VCA2616
VCA2611
VCA
261
6
SBOS234D – MARCH 2002 – REVISED APRIL 2004
Dual, Variable-Gain Amplifier
with Low-Noise Preamp
FEATURES
DESCRIPTION
● LOW-NOISE PREAMP:
– Low Input Noise: 0.95nV/√Hz
– Active Termination Noise Reduction
– Switchable Termination Value
– 80MHz Bandwidth
– 5dB to 25dB Gain
– Differential In and Out
● LOW-NOISE VARIABLE GAIN AMPLIFIER:
– Low-Noise VCA
– Up to 40dB Gain Range
– 40MHz Bandwidth
– Differential In and Out
● LOW CROSSTALK: 66dB at Max Gain, 5MHz
The VCA2616 and VCA2611 are dual, Low-Noise Preamplifiers
(LNP), plus low-noise Variable Gain Amplifiers (VGA). The
VCA2611 is an upgraded version of the VCA2616. The only
difference between the VCA2616 and the VCA2611 is the input
structure to the LNP. The VCA2616 is limited to –0.3V negativegoing input spikes; the VCA2611 is limited to –2.0V negativegoing input spikes. This change allows the user to use slower
and less expensive input clamping diodes prior to the LNP input.
In some designs, input clamping may not be required.
The combination of Active Termination (AT) and Maximum
Gain Select (MGS) allow for the best noise performance. The
VCA2616 and VCA2611 also feature low crosstalk and outstanding distortion performance.
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 termination. The termination value can also be switched to accommodate different sources. The output of the LNP is available for
external signal processing.
● HIGH-SPEED VARIABLE GAIN ADJUST
● SWITCHABLE EXTERNAL PROCESSING
APPLICATIONS
● ULTRASOUND SYSTEMS
● WIRELESS RECEIVERS
● TEST EQUIPMENT
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 highperformance Analog-to-Digital (A/D) converters, and is cleanly
limited for optimum overdrive recovery.
Maximum Gain Select
FBCNTL
LNPOUTN VCAINN
VCACNTL
MGS1 MGS2 MGS3
Input
RF2
FBSW
RF1
FB
VCA2616
(1 of 2 Channels)
Analog
Control
Maximum Gain
Select
Voltage
Controlled
Attenuator
Programmable
Gain Amplifier
24 to 45dB
The combination of low noise, gain, and gain range programmability makes the VCA2616 and VCA2611 versatile building
blocks in a number of applications where noise performance
is critical. The VCA2616 and VCA2611 are available in a
TQFP-48 package.
LNPINP
VCAOUTN
LNP
Gain
Set
LNPGS1
LNPGS2
Low Noise
Preamp
5dB to 25dB
LNPGS3
VCAOUTP
LNPINN
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.
Copyright © 2002-2004, Texas Instruments Incorporated
www.ti.com
ELECTROSTATIC
DISCHARGE SENSITIVITY
ABSOLUTE MAXIMUM RATINGS(1)
Power Supply (+VS) ............................................................................. +6V
VCA2616 Analog Input ............................................ –0.3V to (+VS + 0.3V)
VCA2611 Analog Input ............................................ –2.0V to (+VS + 0.3V)
Logic Input ............................................................... –0.3V to (+VS + 0.3V)
Case Temperature ......................................................................... +100°C
Junction Temperature .................................................................... +150°C
Storage Temperature ...................................................... –40°C to +150°C
NOTE: (1) Stresses above those listed under “Absolute Maximum Ratings” may
cause permanent damage to the device. Exposure to absolute maximum
conditions for extended periods may affect device reliability.
PACKAGE/ORDERING INFORMATION(1)
PRODUCT
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling
and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits
may be more susceptible to damage because very small
parametric changes could cause the device not to meet its
published specifications.
PACKAGE-LEAD
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER
TRANSPORT
MEDIA, QUANTITY
TQFP-48
PFB
–40°C to +85°C
VCA2616
"
"
"
"
VCA2616YT
VCA2616YR
Tape and Reel, 250
Tape and Reel, 2000
TQFP-48
PFB
–40°C to +85°C
VCA2611
"
"
"
"
VCA2611Y/250
VCA2611Y/2K
Tape and Reel, 250
Tape and Reel, 2000
VCA2616
"
VCA2611
"
NOTE: (1) For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet.
ELECTRICAL CHARACTERISTICS
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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.
