LT1567
1
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However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Final Electrical Specifications
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
TYPICAL APPLICATIO
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The LT
1567 is an analog building block optimized for
very low-noise high-frequency filter applications. It con-
tains two wideband operational amplifiers, one of them
internally configured as a unity-gain inverter. With the
addition of two capacitors, the LT1567 becomes a flexible
second-order filter section with cutoff frequency (f
C
) up to
5MHz, ideal for antialiasing or for channel filtering in high-
speed data communications systems.
In addition to low noise and high speed LT1567 features
single-ended to differential conversion for direct driving of
high speed A/D converters. The LT1567 operates from a
total power-supply voltage of 2.7V to 12V and can support
signal-to-noise ratios above 100dB.
The LT1567 is available in an 8-lead MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
s
Low Noise, High Speed Filters to 5MHz
s
Cellular Base Stations
s
Communication Channel or Roofing Filters
s
Antialias or Reconstruction Filtering
s
Video Signal Processing
s
Single-Ended to Differential Conversion
2MHz 3-Pole Antialias Filter with
Single-Ended to Differential Conversion
Frequency Response
A
IN
+A
IN
ADC
1567 TA01
V
IN
0.1
F
0.1
F
270pF
270pF
270pF
0.1
F
V
V
+
1
2
3
4
8
7
6
5
536
536
536
147
147
LTC1420
96dB DIFFERENTIAL SNR AT 3V TOTAL SUPPLY.
LT1567
s
Single-Ended to Differential Conversion
s
Low Noise: 1.4nV/
Hz
s
20
V
RMS
Total Wideband Noise Filter with 2MHz f
C
s
Dynamic Range: 104dB SNR at
5V
s
Supply Voltage 2.7V to 12V Total
s
Rail-to-Rail Outputs
s
DC Accurate: Op Amp V
OS
1mV (Typ)
s
Trimmed Bandwidth for Accurate Filters
s
MSOP-8 Surface-Mount Package
s
No External Clock Required
1.4nV/
Hz 175MHz Op Amp
and Inverter / Filter Building Block
August 2001
FREQUENCY (Hz)
100
GAIN (dB)
12
6
0
6
12
18
24
30
36
1M
10M
1567 TA01a
NOTE: THIS IS RESPONSE FROM
SINGLE-ENDED V
IN
TO DIFFERENTIAL
VOLTAGE ACROSS ADC INPUT,
SO THERE IS A BUILT-IN 6dB GAIN.
LT1567
2
Total Supply Voltage (V
+
to V
) ............................ 12.6V
Input Voltage (Note 2) .............................................
V
S
Input Current (Note 2) ..........................................
5mA
Operating Temperature Range ..................... 0
C to 70
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
ORDER PART
NUMBER
MS8 PART
MARKING
T
JMAX
= 40
C,
JA
= 160
C/W
LTWH
LT1567CMS8
ABSOLUTE AXI U
RATI GS
W
W
W
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PACKAGE/ORDER I FOR ATIO
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W
(Note 1)
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications that apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
S
=
2.5V, R
L
= 1K, V
OUT
= 0 both amplifiers unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Total Supply Voltage
2.7
12
V
Supply Current
V
S
=
1.5V
q
8.5
15
mA
V
S
=
2.5V
q
9
16
mA
V
S
=
5V
q
11
19
mA
OA Output Positive Voltage Swing
V
S
=
1.5V, R
L
= 1k
q
1.30
1.45
V
V
S
=
2.5V, R
L
= 1k
q
2.20
2.40
V
V
S
=
2.5V, R
L
=100
q
2.00
2.25
V
V
S
=
5V, R
L
= 1k
q
4.70
4.85
V
OA Output Negative Voltage Swing
V
S
=
1.5V, R
L
= 1k
q
1.30
1.45
V
V
S
=
2.5V, R
L
= 1k
q
2.20
2.44
V
V
S
=
2.5V, R
L
=100
q
2.00
2.20
V
V
S
=
5V, R
L
= 1k
q
4.70
4.90
V
INV Output Positive Voltage Swing
V
S
=
1.5V, R
L
= 1k
q
1.30
1.40
V
V
S
=
2.5V, R
L
= 1k
q
2.20
2.40
V
V
S
=
5V, R
L
= 1k
q
4.60
4.90
V
INV Output Negative Voltage Swing
V
S
=
1.5V, R
L
= 1k
q
1.30
1.40
V
V
S
=
2.5V, R
L
= 1k
q
2.20
2.40
V
V
S
=
5V, R
L
= 1k
q
4.50
4.80
V
