P-P
Clock-to-Cutoff
Frequency Ratio
32
Max Clock Frequency
(Note 4)
V = 3V
5
9.6
13
MHz
MHz
MHz
S
V = 5V
S
V = ±5V
S
Min Clock Frequency
(Note 5)
3V to ±5V, T < 85°C
3
kHz
A
Input Frequency Range
Aliased Components <–65dB
0.9 • f
CLK
Hz
Note 1: Absolute maximum ratings are those values beyond which the life
of a device may be impaired.
Note 4: The maximum clock frequency is arbitrarily defined as the
frequency at which the filter AC response exhibits >1dB of gain peaking.
Note 2: DC offset is measured with respect to Pin 3.
Note 3: There are several operating modes which reduce the supply
Note 5: The minimum clock frequency is arbitrarily defined as the frequecy
at which the filter DC offset changes by more than 5mV.
current. For V < 4V, the current is reduced by 50%. 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 reduced by 60% independent of the
Note 6: Thermal resistance varies depending upon the amount of PC board
S
2
metal attached to the device. θ is specified for a 2500mm test board
JA
covered with 2oz copper on both sides.
value of V .
S
3
LTC1569-7
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Passband Gain and Group Delay
vs Frequency
Gain vs Frequency
10
1
0
20
V
C
R
= 3V
S
V
= 3V
S
f
= 128kHz 19
f
= 128kHz
C
= 10k
EXT
R
= 10k
EXT
PIN 5 AT V
–
18
17
16
15
14
13
12
11
10
–
PIN 5 AT V
–1
–2
–3
–4
–90
5
10
100
1000
1
10
100
FREQUENCY (kHz)
FREQUENCY (kHz)
1569-7 G03
1569-7 G04
THD vs Input Voltage
THD vs Input Frequency
3V Supply Current
–50
–60
–70
–80
–90
12
11
10
9
–68
–70
–72
–74
–76
–78
V
= 3V
S
PIN 3 = 1.11V
V
= 5V
S
V
= 5V
S
PIN 3 = 2V
PIN 3 = 2V
DIV-BY-1
8
EXT CLK
7
V
= 1.5V
P-P
IN
f
f
= 10kHz
DIV-BY-16
IN
f
= 128kHz
CUTOFF
+
= 128kHz
6
CUTOFF
+
IN TO OUT
R
DIV-BY-4
IN TO OUT
= 10k
EXT
5
R
= 10k
EXT
–
–
PIN 5 AT V
PIN 5 AT V
4
0
1
2
3
4
5
1
10
100
(kHz)
1000
0
10 20 30 40 50 60 70 80 90 100
INPUT FREQUENCY (kHz)
INPUT VOLTAGE (V
)
f
P-P
CUTOFF
1569-7 G05
1569-7 G02
1569-7 G01
5V Supply Current
±
5V Supply Current
35
32
29
26
23
20
17
14
11
8
23
21
DIV-BY-1
DIV-BY-1
19
17
15
13
11
9
EXT CLK
EXT CLK
DIV-BY-16
DIV-BY-16
7
DIV-BY-4
DIV-BY-4
5
5
1
10
100
(kHz)
1000
1
10
100
1000
f
f
(kHz)
CUTOFF
CUTOFF
1569-7 G07
1569-7 G06
4
LTC1569-7
U
U
U
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)is1.0, andtheDCgainfromPin2toPin8is–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.
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
whenDIV/CLKisshortedtoV– (Pin4). Theinternaldivider
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%.
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
usingasingle5V(3V)supply. Forsinglesupplyoperation,
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
DCground. Agroundplaneshouldbeused. Apoorground
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.
When the internal oscillator is disabled (RX 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
faultcurrentinto/outoftheDIV/CLKpinislimitedto40mA.
RX (Pin6):ConnectinganexternalresistorbetweentheRX
pinandV+ (Pin7)enablestheinternaloscillator. Thevalue
oftheresistordeterminesthefrequencyofoscillation. 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 RX 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.
ThemaximumvoltagedifferencebetweenGND(Pin3)and
V+ (Pin 7) should not exceed 5.5V.