VCA2616Y, VCA2611Y
PARAMETER
PREAMPLIFIER
Input Resistance
Input Capacitance
Input Bias Current
CMRR
Maximum Input Voltage
Input Voltage Noise(1)
Input Current Noise
Noise Figure, RS = 75Ω, RIN = 75Ω(1)
Bandwidth
CONDITIONS
f = 1MHz, VCACNTL = 0.2V
Preamp Gain = +5dB
Preamp Gain = +25dB
Preamp Gain = +5dB
Preamp Gain = +25dB
Independent of Gain
RF = 550Ω, Preamp Gain = 22dB,
PGA Gain = 39dB
Gain = 22dB
PROGRAMMABLE VARIABLE GAIN AMPLIFIER
Peak Input Voltage
Differential
–3dB Bandwidth
Slew Rate
Output Signal Range
RL ≥ 500Ω Each Side to Ground
Output Impedance
f = 5MHz
Output Short-Circuit Current
3rd-Harmonic Distortion
f = 5MHz, VOUT = 1VPP, VCACNTL = 3.0V
2nd-Harmonic Distortion
f = 5MHz, VOUT = 1VPP, VCACNTL = 3.0V
IMD, 2-Tone
VOUT = 2VPP, f = 1MHz
VOUT = 2VPP, f = 10MHz
Crosstalk
VCACNTL = 0.2V
Group Delay Variation
1MHz < f < 10MHz, Full Gain Range
DC Output Level, VIN = 0
ACCURACY
Gain Slope
Gain Error
Output Offset Voltage
Total Gain
GAIN CONTROL INTERFACE
Input Voltage (VCACNTL) Range
Input Resistance
Response Time
POWER SUPPLY
Operating Temperature Range
Specified Operating Range
Power Dissipation
MIN
–45
–45
TYP
MAX
UNITS
600
15
1
50
1
112
4.2
0.95
0.35
6.2
kΩ
pF
nA
dB
VPP
mVPP
nV/ √Hz
nV/ √Hz
pA/ √Hz
dB
80
MHz
2
40
300
2
1
±40
–71
–63
–75
–75
–66
±2
2.5
VPP
MHz
V/µs
VPP
Ω
mA
dBc
dBc
dBc
dBc
dB
ns
V
10.9
VCACNTL = 0.2V
VCACNTL = 3.0V
18
47
24
53
0.2 to 3.0
1
0.2
40dB Gain Change, MGS = 111
–40
4.75
Operating, Both Channels
±50
21
50
dB/V
dB
mV
dB
dB
±1(2)
5.0
410
V
MΩ
µs
°C
V
mW
+85
5.25
495
NOTES: (1) For preamp driving VGA.
(2) Referenced to best fit dB-linear curve.
2
VCA2616, VCA2611
www.ti.com
SBOS234D
PIN CONFIGURATION
VCAOUTNA
VCAOUTPA
FBSWCNTL
VCAINSEL
VCACNTL
MGS1
MGS2
MGS3
VCAOUTPB
VCAOUTNB
GNDB
TQFP
GNDA
Top View
48
47
46
45
44
43
42
41
40
39
38
37
VDDA
1
36 VDDB
NC
2
35 NC
NC
3
34 NC
VCAINNA
4
33 VCAINNB
VCAINPA
5
32 VCAINPB
LNPOUTNA
6
LNPOUTPA
7
SWFBA
8
29 SWFBB
FBA
9
28 FBB
31 LNPOUTNB
VCA2616
VCA2611
30 LNPOUTPB
16
17
18
19
20
21
VCM
GNDR
LNPINPB
22
23
24
LNPGS3B
15
LNPGS2B
14
LNPGS1B
13
VBIAS
25 LNPINNB
VDDR
LNPINNA 12
LNPINPA
26 COMP2B
LNPGS1A
COMP2A 11
LNPGS2A
27 COMP1B
LNPGS3A
COMP1A 10
PIN DESCRIPTIONS
PIN
DESIGNATOR
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
VDDA
NC
NC
VCAINNA
VCAINPA
LNPOUTNA
LNPOUTPA
SWFBA
FBA
COMP1A
COMP2A
LNPINNA
LNPGS3A
LNPGS2A
LNPGS1A
LNPINPA
VDDR
VBIAS
VCM
GNDR
LNPINPB
LNPGS1B
LNPGS2B
LNPGS3B
DESCRIPTION
PIN
DESIGNATOR
Channel A +Supply
Do Not Connect
Do Not Connect
Channel A VCA Negative Input
Channel A VCA Positive Input
Channel A LNP Negative Output
Channel A LNP Positive Output
Channel A Switched Feedback Output
Channel A Feedback Output
Channel A Frequency Compensation 1
Channel A Frequency Compensation 2
Channel A LNP Inverting Input
Channel A LNP Gain Strap 3
Channel A LNP Gain Strap 2
Channel A LNP Gain Strap 1
Channel A LNP Noninverting Input
+Supply for Internal Reference
0.01µF Bypass to Ground
0.01µF Bypass to Ground
Ground for Internal Reference
Channel B LNP Noninverting Input
Channel B LNP Gain Strap 1
Channel B LNP Gain Strap 2
Channel B LNP Gain Strap 3
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
LNPINNB
COMP2B
COMP1B
FBB
SWFBB
LNPOUTPB
LNPOUTNB
VCAINPB
VCAINNB
NC
NC
VDDB
GNDB
VCAOUTNB
VCAOUTPB
MGS3
MGS2
MGS1
VCACNTL
VCAINSEL
FBSWCNTL
VCAOUTPA
VCAOUTNA
GNDA
VCA2616, VCA2611
SBOS234D
www.ti.com
DESCRIPTION
Channel B LNP Inverting Input
Channel B Frequency Compensation 2
Channel B Frequency Compensation 1
Channel B Feedback Output
Channel B Switched Feedback Output
Channel B LNP Positive Output
Channel B LNP Negative Output
Channel B VCA Positive Input
Channel B VCA Negative Input
Do Not Connect
Do Not Connect
Channel B +Analog Supply
Channel B Analog Ground
Channel B VCA Negative Output
Channel B VCA Positive Output
Maximum Gain Select 3 (LSB)
Maximum Gain Select 2
Maximum Gain Select 1 (MSB)
VCA Control Voltage
VCA Input Select, HI = External
Feedback Switch Control: HI = ON
Channel A VCA Positive Output
Channel A VCA Negative Output
Channel A Analog Ground
3
TYPICAL CHARACTERISTICS
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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.
