BB VCA2612

VCA2612
®
VCA
261
2
For most current data sheet and other product
information, visit www.burr-brown.com
Dual, VARIABLE GAIN AMPLIFIER
with Low Noise Preamp
TM
FEATURES
DESCRIPTION
● LOW NOISE PREAMP:
• Low Input Noise: 1.25nV/√Hz
• Active Termination Noise Reduction
• Switchable Termination Value
• 80MHz Bandwidth
• 5dB to 25dB Gain
• Differential Input /Output
● LOW NOISE VARIABLE GAIN AMPLIFIER:
• Low Noise VCA: 3.3nV/√Hz, Differential
Programming Optimizes Noise Figure
• 24dB to 45dB Gain
• 40MHz Bandwidth
• Differential Input /Output
The VCA2612 is a highly integrated, dual receive channel, signal processing subsystem. Each channel of the
product consists of a low noise pre-amplifier (LNP) and
a Variable Gain Amplifier (VGA). The LNP circuit
provides the necessary connections to implement Active
Termination (AT), a method of cable termination which
results in up to 4.6dB noise figure improvement. Different cable termination characteristics can be accommodated by utilizing the VCA2612’s switchable LNA feedback pins. The LNP has the ability to accept both
differential and single ended inputs, and generates a
differential output signal. The LNP provides strappable
gains of 5dB, 17dB, 22dB and 25dB.
The output of the LNP can be accessed externally for
further signal processing, or fed directly into the VGA.
The VCA2612’s VGA section consists of two parts, the
Voltage Controlled Attenuator (VCA) and the Programmable Gain Amplifier (PGA). The gain and gain range
of the Programmable Gain Amplifier can be digitally
programmed. The combination of these two programmable elements results in a variable gain ranging from
0dB up to a maximum gain as defined by the user
through external connections. The output of the VGA
can be used in either a single-ended or differential mode
to drive high performance analog-to-digital converters.
The VCA2612 also features low crosstalk and outstanding distortion performance. The combination of low
noise, and gain range programmability make the
VCA2612 a versatile building block in a number of
applications where noise performance is critical. The
VCA2612 is available in a TQFP-48 package.
● LOW CROSSTALK: 52dB at Max Gain, 5MHz
● HIGH-SPEED VARIABLE GAIN ADJUST
● SWITCHABLE EXTERNAL PROCESSING
APPLICATIONS
● ULTRASOUND SYSTEMS
● WIRELESS RECEIVERS
● TEST EQUIPMENT
Maximum Gain Select
FBCNTL
LNPOUTN
VCAINN
VCACNTL
MGS1 MGS2 MGS3
RF2
FBSW
RF1
FB
Input
LNP
Gain Set
VCA2612
(1 of 2 Channels)
Analog
Control
Maximum Gain
Select
LNPINP
LNPGS1
LNPGS2
VCAOUTN
Voltage
Controlled
Attenuator
Low Noise
Preamp
5dB to 25dB
Programmable
Gain Amplifier
24 to 45dB
LNPGS3
VCAOUTP
LNPINN
LNPOUTP
VCAINP
SEL
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111
Twx: 910-952-1111 • Internet: http://www.burr-brown.com/ • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
®
© 2000 Burr-Brown Corporation
PDS-1541B
1
Printed in U.S.A. March, 2000
VCA2612
SPECIFICATIONS
At TA = +25°C, VDD = 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.
VCA2612Y
PARAMETER
CONDITIONS
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
MIN
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
Third Harmonic Distortion
f = 5MHz, VOUT = 1Vp-p, VCACNTL = 3.0V
Second Harmonic Distortion
f = 5MHz, VOUT = 1Vp-p, VCACNTL = 3.0V
IMD, Two-Tone
VOUT = 2Vp-p, f = 1MHz
VOUT = 2Vp-p, f = 10MHz
1dB Compression Point
f = 5MHz, Output Referred, Differential
VOUT = 1Vp-p, f = 1MHz, Max Gain Both Channels
Crosstalk
Group Delay Variation
1MHz < f < 10MHz, Full Gain Range
–45
–45
ACCURACY
Gain Slope
Gain Error
Output Offset Voltage
GAIN CONTROL INTERFACE
Input Voltage (VCACNTL) Range
Input Resistance
Response Time
POWER SUPPLY
Specified Operating Range
Power Dissipation
TYP
MAX
600
15
1
50
1
112
3.5
1.25
350
6.2
kΩ
pF
nA
dB
Vp-p
mVp-p
nV/√Hz
nV/√Hz
fA/√Hz
dB
80
MHz
2
40
300
2.5 ±1
1
±40
–71
–63
–80
–80
6
68
±2
Vp-p
MHz
V/µs
V
Ω
mA
dBc
dBc
dBc
dBc
Vp-p
dB
ns
10.9
±50
4.75
Operating, Both Channels
±1(2)
0 to 3.0
1
0.2
45dB Gain Change, MGS = 111
UNITS
5.0
410
dB/V
dB
mV
V
MΩ
µs
5.25
475
V
mW
NOTE: (1) For preamp driving VGA. (2) