LTC1565-31
650kHz Continuous Time,
Linear Phase Lowpass Filter
FEATURES
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DESCRIPTION
The LTC
®
1565-31 is a 7th order, continuous time, linear
phase lowpass filter. The selectivity of the LTC1565-31,
combined with its linear phase and dynamic range, make
it suitable for filtering in data communications or data
acquisition systems. The filter attenuation is 36dB at
2× f
CUTOFF
and at least 72dB for frequencies above 3×
f
CUTOFF
. Unlike comparable LC filters, the LTC1565-31
achieves this selectivity with a linear phase response in
the passband.
With 5% accuracy of the cutoff frequency, the LTC1565-31
can be used in applications requiring pairs of matched
filters, such as transceiver I and Q channels. Furthermore,
the differential inputs and outputs provide a simple inter-
face for these wireless systems.
With a single 5V supply and a 2V
P-P
input, the LTC1565-31
features an impressive spurious free dynamic range of
75dB. The maximum signal-to-noise ratio is 78dB and it
is achieved with a 2.5V
P-P
input signal.
The LTC1565-31 features a shutdown mode where power
supply current is typically less than 10μA.
For W-CDMA, 3G, CDMA 2000 and other cellular and
noncellular cutoff frequencies or single-ended I/O, please
contact LTC Marketing for additional information.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
7th Order, 650kHz Linear Phase Filter in an SO-8
Differential Inputs and Outputs
Operates on a Single 5V or a ±5V Supply
Low Offset: 5mV Typical
75dB THD and SNR
78dB SNR
Shutdown Mode
Requires No External Components
Requires No External Clock Signal
APPLICATIONS
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CDMA Basestations
Data Communications
Antialiasing Filters
Smoothing or Reconstruction Filters
Matched Filter Pairs
Replacement for LC Filters
TYPICAL APPLICATION
Single 5V Supply, Differential 650kHz Lowpass Filter
V
IN+
V
IN–
1
2
+IN
–IN
+OUT
–OUT
8
7
V
OUT+
V
OUT–
GAIN (dB)
Frequency Response
10
0
–10
–20
–30
–40
–50
–60
–70
15645-31 TA01
2.0
GAIN
1.9
1.8
1.7
1.6
DELAY
1.5
1.4
1.3
1.2
1.1
1.0
10
5
10
6
FREQUENCY (Hz)
0.9
10
7
1565 G01
DELAY (μs)
LTC1565-31
3
0.1μF
4
GND
V
–
6
V
+
5
SHDN
5V
0.1μF
5V
–80
–90
–100
10
4
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LTC1565-31
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
+IN 1
–IN 2
GND 3
V
–
4
8
7
6
5
+OUT
–OUT
V
+
SHDN
Total Supply Voltage ............................................... 11V
Power Dissipation .............................................. 500mW
Operating Temperature Range
LTC1565-31CS8 ...................................... 0°C to 70°C
LTC1565-31IS8 ................................... – 40°C to 85°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) ................ 300°C
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 80°C/ W (NOTE 4)
ORDER INFORMATION
LEAD FREE FINISH
LTC1565-31CS8#PBF
LTC1565-31IS8#PBF
TAPE AND REEL
LTC1565-31CS8#TRPBF
LTC1565-31IS8#TRPBF
PART MARKING
156531
56531I
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
PARAMETER
Operating Supply Voltage
Filter Gain
CONDITIONS
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
S
= 5V, R
LOAD
= 10k from each output to AC ground, and Pin 5 open
unless otherwise specified.