2.0
MGS = 101 MGS = 100
60
1.5
55
1.0
Gain Error (dB)
MGS = 110
50
Gain (dB)
GAIN ERROR vs TEMPERATURE
GAIN vs VCACNTL
65
MGS = 111
45
40
35
30
+85°C
0.5
+25°C
0.0
–0.5
–1.0
25
MGS = 010 MGS = 011
20
–1.5
MGS = 000 MGS = 001
15
–40°C
–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
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)
VCACNTL (V)
GAIN ERROR vs VCACNTL
GAIN ERROR vs VCACNTL
2.0
2.0
1MHz
5MHz
10MHz
1.5
1.5
1.0
Gain Error (dB)
Gain Error (dB)
1.0
0.5
0.0
–0.5
MGS = 011
MGS = 000
0.5
0
–0.5
–1.0
–1.0
–1.5
–1.5
MGS = 111
–2.0
–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
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)
VCACNTL (V)
GAIN MATCH
0.2V CHA to CHB
GAIN MATCH
3.0V CHA to CHB
50
60
45
50
40
35
40
Units
Units
30
25
30
20
20
15
10
10
5
4
0.18
0.12
0.15
0.09
0.05
0.01
0.02
0.04
0.07
–0.14
–0.10
–0.20
–0.17
–0.26
0.36
0.23
0.29
0.16
0.10
0.04
–0.03
–0.16
–0.09
–0.29
–0.22
–0.42
–0.35
–0.48
–0.55
Delta Gain (dB)
–0.23
0
0
Delta Gain (dB)
VCA2616, VCA2611
www.ti.com
SBOS234D
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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 FREQUENCY
GAIN vs FREQUENCY
VCA
(Pre-Amp)
(VCACNTL = 0.2V)
30
5.0
LNA = 25dB
LNA = 22dB
4.0
25
3.0
2.0
Gain (dB)
Gain (dB)
20
15
LNA = 17dB
10
1.0
MGS = 011
–3.0
0
100k
45
1M
10M
MGS = 000
–4.0
LNA = 5dB
–5.0
100k
100M
1M
10M
Frequency (Hz)
Frequency (Hz)
GAIN vs FREQUENCY
VCA
(VCACNTL = 3.0V)
GAIN vs FREQUENCY
LNA and VCA
(VCACNTL = 3.0V)
60
MGS = 111
40
100M
LNP = 25dB
LNP = 22dB
50
35
MGS = 100
30
40
Gain (dB)
Gain (dB)
MGS = 100
–1.0
–2.0
5
25
MGS = 011
20
15
LNP = 17dB
30
LNP = 5dB
20
MGS = 000
10
10
5
0
100k
1M
10M
0
100k
100M
1M
10M
Frequency (Hz)
Frequency (Hz)
GAIN vs FREQUENCY
LNA and VCA
(LNP = 22dB)
OUTPUT-REFERRED NOISE vs VCACNTL
(LNP = 25dB)
60
2000
VCNTL = 3.0V
1800
50
100M
RS= 50Ω
1600
Noise (nV/√Hz)
VCNTL = 1.6V
40
Gain (dB)
MGS = 111
0.0
30
20
1400
1200
MGS = 111
1000
800
600
400
10
VCNTL = 0.2V
0
100k
200
1M
10M
100M
Frequency (Hz)
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)
VCA2616, VCA2611
SBOS234D
MGS = 011
0
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5
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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.
INPUT-REFERRED NOISE vs RS
(LNP = 25dB)
INPUT-REFERRED NOISE vs VCACNTL
(LNP = 25dB)
24
22
14
12
10
8
Noise (nV√Hz)
20
18
16
Noise (nV/√Hz)
10.0
RS = 50Ω
MGS = 111
6
4
2
MGS = 011
0
MGS = 111
1.0
0.1
1
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
10
100
NOISE FIGURE vs RS
(LNP = 25dB)
NOISE FIGURE vs VCACNTL
(LNP = 25dB)
9
8
Noise Figure (dB)
Noise Figure (dB)
7
6
MGS = 111
5
4
3
2
1
0
10
–30
100
VCACNTL (V)
DISTORTION vs FREQUENCY
MGS = 000
2VPP DIFFERENTIAL
DISTORTION vs FREQUENCY
MGS = 011
2VPP DIFFERENTIAL
VC = 0.2, H2
VC = 0.2, H3
VC = 3.0, H2
–60
–65
–70
–75
Distortion (dBc)
Harmonic (dBc)
–55
VC = 3.0, H3
–80
–85
100k
6
MGS = 111
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
1k
–40
–50
30
28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
RS (Ω)
–35
–45
1M
Frequency (Hz)
1k
RS (Ω)
VCACNTL (V)
–30
–35
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
VC = 0.2, H2
VC = 0.2, H3
VC = 3.0, H2
100k
10M
VC = 3.0, H3
1M
Frequency (Hz)
10M
VCA2616, VCA2611
www.ti.com
SBOS234D
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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.