Common Mode (GND) Input Voltage Range
V
S
=
1.5V
q
0.25
0.25
V
(See Pin Functions)
V
S
=
5V
q
2.5
2.5
V
DC Common Mode Rejection Ratio (CMRR)
V
S
=
1.5V, V
CM
= 0.25V to 0.25V
q
90
dB
V
S
=
5V, V
CM
= 2.5V to 2.5V
q
75
90
dB
DC Power-Supply Rejection Ratio (PSRR)
V
S
=
1.5V to
5V, V
CM
= 0V
q
80
100
dB
OA Input Offset Voltage Magnitude
q
1
3
mV
INV Output Offset Voltage Magnitude
q
6
9
mV
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1
2
3
4
OAOUT
OAIN
BYPASS
V
8
7
6
5
V
+
INVOUT
INVIN
GND
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
LT1567
3
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications that apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
S
=
2.5V, R
L
= 1K, V
OUT
= 0 both amplifiers unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OA Input Bias Current
q
3
10
A
GND Input Bias Current
q
6
15
A
OA DC Open-Loop Gain
V
S
=
1.5V, R
L
= 1k, V
O
= 1V to 1V
q
7.5
23
V/mV
V
S
=
2.5V, R
L
= 1k, V
O
= 2V to 2V
q
10
35
V/mV
V
S
=
2.5V, R
L
= 100, V
O
= 1.5V to 1.5V
q
1.2
4.0
V/mV
V
S
=
5V, R
L
= 1k, V
O
= 4V to 4V
q
15
40
V/mV
INV DC Gain Magnitude
V
S
=
1.5V, R
L
= 1k, V
IN
= 1V to 1V
q
0.97
1.04
V/V
V
S
=
2.5V, R
L
= 1k, V
IN
= 2V to 2V
q
0.97
1.04
V/V
V
S
=
2.5V, R
L
= 100, V
IN
= 1.5V to 1.5V
q
0.97
1.04
V/V
V
S
=
5V, R
L
= 1k, V
IN
= 4V to 4V
q
0.97
1.04
V/V
INV DC Input Resistance
V
S
=
2.5V, R
L
= 1k, V
IN
= 2V to 2V
q
450
600
750
OA Gain-Bandwidth Product
Measured at 2MHz, V
S
=
1.5V
q
100
160
MHz
Measured at 2MHz, V
S
=
2.5V
q
110
175
MHz
Measured at 2MHz, V
S
=
5V
q
120
190
MHz
INV AC Gain Magnitude
Measured at 2MHz
q
0.96
1.0
1.05
V/V
OA Slew Rate Magnitude
49
V/
sec
OA Input Voltage Noise Density
f = 100kHz
1.4
nV/
Hz
OA Input Current Noise Density
f = 100kHz
1.0
pA/
Hz
Wideband Output Noise for a Second-Order Filter (Figure 1)
f
C
= 2MHz, BW = 4MHz
20
V
RMS
f
C
= 5MHz, BW = 10MHz
30
V
RMS
Total Harmonic Distortion (THD)
f = 1MHz, f
C
= 2MHz, V
OUT
= 1V
RMS
88
dB
for a Second-Order Filter (Figure 1)
f = 2.5MHz, f
C
= 5MHz, V
OUT
= 1V
RMS
70
dB
Output Short-Circuit Current (Either Output)
35
mA
Output Impedance
f = 100kHz, OA Connected as
0.1
Unity-Gain Inverter
Note 2: The inputs of each op amp are protected by back-to-back diodes.
If either differential input voltage exceeds 1.4V, the input current should be
limited to less than 5mA.
LT1567
4
OAOUT (Pin 1): Output of the Uncommitted Op Amp (OA).
As with most wideband op amps, it is important to avoid
connecting heavy capacitive loads (above about 10pF)
directly to this output. Such loads, exhibiting low imped-
ance (circa 100
) at the op amp's unity-gain crossover
frequency (circa 100MHz), will impair AC stability.
OAIN (Pin 2): Inverting or "" Input of the Uncommitted
Op Amp (OA) in the LT1567. The noninverting or "+" input
of this amplifier is shared with that of the INV amplifier and
accessed via the GND and BYPASS pins. The OA amplifier
is optimized for minimal wideband noise.
BYPASS (Pin 3): AC Ground Bypass. Designed for a
decoupling capacitor, typically 0.1
F, to a printed circuit
ground plane using the shortest possible wiring. Use GND
for DC connection of the amplifier noninverting inputs as
described in the GND (Pin 5) description.
Power Supply Pins (Pins 4, 8): The V
and V
+
pins should
be bypassed with 0.1
F capacitors to an adequate analog
ground plane using the shortest possible wiring. Electri-
cally clean supplies and a low impedance ground are
important for the high dynamic range and bandwidth
available from the LT1567. Low noise linear power sup-
plies are recommended. Switching supplies are not rec-
ommended because of the inevitable risk of their switch-
ing noise coupling into the signal path, reducing dynamic
range.