W
BLOCK DIAGRA
+
IN
IN
1
2
3
4
8
7
6
5
OUT
10TH ORDER
LINEAR PHASE
FILTER NETWORK
–
+
V
R
EXT
POWER
CONTROL
GND
R
X
DIVIDER/
BUFFER
–
V
DIV/CLK
PRECISION
OSCILLATOR
1569-7 BD
5
LTC1569-7
U
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APPLICATIONS INFORMATION
Self-Clocking Operation
reduced. Thisresultsina60%powersavingswithasingle
5V supply.
The LTC1569-7 features a unique internal oscillator which
sets the filter cutoff frequency using a single external
resistor. The design is optimized for VS = 3V, fCUTOFF
Table1. fCUTOFF vs REXT, VS = 3V, TA = 25°C, Divide-by-1 Mode
R
Typical f
Typical Variation of f
±3.0%
=
EXT
CUTOFF
CUTOFF
128kHz, where the filter cutoff frequency error is typically
<1% when a 0.1% external 10k resistor is used. With
different resistor values and internal divider settings, the
cutoff frequency can be accurately varied from 2kHz to
150kHz/300kHz (single 3V/5V supply). As shown in
Figure 1, the divider is controlled by the DIV/CLK (Pin 5).
Table 1 summarizes the cutoff frequency vs external
resistor values for the divide-by-1 mode.
3844Ω
5010Ω
10k
320kHz
256kHz
128kHz
64kHz
±2.5%
±1%
20.18k
40.2k
±2.0%
32kHz
±3.5%
The power reduction in the divide-by-4 and divide-by-16
modes, however, effects the fundamental oscillator fre-
quency. Hence, the effective divide ratio will be slightly
In the divide-by-4 and divide-by-16 modes, the cutoff
frequencies in Table 1 will be lowered by 4 and 16
respectively. When the LTC1569-7 is in the divide-by-4
and divide-by-16 modes the power is automatically
different from 4:1 or 16:1 depending on VS, TA and REXT
Typically this error is less than 1% (Figures 4 and 6).
.
1.04
R
R
R
R
= 5k
EXT
EXT
EXT
EXT
1.03
1.02
1.01
1.00
0.99
0.98
0.97
0.96
= 10k
= 20k
= 40k
1
2
3
8
7
6
+
–
IN
IN
OUT
+
V
R
LTC1569-7
GND
EXT
R
X
DIVIDE-BY-16
DIVIDE-BY-4
100pF
+
–
V
V
4
5
)
–
V
DIV/CLK
128kHz (10k/R
1, 4 OR 16
EXT
f
=
CUTOFF
DIVIDE-BY-1
2
4
6
8
10
1569-7 F01
V
(V)
SUPPLY
1569-7 F02
Figure 1
Figure 2. Filter Cutoff vs VSUPPLY
,
Divide-by-1 Mode, TA = 25°C
1.010
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
4.08
4.04
4.00
3.96
V
V
V
= 3V
R
R
R
R
= 5k
S
S
S
EXT
EXT
EXT
EXT
= 5V
= 10k
= 20k
= 40k
= 10V
–50
–25
0
25
50
75
100
2
4
6
8
10
TEMPERATURE (°C)
V
(V)
SUPPLY
1569-7 F03
1569-7 F04
Figure 3. Filter Cutoff vs Temperature,
Divide-by-1 Mode, REXT = 10k
Figure 4. Typical Divide Ratio in the
Divide-by-4 Mode, TA = 25°C
6
LTC1569-7
U
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APPLICATIONS INFORMATION
1.010
16.32
16.16
16.00
15.84
V
V
V
= 3V
= 5V
= 10V
R
R
R
R
= 5k
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
S
S
S
EXT
EXT
EXT
EXT
= 10k
= 20k
= 40k
–50
–25
0
25
50
75
100
2
4
6
8
10
TEMPERATURE (°C)
V
(V)
SUPPLY
1569-7 F05
1569-7 F06
Figure 6. Typical Divide Ratio in the
Divide-by-16 Mode, TA = 25°C
Figure 5. Filter Cutoff vs Temperature,
Divide-by-4 Mode, REXT = 10k
1.010
V
V
V
= 3V
= 5V
= 10V
1.008
1.006
1.004
1.002
1.000
0.998
0.996
0.994
0.992
0.990
S
S
S
–50
–25
0
25
50
75
100
TEMPERATURE (°C)
1569-7 F07
Figure 7. Filter Cutoff vs Temperature,
Divide-by-16 Mode, REXT = 10k
The cutoff frequency is easily estimated from the equation
in Figure 1. Examples 1 and 2 illustrate how to use the
graphs in Figures 2 through 7 to get a more precise
estimate of the cutoff frequency.
