Page 1
LTC1565-31
Final Electrical Specifications
650kHz Continuous Time,
Linear Phase Lowpass Filter
FEATURES
■
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
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APPLICATIO S
■
CDMA Base Stations
■
Data Communications
■
Antialiasing Filters
■
Smoothing or Reconstruction Filters
■
Matched Filter Pairs
■
Replacement for LC Filters
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March 2000
DESCRIPTIO
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 37dB at 2× f
and at least 72dB for frequencies above 3× f
CUTOFF
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 interface for
these wireless systems.
With a single 5V supply and a 2V
input, the LTC1565-31
P-P
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
input signal.
P-P
The LTC1565-31 features a shutdown mode where power
supply current is reduced to less than 10µA.
CUTOFF
. Unlike
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TYPICAL APPLICATIO
Single 5V Supply, Differential 650kHz Lowpass Filter
0.1µF
1
+
V
IN
V
IN
+IN
2
–
–IN
LTC1565-31
3
GND
4
–
V
+OUT
–OUT
SHDN
8
7
6
+
V
5
V
OUT
V
OUT
5V
+
–
15645-31 TA01
0.1µF
Other cutoff frequencies and single-ended I/O can be provided upon request. Please contact LTC Marketing.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Frequency Response
20
0
–20
5V
–40
–60
ATTENUATION (dB)
–80
–100
4
10
GAIN
GROUP DELAY
5
10
FREQUENCY (Hz)
6
10
1565-31 TA02
2.0
1.8
1.6
DELAY (µs)
1.4
1.2
1.0
0.8
7
10
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
Page 2
LTC1565-31
1
2
3
4
8
7
6
5
TOP VIEW
+OUT
–OUT
V
+
SHDN
+IN
–IN
GND
V
–
S8 PACKAGE
8-LEAD PLASTIC SO
WW
W
ABSOLUTE MAXIMUM RATINGS
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U
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PACKAGE/ORDER INFORMATION
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(Note 1)
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
ORDER PART
NUMBER
LTC1565-31CS8
LTC1565-31IS8
S8 PART MARKING
Lead Temperature (Soldering, 10 sec)................. 300°C
T
= 150°C, θJA = 80°C/W (NOTE 5)
JMAX
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VS = 5V (V+ = 5V, V– = 0V), R
The ● denotes the specifications which apply over the full operating
= 10k from each output to AC ground,
LOAD
and Pin 5 open unless otherwise specified.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Operating Supply Voltage 4.75 11 V
Filter Gain VIN = 1V
f
f
f
f
f
f
f
Filter Phase VIN = 1V
f
f
f
f
f
f
Phase Linearity Ratio of 600kHz Phase/300kHz Phase ● 1.97 2 2.03
Wideband Noise Noise BW = DC to 2 • f
THD fIN = 100kHz, 1V
Filter Differential DC Swing Maximum Difference Between Pins 7 and 8
V
VS = ±5V ● ±2.2 ±2.3 ±2.5 V
Filter DC Common Mode Range (Note 4) Upper V+ – 1.5 V
Lower V
Input Bias Current 0.1 0.3 0.6 µA
Input Offset Current 25 nA
Input Resistance Common Mode, VIN = 1.5V to 3.5V >50 MΩ
Differential >50 MΩ
Input Capacitance 2pF
Output DC Offset (Note 3) VS = 5V ±5 ±12 mV
2
V
S
, fIN = 25kHz ● –0.3 0 0.3 dB
P-P
= 200kHz (Gain Relative to 25kHz) ● –0.2 0 0.1 dB
IN
= 300kHz (Gain Relative to 25kHz) ● –0.7 –0.4 –0.1 dB
IN
= 500kHz (Gain Relative to 25kHz) ● –2.2 –1.6 –1.0 dB
IN
= 650kHz (Gain Relative to 25kHz) ● –4 –3 –2 dB
IN
= 900kHz (Gain Relative to 25kHz) ● –11 –7 dB
IN
= 1.3MHz (Gain Relative to 25kHz) ● –36 –31 dB
IN
= 2.3MHz (Gain Relative to 25kHz) –72 dB
IN
, fIN = 25kHz –13 Deg
P-P
= 200kHz –101 Deg
IN
= 300kHz ● –162 –150 –138 Deg
IN
= 500kHz 113 Deg
IN
= 600kHz ● 34 60 85 Deg
IN
= 650kHz 36 Deg
IN
= 900kHz –92 Deg
IN
CUTOFF
(Note 2) 85 dB
P-P
= 5V ● ±1.4 ±1.7 ±1.9 V
S
–
= ±5V (Note 6) ±5 ±12 mV
156531
56531I
115 µV
+ 0.8 V
RMS