DISTORTION vs FREQUENCY
MGS = 111
2VPP DIFFERENTIAL
–30
–35
VC = 0.2, H2
VC = 0.2, H3
–45
Distortion (dBc)
Distortion (dBc)
–40
–50
–55
VC = 3.0, H2
–60
–65
–70
–75
–30
–35
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
VC = 3.0, H3
1M
10M
VC = 0.2, H3
VC = 0.2, H2
VC = 3.0, H2
1M
Frequency (Hz)
DISTORTION vs FREQUENCY
MGS = 011
1VPP SINGLE-ENDED
DISTORTION vs FREQUENCY
MGS = 111
1VPP SINGLE-ENDED
VC = 0.2, H3
100k
VC = 0.2, H2
VC = 3.0, H2
VC = 3.0, H3
100k
1M
Frequency (Hz)
–30
–35
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
VC = 0.2, H2
VC = 0.2, H3
VC = 3.0, H3
100k
10M
10M
VC = 3.0, H2
1M
Frequency (Hz)
10M
DISTORTION vs VCACNTL
1VPP SINGLE-ENDED
DISTORTION vs VCACNTL
2VPP DIFFERENTIAL
–45
–45
MGS = 111, H2
MGS = 111, H2
–50
–55
MGS = 011, H2
MGS = 000, H2
–60
–65
MGS = 000, H3
Distortion (dBc)
–50
Distortion (dBc)
VC = 3.0, H3
Frequency (Hz)
Distortion (dBc)
Distortion (dBc)
–80
100k
–30
–35
–40
–45
–50
–55
–60
–65
–70
–75
–80
–85
–90
DISTORTION vs FREQUENCY
MGS = 000
1VPP SINGLE-ENDED
–55
MGS = 011, H2 MGS = 000, H2
–60
–65
–70
–70
MGS = 111, H3
MGS = 111, H3
MGS = 011, H3
–75
–75
–80
–80
MGS = 000, H3
MGS = 011, H3
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
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)
VCACNTL (V)
VCA2616, VCA2611
SBOS234D
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7
TYPICAL CHARACTERISTICS (Cont.)
At TA = +25°C, VDDA = VDDB = VDDR = +5V, load resistance = 500Ω on 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.
CROSSTALK vs FREQUENCY
1VPP SINGLE-ENDED
MGS = 011
–5
80.50
80.00
–15
VCACNTRL 0V
79.50
–25
VCACNTRL 1.5V
79.00
–35
ICC (dBFS)
Crosstalk (dB)
ICC vs TEMPERATURE
–45
VCACNTRL 3.0V
–55
78.50
78.00
77.50
–65
77.00
–75
76.50
76.00
–40 –30 –20 –10 0
–85
1M
10M
100M
10 20 30 40 50 60 70 80 90
Temperature (°C)
Frequency (Hz)
GROUP DELAY vs FREQUENCY
16
Group Delay (nS)
14
VC = 3.0
12
10
8
VC = 0.2
6
4
2
0
1M
8
10M
Frequency (Hz)
100M
VCA2616, VCA2611
www.ti.com
SBOS234D
THEORY OF OPERATION
The VCA2616 and VCA2611 are dual-channel systems consisting of three primary blocks: an LNP, a 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 dualchannel system.
op amp. The VCM node shown in Figure 2 is the VCM output
(pin 19). Typical R and C values are shown, yielding a highpass 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
To VCAIN
47nF
Input
Signal
Channel A
Output
1kΩ
VCM (+2.5V)
Channel B
Input
LNP
VCA
Maximum
Gain
Select
MGS
PGA
Channel B
Output
FIGURE 2. Recommended Circuit for Coupling an External
Signal into the VCA Inputs.
External
InB
FIGURE 1. Simplified Block Diagram of the VCA2616.
LNP—OVERVIEW
The LNP input may be connected to provide active-feedback
signal termination, achieving lower system noise performance than conventional passive shunt termination. Further
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 singleended 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 4.8µs time constant (33kHz high-pass characteristic). 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.
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 characteristic 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 VCA2616 and VCA2611.
0
VCA Attenuation (dB)
Analog
Control
VCA
Control
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 demonstrates the recommended coupling method using an external
Minimum Attenuation
–24
Maximum Attenuation
–45
0
3.0
Control Voltage (V)
FIGURE 3. Swept Attenuator Characteristic.
VCA2616, VCA2611
SBOS234D
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9
PGA OVERVIEW AND OVERALL DEVICE
CHARACTERISTICS
the circuit. This reduces the susceptibility to power-supply
variation, ripple, and noise. In addition, separate power
supply and ground connections are provided for each channel and for the reference circuitry, further reducing interchannel
crosstalk.
The differential output of the VCA attenuator is then amplified
by the PGA circuit block. This post-amplifier is programmed
by the same MGS bits that control the VCA attenuator,
yielding an overall swept-gain amplifier characteristic in which
the VCA × PGA gain varies from 0dB (unity) to a programmable peak gain of 24-, 27-, 30-, 33-, 36-, 39-, 42-, or 45dB.
Further details regarding the design, operation, and use of
each circuit block are provided in the following sections.