From Table 1, the part-to-part variation of fCUTOFF will
be ±2%. From the graph in Figure 7, the 0°C to 70°C
drift of fCUTOFF will be –0.2% to 0.2%.
Example 2: LTC1569-7, REXT = 5k, VS = 5V, divide-by-1
Example 1: LTC1569-7, REXT = 20k, VS = 3V, divide-by-16
mode,DIV/CLK(Pin 5)connectedtoV– (Pin4),TA =25°C.
mode,DIV/CLK(Pin 5)connectedtoV+ (Pin7),TA =25°C.
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 128kHz • (10k/5k)
• (1/1) = 256kHz.
Using the equation in Figure 1, the approximate filter
cutoff frequency is fCUTOFF = 128kHz • (10k/20k)
• (1/16) = 4kHz.
For a more precise fCUTOFF estimate, use Table 1 to get
fCUTOFF frequency for REXT = 5k and use Figure 2 to
correct for the supply voltage when VS = 5V. From
Table 1 and Figure 2, fCUTOFF = 256k • (5.01k/5k) •
0.970 = 249kHz.
For a more precise fCUTOFF estimate, use Table 1 to get
a value of fCUTOFF when REXT = 20k and use the graph
in Figure 6 to find the correct divide ratio when VS = 3V
and REXT = 20k. Based on Table 1 and Figure 6, fCUTOFF
= 64kHz • (20.18k/20k) • (1/16.02) = 4.03kHz.
7
LTC1569-7
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APPLICATIONS INFORMATION
The oscillator is sensitive to transients on the positive
supply. The IC should be soldered to the PC board and the
PCB layout should include a 1µF ceramic capacitor be-
tween V+ (Pin 7) and V– (Pin 4) , as close as possible to
theICtominimizeinductance. Avoidparasiticcapacitance
on RX and avoid routing noisy signals near RX (Pin 6). Use
a ground plane connected to V– (Pin 4) for single supply
applications. Connect a ground plane to GND (Pin 3) for
dual supply applications and connect V– (Pin 4) to a
copper trace with low thermal resistance.
input signal at IN+ should be centered around the DC
voltageatIN–. TheinputcanalsobeACcoupled, asshown
in the Typical Applications section.
For inverting single-ended filtering, connect IN+ to GND or
to quiet DC reference voltage. Apply the signal to IN–. The
DCgainfromIN– toOUTis–1,assumingIN– isreferenced
to IN+ and OUT is reference to GND.
Refer to the Typical Performance Characteristics section
to estimate the THD for a given input level.
Dynamic Input Impedance
Input and Output Range
TheuniqueinputsamplingstructureoftheLTC1569-7has
a dynamic input impedance which depends on the con-
figuration, i.e., differential or single-ended, and the clock
frequency. The equivalent circuit in Figure 8 illustrates the
The input signal range includes the full power supply
range. The output voltage range is typically (V– + 50mV)
to (V+ – 0.8V). To maximize the undistorted peak-to-peak
signal swing of the filter, the GND (Pin 3) voltage should
be set to 2V (1.11V) in single 5V (3V) supply applications.
inputimpedancewhenthecutofffrequencyis128kHz. For
other cutoff frequencies replace the 125k value with
125k • (128kHz/fCUTOFF).
The LTC1569-7 can be driven with a single-ended or
differential signal. When driven differentially, the voltage
between IN+ and IN– (Pin 1 and Pin 2) is filtered with a DC
gain of 1. The single-ended output voltage OUT (Pin 8) is
referenced to the voltage of the GND (Pin 3). The common
mode voltage of IN+ and IN– can be any voltage that keeps
the input signals within the power supply range.
