LT1568 Datasheet, PDF (1/16 Pages) Linear Technology – Very Low Noise, High Frequency Active RC, Filter Building Block

LT1568
FEATURES
Very Low Noise,
High Frequency Active RC,
Filter Building Block
DESCRIPTIO
s _{Up to 10MHz Center Frequency on a Single 3V}
Supply
s _{Easy to Use—A Single Resistor Value Sets Lowpass}
Cutoff Frequency (200kHz ≤ ƒ_C ≤ 5MHz), Unequal
Resistor Values Extend Cutoff Frequency Up to
10MHz
s _{Extremely Flexible—Different Resistor Values}
Allow Lowpass Transfer Functions with or Without
Gain (Butterworth, Chebyshev or Custom)
s _{SNR = 92dB (ƒC = 2MHz, 2VP-P)}
s _{THD = –84dB (ƒC = 2MHz, 1VP-P)}
s _{Internal Capacitors Trimmed to ±0.75%}
s _{Single 4-Pole Lowpass Filter or Matched Pair of}
2-Pole Lowpass Filters
s _{Can be Connected as a Bandpass Filter}
s _{Single-Ended or Differential Output}
s _{Operates from Single 3V (2.7V Min) to ±5V Supply}
s _{Rail-to-Rail InputUand Output Voltages}
APPLICATIO S
s _{Replaces Discrete RC Active Filters and LC Filter}
Modules
s _{Antialiasing/Reconstruction Filters}
s _{Dual or I-and-Q Channels (Two Matched 2nd Order}
Filters in One Package)
s _{Single-Ended to Differential Conversion}
s _{Video Signal Processing}
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.
TYPICAL APPLICATIO
Amplitude and Phase Matched Dual Butterworth 2.5MHz Lowpass
Filter with Differential Output. Single 3V Supply Operation
3V
511Ω
V_INA
V_OUTA
V_OUTA
0.1µF
511Ω
1
2
V⁺ _LT1568 V⁺
16
15
INVA INVB
3
SA
14
SB
4
13
OUTA OUTB
511Ω 5
12
OUTA OUTB
6
GNDA
0.1µF ₇
NC
11
GNDB
10
EN
8 _V–
V^{– 9}
511Ω
511Ω
1568 TA01
511Ω
V_INB
V_OUTB
V_OUTB
THE PROPRIETARY ARCHITECTURE
ALLOWS FOR A SIMPLE RESISTOR
CALCULATION:
R = 128Ω • ¹⁰_ƒ^M_C^Hz; ƒ_C = CUTOFF FREQUENCY
Amplitude Response
3
0
–3
–6
–9
–12
–15
–18
–21
–24
–27
100k
1M
FREQUENCY (Hz)
10M
1568 TA02
1568f
1