LOW-NOISE PREAMPLIFIER (LNP)—DETAIL
The Gain vs VCACNTL curve in the Typical Characteristics
shows the composite gain control characteristic of the entire
VCA2616. Setting VCACNTL to 3.0V causes the digital MGS
gain control to step in 3dB increments. Setting VCACNTL to 0V
causes all the MGS-controlled gain curves to converge at
one point. The gain at the convergence point is the LNP gain
less 6dB, because the measurement setup looks at only one
side of the differential PGA output, resulting in 6dB lower
signal amplitude.
The LNP is designed to achieve a low-noise figure, especially when employing active termination. Figure 4 is a
simplified schematic of the LNP, illustrating the differential
input and output capability. The input stage employs low
resistance local feedback to achieve stable low-noise, lowdistortion performance with very high input impedance. Normally, low noise circuits exhibit high power consumption as
a result of the large bias currents required in both input and
output stages. The LNP uses a patented technique that
combines the input and output stages such that they share
the same bias current. Transistors Q4 and Q5 amplify the
signal at the gate-source input of Q4, the +IN side of the LNP.
The signal is further amplified by the Q1 and Q2 stage, and
then by the final Q3 and RL gain stage, which uses the same
bias current as the input devices Q4 and Q5. Devices Q6
through Q10 play the same role for signals on the –IN side.
ADDITIONAL FEATURES—OVERVIEW
Overload protection stages are placed between the attenuator and the PGA, providing a symmetrically clipped output
whenever the input becomes large enough to overload the
PGA. A comparator senses the overload signal amplitude
and substitutes a fixed DC level to prevent undesirable
overload recovery effects. As with the previous stages, the
VCA is AC-coupled into the PGA. In this case, the coupling
time constant varies from 5µs at the highest gain (45dB) to
59µs at the lowest gain (25dB).
The differential gain of the LNP is given in Equation 1:
R
Gain = 2 × L
RS
The VCA2616 includes a built-in reference, common to both
channels, to supply a regulated voltage for critical areas of
COMP2A
VDD
COMP1A
RL
93Ω
Q2
RL
93Ω
LNPOUTN
To Bias
Circuitry
Q9
LNPOUTP
Buffer
CCOMP
(External
Capacitor)
(1)
Buffer
Q3
Q8
RS1
105Ω
RW
RS2
34Ω
Q4
LNPINP
LNPGS1
RW
Q7
LNPINN
LNPGS2
RS3
17Ω
Q10
LNPGS3
Q1
To Bias
Circuitry
Q5
Q6
FIGURE 4. Schematic of the Low-Noise Preamplifier (LNP).
10
VCA2616, VCA2611
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SBOS234D
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 combinations 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
LNP GAIN (dB)
LNPGS1, LNPGS2, LNPGS3 Connected Together
LNPGS1 Connected to LNPGS3
LNPGS1 Connected to LNPGS2
All Pins Open
25
22
17
5
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 (see Figure 4) should be combined
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:
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), depending 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 external resistors with the internal values to create an effective RS
value, note that the internal resistors have a typical temperature coefficient of +700ppm/°C and an absolute value tolerance of approximately ±5%, yielding somewhat less predictable and stable gain settings. With or without external resistors, the board layout should use short Gain Strap connections to minimize parasitic resistance and inductance effects.
The overall noise performance of the VCA2616 and VCA2611
will vary as a function of gain. Table II shows the typical inputand-output-referred noise densities of the entire VCA2616 and
VCA2611 for maximum VCA and PGA gain; that is, VCACNTL
set to 3.0V and all MGS bits set to 1. Note that the inputreferred noise values include the contribution of a 50Ω fixed
source impedance, and are therefore somewhat larger than
the intrinsic input noise. As the LNP gain is reduced, the noise
contribution 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 10Ω will contribute 0.4nV/√Hz.
Output-Referred
25
22
17
5
1.35
1.41
1.63
4.28
2260
1650
1060
597
TABLE II. Equivalent Noise Performance for MGS = 111 and
VCACNTL = 3.0V with 50Ω source impedance.
The VCA2611 is an upgraded version of the VCA2616. The
only difference between the VCA2616 and the VCA2611 is the
input structure to the LNP. The VCA2616 is limited to –0.3V
negative-going input spikes; the VCA2611 is limited to –2.0V
negative-going input spikes. This change allows the user to
use slower and less expensive input clamping diodes prior to
the LNA input. In some designs, input clamping may not be
required.
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, essentially because no signal current is wasted in the termination resistor itself. Another way to understand this is to
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 theoretical SNR
degradation is 3dB, assuming a noise-free amplifier input. (In
practice, the amplifier noise contribution will degrade both
the unterminated and the terminated noise figures, somewhat reducing the distinction between them.)
See Figure 5 for an amplifier using active feedback. This
diagram appears very similar to a traditional inverting amplifier. 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 between the LNPINP and FB terminals for each channel), A is
VCA2616, VCA2611
SBOS234D
Input-Referred
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.
TABLE I. Pin Strappings of the LNP for Various Gains.
REXT =
NOISE (nV/√Hz)
LNP GAIN (dB)
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11
RF
VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB
14
RS
LNP Noise
nV/√Hz
6.0E-10
8.0E-10
1.0E-09
1.2E-09
1.4E-09
1.6E-09
1.8E-09
2.0E-09
12
LNPIN
Noise Figure (dB)
A
RIN
Active Feedback
RIN =
RF
1+A
= RS
10
8
6
4
2
RS
0
0
100 200 300 400 500
A
600 700 800 900 1000
Source Impedance (Ω)
RS
FIGURE 7. Noise Figure for Conventional Termination.