P
P
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LTC1565-31
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VS = 5V (V+ = 5V, V– = 0V), R
and Pin 5 open unless otherwise specified.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output DC Offset Drift VS = 5V –400 µV/°C
= ±5V –400 µV/°C
V
S
Ground Voltage (Pin 3) in VS = 5V ● 2.49 2.51 2.52 V
Single Supply Applications
SHDN Pin Logic Thresholds VS = 5V, Minimum Logical “1” 4.2 V
V
= 5V, Maximum Logical “0” 3.3 V
S
VS = ±5V, Minimum Logical “1” 2.75 V
= ±5V, Maximum Logical “0” 2.50 V
V
S
SHDN Pin Pull-Up Current VS = 5V 5 µA
= ±5V 9 µA
V
S
Power Supply Current VS = 5V ● 24 31 mA
= ±5V ● 25 33 mA
V
S
Power Supply Current in Shutdown Mode Shutdown. Includes SHDN Pull-Up Current
V
= 5V ● 4816 µA
S
= ±5V ● 10 20 40 µA
V
S
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
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: A 250mV
The DC voltages at Pins 1 and 2 are equal. This is the “common mode
, 100kHz differential signal is applied to Pins 1 and 2.
P-P
The ● denotes the specifications which apply over the full operating
= 10k from each output to AC ground,
LOAD
voltage.” The “common mode range” is the range of common mode
voltages for which the 250mV
2nd or 3rd harmonic distortion.
Note 5: Thermal resistance varies depending upon the amount of PC board
metal attached to the device. θ
board covered with 2 oz copper on both sides.
Note 6: Output DC offset measurements are performed by automatic test
equipment approximately 0.5 seconds after application of power.
differential output has better than 65dB
P-P
is specified for a 3.8 square inch test
JA
UUU
PIN FUNCTIONS
+IN, –IN (Pins 1, 2): Input Pins. Signals can be applied to
either or both input pins. The DC gain from differential
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.
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.
3
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LTC1565-31
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PIN FUNCTIONS
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.
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BLOCK DIAGRA
+IN
–IN
1
2
+
–
+
–
–
+
+
V
INPUT BUFFERS
WITH COMMON MODE
TRANSLATION CIRCUIT
– 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.
+OUT
8
R
R
7th ORDER
LINEAR
PHASE
FILTER
NETWORK
OUTPUT
BUFFER
OUTPUT
BUFFER
–OUT
7
SHUTDOWN
~1M
SWITCH
5k
GND
3 6
5k
SHUTDOWN
~1M
SWITCH
–
V
–
4 5
V
SHUTDOWN SHDN
+
V
+
V
4µA
1565-31 BD
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LTC1565-31
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APPLICATIONS INFORMATION
Interfacing to the LTC1565-31
The difference between the voltages at Pin 1 and Pin 2 is
the “differential input voltage.” The average of the voltages
at Pin 1 and Pin 2 is the “common mode input voltage.”
The difference between the voltages at Pin 7 and Pin 8 is
the “differential output voltage.” The average of the voltages at Pin 7 and Pin 8 is the “common mode output
voltage.” The input and output common mode voltages
are independent. The input common mode voltage is set
by the signal source, if DC coupled, or by the biasing
network if AC coupled (Figures 1 and 2). The output
common mode voltage is equal to the voltage of Pin 3, the
GND pin. The GND pin is biased to one-half of the supply
voltage by an internal resistive divider (see Block Diagram). To alter the common mode output voltage, Pin 3
can be driven with an external voltage source or resistor
network. If external resistors are used, it is important to
note that the internal 5k resistors can vary ±20% (their
ratio only varies ±2%). The output can also be AC coupled.