For noninverting single-ended applications, connect IN–
to GND or to a quiet DC reference voltage and apply the
input signal to IN+. If the input is DC coupled then the DC
gain from IN+ to OUT will be 1. This is true given IN+ and
OUT are referenced to the same voltage, i.e., GND, V– or
some other DC reference. To achieve the distortion levels
shown in the Typical Performance Characteristics the
When driven with a single-ended signal into IN– with IN+
tied to GND, the input impedance is very high (~10MΩ).
When driven with a single-ended signal into IN+ with IN–
tiedtoGND,theinputimpedanceisa125kresistortoGND.
When driven with a complementary signal whose com-
mon mode voltage is GND, the IN+ input appears to have
125k to GND and the IN– input appears to have –125k to
GND. To make the effective IN– impedance 125k when
driven differentially, place a 62.5k resistor from IN– to
GND. For other cutoff frequencies use 62.5k • (128kHz/
fCUTOFF), asshownintheTypicalApplicationssection. The
typical variation in dynamic input impedance for a given
clock frequency is ±10%.
–
IN
2
+
–
Wideband Noise
+
IN – GND
125k
The wideband noise of the filter is the RMS value of the
device’s output noise spectral density. The wideband
noise data is used to determine the operating signal-to-
noise at a given distortion level. The wideband noise is
nearly independent of the value of the clock frequency and
excludes the clock feedthrough. Most of the wideband
noise is concentrated in the filter passband and cannot be
removed with post filtering (Table 2). Table 3 lists the
typical wideband noise for each supply.
i =
8
OUT
125k
125k
+
1
IN
–
+
3
GND
1569-7 F08
Figure 8
8
LTC1569-7
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APPLICATIONS INFORMATION
Table 2. Wideband Noise vs Supply Voltage, Single 3V Supply
12-bit DC accuracy. Figure 9 illustrates the typical DC
accuracy of the LTC1569-7 on a single 5V supply.
Bandwidth
DC to f
Total Integrated Noise
105µV
125µV
155µV
CUTOFF
RMS
RMS
RMS
488
DC to 2 • f
CUTOFF
DC to f
CLK
244
000
Table 3. Wideband Noise vs Supply Voltage, fCUTOFF = 128kHz
Total Integrated Noise
Power Supply
DC to 2 • f
CUTOFF
3V
125µV
135µV
145µV
RMS
–244
V
= 5V
S
EXT
= 25°C
5V
RMS
R
T
= 10k
±5V
A
RMS
–488
–1.5 –1.0 –0.5
0
0.5
1.0
1.5
V
DC (V)
IN
Clock Feedthrough
1569-7 F09
Figure 9
ClockfeedthroughisdefinedastheRMSvalueoftheclock
frequency and its harmonics that are present at the filter’s
OUT pin (Pin 8). The clock feedthrough is measured with
IN+ and IN– (Pins 1 and 2) grounded and depends on the
PCboardlayoutandthepowersupplydecoupling. Table 4
shows the clock feedthrough (the RMS sum of the first 11
harmonics) when the LTC1569-7 is self-clocked with
REXT =10k, DIV/CLK(Pin5)open(divide-by-4mode). The
clock feedthrough can be reduced with a simple RC post
filter.
DC Offset
The output DC offset of the LTC1569-7 is trimmed to less
than ±5mV. The trimming is performed with VS = 1.9V,
–1.1V with the filter cutoff frequency set to 8kHz (REXT
=
10k, DIV/CLKshortedtoV+). ToobtainoptimumDCoffset
performance, appropriate PC layout techniques should be
used. The filter IC should be soldered to the PC board. The
power supplies should be well decoupled including a 1µF
ceramic capacitor from V+ (Pin 7) to V– (Pin 4). A ground
plane should be used. Noisy signals should be isolated
from the filter input pins.