Conventional Cable Termination
FIGURE 5. Configurations for Active Feedback and Conventional Cable Termination.
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
of 2 (6dB) before being re-amplified by the A gain setting.
This avoids the extra 3dB degradation due to the square-root
effect described earlier, the key advantage of the active
termination technique.
This previous explanation ignored the input noise contribution of the LNP itself. Also, the noise contribution of the
feedback resistor must be included for a completely correct
analysis. The curves given in Figures 6 and 7 allow the
VCA2616 and VCA2611 user to compare the achievable
noise figure for active and conventional termination methods.
The left-most set of data points in each graph give the results
for typical 50Ω cable termination, showing the worst noise
figure but also the greatest advantage of the active feedback
method.
A switch, controlled by the FBSWCNTL signal on pin 45,
enables the user to reduce the feedback resistance by
adding an additional parallel component, connected between
the LNPINP and SWFB terminals. The two different values of
feedback resistance will result in two different values of
active-feedback input resistance. Thus, the active-feedback
impedance can be optimized at two different LNP gain
settings. The switch is connected at the buffered output of
the LNP and has an ON resistance of approximately 1Ω.
When employing active feedback, the user should be careful
to avoid low-frequency instability or overload problems. Figure 8 illustrates the various low-frequency time constants.
RF
VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB
9
LNP Noise
nV/√Hz
6.0E-10
8.0E-10
1.0E-09
1.2E-09
1.4E-09
1.6E-09
1.8E-09
2.0E-09
8
Noise Figure (dB)
7
6
5
4
3
VCM
CF
0.001µF
200kΩ
44pF
CC
Buffer
LNPOUTN
RS
44pF
2
LNPOUTP
Gain
Stage
1
200kΩ
Buffer
0
0
100 200 300 400 500 600 700 800
VCM
900 1000
(VCA) LNP
Source Impedance (Ω)
FIGURE 6. Noise Figure for Active Termination.
12
FIGURE 8. Low-Frequency LNP Time Constants.
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SBOS234D
Referring again to the input resistance calculation of Equation (3), and considering that the gain term “A” falls off below
21kHz, it is evident that the effective LNP input impedance
will rise below 3.6kHz, with a DC limit of approximately RF. To
avoid interaction with the feedback pole/zero at low frequencies, and to avoid the higher signal levels resulting from the
rising impedance characteristic, it is recommended that the
external RFCC time constant be set to about 5µs.
Achieving the best active-feedback architecture is difficult
with conventional op amp circuit structures. The overall gain
A must be negative in order to close the feedback loop, the
input impedance must be high to maintain low current noise
and good gain accuracy, but the gain ratio must be set with
very low value resistors to maintain good voltage noise.
Using a two-amplifier configuration (noninverting for high
impedance plus inverting for negative feedback reasons)
results in excessive phase lag and stability problems when
the loop is closed. The VCA2616 and VCA2611 use a
patented architecture that achieves these requirements, with
the additional benefits of low power dissipation and differential signal handling at both input and output.
For greatest flexibility and lowest noise, the user may wish to
shape the frequency response of the LNP. The COMP1 and
COMP2 pins for each channel (pins 10 and 11 for channel A,
pins 26 and 27 for channel B) correspond to the drains of Q3
and Q8, see Figure 4. A capacitor placed between these pins
will create a single-pole low-pass response, in which the
effective R of the RC time constant is approximately 186Ω.
RF
RI
Input
C
BW =
(A + 1) RI + RF
2πC(RI )(RF )
–3dB Bandwidth
Gain
25dB
180MHz
(4)
AVOIDING UNSTABLE PERFORMANCE
The VCA2612 and the VCA2616 are very similar in performance in all respects, except in the area of noise performance.
See Figure 4 for a schematic of the LNP. This brings the input
noise of the VCA2616 and VCA2611 down to 1.0nV/√Hz
compared to the input on the VCA2612 1.25nV/√Hz impedance at the gate of either Q4 or Q7, as can be approximated
by the network shown in Figure 11. The resistive component
shown in Figure 11 is negative, which gives rise to unstable
behavior when the signal source resistance has both inductive
and capacitive elements. It should be noted that this negative
resistance is not a physical resistor, but an equivalent resistance that is a function of the devices shown in Figure 4.
Normally, when an inductor and capacitor are placed in series
or parallel, there is a positive resistance in the loop that
prevents unstable behavior.
24pF
–93Ω
57pF
FIGURE 11. VCA2616 and VCA2611 Input Impedance.
For the VCA2616 and VCA2611, the situation can be remedied by placing an external resistor with a value of approximately 15Ω or higher in series with the input lead. The net
series resistance will be positive, and there will be no
observed instability.
Although this technique will prevent oscillations, it is not
recommended, as it will also increase the input noise. The
preferred technique is to place an external capacitor between
pins COMP2A (pin 11) and LNPINPA (pin 16), and between
pins COMP2B (pin 26) and LNPINPB (pin 21). This has the
effect of making the input impedance always capacitive due
to the feedback effect of the compensation capacitor and the
gain of the LNP. Using capacitive feedback, the LNP becomes unconditionally stable, as there is no longer a negative component to the input impedance. The compensation
capacitor mentioned above will be reflected to the input by
the formula:
CIN = (A + 1)CCOMP
FIGURE 9. Open-Loop Gain Characteristic of LNP.