+
+
V
IN
–
DC COUPLED INPUT
V
IN
V
OUT
–
+
V
IN
–
0.1µF
(COMMON MODE) =
(COMMON MODE) = =
1
+IN
2
–IN
3
GND
4
V
LTC1565-31
–
+
V
+ V
IN
V
OUT
2
+OUT
–OUT
SHDN
IN
+
+ V
2
8
7
6
+
V
5
–
–
OUT
+
V
OUT
–
V
OUT
5V
0.1µF
15645-31 F01
+
V
2
Input Common Mode and Differential Voltage Range
The range of voltage each input can support while operating in its linear region is typically 0.8V to 3.5V for a single
5V supply and –4.2V to 3.2V for a ±5V supply. Therefore,
the filter can accept a variety of common mode input
voltages. Figures 3 and 4 show the THD of the filter versus
common mode input voltage with a 2V
differential input
P-P
signal.
–30
–40
–50
–60
THD (dB)
–70
VIN = 2V
–80
–90
Figure 3. THD vs Common Mode Input Voltage
–30
–40
–50
THD (dB)
–60
P-P
VS = ±5V
= 100kHz
f
IN
–3 –1 1 3
INPUT COMMON MODE VOLTAGE (V)
5–4–5 –2 0 2 4
1565-31 F03
Figure 1
0.1µF
+
+
V
IN
–
–
+
V
IN
0.1µF
–
1µF
AC COUPLED INPUT
V
(COMMON MODE) = V
IN
Figure 2
1
+IN
2
–IN
100k100k
3
GND
4
V
LTC1565-31
–
+OUT
–OUT
SHDN
8
7
6
+
V
5
5V
V
OUT
V
OUT
+
–
0.1µF
15645-31 F02
Figure 5 shows the THD and S/N ratio versus differential
input voltage level for both a single 5V supply and a ±5V
supply. The common mode voltage of the input signal is
(COMMON MODE)
OUT
+
V
=
2
one-half the total power supply voltage of the filter. The
spurious free dynamic range, where the THD and S/N ratio
are equal, is 75dB to 77dB when the differential input
voltage level is 2V
–70
VIN = 2V
P-P
VS = ±5V
= 100kHz
f
IN
–80
0.5
1.0
1.5
INPUT COMMON MODE VOLTAGE (V)
2.0 2.5
3.0
1565-31 F04
3.5
Figure 4. THD vs Common Mode Input Voltage
; that is, for a single 5V supply, the
P-P
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LTC1565-31
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APPLICATIONS INFORMATION
–30
–40
–50
–60
THD, SNR (dB)
–70
–80
–90
Figure 5. Dynamic Range Diff-In, Diff-Out
input voltages are Pin 1 = 2.5V DC ±0.5V and Pin 2 = 2.5V
DC ±0.5V. Also note Figure 5 shows a 78dB SNR ratio for
higher THD levels.
As seen in Figures 3 and 4, the spurious free dynamic
range can be optimized by setting the input common mode
voltage slightly below one-half of the power supply voltage, i.e., 2V for a single 5V supply and –0.5V to – 1V for a
±5V supply. Figure 6 shows the THD and SNR ratio versus
differential input voltage level for both a single 5V supply
and a ±5V supply when the common mode input voltage
is 2V and –0.5V respectively.
For best performance, the inputs should be driven differentially. For single-ended signals, connect the unused
input to Pin 3 or a common mode reference.
–40
–50
–60
–70
THD, SNR (dB)
–80
–90
Figure 6. THD vs VIN for a Common Mode
Input Voltage 0.5V Below Mid Supply
THD: VS = 5V
= ±5V
THD: V
S
SNR
fIN = 100kHz
0.5
fIN = 100kHz
0.5
1.5 2.0 2.5
1.0
DIFFERENTIAL INPUT (
THD: VS = 5V
= ±5V
THD: V
S
SNR
1.5 2.0 2.5
1.0
DIFFERENTIAL INPUT VOLTAGE (V
P-P
3.0 3.5
)
1565-31 F05
3.0 3.5
P-P
1565-31 F06
)
Output Common Mode and Differential Voltage Range
The output is a fully differential signal with a common mode
level equal to the voltage at Pin 3. The specifications in the
Electrical Characteristics table assume the inputs are driven
differentially and the output is observed differentially.
However, Pin 8 can be used as a single-ended output by
simply floating Pin 7. Pin 7 can be used as an inverting
single-ended output by floating Pin 8. Using Pins 7 or 8 as
single-ended outputs will decrease the performance.