Table 4. Clock Feedthrough
Power Supply
Feedthrough
3V
0.4mV
0.6mV
0.9mV
RMS
RMS
RMS
When the power supply is 3V, the output DC offset should
not change more than ±2mV when the clock frequency
varies from 64kHz to 8192kHz. When the clock frequency
isfixed,theoutputDCoffsetwilltypicallychangeby±3mV
(±15mV) when the power supply varies from 3V to 5V
(±5V) in the divide-by-1 mode. In the divide-by-4 or
divide-by-16 modes, the output DC offset will typically
change –9mV (–27mV) when the power supply varies
from 3V to 5V (±5V). The offset is measured with respect
to GND (Pin 3).
5V
±5V
DC Accuracy
DC accuracy is defined as the error in the output voltage
after DC offset and DC gain errors are removed. This is
similar to the definition of the integral nonlinearity in A/D
converters.Forexample,aftermeasuringvaluesofVOUT(DC)
vs VIN(DC) for a typical LTC1569-7, a linear regression
shows that VOUT(DC) = VIN(DC) • 0.99854 + 0.00134V is the
straight line that best fits the data. The DC accuracy
describes how much the actual data deviates from this
straightline(i.e.,DCERROR=VOUT(DC) –(VIN(DC) •0.99854
+ 0.00134V). In a 12-bit system with a full-scale value of
2V, the LSB is 488µV. Therefore, if the DCERROR of the
filter is less than 488µV over a 2V range, the filter has
Aliasing
Aliasing is an inherent phenomenon of sampled data
filters. In lowpass filters significant aliasing only occurs
when the frequency of the input signal approaches the
sampling frequency or multiples of the sampling fre-
quency. The LTC1569-7 samples the input signal twice
9
LTC1569-7
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APPLICATIONS INFORMATION
clocked externally, the supply current is reduced by 50%
for supply voltages below 4V. For the divide-by-4 and
divide-by-16 modes, the supply current is reduced by
60% relative to the current when clocked externally,
independent of the power supply voltage. Power supply
current versus cutoff frequency for various operating
modes is shown in the “Typical Performance Characteris-
tics” section.
every clock period. Therefore, the sampling frequency is
twice the clock frequency and 64 times the filter cutoff
frequency. Input signals with frequencies near 2 • fCLK
± fCUTOFF will be aliased to the passband of the filter and
appear at the output unattenuated.
Power Supply Current
Thepowersupplycurrentdependsontheoperatingmode.
When the LTC1569-7 is in the divide-by-1 mode, or when
U
TYPICAL APPLICATIO S
Single 3V, AC Coupled Input,
128kHz Cutoff Frequency
Single 3V Operation, AC Coupled Input,
128kHz Cutoff Frequency
0.1µF
1
2
8
7
+
–
16µs
14µs
12µs
V
IN
IN
OUT
V
IN
OUT
R
= 10k
3V
EXT
+
3V
1µF
V
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
0
20k 40k 60k 80k 100k 120k 140k
LTC1569-7
GND
3.48k
2k
3
4
6
5
R
X
1µF
–
V
DIV/CLK
1569-7 TA02
128kHz
10k
f
=
CUTOFF
(
)(
R
)
n = 1
EXT
n = 1, 4, 16 FOR PIN 5 AT
+
0
80k 100k 120k 140k 160k 180k 200k 220k 240k 260k 280k 300k
FREQUENCY (Hz)
GROUND, OPEN, V
1569-7 TA02a
