LTC1560-1
1MHz/500kHz
Continuous Time,
Low Noise, Lowpass Elliptic Filter
FEATURES
s
s
s
s
s
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s
5th Order, 1MHz Elliptic Filter in SO-8 Package
Pin Selectable 1MHz/500kHz Cutoff Frequency
Signal-to-Noise Ratio (SNR): 75dB
Signal-to-Noise Ratio with – 63dB THD: 69dB
Passband Ripple (f
CUTOFF
= 1MHz):
±0.3dB
Stopband Attenuation Better Than 60dB
No External Components Required
either 500kHz (Pin 5 to V
+
) or 1MHz (Pin 5 to V
–
). When
programmed for 1MHz, the passband ripple is typically
±0.2dB
up to 0.55f
CUTOFF
and
±0.3dB
to 0.9f
CUTOFF
. The
transition band gain is – 24dB at 1.4f
CUTOFF
and – 51dB at
2f
CUTOFF
. Stopband attenuation is 63dB at 2.43f
CUTOFF
and
above, remaining at least 60dB to 10MHz with proper
board layout. When the LTC1560-1 is programmed for
f
CUTOFF
= 500kHz, the filter response closely follows the
1MHz case with the exception of passband flatness near
the cutoff frequency; the gain at f
CUTOFF
is – 1.3dB.
The LTC1560-1, unlike other high frequency filters, is
designed for low noise and low distortion. With a 1V
RMS
input signal, the signal-to-noise ratio is 69dB and the THD
is – 63dB. The maximum SNR of 75dB is obtained with a
2.1V
RMS
input signal. This results in – 46dB THD.
The LTC1560-1 operates with
±5V
supplies, has a power
saving mode and is available in an SO-8 surface mount
package.
Other cutoff frequencies from 450kHz to 1.5MHz can be
obtained. Demo board DC135A is available for the
LTC1560-1. For more information please contact LTC
Marketing.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIONS
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s
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Antialiasing Filters
Smoothing or Reconstruction Filters
Communication Filters
DESCRIPTION
The LTC
®
1560-1 is a 5th order, continuous-time, lowpass
filter.
The elliptic transfer function of the LTC1560-1 was
carefully chosen to reach a compromise between selectiv-
ity, for antialiasing applications, and transient response.
The filter cutoff frequency, f
CUTOFF
, is pin selectable to
TYPICAL APPLICATION
Frequency Response
1MHz/500kHz Elliptic Lowpass Filter
1
2
GND
V
IN
V
OUT
SHDN
8
7
6
5
0.1µF
V
OUT
GAIN (dB)
10
0
–10
–20
–30
–40
–50
– 60
–70
V
IN
LTC1560-1
3
GND
V
+
– 5V
0.1µF
0.01µF
4
V
–
0.5f
C
/f
C
U
U
U
(OR – 5V)
5V
0.01µF
– 5V
1MHz
5V
500kHz
1560-1 TA01
– 80
f
CUTOFF
= 1MHz/500kHz
– 90
1
0.1
FREQUENCY (MHz)
10
1560-1 TA02
1
LTC1560-1
ABSOLUTE
MAXIMUM
RATINGS
Total Supply Voltage (V
+
to V
–
) ............................. 12V
Power Dissipation............................................. 400mW
Burn-In Voltage ...................................................
±5.5V
Operating Temperature Range
LTC1560-1C ........................................... 0°C to 70°C
LTC1560-1I ....................................... – 40°C to 85°C
Maximum Junction Temperature ......................... 150°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
GND 1
V
IN
2
GND 3
V
–
4
8
7
6
5
V
OUT
SHDN
V
+
0.5f
C/
f
C
ORDER PART
NUMBER
LTC1560-1CS8
LTC1560-1IS8
S8 PART MARKING
15601
15601I
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 150°C,
θ
JA
= 125°C/ W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Operating Supply Voltage Range
Passband Gain (f
CUTOFF
= 1MHz)
CONDITIONS
V
S
=
±5V,
T
A
= 25°C, Pin 5 = – 5V (f
CUTOFF
= 1MHz), Pin 7 = 0V unless otherwise specified.
