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PDF VCA2617 Data sheet ( Hoja de datos )
| Número de pieza | VCA2617 | |
| Descripción | Variable Gain Amplifier | |
| Fabricantes | Burr-Brown | |
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VCA2617
Dual, Variable Gain Amplifier
SBOS326 −AUGUST 2005
FEATURES
D INDEPENDENT CHANNEL CONTROLS:
− Gain Range: 48dB
− Clamping Levels
− Post-Gain: 0, +6dB
D LOW NOISE: 4.1nV//Hz
D LOW POWER: 52mW/Channel
D BANDWIDTH: 50MHz
D HARMONIC DISTORTION: −53dBc at 5MHz
D CROSSTALK: −61dB at 5MHz
D 5V SINGLE SUPPLY
D POWER-DOWN MODE
D SMALL QFN-32 PACKAGE (5x5mm)
APPLICATIONS
D MEDICAL AND INDUSTRIAL ULTRASOUND
SYSTEMS
− Suitable for 10-Bit and 12-Bit Systems
D TEST EQUIPMENT
D SONAR
DESCRIPTION
The VCA2617 is a dual-channel, continuously variable,
voltage-controlled gain amplifier well-suited for a variety of
ultrasound systems as well as applications in proximity
detectors and test equipment. The VCA2617 uses a true
variable-gain amplifier architecture, achieving very good
noise performance at low gains, while not sacrificing high gain
distortion performance.
Following a linear-in-dB response, the VCA2617 gain can be
varied over a 48dB range with a 0.2V to 2.3V control voltage.
Two separate high-impedance control inputs allow for a
channel independent variation of the gains. Each channel of
the VCA2617 can be configured to provide a gain range of
−10dB to 38dB, or −16dB to 32dB, depending on the gain
select pin (HG). This post-gain feature allows the user to
optimize the output swing of VCA2617 for a variety of
high-speed analog-to-digital converters (ADC). As a means to
improve system overload recovery time, the VCA2617 also
provides an internal clamping circuitry where an externally
applied voltage sets the desired output clamping level.
The VCA2617 operates on a single +5V supply while
consuming only 52mW per channel. It is available in a small
QFN-32 package (5x5mm).
RELATED PRODUCTS
PART NUMBER
DESCRIPTION
VCA2615
Dual, Low-Noise, Variable-Gain Amplifier with
Preamp
In A+
In A−
In B+
In B−
VCNTLA
V− I
V− I
VCLMPA
Gain CEXTA
Select A
Clamping
Circuitry
I−V
Clamping
Circuitry
I−V
Out A+
Out A−
Out B+
Out B−
VCNTLB
VCLMPB
Gain
Select B CEXTB
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Products
conform to specifications per the terms of Texas Instruments standard warranty.
Production processing does not necessarily include testing of all parameters.
Copyright 2005, Texas Instruments Incorporated
www.ti.com
1 page  
VCA2617
www.datasheet4wuw.cwom.ti.com
SBOS326 −AUGUST 2005
TYPICAL CHARACTERISTICS
All specifications at TA = +25°C, VDD = 5V, load resistance = 500Ω on each output to ground, differential output (1VPP), CA, CB = 3.9µF,
single-ended input configuration, fIN = 5MHz, HG = Low (High-Gain Mode), VCNTL = 2.3V, unless otherwise noted.