MIN
4.75
V
IN
= 1V
P-P
, f
IN
= 25kHz
f
IN
= 200kHz (Gain Relative to 25kHz)
f
IN
= 300kHz (Gain Relative to 25kHz)
f
IN
= 500kHz (Gain Relative to 25kHz)
f
IN
= 650kHz (Gain Relative to 25kHz)
f
IN
= 900kHz (Gain Relative to 25kHz)
f
IN
= 1.3MHz (Gain Relative to 25kHz)
f
IN
= 2.3MHz (Gain Relative to 25kHz)
V
IN
= 1V
P-P
, f
IN
= 25kHz
f
IN
= 200kHz
f
IN
= 300kHz
f
IN
= 500kHz
f
IN
= 600kHz
f
IN
= 650kHz
f
IN
= 900kHz
Ratio of 600kHz Phase/300kHz Phase
Noise BW = DC to 2 • f
CUTOFF
f
IN
= 100kHz, 1V
P-P
(Note 2)
Maximum Difference Between Pins 7 and 8
V
S
= 5V
V
S
= ±5V
l
l
l
l
l
l
l
l
l
TYP
0
0
–0.4
–1.6
–3
–11
–36
–72
–13
–101
–150
113
60
36
–92
2
118
86
MAX
11
0.3
0.1
–0.1
–0.95
–2
–7
–31
UNITS
V
dB
dB
dB
dB
dB
dB
dB
dB
Deg
Deg
Deg
Deg
Deg
Deg
Deg
μV
RMS
dB
V
V
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–0.3
–0.2
–0.7
–2.2
–4
Filter Phase
l
l
–162
34
–138
85
Phase Linearity
Wideband Noise
THD
Filter Differential DC Swing
l
1.95
2.03
±1.4
±2.2
±1.7
±2.3
2
LTC1565-31
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Bias Current
Input Offset Current
Input Resistance
Input Capacitance
Output DC Offset (Note 3)
Output DC Offset Drift
Ground Voltage (Pin 3) in
Single Supply Applications
SHDN
Pin Logic Thresholds
V
S
= 5V
V
S
= ±5V (Note 5)
V
S
= 5V
V
S
= ±5V
V
S
= 5V
V
S
= 5V, Minimum Logical “1”
V
S
= 5V, Maximum Logical “0”
V
S
= ±5V, Minimum Logical “1”
V
S
= ±5V, Maximum Logical “0”
SHDN
Pin Pull-Up Current
Power Supply Current
Power Supply Current in Shutdown Mode
V
S
= 5V
V
S
= ±5V
V
S
= 5V
V
S
= ±5V
Shutdown. Includes
SHDN
Pull-Up Current
V
S
= 5V
V
S
= ±5V
l
l
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
S
= 5V, R
LOAD
= 10k from each output to AC ground, and Pin 5 open
unless otherwise specified.
CONDITIONS
MIN
0.1
Common Mode, V
IN
= 2.5V
Differential
TYP
0.3
±10
75
145
3
±5
±5
–400
–400
2.49
2.51
2.52
4.2
3.3
2.9
2.4
5
9
24
25
8
20
31
33
16
40
±12
±12
MAX
0.6
UNITS
μA
nA
MΩ
MΩ
pF
mV
mV
μV/°C
μV/°C
V
V
V
V
V
μA
μA
mA
mA
μA
μA
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
Input and output voltages expressed as peak-to-peak numbers are
assumed to be fully differential.
Note 3:
Output DC offset is measured between Pin 8 and Pin 7 with Pin 1
and Pin 2 connected to Pin 3.
Note 4:
Thermal resistance varies depending upon the amount of PC board
metal attached to the device.
θ
JA
is specified for a 3.8 square inch test
board covered with 2 oz copper on both sides.
Note 5:
Output DC offset measurements are performed by automatic test
equipment approximately 0.5 seconds after application of power.
