LT1568
1
1568f
The LT
®
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.
■
Up to 10MHz Center Frequency on a Single 3V
Supply
■
Easy to Use—A Single Resistor Value Sets Lowpass
Cutoff Frequency (200kHz ≤ ƒ
C
≤ 5MHz), Unequal
Resistor Values Extend Cutoff Frequency Up to
10MHz
■
Extremely Flexible—Different Resistor Values
Allow Lowpass Transfer Functions with or Without
Gain (Butterworth, Chebyshev or Custom)
■
SNR = 92dB (ƒ
C
= 2MHz, 2V
P-P
)
■
THD = –84dB (ƒ
C
= 2MHz, 1V
P-P
)
■
Internal Capacitors Trimmed to ±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 ±5V Supply
■
Rail-to-Rail Input and Output Voltages
Very Low Noise,
High Frequency Active RC,
Filter Building Block
■
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
V
+
INVA
SA
OUTA
OUTA
GNDA
NC
V
–
V
+
INVB
SB
OUTB
OUTB
GNDB
EN
V
–
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
LT1568
511Ω
0.1µF
0.1µF
511Ω 511Ω511Ω
511Ω
1568 TA01
V
INA
3V
V
OUTA
V
OUTA
V
INB
THE PROPRIETARY ARCHITECTURE
ALLOWS FOR A SIMPLE RESISTOR
CALCULATION:
V
OUTB
V
OUTB
511Ω
R = 128Ω •; ƒ
C
= CUTOFF FREQUENCY
10MHz
ƒ
C
Amplitude and Phase Matched Dual Butterworth 2.5MHz Lowpass
Filter with Differential Output. Single 3V Supply Operation
FREQUENCY (Hz)
100k
–27
GAIN (dB)
–21
–15
–9
–3
1M 10M
1568 TA02
3
–24
–18
–12
–6
0
Amplitude Response
DESCRIPTIO
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FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
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