VCA2616, VCA2611
SBOS234D
Output
FIGURE 10. LNP with Compensation Capacitor.
COMPENSATION WHEN USING ACTIVE FEEDBACK
The typical open-loop gain versus frequency characteristic for
the LNP is shown in Figure 9. The –3dB bandwidth is approximately 180MHz and the phase response is such that when
feedback is applied, the LNP will exhibit a peaked response or
might even oscillate. One method for compensating for this
undesirable behavior is to place a compensation capacitor at
the input to the LNP, as shown in Figure 10. This method is
effective when the desired –3dB bandwidth is much less than
the open-loop bandwidth of the LNP. This compensation
technique also allows the total compensation capacitor to
include any stray or cable capacitance that is associated with
the input connection. Equation 4 relates the bandwidth to the
various impedances that are connected to the LNP.
A
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(5)
13
The capacitance that is determined in Equation 5 should be
added to the capacitance of Equation 4 to determine the
overall bandwidth of the LNP. The LNPINNA (pin 12) and the
LNPINNB (pin 25) should be bypassed to ground by the
shortest means possible to avoid any inductance in the lead.
The attenuator is comprised of two sections, with five parallel
clipping amplifier/FET combinations in each. Special reference circuitry is provided so that the (VCM – VT) limit voltage
will track temperature and IC process variations, minimizing
the effects on the attenuator control characteristic.
In addition to the analog VCACNTL gain setting input, the
attenuator architecture provides digitally programmable adjustment in eight steps, via the three MGS bits. These adjust
the maximum achievable gain (corresponding to minimum
attenuation in the VCA, with VCACNTL = 3.0V) in 3dB increments. This function is accomplished by providing multiple
FET sub-elements for each of the Q1 to Q10 FET shunt
elements (see Figure 12). In the simplified diagram of
Figure 13, each shunt FET is shown as two sub-elements,
QNA and QNB. Selector switches, driven by the MGS bits,
activate either or both of the sub-element FETs to adjust the
maximum RON and thus achieve the stepped attenuation
options.
LNP OUTPUT BUFFER
The differential LNP output is buffered by wideband class AB
voltage followers which are designed to drive low impedance
loads. This is necessary to maintain LNP gain accuracy,
since the VCA input exhibits gain-dependent input impedance. The buffers are also useful when the LNP output is
brought out to drive external filters or other signal processing
circuitry. Good distortion performance is maintained with
buffer loads as low as 135Ω. As mentioned previously, the
buffer inputs are AC-coupled to the LNP outputs with a
3.6kHz high-pass characteristic, and the DC common-mode
level is maintained at the correct VCM for compatibility with
the VCA input.
The VCA can be used to process either differential or singleended signals. Fully differential operation will reduce 2ndharmonic distortion by about 10dB for full-scale signals.
VOLTAGE-CONTROLLED ATTENUATOR (VCA)—DETAIL
Input impedance of the VCA will vary with gain setting, due
to the changing resistances of the programmable voltage
divider structure. At large attenuation factors (that is, low gain
settings), the impedance will approach the series resistor
value of approximately 135Ω.
The VCA is designed to have a dB-linear attenuation characteristic; that is, the gain loss in dB is constant for each equal
increment of the VCACNTL control voltage. See Figure 1 for a
block diagram of the VCA. The attenuator is essentially a
variable voltage divider consisting of one series input resistor, RS, and ten identical shunt FETs, placed in parallel and
controlled by sequentially activated clipping amplifiers. Each
clipping amplifier can be thought of as a specialized voltage
comparator with a soft transfer characteristic and well-controlled output limit voltages. The reference voltages V1 through
V10 are equally spaced over the 0V to 3.0V control voltage
range. As the control voltage rises through the input range of
each clipping amplifier, the amplifier output will rise from 0V
(FET completely ON) to VCM – VT (FET nearly OFF), where
VCM is the common source voltage and VT is the threshold
voltage of the FET. As each FET approaches its OFF state
and the control voltage continues to rise, the next clipping
amplifier/FET combination takes over for the next portion of
the piecewise-linear attenuation characteristic. Thus, low
control voltages have most of the FETs turned ON, while
high control voltages have most turned OFF. Each FET acts
to decrease the shunt resistance of the voltage divider
formed by RS and the parallel FET network.
As with the LNP stage, the VCA output is AC-coupled into the
PGA. This means that the attenuation-dependent DC common-mode voltage will not propagate into the PGA, and so
the PGA’s DC output level will remain constant.
Finally, note that the VCACNTL input consists of FET gate
inputs. This provides very high impedance and ensures that
multiple VCA2616 and VCA2611 devices may be connected
in parallel with no significant loading effects. The nominal
voltage range for the VCACNTL input spans from 0V to 3V.
Overdriving this input (≤ 5V) does not affect the performance.
INPUT OVERLOAD RECOVERY
One of the most important applications for the VCA2616 and
VCA2611 is processing signals in an ultrasound system. The
ultrasound signal flow begins when a large signal is applied to
a transducer, which converts electrical energy to acoustic
energy. It is not uncommon for the amplitude of the electrical
signal that is applied to the transducer to be ±50V or greater.
