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PDF VCA2613 Data sheet ( Hoja de datos )
| Número de pieza | VCA2613 | |
| Descripción | Dual/ VARIABLE GAIN AMPLIFIER with Low-Noise Preamp | |
| Fabricantes | Burr-Brown Corporation | |
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VCA2613
VCA2613
SBOS179D – DECEMBER 2000 – REVISED OCTOBER 2004
Dual, VARIABLE GAIN AMPLIFIER
with Low-Noise Preamp
FEATURES
q LOW NOISE PREAMP:
Low Input Noise: 1.0nV/√Hz
Active Termination Noise Reduction
Switchable Termination Value
80MHz Bandwidth
5dB to 25dB Gain
Differential In and Out
q LOW NOISE VARIABLE GAIN AMPLIFIER:
Low Noise VCA: 3.3nV/√Hz, Differential
Programming Optimizes Noise Figure
24dB to 45dB Gain
40MHz Bandwidth
Differential In and Out
q LOW CROSSTALK: 52dB at Max Gain, 5MHz
q HIGH-SPEED VARIABLE GAIN ADJUST
q SWITCHABLE EXTERNAL PROCESSING
APPLICATIONS
q ULTRASOUND SYSTEMS
q WIRELESS RECEIVERS
q TEST EQUIPMENT
DESCRIPTION
The VCA2613 is a dual, Low-Noise Preamplifier (LNP), plus
low-noise Variable Gain Amplifier (VGA). The combination of
Active Termination (AT) and Maximum Gain Select (MGS)
allow for the best noise performance. The VCA2613 also
features low crosstalk and outstanding distortion perfor-
mance.
The LNP has differential input and output capability and is
strappable for gains of 5dB, 17dB, 22dB or 25dB. Low input
impedance is achieved by AT, resulting in as much as a 4.6dB
improvement in noise figure over conventional shunt termina-
tion. The termination value can also be switched to accommo-
date different sources. The output of the LNP is available for
external signal processing.
The variable gain is controlled by an analog voltage whose
gain varies from 0dB to the gain set by the MGS. The ability
to program the variable gain also allows the user to optimize
dynamic range. The VCA input can be switched from the
LNP to external circuits for different applications. The output
can be used in either a single-ended or differential mode to
drive high-performance Analog-to-Digital (A/D) converters,
and is cleanly limited for optimum overdrive recovery.
The combination of low noise, gain, and gain range program-
mability makes the VCA2613 a versatile building block in a
number of applications where noise performance is critical.
The VCA2613 is available in a TQFP-48 package.
FBCNTL
LNPOUTN VCAINN
RF2 FBSW
RF1 FB
VCA2613
(1 of 2 Channels)
VCACNTL
Analog
Control
Input
LNPINP
LNPGS1
LNP LNPGS2
Gain Set
LNPGS3
LNPINN
Low Noise
Preamp
5dB to 25dB
Voltage
Controlled
Attenuator
Maximum Gain Select
MGS0 MGS1 MGS2
Maximum Gain
Select
Programmable
Gain Amplifier
24 to 45dB
VCAOUTN
VCAOUTP
LNPOUTP VCAINP
SEL
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.
www.ti.com
Copyright © 2000-2004, Texas Instruments Incorporated
1 page  
THEORY OF OPERATION
The VCA2613 is a dual-channel system consisting of three
primary blocks: a Low Noise Preamplifier (LNP), a Voltage
Controlled Attenuator (VCA), and a Programmable Gain
Amplifier (PGA). For greater system flexibility, an onboard
multiplexer is provided for the VCA inputs, selecting either
the LNP outputs or external signal inputs. Figure 1 shows a
simplified block diagram of the dual-channel system.
op amp. The VCM node shown in the drawing is the VCM
output (pin 19). Typical R and C values are shown, yielding
a high-pass time constant similar to that of the LNP. If a
different common-mode referencing method is used, it is
important that the common-mode level be within 10mV of the
VCM output for proper operation.
