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PDF VCA2614 Data sheet ( Hoja de datos )
| Número de pieza | VCA2614 | |
| Descripción | Dual/ VARIABLE GAIN AMPLIFIER with Input Buffer | |
| Fabricantes | Burr-Brown Corporation | |
| Logotipo |  |
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VCA2614
VCA2614
SBOS185D – JANUARY 2001 – REVISED MARCH 2003
Dual, VARIABLE GAIN AMPLIFIER
with Input Buffer
FEATURES
q GAIN RANGE: 40dB
q 40MHz BANDWIDTH
q LOW CROSSTALK: 70dB at Max Gain, 5MHz
q HIGH-SPEED VARIABLE GAIN ADJUST
q POWER SHUTDOWN MODE
q HIGH IMPEDANCE INPUT BUFFER
APPLICATIONS
q ULTRASOUND SYSTEMS
q GAMMA CAMERAS
q WIRELESS RECEIVERS
q TEST EQUIPMENT
CP2A
CP1A
DESCRIPTION
The VCA2614 is a highly integrated, dual receive channel,
Variable Gain Amplifier (VGA) with analog gain control.
The VCA2614’s VGA section consists of two parts: the Volt-
age Controlled Attenuator (VCA) and the Programmable Gain
Amplifier (PGA). The gain and gain range of the PGA can be
digitally programmed. The combination of these two program-
mable elements results in a variable gain ranging from 0dB up
to a maximum gain as defined by the user through external
connections. The single-ended unity gain input buffer provides
predictable high input impedance. The output of the VGA can
be used in either a single-ended or differential mode to drive
high-performance Analog-to-Digital Converters (ADCs). A sepa-
rate power-down pin reduces power consumption.
The VCA2614 also features low crosstalk and outstanding
distortion performance. The combination of low noise and gain
range programmability makes the VCA2614 a versatile build-
ing block in a number of applications where noise perfor-
mance is critical. The VCA2614 is available in a TQFP-32
package.
VCA2614
(1 of 2 Channels)
Voltage
INA
Buffer
Control
Attenuator
Programmable
Gain Amplifier
NOUTA
POUTA
VCACNTL
Analog
Control
Maximum Gain
Select
MGS1
MGS2
MGS3
Maximum
Gain Select
Voltage
INB
Buffer
Control
Attenuator
Programmable
Gain Amplifier
NOUTB
POUTB
CP2B
CP1B
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.
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.
www.ti.com
Copyright © 2001-2003, Texas Instruments Incorporated
1 page  
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VDD = 5V, load resistance = 500Ω on each output to ground, differential output (2Vp-p) MGS = 011, and fIN = 5MHz, unless otherwise noted.
50
45
40
35
30
25
20
15
10
5
0
100k
GAIN vs FREQUENCY
(VCACNTL = 3.0V)
MGS = 111
MGS = 011
MGS = 001
1M 10M
Frequency (Hz)
100M
35
30
25
20
15
10
5
0
–5
–10
–15
100k
GAIN vs FREQUENCY
VCACNTL = 3.0V
VCACNTL = 1.6V
VCACNTL = 0.2V
1M 10M
Frequency (Hz)
100M
OUTPUT REFERRED NOISE vs VCACNTL
450
RS= 50Ω
400
MGS = 111
350
300
250
200
MGS = 011
150
100
50
0
0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
VCACNTL (V)
INPUT REFERRED NOISE vs RS
100
10
1
1 10 100 1k
RS (Ω)
INPUT REFERRED NOISE vs VCACNTL
220
200 RS= 50Ω
180
160
140
120 MGS = 111
100
80
60
MGS = 011
40
20
0
0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
VCACNTL (V)
24
22
20
18
16
14
12
10
8
6
4
2
10
NOISE FIGURE vs RS
100
RS (Ω)
1k
VCA2614
SBOS185D
www.ti.com
5
5 Page 
PGA POST-AMPLIFIER
Figure 5 shows a simplified circuit diagram of the PGA block.
As stated before, the input to the PGA is AC-coupled by an
internal capacitor. Provisions are made so that an external
capacitor can be placed in parallel with the internal capacitor,
thus lowering the usable low-frequency bandwidth. The low-
frequency bandwidth is set by the following equation:
1
( )2 • π • 500kΩ • (220pF + CEXTERNAL )
where CEXTERNAL is the external capacitor value in picofarads.
Care should be taken to avoid using too large a value of
capacitor, as this can increase the power-on delay time.
As described previously, the PGA gain is programmed with
the same MGS bits that control the VCA maximum attenua-
tion factor. Specifically, the maximum PGA gain at each
MGS setting is the inverse (reciprocal) of the maximum VCA
attenuation at that setting. Therefore, the VCA + PGA overall
gain will always be 0dB (unity) when the analog VCACNTL
input is set to 0V (the maximum attenuation for VCA). For
VCACNTL = 3V (no attenuation), the VCA + PGA gain will be
controlled by the programmed PGA gain. For clarity, the gain
and attenuation factors are detailed in Table I.
The PGA architecture converts the single-ended signal from
the VCA into a differential signal. Low input noise was also
a requirement of the PGA design due to the large amount of
signal attenuation that can be asserted before the PGA. At
minimum VCA attenuation (used for small input signals), the
MGS
SETTING
000
001
010
011
100
101
110
111
ATTENUATOR GAIN
VCACNTL = 0.02V to 3V
Not Valid
–24.1dB to 0dB
–26.9dB to 0dB
–29.5dB to 0dB
–32.4dB to 0dB
–34.8dB to 0dB
–37.3dB to 0dB
–40.0dB to 0dB
TABLE I. MGS Settings.
ATTENUATOR +
DIFFERENTIAL PGA GAIN
Not Valid
2.6dB to 26.7dB
2.6dB to 29.5dB
3.0dB to 35.6dB
3.1dB to 35.5dB
3.4dB to 38.3dB
3.7dB to 44.1dB
4.1dB to 44.2dB
input buffer noise dominates; at maximum VCA attenuation
(large input signals), the PGA noise dominates. Note that if
the PGA output is used single-ended, the apparent gain will
be 6dB lower.
LAYOUT CONSIDERATIONS
The VCA2614 is an analog amplifier capable of high gain.
When working on a PCB layout for the VCA2614, it is
recommended to utilize a solid ground plane that is con-
nected to analog ground. This helps to maximize the noise
performance of the VCA2614.
Adequate power-supply decoupling must be used in order to
achieve the best possible performance. Decoupling capaci-
tors on the VCACNTL voltage should also be used to help
minimize noise. Recommended values can be obtained from
the layout diagram of Figure 6.
VCAOUTP
RL Q1
Q11
VDD
Q12
To Bias
Circuitry
Q9 RL
VCM
+In
Q3
Q4
Q2
RS1 Q13
RS2
Q14
Q5 Q6
Q8
VCM
Q7
Q10
To Bias
Circuitry
–In
VCAOUTN
FIGURE 5. Simplified Block Diagram of the PGA Section with the VCA2614.
VCA2614
SBOS185D
www.ti.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet VCA2614.PDF ] | |
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