The common mode output voltage can be adjusted by
overdriving the voltage present on Pin 3. The best performance is achieved using a common mode output voltage
that is equal to mid supply (the default Pin 3 voltage). Figures 7 and 8 illustrate the THD versus output common mode
voltage for a 2V
differential input voltage and a common
P-P
mode input voltage that is 0.5V below mid supply.
0
VIN = 2V
V
–10
V
–20
–30
–40
THD (dB)
–50
–60
–70
–80
1.5
Figure 7. THD vs Common Mode Output Voltage
0
–10
–20
–30
–40
–50
THD (dB)
–60
–70
–80
–90
–4
Figure 8. THD vs Common Mode Output Voltage
100kHz
P-P
= 5V
S
= 2V
IN(CM)
2.0 2.5 3.5
COMMON MODE OUTPUT VOLTAGE (V)
VIN = 2V
P-P
= ±5V
V
S
= –0.5V
V
IN(CM)
–2 0 2
COMMON MODE OUTPUT VOLTAGE (V)
3.0
100kHz
4.0
1565-31 F07
4
1565-31 F08
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LTC1565-31
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APPLICATIONS INFORMATION
Output Drive
Pin 7 and Pin 8 can drive a 1kΩ or 300pF load connected
to AC ground with a ±0.5V signal (corresponding to a
2V
differential signal). For differential loads (loads
P-P
connected from Pin 7 to Pin 8) the outputs can produce
a 2V
smaller signal amplitudes the outputs can drive correspondingly larger loads.
Noise
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-tonoise at a given distortion level. Most of the noise is
concentrated in the filter passband and cannot be removed
with post filtering (Table 1). Table 2 lists the typical change
in wideband noise with supply voltage.
differential signal across 2kΩ or 150pF. For
P-P
Table 1. Wideband Noise vs Bandwidth, Single 5V Supply
BANDWIDTH TOTAL INTEGRATED NOISE
DC to f
CUTOFF
DC to 2 • f
CUTOFF
Table 2. Wideband Noise vs Supply Voltage, f
POWER SUPPLY DC TO 2 • f
5V 115µV
±5V 117µV
110µV
RMS
115µV
RMS
= 650kHz
CUTOFF
TOTAL INTEGRATED NOISE
CUTOFF
RMS
RMS
DC Offset
The output DC offset of the LTC1565-31 is trimmed to less
than ±5mV. The trimming is done with VS = ±2.5V. The
output DC offset will typically change by ±1mV when the
power supply varies from 5V to ±5V.
PACKAGE DESCRIPTION
0.010 – 0.020
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.016 – 0.050
(0.406 – 1.270)
*
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
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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)
× 45°
0°– 8° TYP
0.228 – 0.244
(5.791 – 6.197)
0.053 – 0.069
(1.346 – 1.752)
0.014 – 0.019
(0.355 – 0.483)
TYP
7
8
1
2
5
6
0.150 – 0.157**
(3.810 – 3.988)
3
4
0.050
(1.270)
BSC
0.004 – 0.010
(0.101 – 0.254)
SO8 1298
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Page 8
LTC1565-31
TYPICAL APPLICATIO
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Narrowband Cellular Base Station Receiver
RELATED PARTS
RF/IF
SECTION
90°
0°
90°
LTC1565-31
LPF
LO
LTC1565-31
LPF
ADC
ADC
1565-31 TA03
I
DSP
Q
PART NUMBER DESCRIPTION COMMENTS
LTC1560-1 1MHz/500kHz Continuous Time, Low Noise, Lowpass Elliptic Filter f
LTC1562/LTC1562-2 Universal 8th Order Active RC Filters f
LTC1563-2/LTC1563-3 4th Order Active RC Lowpass Filters f
LTC1569-6/LTC1569-7 Self Clocked, 10th Order Linear Phase Lowpass Filters f
= 500kHz or 1MHz
CUTOFF
CUTOFF(MAX)
f
CUTOFF(MAX)
CUTOFF(MAX)
CLK/fCUTOFF
f
CLK/fCUTOFF
Linear Technology Corporation
8
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
= 150kHz (LTC1562),
= 300kHz (LTC1562-2)
= 256kHz
= 64/1, f
= 32/1, f
CUTOFF(MAX)
CUTOFF(MAX)
156531i LT/TP 0300 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2000
= 75kHz (LTC1569-6)
= 300kHz (LTC1569-7)
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