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PDF LT6604-15 Data sheet ( Hoja de datos )
| Número de pieza | LT6604-15 | |
| Descripción | Dual Very Low Noise Differential Amplifier and 15MHz Lowpass Filter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n Dual Differential Amplifier with 15MHz Lowpass
Filters
4th Order Filters
Approximates Chebyshev Response
Guaranteed Phase and Gain Matching
Resistor-Programmable Differential Gain
n 76dB Signal-to-Noise (3V Supply, 2VP-P Output)
n Low Distortion, 2VP-P, 800Ω Load, VS = 3V
1MHz: 86dBc 2nd, 90dBc 3rd
10MHz: 63dBc 2nd, 69dBc 3rd
n Specified for Operation with 3V, 5V and ±5V Supplies
n Fully Differential Inputs and Outputs
n Adjustable Output Common Mode Voltage
n Small 4mm × 7mm × 0.75mm QFN Package
APPLICATIONS
n Dual Differential ADC Driver Plus Filter
n Single-Ended to Differential Converter
n Matched, Dual, Differential Filter Stage
n Common Mode Translation of Differential Signals
n High Speed ADC Antialiasing and DAC Smoothing in
Wireless Infrastructure or Networking Applications
n High Speed Test and Measurement Equipment
n Medical Imaging
LT6604-15www.DataSheet4U.com
Dual Very Low Noise,
Differential Amplifier and
15MHz Lowpass Filter
DESCRIPTION
The LT®6604-15 consists of two matched, fully differential
amplifiers, each with a 4th order, 15MHz lowpass filter. The
fixed frequency lowpass filter approximates a Chebyshev
response. By integrating a filter and a differential ampli-
fier, distortion and noise are made exceptionally low. At
unity gain, the measured in band signal-to-noise ratio is
an impressive 76dB. At higher gains, the input referred
noise decreases, allowing the part to process smaller
input differential signals without significantly degrading
the signal-to-noise ratio.
Gain and phase are highly matched between the two chan-
nels. Gain for each channel is independently programmed
using two external resistors. The LT6604-15 enables level
shifting by providing an adjustable output common mode
voltage, making it ideal for directly interfacing to ADCs.
The LT6604-15 is fully specified for 3V operation. The
differential design enables outstanding performance at
a 2VP-P signal level for a single 3V supply. See the back
page of this datasheet for a complete list of related single
and dual differential amplifiers with integrated 2.5MHz to
20MHz lowpass filters.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
536Ω
0.01μF +
536Ω
–
LT6604-15
+INA
VMIDA
VOCMA
+
–INA –
–
+
536Ω
0.01μF +
536Ω
–
+INB
VMIDB
VOCMB
+
–INB –
–
+
V–
V+A
–OUTA
3V
50Ω
+OUTA
50Ω
V+B
–OUTB
3V
50Ω
+OUTB
50Ω
3V
LTC22xx
DUAL ADC
+
18pF AIN
–
DOUT
+
18pF AIN
–
DOUT
660415 TA01
Channel to Channel Gain Matching
16
50 TYPICAL UNITS
14
TA = 25°C
GAIN = 1
12 fIN = 15MHz
10
8
6
4
2
0
–0.25–0.2–0.15–0.1–0.05 0 0.05 0.1 0.15 0.2 0.25
GAIN MATCH (dB)
660415 TA01b
660415fa
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT6604-15www.DataSheet4U.com
Amplitude Response
10
0
–10
–20
–30
–40
–50
VS = 5V
GAIN = 1
TA = 25°C
–60
0.1
1 10
FREQUENCY (MHz)
100
660415 G01
Passband Gain and Phase
1
VS = 5V
0 GAIN = 1
–1
GAIN
TA = 25°C
225
180
135
–2 90
–3
PHASE
–4
45
0
–5 –45
–6 –90
–7 –135
–8 –180
–9 –225
0 5 10 15 20 25
FREQUENCY (MHz)
660415 G02
Passband Gain and Delay
1
VS = 5V
0 GAIN = 1
–1
GAIN
TA = 25°C
50
45
40
–2 35
–3 DELAY
30
–4 25
–5 20
–6 15
–7 10
–8 5
–9 0
0 5 10 15 20 25
FREQUENCY (MHz)
660415 G03
Passband Gain and Delay
14
12
10 GAIN
VS = 5V
GAIN = 4
TA = 25°C
50
45
40
8 35
6 30
DELAY
4 25
2 20
0 15
–2 10
–4 5
–6 0
0 5 10 15 20 25
FREQUENCY (MHz)
660415 G04
Power Supply Rejection Ratio
80
70
60
50
40
30
20 VS = 3V
10
VIN = 200mVP-P
VTA+
= 25°C
TO DIFFOUT
0
0.1 1
10
FREQUENCY (MHz)
100
660415 G07
Output Impedance
100
VS = 5V
GAIN = 1
TA = 25°C
10
1
0.1
0.1
1 10
FREQUENCY (MHz)
100
660415 G05
Common Mode Rejection Ratio
80
VIN = 1VP-P
75 VS = 5V
GAIN = 1
70 TA = 25°C
65
60
55
50
45
40
35
30
0.1
1 10
FREQUENCY (MHz)
100
660415 G06
Distortion vs Frequency
–50
VIN = 2VP-P
VS = 3V
–60 RL = 800Ω AT
EACH OUTPUT
GAIN = 1
–70 TA = 25°C
–80
–90
–100
–110
0.1
1 10
FREQUENCY (MHz)
100
660415 G08
DIFFERENTIAL INPUT, 2ND HARMONIC
DIFFERENTIAL INPUT, 3RD HARMONIC
SINGLE-ENDED INPUT, 2ND HARMONIC
SINGLE-ENDED INPUT, 3RD HARMONIC
Distortion vs Signal Level
–40
VS = 3V
3RD HARMONIC
–50
RL = 800Ω AT
EACH OUTPUT
10MHz INPUT
GAIN = 1
–60 TA = 25°C
–70
–80
–90
–100
2ND
HARMONIC
10MHz INPUT
2ND
HARMONIC
1MHz INPUT
3RD
HARMONIC
1MHz INPUT
–110
0
12345
INPUT LEVEL (VP-P)
660415 G09
660415fa
5
5 Page 
LT6604-15www.DataSheet4U.com
APPLICATIONS INFORMATION
where impedance must be considered is the evaluation of
the LT6604-15 with a network analyzer.
