LTC6601-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
LTC6601-1
Linear Technology
'LTC6601-1' PDF : 40 Pages View PDF
LTC6601-1
APPLICATIONS INFORMATION
FUNCTIONAL DESCRIPTION
The LTC6601 is designed to make the implementation of
high frequency fully-differential filtering functions very
easy. A very low noise amplifier is surrounded by 8 precision
matched resistors and 12 precision matched capacitors
so that a myriad of filter transfer functions limited only by
possible combinations and imagination can be configured
by hard wiring pins. The amplifier itself is a wide band, low
noise and low distortion fully-differential amplifier with ac-
curate output phase balancing. It is optimized for driving low
voltage, single-supply, differential input, analog-to-digital
converters (ADCs). The LTC6601’s outputs are capable
of swinging rail-to-rail on supplies as low as 2.7V, which
makes the amplifier ideal for converting ground referenced,
single-ended signals into VOCM referenced differential
signals. Unlike traditional op amps which have a single
output, the LTC6601 has two outputs to process signals
differentially. This allows for two times the signal swing
in low voltage systems when compared to single-ended
output amplifiers. The balanced differential nature of the
amplifier and matched surrounding components provide
even-order harmonic distortion cancellation, and less
susceptibility to common mode noise (like power supply
noise). The LTC6601 can be used as a single-ended input
to differential output amplifier, or as a differential input to
differential output amplifier.
Figure 3 shows the basic filter architecture. The Laplace
transfer function from VINDIFF to VOUTDIFF is given by the
following generalized equation for a 2nd order lowpass
filter:
( ) VOUTDIFF
VINDIFF
=
1+
s
2πfO
Gain
•Q +
s2
2πfO
2
Both Gain and Q of the filter are based on component ratios,
which match and track extremely well over temperature.
The corner frequency of the filter is a function of an RC
product. This RC product is trimmed to ±1% (typical) and
is not expected to drift by more than ±1% from nominal
over the entire temperature range –40°C to 85°C. As a
result, fully differential filters with tight magnitude, phase
tolerance and repeatability are achieved.
Although Figure 3 implies a differential input, the LTC6601
easily accepts single-ended inputs to either input, and will
faithfully replicate the signal at the output in differential
form.
The LTC6601’s output common mode voltage, defined as
the average of the two output voltages, is independent of
the input common mode voltage, and is adjusted by apply-
ing a voltage on the VOCM pin. If the pin is left open, there
is an internal resistive voltage divider, which develops a
R1 R3
VIN(DIFF)
R1 R3
R2
C2
C1
+–
–+
C1
C2
R2
fO = 2π
1
R2 • R3 • C1• C2
( ) Q =
C2 R3
C1 R2
•
1+
1+
1
GAIN
• R3
–
C2
R2 C1
GAIN
=
R2
R1
VOUT(DIFF)
fO •
f3dB =
6089 •
( ) ( ) 3568 • Q4
1788 • Q2
+ 447
+ 1.287 • 105
•
2 • Q2
1
507.6 • Q
0.2236 • fO •
Q=
( ) ( ) 2.109 • 105 •
9.891 • 1012 • f3dB4 5.486 • 109 • fO4
+ 120 •
5.526 • 109 • f3dB2 + 3.082 • 106 • fO2
( ( ) ) 16 • fO2 • 8.29 • 109 • f3dB2 + 4.127 • 109 • fO2 6.638 • 1010 • f3dB4
66011 F03
Figure 3. Basic Filter Topology and Equations
66011f
16
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