MIN
±4.5
V
IN
= 0.5V
RMS
, f
IN
= 20kHz
f
IN
= 100kHz
f
IN
= 300kHz
f
IN
= 550kHz (Gain Relative to 100kHz)
f
IN
= 850kHz (Gain Relative to 100kHz)
f
IN
= 950kHz (Gain Relative to 100kHz)
f
IN
= f
CUTOFF
= 1MHz (Gain Relative to 100kHz)
V
IN
= 0.5V
RMS
, f
IN
= 1.4MHz
f
IN
= 1.9MHz
f
IN
= 2.0MHz
f
IN
= 2.44MHz
f
IN
= 3.0MHz
f
IN
= 6.0MHz
f
IN
= 100kHz, Pin 5 = 5V
f
IN
= f
CUTOFF
= 500kHz
f
IN
= 1.4MHz
R
L
= 5k
q
q
q
q
q
q
TYP
±5.0
0.17
0.18
0.08
0.05
– 0.3
0.6
– 1.0
– 24
– 42
– 51
– 70
– 68
– 66.1
MAX
±5.5
0.6
0.3
0
0.5
1.0
–18
UNITS
V
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
V
mV
– 0.3
– 0.35
– 0.8
– 3.0
– 5.0
Transition Band Gain (Note 1)
Stopband Gain (f
CUTOFF
= 1MHz) (Note 2)
q
– 65
Passband Gain (f
CUTOFF
= 500kHz)
q
q
–4
±1.9
0.14
– 1.6
– 45
±3
±250
22
1
350
322
– 63
– 61
– 62
– 62
– 63
0.5
Output Voltage Swing
Output DC Offset (V
OS
)
Power Supply Current (I
S
)
Power Supply Current in Shutdown Mode
Total Output Noise
Total Harmonic Distortion (THD)
q
29
Pin 7 at 5V
V
IN
(Pin 2) Tied to Ground, f
CUTOFF
= 1MHz, BW = 2MHz
V
IN
(Pin 2) Tied to Ground, f
CUTOFF
= 0.5MHz, BW = 1MHz
V
IN
= 1V
RMS
, f
IN
= 200kHz, f
CUTOFF
= 1MHz, BW = 1MHz
f
IN
= 300kHz, f
CUTOFF
= 1MHz, BW = 1MHz
f
IN
= 1MHz, f
CUTOFF
= 1MHz, BW = 2MHz
f
IN
= 300kHz, f
CUTOFF
= 0.5MHz, BW = 1MHz
f
IN
= 500kHz, f
CUTOFF
= 0.5MHz, BW = 1MHz
µV
RMS
µV
RMS
dB
dB
dB
dB
dB
10
kΩ
Input Resistance (R
IN
)
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
To properly measure high frequency characteristics of the filter, a
noninverting output buffer is recommended as shown on the demo board
q
6
8
connection diagram, Figure 2. A small resistor (e.g. 100Ω) can also be
used instead of the buffer to isolate any high capacitive load (C
L
> 10pF)
from the filter output.
Note 2:
The stopband gain at 2.44MHz is guaranteed by design.
2
U
W
U
U
W W
W
mA
mA
LTC1560-1
TYPICAL PERFORMANCE CHARACTERISTICS
Frequency Response
10
0
–10
–20
f
CUTOFF
= 1MHz
10
0
–10
–20
GAIN (dB)
GAIN (dB)
–30
– 40
–50
– 60
–70
– 80
0
1
2
FREQUENCY (MHz)
1560-1 G01
– 40
–50
– 60
–70
– 80
–90
GAIN (dB)
Passband Gain
0.4
0.2
0
f
CUTOFF
= 500kHz
GROUP DELAY (µs)
– 0.2
GROUP DELAY (µs)
GAIN (dB)
– 0.4
– 0.6
– 0.8
–1.0
–1.2
–1.4
0.1
0.2
0.3
0.4
FREQUENCY (MHz)
0.5
1560-1 G04
Phase vs Frequency
45
0
– 45
– 90
0
f
CUTOFF
= 500kHz
– 45
– 90
PHASE (DEG)
PHASE (DEG)
–135
–180
–225
20
100
U W
3
Frequency Response
f
CUTOFF
= 500kHz
0.6
0.4
0.2
0
– 0.2
– 0.4
– 0.6
0
0.5
1.0
FREQUENCY (MHz)
1560-1 G02
Passband Gain
f
CUTOFF
= 1MHz
–30
4
1.5
2.0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
FREQUENCY (MHz)
1560-1 G03
Group Delay
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.25 0.50 0.75 1.0 1.25 1.50 1.75 2.0
FREQUENCY (MHz)
1560-1 G05
Group Delay
2.25
f
CUTOFF
= 500kHz
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
FREQUENCY (MHz)
1560-1 G06
f
CUTOFF
= 1MHz
Phase vs Frequency
f
CUTOFF
= 1MHz
–135
–180
–225
–270
180 260 340 420
FREQUENCY (kHz)
500
1560-1 G07
20
180
340
500 660 820
FREQUENCY (kHz)
980
1560-1 G08
3
LTC1560-1
TYPICAL PERFORMANCE CHARACTERISTICS
Transient Response
Transient Response
60
54
48
OUTPUT NOISE (µV
RMS
)
1V/DIV
1V/DIV
f
CUTOFF
= 0.5MHz
V
IN
= 5V
P-P
f
IN
= 50kHz
2µs/DIV
Output Noise vs Frequency
60
54
48
OUTPUT NOISE (µV
RMS
)
f
CUTOFF
= 0.5MHz
TOTAL OUTPUT NOISE = 198µV
RMS
42
36
30
24
18
12
6
0
50
100
200
400
FREQUENCY (kHz)
600
1560-1 G12
THD + NOISE
THD + Noise vs Input Frequency