RS
OUTPUT
INPUT
Q1A
Q1B
Q2A
Q2B
Q3A
Q3B
Q4A
Q4B
Q5A
Q5B
VCM
A1
A2
A3
A4
A5
B1
B2
Programmable Attenuator Section
FIGURE 13. Programmable Attenuator Section.
14
VCA2616, VCA2611
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SBOS234D
Attenuator
Input
RS
A1-A10 Attenuator Stages
Attenuator
Output
QS
Q1
VCM
A1
Q2
A2
C1
A3
C2
V1
Q3
A4
C3
V2
Q4
A5
C4
V3
V4
Control
Input
Q5
Q6
A6
C5
A7
C6
V5
Q7
V6
Q8
A8
C7
V7
Q9
A9
C8
Q10
A10
C9
V8
C10
V9
V10
C1-C10 Clipping Amplifiers
0dB
–4.5dB
Attenuation Characteristic of Individual FETs
VCM-VT
0
V1
V2
V3
V4
V5
V6
V7
V8
V9
Characteristic of Attenuator Control Stage Output
V10
Overall Control Characteristics of Attenuator
0dB
–45dB
0.3V
Control Signal
3V
FIGURE 12. Piecewise Approximation to Logarithmic Control Characteristics.
VCA2616, VCA2611
SBOS234D
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15
(= maximum attenuation). For VCACNTL = 3V (no attenuation),
the VCA + PGA gain will be controlled by the programmed
PGA gain (24 to 45 dB in 3dB steps). For clarity, the gain and
attenuation factors are detailed in Table III.
VDD
CF
RF
LNPINP
Protection
Network
LNP
MGS
SETTING
ATTENUATOR GAIN
VCACNTL = 0V to 3V
DIFFERENTIAL
PGA GAIN
ATTENUATOR +
DIFF. PGA GAIN
000
–24dB to 0dB
24dB
0dB to 24dB
001
–27dB to 0dB
27dB
0dB to 27dB
010
–30dB to 0dB
30dB
0dB to 30dB
011
–33dB to 0dB
33dB
0dB to 33dB
100
–36dB to 0dB
36dB
0dB to 36dB
101
–39dB to 0dB
39dB
0dB to 39dB
110
–42dB to 0dB
42dB
0dB to 42dB
111
–45dB to 0dB
45dB
0dB to 45dB
LNPOUTN
ESD Diode
FIGURE 14. VCA2616 and VCA2611 Diode Bridge Protection
Circuit.
TABLE III. MGS Settings.
The PGA architecture consists of a differential, programmable-gain voltage to current converter stage followed by
transimpedance amplifiers to create and buffer each side of
the differential output. The circuitry associated with the voltage to current converter is similar to that previously described for the LNP, with the addition of eight selectable PGA
gain-setting resistor combinations (controlled by the MGS
bits) in place of the fixed resistor network used in the LNP.
Low input noise is also a requirement of the PGA design due
to the large amount of signal attenuation which can be
inserted between the LNP and the PGA. At minimum VCA
attenuation (used for small input signals) the LNP 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.
To prevent damage, it is necessary to place a protection circuit
between the transducer and the VCA2616 and VCA2611 (see
Figure 14). Care must be taken to prevent any signal from
turning the ESD diodes on. Turning on the ESD diodes inside
the VCA2616 and VCA2611 could cause the input coupling
capacitor (CC) to charge to the wrong value.
PGA POST-AMPLIFIER—DETAIL
Figure 15 shows a simplified circuit diagram of the PGA block.
As described previously, the PGA gain is programmed with
the same MGS bits which control the VCA maximum attenuation factor. Specifically, the 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
VDD
To Bias
Circuitry
Q1
RL
Q11
VCAOUTP
Q12
Q9
Q3
RL
VCAOUTN
Q8
VCM
RS1
VCM
Q13
RS2
Q4
+In
Q7
–In
Q14
Q2
Q10
Q5
Q6
To Bias
Circuitry
FIGURE 15. Simplified Block Diagram of the PGA Section Within the VCA2616 and VCA2611.
16
VCA2616, VCA2611
www.ti.com
SBOS234D
PACKAGE OPTION ADDENDUM
www.ti.com
20-Apr-2004
PACKAGING INFORMATION
ORDERABLE DEVICE
STATUS(1)
PACKAGE TYPE
PACKAGE DRAWING
PINS
PACKAGE QTY
VCA2611Y/250
ACTIVE
TQFP
PFB
48
250
VCA2611Y/2K
ACTIVE
TQFP
PFB
48
2000
VCA2616YR
ACTIVE
TQFP
PFB
48
2000
VCA2616YT
ACTIVE
TQFP
PFB
48
250
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in
a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
MECHANICAL DATA
MTQF019A – JANUARY 1995 – REVISED JANUARY 1998
PFB (S-PQFP-G48)
PLASTIC QUAD FLATPACK
0,27
0,17
0,50
36
0,08 M
25
37
24
48
13
0,13 NOM
1
12
5,50 TYP
7,20
SQ
6,80
9,20
SQ
8,80
Gage Plane
0,25
0,05 MIN
0°– 7°
1,05
0,95
Seating Plane
0,75
0,45
0,08
1,20 MAX
4073176 / B 10/96
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Falls within JEDEC MS-026
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