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PDF LTC1562C Data sheet ( Hoja de datos )
| Número de pieza | LTC1562C | |
| Descripción | Very Low Noise/ Low Distortion Active RC Quad Universal Filter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1562
Very Low Noise, Low Distortion
Active RC Quad Universal Filter
FEATURES
s Continuous Time—No Clock
s Four 2nd Order Filter Sections, 10kHz to 150kHz
Center Frequency
s ±0.5% Typical Center Frequency Accuracy
s ±0.3% Typical Center Frequency Accuracy (A Grade)
s Wide Variety of Response Shapes
s Lowpass, Bandpass and Highpass Responses
s 103dB Typical S/N, ±5V Supply (Q = 1)
s 97dB Typical S/N, Single 5V Supply (Q = 1)
s 96dB Typical S/(N +THD) at ±5V Supply, 20kHz Input
s Rail-to-Rail Input and Output Voltages
s DC Accurate to 3mV (Typ)
s “Zero-Power” Shutdown Mode
s Single or Dual Supply, 5V to 10V Total
Us Resistor-Programmable fO, Q, Gain
APPLICATIONS
s High Resolution Systems (14 Bits to 18 Bits)
s Antialiasing/Reconstruction Filters
s Data Communications, Equalizers
s Dual or I-and-Q Channels (Two Matched 4th Order
Filters in One Package)
s Linear Phase Filtering
s Replacing LC Filter Modules
DESCRIPTION
The LTC®1562 is a low noise, low distortion continuous-time
filter with rail-to-rail inputs and outputs, optimized for a
center frequency (fO) of 10kHz to 150kHz. Unlike most
monolithic filters, no clock is needed. Four independent 2nd
order filter blocks can be cascaded in any combination, such
as one 8th order or two 4th order filters. Each block’s
response is programmed with three external resistors for
center frequency, Q and gain, using simple design formulas.
Each 2nd order block provides lowpass and bandpass out-
puts. Highpass response is available if an external capacitor
replaces one of the resistors. Allpass, notch and elliptic
responses can also be realized.
The LTC1562 is designed for applications where dynamic
range is important. For example, by cascading 2nd order
sections in pairs, the user can configure the IC as a dual 4th
order Butterworth lowpass filter with 94dB signal-to-noise
ratio from a single 5V power supply. Low level signals can
exploit the built-in gain capability of the LTC1562. Varying the
gain of a section can achieve a dynamic range as high as
118dB with a ±5V supply.
Other cutoff frequency ranges can be provided upon request.
Please contact LTC Marketing.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
Dual 4th Order 100kHz Butterworth Lowpass Filter
RIN1
10k
VIN2
5V
0.1µF
RIN3
10k
VIN1
RIN2, 10k
RQ1, 5.62k
R21, 10k
R23, 10k
RQ3, 5.62k
1
INV B
2
V1 B
20
INV C
19 RQ2, 13k
V1 C
3
V2 B
18 R22, 10k
V2 C
5 V+ LTC1562 V– 16
6
SHDN
15
AGND
0.1µF
8
V2 A
9
V1 A
10
INV A
13
V2 D
12
V1 D
11
INV D
R24, 10k
RQ4, 13k
1562 TA01
VOUT2
–5V
SCHEMATIC INCLUDES PIN
NUMBERS FOR 20-PIN PACKAGE.
PINS 4, 7, 14, 17 (NOT SHOWN)
ALSO CONNECT TO V –
VOUT1
SEE TYPICAL APPLICATIONS
FOR OTHER CUTOFF FREQUENCIES
DC ACCURATE, NONINVERTING,
UNITY-GAIN, RAIL-TO-RAIL
INPUT AND OUTPUTS. PEAK
SNR ≈ 100dB WITH ±5V SUPPLIES
RIN4, 10k
10
0
–10
–20
–30
–40
–50
–60
–70
–80
10k
Amplitude Response
100k
FREQUENCY (Hz)
1M
1562 TA03b
1
1 page  
LTC1562
PIN FUNCTIONS
(Figure 1). For single supply operation, the AGND pin
should be bypassed to the ground plane with at least a
0.1µF capacitor (at least 1µF for best AC performance)
(Figure 2).
ANALOG
GROUND
PLANE
V+
0.1µF
1 20
2 19
3 18
4 17
5 LTC1562 16
6 15
7 14
8 13
9 12
10 11
V–
0.1µF
SINGLE-POINT
SYSTEM GROUND
DIGITAL
GROUND PLANE
(IF ANY)
1562 F01
Figure 1. Dual Supply Ground Plane Connection
(Including Substrate Pins 4, 7, 14, 17)
ANALOG
GROUND
PLANE
V+
0.1µF
1 20
2 19
3 18
4 17
5 LTC1562 16
6 15
7 14 1µF
8 13
9 12
10
11
V +/2
REFERENCE
SINGLE-POINT
SYSTEM GROUND
DIGITAL
GROUND PLANE
(IF ANY)
1562 F01
Figure 2. Single Supply Ground Plane Connection
(Including Substrate Pins 4, 7, 14, 17)
Shutdown (SHDN): When the SHDN input goes high or is
open-circuited, the LTC1562 enters a “zero-power” shut-
down state and only junction leakage currents flow. The
AGND pin and the amplifier outputs (see Figure 3) assume
a high impedance state and the amplifiers effectively
disappear from the circuit. (If an input signal is applied to
a complete filter circuit while the LTC1562 is in shutdown,
some signal will normally flow to the output through
passive components around the inactive op amps.)
