LTC1569-7_15 Datasheet, PDF (1/12 Pages) Linear Technology – Linear Phase, DC Accurate, Tunable, 10th Order Lowpass Filter

LTC1569-7
Linear Phase, DC Accurate,
Tunable, 10th Order Lowpass Filter
FEATURES
s _{One External R Sets Cutoff Frequency}
s _{Root Raised Cosine Response}
s _{Up to 300kHz Cutoff on a Single 5V Supply}
s _{Up to 150kHz Cutoff on a Single 3V Supply}
s _{10th Order, Linear Phase Filter in an SO-8}
s _{DC Accurate, VOS(MAX) = 5mV}
s _{Low Power Modes}
s _{Differential or Single-Ended Inputs}
s _{80dB CMRR (DC)}
s _{80dB Signal-to-Noise Ratio, VS = 5V}
s _{Operates from 3V to ±5V Supplies}
U
APPLICATIO S
s _{Data Communication Filters for 3V Operation}
s _{Linear Phase and Phase Matched Filters for I/Q}
Signal Processing
s _{Pin Programmable Cutoff Frequency Lowpass Filters}
DESCRIPTIO
The LTC^®1569-7 is a 10th order lowpass filter featuring
linear phase and a root raised cosine amplitude response.
The high selectivity of the LTC1569-7 combined with its
linear phase in the passband makes it suitable for filtering
both in data communications and data acquisition sytems.
Furthermore, its root raised cosine response offers the
optimum pulse shaping for PAM data communications.
The filter attenuation is 57dB at 1.5 • f_CUTOFF, 60dB at 2 •
f_CUTOFF, and in excess of 80dB at 6 • f_CUTOFF. DC-accuracy-
sensitive applications benefit from the 5mV maximum DC
offset.
The LTC1569-7 is the first sampled data filter which does
not require an external clock yet its cutoff frequency can be
set with a single external resistor with a typical accuracy
of 3.5% or better. The external resistor programs an
internal oscillator whose frequency is divided by either 1,
4 or 16 prior to being applied to the filter network. Pin 5
determines the divider setting. Thus, up to three cutoff
frequencies can be obtained for each external resistor
value. Using various resistor values and divider settings,
the cutoff frequency can be programmed over a range of
seven octaves. Alternatively, the cutoff frequency can be
set with an external clock and the clock-to-cutoff fre-
quency ratio is 32:1. The ratio of the internal sampling rate
to the filter cutoff frequency is 64:1.
The LTC1569-7 is fully tested for a cutoff frequency of
256kHz/128kHz with single 5V/3V supply although up to
300kHz cutoff frequencies can be obtained.
The LTC1569-7 features power savings modes and it is
available in an SO-8 surface mount package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Single 3V Supply, 128kHz/32kHz/8kHz Lowpass Filter
3V
3.48k
2k
V_IN ¹ IN⁺
OUT ⁸ V_OUT
2 _IN–
V^{+ 7 REXT = 10k}
LTC1569-7
3 _GND
R_X ⁶
1µF
4 _V–
1/16
DIV/CLK ⁵
1/4
EASY TO SET f_CUTOFF:
1/1
f_CUTOFF = ^{128kHz (10k/REXT)}
1, 4 OR 16
3V
1µF
3V
100pF
1569-7 TA01
Frequency Response, f_CUTOFF = 128kHz/32kHz/8kHz
0
–20
–40
–60
–80
–100
1
10
100
FREQUENCY (kHz)
1000
1569-7 TA01a
1