U
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PI FU CTIO S
GND (Pin 5): DC Ground Input. Sets the noninverting
inputs for the two internal amplifiers; designed for use as
a DC reference, not a signal input.The GND input includes
a small series resistor, both to balance DC offsets in the
presence of input bias currents and also to suppress the
"Q" factor of possible parasitic high-frequency resonant
circuits introduced by wiring inductance. The on-chip
ground reference at the noninverting inputs of the two
amplifiers is decoupled for very high frequencies with a
small internal capacitor to the chip substrate, nominally
7pF. An external capacitor, typically 0.1
F, to a nearby
ground plane should be added at the BYPASS pin for a
clean wideband ground reference.
INVIN (Pin 6): Unity-Gain Inverter Input. The "inverter"
(INV) amplifier in the LT1567 is connected to internal
resistors (nominally 600
each) to form a closed-loop
amplifier with a wideband voltage gain of nominally 1.
The amplifier in this position is similar to the uncommitted
op amp (OA) but is optimized for high frequency linearity.
INVOUT (Pin 7): Output of the INV or "Inverter" Amplifier,
with a Nominal Gain of 1 from the INVIN Pin. As with
most wideband op amps, it is important to avoid connect-
ing heavy capacitive loads (above about 10pF) directly to
this output. Such loads, exhibiting low impedance (circa
100 ohms) at the op amp's unity-gain crossover frequency
(circa 100MHz), will impair AC stability.
BLOCK DIAGRA
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1
2
3
4
OAOUT
OAIN
BYPASS
V
V
+
INVOUT
INVIN
GND
+
+
600
600
7pF
150
8
7
6
5
Block Diagram with Top View of Pins
LT1567
5
Functional Description
The LT1567 contains two low-noise wideband operational
amplifiers, one of them connected internally as a unity-
gain inverter. These two amplifiers can form a second-
order multiple-feedback filter configuration (Figure 1) for
megahertz signal frequencies, with exceptionally low total
noise. The amplifier in the dedicated inverter (INV) is
optimized for better high frequency linearity while the
uncommitted operational amplifier (OA) is optimized for
lower input noise voltage, according to the different
sensitivities to these effects in the filter section. This
combination produces a low-noise filter with better distor-
tion performance than would be possible with identical
amplifiers.
Signal Ground
Both operational amplifiers within the LT1567 are de-
signed for inverting operation (constant common mode
input) and they share a single ground reference node on
the chip. Two pins permit access to this node: GND and
BYPASS. For a clean on-chip ground reference over a wide
bandwidth, the normal procedure is to connect GND to a
DC ground potential and BYPASS to a decoupling capaci-
tor that returns to a ground plane.
Differential Output Feature
The multiple-feedback filter section of Figure 1 inherently
includes two outputs of opposite signal polarity: a DC-
inverting output from the OA (Pin 1) and a DC noninverting
output from the INV block (Pin 7). These two outputs
maintain equal gain and 180 phase shift over a wide
frequency range. This feature permits choosing the signal
polarity in single-ended applications, and also performs
single-ended-to-differential conversion. The latter prop-
erty is useful in an antialias filter to drive standard mono-
lithic A/D converters having differential inputs, as illus-
trated on page 1.
Dealing with High Source Impedances
The voltage V
IN
in Figure 1 , on the left side of R1, is the
signal voltage that the filter sees. If a voltage source with
significant internal impedance drives the V
IN
node in
Figure 1, then the filter input V
IN
may differ from the
source's open-circuit output, and the difference can be
complex, because the filter presents a complex imped-
ance to V
IN
. A rule of thumb is that a source impedance is
negligibly "low" if it is much smaller than R1 at frequencies
of interest. Otherwise, the source impedance (resistive or
reactive) effectively adds to R1 and may change the signal
frequency response compared to that with a low source
impedance. If the source is resistive and predictable, then
it may be possible to design for it by reducing R1.
Unpredictable or nonresistive source impedances that are
not well below R1 should be buffered.
Construction and Instrumentation Cautions
Electrically clean construction is important in applications
seeking the full dynamic range and bandwidth of the
LT1567. Using the shortest possible wiring or printed-
circuit paths will minimize parasitic capacitance and in-
ductance. High quality supply bypass capacitors of 0.1
F
near the chip, connected to a ground plane, provide good
decoupling from a clean, low inductance power source.
But several inches of wire (i.e., a few microhenrys of
inductance) from the power supplies, unless decoupled
by substantial capacitance (
10
F) near the chip, can
cause a high Q LC resonance in the hundreds of kHz in the
chip's supplies or ground reference. This may impair filter
performance at those frequencies. In stringent filter appli-
cations we have often found that a compact, carefully laid
out printed circuit board with good ground plane makes a
difference in both stopband rejection and distortion.
Finally, equipment to measure filter performance can itself
introduce distortion or noise floors. Checking for these
limits with a wire replacing the filter is a prudent routine
procedure.
APPLICATIO S I FOR ATIO
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