Figure 5 is a laboratory setup that can be used to char-
acterize the LT6604-15 using single-ended instruments
with 50Ω source impedance and 50Ω input impedance.
For a unity gain configuration the LT6604-15 requires
an 536Ω source resistance yet the network analyzer
output is calibrated for a 50Ω load resistance. The 1:1
transformer, 52.3Ω and 523Ω resistors satisfy the two
constraints above. The transformer converts the single-
ended source into a differential stimulus. Similarly, the
output of the LT6604-15 will have lower distortion with
larger load resistance yet the analyzer input is typically
50Ω. The 4:1 turns (16:1 impedance) transformer and the
two 402Ω resistors of Figure 5, present the output of the
LT6604-15 with a 1600Ω differential load, or the equiva-
lent of 800Ω to ground at each output. The impedance
seen by the network analyzer input is still 50Ω, reducing
reflections in the cabling between the transformer and
analyzer input.
Differential and Common Mode Voltage Ranges
The differential amplifiers inside the LT6604-15 contain
circuitry to limit the maximum peak-to-peak differential
voltage through the filter. This limiting function prevents
excessive power dissipation in the internal circuitry and
provides output short-circuit protection. The limiting
function begins to take effect at output signal levels
20 1dB COMPRESSION
POINTS
25°C
0 85°C
–20 3RD HARMONIC
85°C
–40 3RD HARMONIC
25°C
–60 2ND
HARMONIC
–80 85°C
–100
0
2ND HARMONIC, 25°C
1 2 34 5 6 7
1MHz INPUT LEVEL (VP-P)
660415 F06
Figure 6. Output Level vs Input Level, Differential
1MHz Input, Gain = 1
above 2VP-P and it becomes noticeable above 3.5VP-P.
This is illustrated in Figure 6; the LT6604-15 channel was
configured with unity passband gain and the input of the
filter was driven with a 1MHz signal. Because this voltage
limiting takes place well before the output stage of the
filter reaches the supply rails, the input/output behavior
of the IC shown in Figure 6 is relatively independent of
the power supply voltage.
The two amplifiers inside the LT6604-15 channel have
independent control of their output common mode voltage
(see the Block Diagram section). The following guidelines
will optimize the performance of the filter.
VMID can be allowed to float, but it must be bypassed to an
AC ground with a 0.01μF capacitor or some instability may
be observed. VMID can be driven from a low impedance
source, provided it remains at least 1.5V above V– and at
least 1.5V below V+. An internal resistor divider sets the
voltage of VMID. While the internal 11k resistors are well
matched, their absolute value can vary by ±20%. This
should be taken into consideration when connecting an
external resistor network to alter the voltage of VMID.
VOCM can be shorted to VMID for simplicity. If a different
common mode output voltage is required, connect VOCM
to a voltage source or resistor network. For 3V and 3.3V
supplies the voltage at VOCM must be less than or equal
to the mid supply level. For example, voltage (VOCM) ≤
1.65V on a single 3.3V supply. For power supply voltages
higher than 3.3V the voltage at VOCM can be set above mid
supply. The voltage on VOCM should not be more than 1V
below the voltage on VMID. The voltage on VOCM should
not be more than 2V above the voltage on VMID. VOCM is
a high impedance input.
The LT6604-15 was designed to process a variety of input
signals including signals centered on the mid-supply volt-
age and signals that swing between ground and a positive
voltage in a single supply system (Figure 1). The range of
allowable input common mode voltage (the average of VIN+
and VIN– in Figure 1) is determined by the power supply
level and gain setting (see Distortion vs Input Common
Mode Level in the Typical Performance Characteristics).
660415fa
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT6604-15.PDF ] | |
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