GAIN vs VCNTL
60
55
50
45
40
35 HG = 0
30
25
20
15
10
5
HG = 1
0
−5
−10
−15
−20
VCNTL (V)
Figure 1
2.0
1.5
1.0
0.5
0
−0.5
−1.0
−1.5
−2.0
GAIN ERROR vs VCNTL
HG = 0
HG = 1
VCNTL (V)
Figure 2
GAIN vs VCNTL vs FREQUENCY
50
40
30
20
10
0 1MHz
2MHz
−10 5MHz
10MHz
−20
VCNTL (V)
Figure 3
2.0
1.5
1.0
0.5
0
−0.5
−1.0
−1.5
−2.0
GAIN ERROR vs VCNTL vs FREQUENCY
1MHz
2MHz
5MHz
10MHz
VCNTL (V)
Figure 4
GAIN vs VCNTL vs TEMPERATURE
45
40
35
30 −40_ C
25
20
15 +25_ C
10
5 +85_ C
0
−5
−10
−15
VCNTL (V)
Figure 5
2.0
1.5
1.0
0.5
0
−0.5
−1.0
−1.5
−2.0
GAIN ERROR vs VCNTL vs TEMPERATURE
+25_C
−40_C
+85_C
VCNTL (V)
Figure 6
5
5 Page 
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THEORY OF OPERATION
The VCA2617 is a dual-channel variable gain amplifier
(VGA) with each channel being independant. The VGA is
a true variable-gain amplifier, achieving lower noise output
at lower gains. The output amplifier has two gains, allowing
for further optimization with different analog-to-digital
converters. Figure 34 shows a simplified block diagram of
a single channel of the dual-channel system. The VGA can
be powered down in order to conserve system power when
necessary.
VGA
Figure 34. Simplified Block Diagram of VCA2617
VGA—OVERVIEW
The VGA that is used with the VCA2617 is a true
variable-gain amplifier; as the gain is reduced, the noise
contribution from the VGA itself is also reduced. This
design is in contrast with another popular device
architecture (used by the VCA2619), where an effective
VCA characteristic is obtained by a voltage-variable
attenuator succeeded by a fixed-gain amplifier. At the
highest gain, systems with either architecture are
dominated by the noise produced at the input to either the
fixed or variable gain amplifier. At low gains, however, the
noise output is dominated by the contribution from the
VGA. Therefore, the overall system with lower VGA gain
will produce less noise.
The following example will illustrate this point. Figure 34
shows a block diagram of the variable-gain amplifier;
Figure 35 shows a block diagram of a variable attenuation
attenuator followed by a fixed gain amplifier. For purposes
of this example, let us assume the performance
characteristics shown in Table 1; these values are the
typical performance data of the VCA2617 and the
VCA2619.
VCA2617
SBOS326 −AUGUST 2005
Table 1. Gain and Noise Performance of Various
VCA Blocks
BLOCK
Buffer
Attenuator (VCA2619)
Attenuator (VCA2619)
VCA1 (VCA2617)
VCA1 (VCA2617)
VCA1 (VCA2619)
GAIN (Loss) dB
0
0
−40
40
0
40
NOISE nV/√Hz
3.9
2.2
2.2
4.1
90
3.9
When the block diagram shown in Figure 34 has a gain of
40dB, the noise referred to the input (RTI) is:
Total Noise (RTI) + 4.1nVń ǸHz
(1)
When the block diagram shown in Figure 35 has the
combined gain of 60dB, the noise referred to the input
(RTI) is given by the expression:
Total Noise (RTI) +
Ǹ(Buffer Noise)2 ) (ATTEN Noise)2 ) (VCA Noise)2
Ǹ+ (3.9)2 ) (2.2)2 ) (3.9)2 + 5.9nVń ǸHz
(2)
Repeating the above measurements for both VCA
configurations when the overall gain is 10dB yields the
following results:
For the VCA with a variable gain amplifier (Figure 34):
Total Noise (RTI) + 90nVń ǸHz
(3)
For the VCA with a variable attenuation attenuator
(Figure 35):
Total Noise + Ǹ(3.9)2 ) (2.2)2 ) (2.0ń0.10)2
+ 14nVń ǸHz
(4)
The VGA has a continuously-variable gain range of 48dB
with the ability to select either of two options. The gain of
the VGA can either be varied from −10dB to 38dB, or from
−16dB to 32dB. The VGA output can be programmed to
clip at a predetermined voltage that is selected by the user.
When the user applies a voltage to the VCLMP-pin, the
output will have a peak-to-peak voltage that is given by the
graph shown in Figure 26.
Buffer
ATTENUATOR
Amplifier
Figure 35. Block Diagram of Older VCA Models
11
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| PDF Descargar | [ Datasheet VCA2617.PDF ] | |
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