LTC1562-2 Linear Technology, LTC1562-2 Datasheet - Page 7

• Manufacturer Part Number: LTC1562-2
• Description: Very Low Noise/ Low Distortion Active RC Quad Universal Filter
• Manufacturer: Linear Technology

APPLICATIONS
The LTC1562-2 contains four matched, 2nd order,
3-terminal universal continuous-time filter blocks, each
with a virtual-ground input node (INV) and two rail-to-rail
outputs (V1, V2). In the most basic application, one such
block and three external resistors provide 2nd order
lowpass and bandpass responses simultaneously (Figure
3, with a resistor for Z
program f
sion components and external resistor R2 sets the center
frequency f
trimmed at manufacture so that f
if the external resistor R2 is exactly 7958 . The LTC1562-
2 is a higher frequency, pin compatible variant of the
LTC1562, with different internal R and C values and higher
speed amplifiers.
However, lowpass/bandpass filtering is only one specific
application for the 2nd order building blocks in the
LTC1562-2. Highpass response results if the external
impedance Z
value sets only gain, not critical frequencies) as described
below. Responses with zeroes (e.g, elliptic or notch
responses) are available by feedforward connections with
multiple 2nd order blocks (see Typical Applicatons). More-
over, the virtual-ground input gives each 2nd order sec-
tion the built-in capability for analog operations such as
gain (preamplification), summing and weighting of mul-
tiple inputs, or accepting current or charge signals di-
rectly. These Operational Filter
building blocks are nearly as versatile as operational
amplifiers.
The user who is not copying exactly one of the Typical
Applications schematics shown later in this data sheet is
urged to read carefully the next few sections through at
least Signal Swings, for orientation about the LTC1562-2,
before attempting to design custom application circuits.
Also available free from LTC, and recommended for de-
signing custom filters, is the general-purpose analog filter
design software FilterCAD
includes tools for finding the necessary f
parameters to meet target filter specifications such as
frequency response.
O
, Q and gain. A combination of internal preci-
O
IN
of each 2nd order block. The LTC1562-2 is
in Figure 3 becomes a capacitor C
U
IN
INFORMATION
). The three external resistors
U
TM
for Windows
O
TM
will be 200kHz 0.5%
W
frequency-selective
®
. This software
0
, Q and gain
U
IN
(whose
Setting f
Each of the four 2nd order sections in the LTC1562-2 can
be programmed for a standard filter function (lowpass,
bandpass or highpass) when configured as in Figure 3
with a resistor or capacitor for Z
tions all have the same denominator, a complex pole pair
with center frequency
(The numerators depend on the response type as de-
scribed below.) External resistors R2 and R
as follows:
R1 = 7958 and C = 100pF are internal to the LTC1562-2
while R2 and R
A typical design procedure proceeds from the desired f
and Q as follows, using finite-tolerance fixed resistors.
First find the ideal R2 value for the desired f
Then select a practical R2 value from the available finite-
tolerance resistors. Use the actual R2 value to find the
desired R
tolerance:
The f
mainly by the magnitudes of the external resistors
required. As shown above, R2 varies with the inverse
square of f
tolerance (by a factor of 2 incrementally), but it also
implies that R2 has a wider range than f
Operational Filter and FilterCAD are trademarks of Linear Technology Corporation.
Windows is a registered trademark of Microsoft Corporation.
Q
R Ideal
R
f
O
2
Q
O
range is approximately 20kHz to 300kHz, limited
O
Q
2
Q
and Q
( )
, which also will be approximated with finite
R R
O
R
C R R
(
. This relationship desensitizes f
7958
1 2
Q
( )
1
Q
200
are external.
1 2
f
O
kHz
)
R
2
O
7958
= 2 f
2
R
7958
Q
7958
O
R
and quality parameter Q.
IN
R
2
2
. These transfer func-
LTC1562-2
O
R
. (R
200
R
Q
2
Q
Q
kHz
O
200
and R
set f
:
O
f
O
kHz
O
to R2’s
IN
and Q
also
7
O