1kΩ
External
InA
Channel A
Input
LNP
VCA
PGA
Channel A
Output
VCA
Control
Analog
Control
Maximum
Gain
Select
MGS
Input
Signal
47nF
1kΩ
To VCAIN
VCM (+2.5V)
FIGURE 2. Recommended Circuit for Coupling an External
Signal into the VCA Inputs.
Channel B
Input
LNP
VCA
PGA
Channel B
Output
External
InB
FIGURE 1. Simplified Block Diagram of the VCA2613.
LNP—OVERVIEW
The LNP input may be connected to provide active-feedback
signal termination, achieving lower system noise perfor-
mance than conventional passive shunt termination. Even
lower noise performance is obtained if signal termination is
not required. The unterminated LNP input impedance is
600kΩ. The LNP can process fully differential or single-
ended signals in each channel. Differential signal processing
results in significantly reduced 2nd-harmonic distortion and
improved rejection of common-mode and power-supply noise.
The first gain stage of the LNP is AC-coupled into its output
buffer with a 44µs time constant (3.6kHz high-pass charac-
teristic). The buffered LNP outputs are designed to drive the
succeeding VCA directly or, if desired, external loads as low
as 135Ω with minimal impact on signal distortion. The LNP
employs very low impedance local feedback to achieve
stable gain with the lowest possible noise and distortion.
Four pin-programmable gain settings are available: 5dB,
17dB, 22dB, and 25dB. Additional intermediate gains can be
programmed by adding trim resistors between the Gain Strap
programming pins.
The common-mode DC level at the LNP output is nominally
2.5V, matching the input common-mode requirement of the
VCA for simple direct coupling. When external signals are
fed to the VCA, they should also be set up with a 2.5VDC
common-mode level. Figure 2 shows a circuit that demon-
strates the recommended coupling method using an external
VCA—OVERVIEW
The magnitude of the differential VCA input signal (from the
LNP or an external source) is reduced by a programmable
attenuation factor, set by the analog VCA Control Voltage
(VCACNTL) at pin 43. The maximum attenuation factor is
further programmable by using the three MGS bits (pins 40-
42). Figure 3 illustrates this dual-adjustable characteristic.
Internally, the signal is attenuated by having the analog
VCACNTL vary the channel resistance of a set of shunt-
connected FET transistors. The MGS bits effectively adjust
the overall size of the shunt FET by switching parallel
components in or out under logic control. At any given
maximum gain setting, the analog variable gain characteris-
tic is linear in dB as a function of the control voltage, and is
created as a piecewise approximation of an ideal dB-linear
transfer function. The VCA gain control circuitry is common
to both channels of the VCA2613.
0
Minimum Attenuation
–24
–45
0
Maximum Attenuation
Control Voltage
FIGURE 3. Swept Attenuator Characteristic.
3.0V
VCA2613
SBOS179D
www.ti.com
5
5 Page 
Attenuator
Input
RS
A1 - A10 Attenuator Stages
QS
Attenuator
Output
VCM
A1
Q1
A2
Q2
A3
Q3
A4
Q4
A5
Q5
A6
Q6
A7
Q7
A8
Q8
A9
Q9
A10
Q10
C1 C2
C3 C4
C5
C6 C7 C8 C9 C10
V1 V2
V3 V4
V5
V6 V7 V8 V9 V10
Control
Input
C1 - C10 Clipping Amplifiers
0dB
–4.5dB
VCM-VT
Attenuation Characteristic of Individual FETs
0
V1 V2 V3 V4 V5 V6 V7 V8 V9 V10
Characteristic of Attenuator Control Stage Output
OVERALL CONTROL CHARACTERISTICS OF ATTENUATOR
0dB
–4.5dB
0.3V
Control Signal
FIGURE 12. Piecewise Approximation to Logarithmic Control Characteristics.
VCA2613
SBOS179D
www.ti.com
3V
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet VCA2613.PDF ] | |
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