– 52
– 54
– 56
– 58
THD (dB)
THD (dB)
f
CUTOFF
= 500kHz
– 60
– 62
– 64
– 66
– 68
–70
–72
40
60
80 100 120 140 160 180 200
INPUT FREQUENCY (kHz)
1560-1 G14
4
U W
1560-1 G09
Output Noise vs Frequency
f
CUTOFF
= 1MHz
TOTAL OUTPUT NOISE = 232µV
RMS
42
36
30
24
18
12
6
0
0.1
0.5
FREQUENCY (MHz)
1.0
1.5
f
CUTOFF
= 1MHz
V
IN
= 5V
P-P
f
IN
= 50kHz
2µs/DIV
1560-1 G10
1560-1 G11
Dynamic Range
– 20
– 30
– 40
– 50
– 60
– 70
– 80
– 90
0.1
f
CUTOFF
= 500kHz OR 1MHz
f
IN
= 45kHz
1
INPUT VOLTAGE (V
RMS
)
1560-1 G13
3
THD + Noise vs Input Frequency
– 52
– 54
– 56
– 58
f
CUTOFF
= 1MHz
V
IN
= 1V
RMS
S/N = 74dB
– 60
– 62
– 64
– 66
– 68
–70
–72
40
60
80 100 120 140 160 180 200
INPUT FREQUENCY (kHz)
1560-1 G15
V
IN
= 1V
RMS
S/N = 72dB
V
IN
= 0.6V
RMS
S/N = 69.5dB
V
IN
= 0.6V
RMS
S/N = 68dB
LTC1560-1
PIN FUNCTIONS
GND (Pins 1, 3):
Analog Ground Pins. The quality of the
analog ground can affect the filter performance. For dual
supply operation the analog ground pin should be con-
nected to an analog ground plane surrounding the pack-
age. The analog ground plane should be connected to a
digital ground plane (if any) at a single point. For single
supply operation, the analog ground pin should be biased
at one-half the power supply across the device (see
Figure 1) and the analog ground plane should then be
connected to V
–
(Pin 4).
V
IN
(Pin 2):
The filter input is internally connected to the
inverting input of a high frequency op amp through an 8k
resistor.
V
–
, V
+
(Pins 4, 6):
Power Supply Pins. The negative and
positive power supply (Pins 4 and 6 respectively) should
be decoupled with a 0.1µF capacitor in parallel with a
0.01µF. Both capacitors should be types designed for
decoupling video frequencies and they should be placed
as close as possible to the power supply pins of the filter.
Parallel routing of high frequency signal paths should be
avoided; they will couple into the device’s power supply
pins and cause gain inaccuracy and stopband degrada-
tion. The power supplies can be applied in any order, that
is, the positive supply can be applied before the negative
supply and vice versa. Switching power supplies are not
recommended.
0.5f
C
/f
C
(Pin 5):
By tying Pin 5 high the filter cutoff
frequency is internally programmed for 500kHz. By tying
Pin 5 low the cutoff frequency will switch to 1MHz. Pin 5
should not be left floating. The logic threshold of Pin 5 is
approximately 0.4 times the total power supply across the
device.
SHDN (Pin 7):
Shutdown. Under normal operating condi-
tions, Pin 7 should be shorted either to the analog ground
(Pin 1) or to V
–
(Pin 4). If Pin 7 is pulled high to V
+
, the filter
operation will stop and the IC will be placed in a power
saving mode. The power supply current will then be
reduced to 1mA. For a
±5V
supply, the logic threshold of
Pin 7 is 2.5V. Pin 7 is internally connected to the analog
ground pin via a 50k resistor.
V
OUT
(Pin 8):
The filter output pin can sink or source 1mA.
The total harmonic distortion of the filter will degrade
when driving coaxial cables or loads less than 10k without
an output buffer.
U
U
U
V
+
10k
0.1µF
0.01µF
1
1µF
0.01µF
2
3
4
GND
V
IN
V
OUT
SHDN
8
7
6
5
GND OR V
+
V
OUT
10k
V
IN
LTC1560-1
GND
V
+
V
–
0.5f
C
/f
C
ANALOG GROUND PLANE
SYSTEM GROUND
DIGITAL GROUND
PLANE
1560-1 F01
Figure 1. Connections for Single Supply Operation
5
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