LTC6605-14 Linear Technology, LTC6605-14 Datasheet - Page 10

• Manufacturer Part Number: LTC6605-14
• Description: Dual Matched 14MHz Filter
• Manufacturer: Linear Technology

LTC6605-14
Functional Description
The LTC6605-14 is designed to make the implementation
of high frequency fully differential fi ltering functions very
easy. Two very low noise amplifi ers are surrounded by
precision matched resistors and precision matched capaci-
tors enabling various fi lter functions to be implemented by
hard wiring pins. The amplifi ers are wide band, low noise
and low distortion fully differential amplifi ers with accurate
output phase balancing. They are optimized for driving
low voltage, single-supply, differential input analog-to-
digital converters (ADCs). The LTC6605-14 operates with
a supply voltage as low as 2.7V and accepts inputs up to
325mV below the V
converting ground referenced, single-ended signals into
differential signals that are referenced to the user-supplied
common mode voltage. This is ideal for driving low volt-
age, single-supply, differential input ADCs. The balanced
differential nature of the amplifi er and matched surround-
ing components provide even-order harmonic distortion
cancellation, and low susceptibility to common mode
noise (like power supply noise). The LTC6605-14 can be
operated with a single-ended input and differential output,
or with a differential input and differential output.
The outputs of the LTC6605-14 can swing rail-to-rail.
They can source or sink a transient 70mA of current. Load
APPLICATIONS INFORMATION
10
+
–
V
IN(DIFF)
R1
R1
R4A
R
R4B
–
EXT
power rail, which makes it ideal for
125Ω
125Ω
200Ω
R3
R3
200Ω
R2
R2
R4 = R4A + R4B + R
+
–
–
+
Figure 3. Filter Architecture and Equations
C2
81.5pF
C1
48.2pF
C1
48.2pF
C2
81.5pF
EXT
V
OUT(DIFF)
–
+
capacitances should be decoupled with at least 25Ω of
series resistance from each output.
Filter Frequency Response and Gain Adjustment
Figure 3 shows the fi lter architecture. The Laplace transfer
function can be expressed in the form of the following
generalized equation for a 2nd order lowpass fi lter:
with GAIN, f
Note that GAIN and Q of the fi lter are based on component
ratios, which both match and track extremely well over
temperature. The corner frequency f
function of an RC product. This RC product is trimmed to
±1% 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 fi lters with tight magnitude,
phase tolerance and repeatability are achieved.
Various values for resistors R1 and R4 can be formed
by pin-strapping the internal 100Ω and 200Ω resis-
tors, and optionally by including one or more external
resistors. Note that non-zero source resistance should be
combined with, and included in, R1.
V
V
OUT(DIFF)
IN(DIFF)
O
and Q as given in Figure 3.
=
1+
2πf
O
s
GAIN
• Q
+
(
2πf
www.DataSheet4U.com
s
2
O
)
O
2
of the fi lter is a
,
660514 F03
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