LTC1068IG Linear Technology, LTC1068IG Datasheet - Page 13

• Manufacturer Part Number: LTC1068IG
• Description: IC FILTR BUILDNG BLK QUAD 28SSOP
• Manufacturer: Linear Technology

Specifications of LTC1068IG

• Filter Type: Universal Switched Capacitor
• Frequency - Cutoff Or Center: 50kHz
• Number Of Filters: 4
• Max-order: 8th
• Voltage - Supply: 3.14 V ~ 11 V, ±3.14 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
Operating Limits
The Maximum Q vs Center Frequency (f
Typical Performance Characteristics, define an upper limit
of operating Q for each LTC1068 device 2nd order section.
These graphs indicate the power supply, f
conditions under which a filter implemented with an
LTC1068 device will remain stable when operated at
temperatures of 70°C or less. For a 2nd order section, a
bandpass gain error of 3dB or less is arbitrarily defined as
a condition for stability.
When the passband gain error begins to exceed 1dB, the use
of capacitor C
connected from the lowpass node to the inverting node of a
2nd order section). Please refer to Figures 4 through 7. The
value of C
guide it should be about 5pF for each 1dB of gain error and not
to exceed 15pF. When operating an LTC1068 device near the
limits defined by the Maximum Q vs Frequency graphs,
passband gain variations of 2dB or more should be expected.
Clock Feedthrough
Clock feedthrough is defined as the RMS value of the clock
frequency and its harmonics that are present at the filter’s
output pins. The clock feedthrough is tested with the
filter’s input grounded and depends on PC board layout
and on the value of the power supplies. With proper layout
techniques, the typical values of clock feedthrough are
listed under Electrical Characteristics.
Any parasitic switching transients during the rising and
falling edges of the incoming clock are not part of the clock
feedthrough specifications. Switching transients have fre-
quency contents much higher than the applied clock; their
amplitude strongly depends on scope probing techniques
as well as grounding and power supply bypassing. The
clock feedthrough, can be greatly reduced by adding a
simple RC lowpass network at the final filter output. This
RC will completely eliminate any switching transients.
Wideband Noise
The wideband noise of the filter is the total RMS value of
the device’s noise spectral density and is used to deter-
C
can be best determined experimentally, and as a
C
will reduce the gain error (capacitor C
U
INFORMATION
U
W
O
) graphs, under
O
and Q value
U
C
is
mine the operating signal-to-noise ratio. Most of its fre-
quency contents lie within the filter passband and cannot
be reduced with post filtering. For a notch filter the noise
of the filter is centered at the notch frequency.
The total wideband noise (µV
the value of the clock. The clock feedthrough specifica-
tions are not part of the wideband noise.
For a specific filter design, the total noise depends on the
Q of each section and the cascade sequence. Please refer
to the Noise vs Q graphs under the Typical Performance
Characteristics.
Aliasing
Aliasing is an inherent phenomenon of switched-capacitor
filters and occurs when the frequency of the input signals
that produce the strongest aliased components have a
frequency, f
filter’s passband. For an LTC1068 device the sampling
frequency is twice f
band-limited, aliasing may occur.
Demonstration Circuit 104
DC104 is a surface mount printed circuit board for the
evaluation of Linear Technology’s LTC1068 product fam-
ily in a 28-lead SSOP package. The LTC1068 product
family consists of four monolithic clock-tunable filter
building blocks.
Demo Board 104 is available in four assembled versions:
Assembly 104-A features the low noise LTC1068CG (clock-
to-center frequency ratio = 100), assembly 104-B features
the low noise LTC1068-200CG (clock-to-center frequency
ratio = 200), assembly 104-C features the high frequency
LTC1068-25CG (clock-to-center frequency ratio = 25) and
assembly 104-D features the low power LTC1068-50CG
(clock-to-center frequency ratio = 50).
All DC104 boards are assembled with input, output and
power supply test terminals, a 28-lead SSOP filter device
(LTC1068CG Series), a dual op amp in an SO-8 for input
or output buffers and decoupling capacitors for the filter
and op amps. The filter and dual op amps share the power
IN
, such as (f
CLK
. If the input signal spectrum is not
SAMPLING
RMS
LTC1068 Series
) is nearly independent of
– f
IN
) that falls into the
13
1068fb