FEATURES
s
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LT1568
Very Low Noise,
High Frequency Active RC,
Filter Building Block
DESCRIPTIO
The LT
廬
1568 is an easy-to-use, active-RC filter building
block with rail-to-rail inputs and outputs. The internal ca-
pacitors of the IC and the GBW product of the internal low
noise op amps are trimmed such that consistent and repeat-
able filter responses can be achieved. With a single resis-
tor value, the LT1568 provides a pair of
matched
2-pole
Butterworth lowpass filters with unity gain suitable for I/Q
channels.
By using unequal-valued external resistors, the two 2-pole
sections can create different frequency responses or
gains. In addition, the two stages may be cascaded to
create a single 4-pole filter with a programmable re-
sponse. Capable of cutoff frequencies up to 10MHz, the
LT1568 is ideal for antialiasing or channel filtering in high
speed data communications systems. The LT1568 can
also be used as a bandpass filter.
The LT1568 features very low noise, supporting signal-to-
noise ratios of over 90dB. It also provides single-ended to
differential signal conversion for directly driving high
speed A/D converters. The LT1568 has a shutdown mode
that reduces supply current to approximately 0.5mA on a
5V supply.
The LT1568 is available in a narrow 16-lead SSOP
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Up to 10MHz Center Frequency on a Single 3V
Supply
Easy to Use鈥擜 Single Resistor Value Sets Lowpass
Cutoff Frequency (200kHz
鈮?茠
C
鈮?/div>
5MHz), Unequal
Resistor Values Extend Cutoff Frequency Up to
10MHz
Extremely Flexible鈥擠ifferent Resistor Values
Allow Lowpass Transfer Functions with or Without
Gain (Butterworth, Chebyshev or Custom)
SNR = 92dB (茠
C
= 2MHz, 2V
P-P
)
THD = 鈥?4dB (茠
C
= 2MHz, 1V
P-P
)
Internal Capacitors Trimmed to
鹵0.75%
Single 4-Pole Lowpass Filter or
Matched Pair
of
2-Pole Lowpass Filters
Can be Connected as a Bandpass Filter
Single-Ended or Differential Output
Operates from Single 3V (2.7V Min) to
鹵5V
Supply
Rail-to-Rail Input and Output Voltages
APPLICATIO S
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Replaces Discrete RC Active Filters and LC Filter
Modules
Antialiasing/Reconstruction Filters
Dual or I-and-Q Channels (Two Matched 2nd Order
Filters in One Package)
Single-Ended to Differential Conversion
Video Signal Processing
TYPICAL APPLICATIO
3V
0.1碌F
1
511鈩?/div>
V
INA
V
OUTA
V
OUTA
511鈩?/div>
511鈩?/div>
2
3
4
5
6
0.1碌F 7
8
Amplitude and Phase Matched Dual Butterworth 2.5MHz Lowpass
Filter with Differential Output. Single 3V Supply Operation
16
V
+
LT1568
15
INVA
INVB
14
SA
SB
13
OUTA
OUTB
12
OUTA
OUTB
11
GNDA GNDB
10
NC
EN
9
V
鈥?/div>
V
鈥?/div>
V
+
Amplitude Response
3
0
鈥?
511鈩?/div>
511鈩?/div>
GAIN (dB)
鈥?
V
INB
V
OUTB
511鈩?/div>
V
OUTB
THE PROPRIETARY ARCHITECTURE
ALLOWS FOR A SIMPLE RESISTOR
CALCULATION:
10MHz
R = 128鈩?鈥?/div>
;
茠
C
= CUTOFF FREQUENCY
茠
C
鈥?
鈥?2
鈥?5
鈥?8
鈥?1
鈥?4
鈥?7
100k
1M
FREQUENCY (Hz)
10M
1568 TA02
1568 TA01
U
U
U
1568f
1
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