Final Electrical Specifications
LTC1565-31
650kHz Continuous Time,
Linear Phase Lowpass Filter
March 2000
FEATURES
s
s
s
s
s
s
s
s
s
DESCRIPTIO
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
APPLICATIO S
s
s
s
s
s
s
CDMA Base Stations
Data Communications
Antialiasing Filters
Smoothing or Reconstruction Filters
Matched Filter Pairs
Replacement for LC Filters
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 acqui-
sition systems. The filter attenuation is 37dB at 2× f
CUTOFF
and at least 72dB for frequencies above 3× f
CUTOFF
. Unlike
comparable LC filters, the LTC1565-31 achieves this selec-
tivity 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
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 reduced to less than 10µA.
Other cutoff frequencies and single-ended I/O can be pro-
vided upon request. Please contact LTC Marketing.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
Frequency Response
20
2.0
GAIN
1.8
1.6
Single 5V Supply, Differential 650kHz Lowpass Filter
ATTENUATION (dB)
V
IN+
V
IN–
1
2
+IN
–IN
+OUT
–OUT
8
7
V
OUT+
V
OUT–
5V
6
5
5V
0.1µF
0
–20
GROUP DELAY
–40
–60
–80
1.4
1.2
1.0
0.8
10
7
1565-31 TA02
LTC1565-31
3
0.1µF
4
GND
V
–
V
+
SHDN
15645-31 TA01
–100
10
4
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
DELAY (µs)
10
5
10
6
FREQUENCY (Hz)
U
U
1
LTC1565-31
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
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
ORDER PART
NUMBER
LTC1565-31CS8
LTC1565-31IS8
S8 PART MARKING
156531
56531I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 80°C/ W (NOTE 5)
Consult factory for Military grade parts.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
S
= 5V (V
+
= 5V, V
–
= 0V), R
LOAD
= 10k from each output to AC ground,
and Pin 5 open unless otherwise specified.
PARAMETER
Operating Supply Voltage
Filter Gain
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
Upper
Lower
0.1
Common Mode, V
IN
= 1.5V to 3.5V
Differential
V
S
= 5V
V
S
=
±5V
(Note 6)
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
4.75
– 0.3
– 0.2
– 0.7
– 2.2
–4
TYP
0
0
–0.4
–1.6
–3
–11
–36
–72
–13
–101
–150
113
60
36
– 92
2
115
85
MAX
11
0.3
0.1
– 0.1
– 1.0
–2
–7
– 31
UNITS
V
dB
dB
dB
dB
dB
dB
dB
dB
Deg
Deg
Deg
Deg
Deg
Deg
Deg
µV
RMS
dB
Filter Phase
q
q
– 162
34
– 138
85
Phase Linearity
Wideband Noise
THD
Filter Differential DC Swing
q
1.97
2.03
±1.4
±2.2
±1.7
±2.3
V
+
– 1.5
V
–
+ 0.8
0.3
25
>50
>50
2
±5
±5
±1.9
±2.5
Filter DC Common Mode Range (Note 4)
Input Bias Current
Input Offset Current
Input Resistance
Input Capacitance
Output DC Offset (Note 3)
0.6
±12
±12
2
U
W
U
U
W W
W
V
P
V
P
V
V
µA
nA
MΩ
MΩ
pF
mV
mV
LTC1565-31
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
S
= 5V (V
+
= 5V, V
–
= 0V), R
LOAD
= 10k from each output to AC ground,
and Pin 5 open unless otherwise specified.
PARAMETER
Output DC Offset Drift
Ground Voltage (Pin 3) in
Single Supply Applications
SHDN Pin Logic Thresholds
CONDITIONS
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
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
MIN
TYP
– 400
– 400
MAX
UNITS
µV/°C
µV/°C
2.49
2.51
4.2
3.3
2.75
2.50
5
9
24
25
2.52
V
V
V
V
V
µA
µA
31
33
16
40
mA
mA
µA
µA
4
10
8
20
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
P-P
, 100kHz differential signal is applied to Pins 1 and 2.
The DC voltages at Pins 1 and 2 are equal. This is the “common mode
voltage.” The “common mode range” is the range of common mode
voltages for which the 250mV
P-P
differential output has better than 65dB
2nd or 3rd harmonic distortion.
Note 5:
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 6:
Output DC offset measurements are performed by automatic test
equipment approximately 0.5 seconds after application of power.
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.
U
U
U
3
LTC1565-31
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.
– 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 DIAGRA
+IN 1
–IN 2
GND 3
5k
SHUTDOWN
SWITCH
V
+
V
–
4µA
SHUTDOWN
V
–
4
4
W
U
U
U
+
8 +OUT
–
+
R
7th ORDER
LINEAR
PHASE
FILTER
NETWORK
OUTPUT
BUFFER
R
–
+
V
+
SHUTDOWN
SWITCH
–
INPUT BUFFERS
WITH COMMON MODE
TRANSLATION CIRCUIT
OUTPUT
BUFFER
7 –OUT
~1M
5k
6 V
+
~1M
5
SHDN
1565-31 BD
LTC1565-31
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 volt-
ages 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 Dia-
gram). 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.
1
2
+IN
–IN
+OUT
–OUT
8
7
V
OUT+
V
OUT–
5V
6
5
0.1µF
15645-31 F01
THD (dB)
+
–
V
IN+
+
–
V
IN–
3
LTC1565-31
GND
V
–
V
+
SHDN
0.1µF
4
DC COUPLED INPUT
V
+
+ V
IN–
V
IN
(COMMON MODE) =
IN
2
V
OUT+
+ V
OUT–
V
+
=
V
OUT
(COMMON MODE) =
2
2
THD (dB)
Figure 1
0.1µF
1
2
+IN
–IN
+OUT
–OUT
8
7
V
OUT
+
+
–
V
IN+
+
–
V
IN–
0.1µF 100k
1µF
100k
3
4
LTC1565-31
GND
V
–
6
V
+
5
SHDN
AC COUPLED INPUT
V
IN
(COMMON MODE) = V
OUT
(COMMON MODE)
=
V
+
2
Figure 2
U
W
U
U
Input Common Mode and Differential Voltage Range
The range of voltage each input can support while operat-
ing 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
P-P
differential input
signal.
–30
–40
–50
–60
–70
–80
–90
V
IN
= 2V
P-P
V
S
=
±5V
f
IN
= 100kHz
–5 –4 –3 –2 –1 0 1 2 3 4
INPUT COMMON MODE VOLTAGE (V)
5
1565-31 F03
Figure 3. THD vs Common Mode Input Voltage
–30
–40
–50
–60
–70
–80
V
IN
= 2V
P-P
V
S
=
±5V
f
IN
= 100kHz
0.5
3.0
1.0
2.0
2.5
1.5
INPUT COMMON MODE VOLTAGE (V)
3.5
V
OUT–
5V
0.1µF
15645-31 F02
1565-31 F04
Figure 4. THD vs Common Mode Input Voltage
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
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
P-P
; that is, for a single 5V supply, the
5
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