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
10
0
–10
–20
GAIN (dB)
Passband Gain and Delay
vs Frequency
2.0
0.5
0
–0.5
–1.0
GAIN
1.9
1.8
1.7
1.5
1.4
1.3
1.2
1.1
1.0
0.9
10
7
1565 G01
GAIN
5V
±5V
2.0
1.9
1.8
1.7
–40
–50
–60
–70
–80
–90
–100
10
4
DELAY
GAIN (dB)
–30
1.6
DELAY (μs)
DELAY (μs)
–1.5
–2.0
–2.5
–3.0
–3.5
–4.0
T
A
= 25°C
100k
FREQUENCY (Hz)
DELAY
1.6
1.5
1.4
1.3
1.2
1.1
1.0
1M
1565 G02
10
5
10
6
FREQUENCY (Hz)
–4.5
25k
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LTC1565-31
TYPICAL PERFORMANCE CHARACTERISTICS
Passband Gain vs Frequency
Over Temperature
0.5
0.4
0.3
0.2
GAIN (dB)
Stopband Gain vs Frequency
–40
–40
Stopband Gain vs Frequency
Over Temperature
V
S
= 5V
V
S
= 5V
–50
–40°C
–50
–40°C
25°C
85°C
GAIN (dB)
0
–0.1
–0.2
–0.3
–0.4
–0.5
25k
85°C
25°C
–70
V
S
= 5V
GAIN (dB)
0.1
–60
–60
–70
–80
V
S
= ±5V
–80
100k
FREQUENCY (Hz)
400k
1565 G03
–90
1.5
1.8
2.4
2.1
FREQUENCY (MHz)
2.7
3.0
1565 G04
–90
1.5
1.8
2.4
2.1
FREQUENCY (MHz)
2.7
3.0
1565 G05
Common Mode Rejection Ratio
110
V
IN
= 1V
P-P
V
S
= 5V
100 T
A
= 25°C
90
80
Power Supply Rejection Ratio
V
IN
= 200mV
P-P
V
S
= 5V
T
A
= 25°C
SUPPLY CURRENT (mA)
Supply Current vs Temperature
26
70
25
V
S
= ±5V
CMRR (dB)
80
70
60
50
10
3
PSRR (dB)
60
50
V
S
= 5V
24
40
10
4
10
5
10
6
FREQUENCY (Hz)
10
7
1565 G06
30
10
3
10
4
10
5
10
6
FREQUENCY (Hz)
10
7
1565 G07
23
–50 –30
30
50
–10 10
TEMPERATURE (°C)
70
90
1565 G08
PIN FUNCTIONS
+IN, –IN (Pins 1, 2):
Input Pins. Signals can be applied
to either or both input pins. The typical DC gain from dif-
ferential inputs (Pin 1 to Pin 2) to the differential outputs
(Pin 8 to Pin 7) is 1.0V/V. The input range is described in
the Applications Information section.
GND (Pin 3):
Ground. The ground pin is the reference
voltage for the filter and is internally biased to one-half
the total power supply voltage of the filter, maximizing the
dynamic range of the filter. For single supply operation,
the ground pin should be bypassed with a quality 0.1μF
ceramic capacitor to Pin 4. For dual supply operation,
connect Pin 3 to a high quality DC ground. A ground
plane should be used. A poor ground will increase noise
and distortion.
The impedance seen at Pin 3 is 2.5kΩ in normal mode. In
shutdown, the pin is internally biased to the same levels
as normal mode. The impedance in shutdown mode
is typically 500kΩ but varies with supply voltage and
temperature.
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LTC1565-31
PIN FUNCTIONS
V
–
, V
+
(Pins 4, 6):
Power Supply Pins. For a single 5V
supply (Pin 4 grounded), a quality 0.1μF ceramic bypass
capacitor is required from the positive supply pin (Pin 6)
to the negative supply pin (Pin 4). The bypass should be
as close as possible to the IC. For dual supply applications
(Pin 3 is grounded), bypass Pin 6 to Pin 3 and Pin 4 to
Pin 3 with a quality 0.1μF ceramic capacitor.
The maximum voltage difference between the ground
pin (Pin 3) and the positive supply pin (Pin 6) should not
exceed 5.5V.
SHDN
(Pin 5):
Shutdown. When the Pin 5 voltage is low,
the LTC1565-31 goes into the current saving shutdown
mode. Pin 5 has a 4μA pull-up current. Leaving Pin 5 open
will place the LTC1565-31 in its normal operating mode.
– OUT, +OUT (Pins 7, 8):
Output Pins. Pins 7 and 8 are the
filter differential output. Each pin can drive 1kΩ or 300pF
loads. The common mode voltage at the output pins is
the same as the voltage at Pin 3.
BLOCK DIAGRAM
+IN 1
+
8 +OUT
–
+
R
7th ORDER
LINEAR
PHASE
FILTER
NETWORK
OUTPUT
BUFFER
R
–
–IN 2
–
INPUT BUFFERS
WITH COMMON MODE
TRANSLATION CIRCUIT
OUTPUT
BUFFER
7 –OUT
+
V
+
~1M
SHUTDOWN
SWITCH
5k
GND 3
5k
~1M
SHUTDOWN
SWITCH
V
+
V
–
4μA
SHUTDOWN
5
SHDN
6 V
+
V
–
4
1565-31 BD
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