A small pull-up current source at the SHDN input defaults
the LTC1562 to the shutdown state if the SHDN pin is left
floating. Therefore, the user must connect the SHDN pin
to a logic “low” (0V for ±5V supplies, V – for 5V total
supply) for normal operation of the LTC1562. (This con-
vention permits true “zero-power” shutdown since not
even the driving logic must deliver current while the part
is in shutdown.) With a single supply voltage, use V – for
logic “low”— do not connect SHDN to the AGND pin.
1/4 LTC1562
1
sR1C*
*R1 AND C ARE PRECISION
INTERNAL COMPONENTS
C
–
+
V2
R2
INV
ZIN
+– VIN
RQ
V1
1562 F01
ZIN TYPE
R
C
RESPONSE
AT V1
BANDPASS
HIGHPASS
RESPONSE
AT V2
LOWPASS
BANDPASS
IN EACH CASE,
( )fO = (100kHz)
10kΩ
R2
( )Q =
RQ
R2
100kHz
fO
Figure 3. Equivalent Circuit of a Single 2nd Order Section
(Inside Dashed Line) Shown in Typical Connection. Form of ZIN
Determines Response Types at the Two Outputs (See Table)
5
5 Page 
LTC1562
APPLICATIONS INFORMATION
external component ZIN, usually a resistor or capacitor.
This component must of course be rated to sustain the
magnitude of voltage imposed on it.
Lowpass “T” Input Circuit
The virtual ground INV input in the Operational Filter block
provides a means for adding an “extra” lowpass pole to
any resistor-input application (such as the basic lowpass,
Figure 5, or bandpass, Figure 6a). The resistor that would
otherwise form ZIN is split into two parts and a capacitor
to ground added, forming an R-C-R “T” network (Figure
9). This adds an extra, independent real pole at a fre-
quency:
fP
=
1
2πRPCT
where CT is the new external capacitor and RP is the
parallel combination of the two input resistors RINA and
RINB. This pair of resistors must normally have a pre-
scribed series total value RIN to set the filter’s gain as
described above. The parallel value RP can however be set
arbitrarily (to RIN/4 or less) which allows choosing a
convenient standard capacitor value for CT and fine tuning
the new pole with RP.
RINA
VIN
RINB
CT RQ R2
INV V1 V2
2nd ORDER
1/4 LTC1562
1562 F09
Figure 9. Lowpass “T” Input Circuit
A practical limitation of this technique is that the CT capaci-
tor values that tend to be required (hundreds or thousands
of pF) can destabilize the op amp in Figure 3 if RINB is too
small, leading to AC errors such as Q enhancement. For this
reason, when RINA and RINB are unequal, preferably the
larger of the two should be placed in the RINB position.
Highpass “T” Input Circuit
A method similar to the preceding technique adds an
“extra” highpass pole to any capacitor-input application
(such as the bandpass of Figure 6b or the highpass of
Figure 7). This method splits the input capacitance CIN into
two series parts CINA and CINB, with a resistor RT to ground
between them (Figure 10). This adds an extra 1st order
highpass corner with a zero at DC and a pole at the
frequency:
fP
=
1
2πRTCP
where CP = CINA + CINB is the parallel combination of the
two capacitors. At the same time, the total series capaci-
tance CIN will control the filter’s gain parameter (HH in
Basic Highpass). For a given series value CIN, the parallel
value CP can still be set arbitrarily (to 4CIN or greater).
CINA
CINB
VIN
RT
RQ R2
INV V1 V2
2nd ORDER
1/4 LTC1562
1562 F10
Figure 10. Highpass “T” Input Circuit
The procedure therefore is to begin with the target extra
pole frequency fP. Determine the series value RIN from the
gain requirement. Select a capacitor value CT such that RP
= 1/(2πfPCT) is no greater than RIN/4, and then choose
RINA and RINB that will simultaneously have the parallel
value RP and the series value RIN. Such RINA and RINB can
be found directly from the expression:
1
( )2
RIN
±
1
2
RIN2 –
4RINRP
The procedure then is to begin with the target corner (pole)
frequency fP. Determine the series value CIN from the gain
requirement (for example, CIN = HH(159pF) for a highpass).
Select a resistor value RT such that CP = 1/(2πRTfP) is at
least 4CIN, and select CINA and CINB that will simultaneously
have the parallel value CP and the series value CIN. Such
CINA and CINB can be found directly from the expression:
( )1
2
CP
±
1
2
2
CP –
4CINCP
11
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| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC1562C.PDF ] | |
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