Single 3V Supply Operation, DC Coupled,
32kHz Cutoff Frequency
Single 5V Operation, 300kHz Cutoff Frequency,
DC Coupled Differential Inputs with Balanced Input Impedance
1
2
8
7
+
–
1
2
8
7
+
–
+
–
V
V
V
IN
IN
OUT
V
IN
IN
IN
OUT
V
IN
IN
OUT
R
OUT
R
= 10k
3V
= 4.1k
5V
IN
EXT
EXT
+
+
3V
V
5V
1µF
V
1µF
LTC1569-7
GND
3.48k
LTC1569-7
GND
27k
LT®1460-2.5
(SOT-23)
3
4
6
5
3
4
6
5
R
R
OUT
GND
X
X
1µF
1µF
2k
–
–
V
DIV/CLK
V
DIV/CLK
1569-7 TA03
100pF
128kHz
10k
128kHz
10k
1569-7 TA04
f
=
f
~
CUTOFF
CUTOFF
(
)(
R
)
(
)(
)
n = 4
n = 1
4.1k
EXT
n = 1, 4, 16 FOR PIN 5 AT
n = 1, 4, 16 FOR PIN 5 AT
+
+
GROUND, OPEN, V
GROUND, OPEN, V
10
LTC1569-7
U
TYPICAL APPLICATION
Dual 5V Supply Operation,
DC Coupled Filter with External Clock Source
Single 5V Supply Operation, DC Coupled Input,
128kHz Cutoff Frequency
1
2
8
7
+
–
1
2
8
7
V
+
–
IN
IN
OUT
V
OUT
CUTOFF CLK
IN
V
IN
IN
OUT
V
IN
OUT
R
f
= f /32
= 10k
5V
EXT
+
+
5V
V
5V
1µF
V
0.1µF
LTC1569-7
GND
LTC1569-7
GND
2.49k
1.65k
3
4
6
5
3
4
6
5
R
X
R
X
0.1µF
1µF
–
5V
0V
–
V
DIV/CLK
–5V
V
DIV/CLK
1569-7 TA06
f
≤ 10MHz
CLK
1569-7 TA05
128kHz
10k
f
=
CUTOFF
(
)(
)
n = 1
R
EXT
1µF
n = 1, 4, 16 FOR PIN 5 AT
+
GROUND, OPEN, V
U
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.053 – 0.069
3
4
2
0.010 – 0.020
(0.254 – 0.508)
× 45°
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
SO8 0996
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LTC1569-7
U
TYPICAL APPLICATIO S
Pulse Shaping Circuit for Single 3V Operation, 300kbps
2 level data, 150kHz Cutoff Filter
Pulse Shaping Circuit for Single 3V Operation, 400kbps
(200ksps) 4 Level Data, 128kHz Cutoff Filter
+3V
+3V
200ksps
DATA
20k
20k
4.99k
4.99k
10k
D
D
1
1
2
8
7
1
2
8
7
+
–
+
–
IN
IN
OUT
V
IN
IN
OUT
V
OUT
OUT
R
= 8.56k
R
= 8.56k
+3V
+3V
3.48k
EXT
EXT
20k
+
+
+3V
+3V
V
V
0
300kbps
DATA
1µF
1µF
3.48k
LTC1569-7
GND
LTC1569-7
GND
3
6
5
3
6
5
R
X
R
X
1µF
4
1µF
4
2k
2k
20k
–
–
V
DIV/CLK
V
DIV/CLK
1569-7 TA09
1569-7 TA10
4-Level, 400kbps (200ksps)
Eye Diagram
2-Level, 300kbps Eye Diagram
1µs/DIV
1µs/DIV
1569-7 TA07
1569-7 TA08
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1064-3
Linear Phase, Bessel 8th Order Filter
Linear Phase, 8th Order Lowpass Filter
Universal, 8th Order Filter
f
f
f
f
f
f
/f
= 75/1 or 150/1, Very Low Noise
CLK CUTOFF
LTC1064-7
/f
= 50/1 or 100/1, f
= 100kHz
CUTOFF(MAX)
CLK CUTOFF
LTC1068-x
/f
= 25/1, 50/1, 100/1 or 200/1, f
= 200kHz
CUTOFF(MAX)
CLK CUTOFF
LTC1069-7
Linear Phase, 8th Order Lowpass Filter
/f
= 25/1, f
= 200kHz, SO-8
CUTOFF(MAX)
CLK CUTOFF
LTC1164-7
Low Power, Linear Phase Lowpass Filter
Linear Phase, 8th Order Lowpass Filter
Universal, 8th Order Active RC Filter
/f
= 50/1 or 100/1, I = 2.5mA, V = 5V
CLK CUTOFF
S
S
LTC1264-7
/f
= 25/1 or 50/1, f
= 200kHz
CLK CUTOFF
CUTOFF(MAX)
LTC1562/LTC1562-2
f
f
= 150kHz (LTC1562)
= 300kHz (LTC1562-2)
CUTOFF(MAX)
CUTOFF(MAX)
15697f LT/TP 0300 4K • PRINTED IN THE USA
LINEAR TECHNOLOGY CORPORATION 1998
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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