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부품번호 VCA2613 기능
기능 Dual/ VARIABLE GAIN AMPLIFIER with Low-Noise Preamp
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VCA2613 데이터시트, 핀배열, 회로
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




VCA2613 pdf, 반도체, 판매, 대치품
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500on each output to ground, MGS = 011, LNP = 22dB and fIN = 5MHz, unless otherwise noted.
The input to the preamp (LNP) is single-ended, and the output from the VCA is single-ended unless otherwise noted. This results in a 6dB reduction in signal
amplitude compared to differential operation.
GAIN vs VCACNTL
65
MGS = 111
60
MGS = 110
55
MGS = 101
50
45
MGS = 100
40
35
MGS = 011
30
MGS = 010
25
MGS = 001
20
MGS = 000
15
0.2 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)
2000
OUTPUT REFERRED NOISE vs VCACNTL
1800
1600
RS = 50
1400
1200
1000
800
MGS = 111
600
400
200
MGS = 011
0
0.2 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 VCACNTL
20
18
RS = 50
16
14
12
10
MGS = 111
8
6
4
MGS = 011
2
0
0.2 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)
10.0
INPUT REFERRED NOISE vs RS
1.0
0.1
1
10 100
RS ()
1000
9
8
7
6
5
4
3
2
1
0
10
NOISE FIGURE vs RS
100
RS ()
1000
NOISE FIGURE vs VCACNTL
20
18
16
14
12
10
8
6
4
2
0
0.2 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)
4 VCA2613
www.ti.com
SBOS179D

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VCA2613 전자부품, 판매, 대치품
where RL is the load resistor in the drains of Q3 and Q8, and
RS is the resistor connected between the sources of the input
transistors Q4 and Q7. The connections for various RS com-
binations are brought out to device pins LNPGS1, LNPGS2,
and LNPGS3 (pins 13-15 for channel A, 22-24 for channel B).
These Gain Strap pins allow the user to establish one of four
fixed LNP gain options as shown in Table I.
LNP PIN STRAPPING
LNPGS1, LNPGS2, LNPGS3 Connected Together
LNPGS1 Connected to LNPGS3
LNPGS1 Connected to LNPGS2
All Pins Open
LNP GAIN (dB)
25
22
17
5
TABLE I. Pin Strappings of the LNP for Various Gains.
It is also possible to create other gain settings by connecting
an external resistor between LNPGS1 on one side, and
LNPGS2 and/or LNPGS3 on the other. In that case, the
internal resistor values shown in Figure 4 should be com-
bined with the external resistor to calculate the effective
value of RS for use in Equation (1). The resulting expression
for external resistor value is given in Equation (2).
REXT
=
2RS1RL
+ 2RFIXRL Gain RS1RFIX
Gain RS1 2RL
(2)
where REXT is the externally selected resistor value needed
to achieve the desired gain setting, RS1 is the fixed parallel
resistor in Figure 4, and RFIX is the effective fixed value of the
remaining internal resistors: RS2, RS3, or (RS2 || RS3) depend-
ing on the pin connections.
Note that the best process and temperature stability will be
achieved by using the pre-programmed fixed gain options of
Table I, since the gain is then set entirely by internal resistor
ratios, which are typically accurate to ±0.5%, and track quite
well over process and temperature. When combining exter-
nal resistors with the internal values to create an effective RS
value, note that the internal resistors have a typical tempera-
ture coefficient of +700ppm/°C and an absolute value toler-
ance of approximately ±5%, yielding somewhat less predict-
able and stable gain settings. With or without external resis-
tors, the board layout should use short Gain Strap connec-
tions to minimize parasitic resistance and inductance effects.
The overall noise performance of the VCA2613 will vary as
a function of gain. Table II shows the typical input- and
output-referred noise densities of the entire VCA2613 for
maximum VCA and PGA gain; i.e., VCACNTL set to 3.0V and
all MGS bits set to 1. Note that the input-referred noise
values include the contribution of a 50fixed source imped-
ance, and are therefore somewhat larger than the intrinsic
input noise. As the LNP gain is reduced, the noise contribu-
tion from the VCA/PGA portion becomes more significant,
resulting in higher input-referred noise. However, the output-
referred noise, which is indicative of the overall SNR at that
gain setting, is reduced.
To preserve the low noise performance of the LNP, the user
should take care to minimize resistance in the input lead. A
parasitic resistance of only 10will contribute 0.4nV/Hz.
LNP GAIN (dB)
25
22
17
5
NOISE (nV/Hz)
Input-Referred
Output-Referred
1.54
1.59
1.82
4.07
2260
1650
1060
597
TABLE II. Noise Performance for MGS = 111 and VCACNTL = 3.0V.
The LNP is capable of generating a 2VPP differential signal.
The maximum signal at the LNP input is therefore 2VPP
divided by the LNP gain. An input signal greater than this
would exceed the linear range of the LNP, an especially
important consideration at low LNP gain settings.
ACTIVE FEEDBACK WITH THE LNP
One of the key features of the LNP architecture is the ability
to employ active-feedback termination to achieve superior
noise performance. Active-feedback termination achieves a
lower noise figure than conventional shunt termination, es-
sentially because no signal current is wasted in the termina-
tion resistor itself. Another way to understand this is as
follows: Consider first that the input source, at the far end of
the signal cable, has a cable-matching source resistance of
RS. Using conventional shunt termination at the LNP input, a
second terminating resistor of value RS is connected to
ground. Therefore, the signal loss is 6dB due to the voltage
divider action of the series and shunt RS resistors. The
effective source resistance has been reduced by the same
factor of 2, but the noise contribution has been reduced by
only the 2, only a 3dB reduction. Therefore, the net theoreti-
cal SNR degradation is 3dB, assuming a noise-free amplifier
input. (In practice, the amplifier noise contribution will de-
grade both the unterminated and the terminated noise fig-
ures, somewhat reducing the distinction between them.)
See Figure 5 for an amplifier using active feedback. This
diagram appears very similar to a traditional inverting ampli-
fier. However, the analysis is somewhat different because
the gain A in this case is not a very large open-loop op amp
gain; rather it is the relatively low and controlled gain of the
LNP itself. Thus, the impedance at the inverting amplifier
terminal will be reduced by a finite amount, as given in the
familiar relationship of Equation (3):
RIN
=
RF
(1+ A)
(3)
where RF is the feedback resistor (supplied externally be-
tween the LNPINP and FB terminals for each channel), A is
the user-selected gain of the LNP, and RIN is the resulting
amplifier input impedance with active feedback. In this case,
unlike the conventional termination above, both the signal
voltage and the RS noise are attenuated by the same factor
VCA2613
SBOS179D
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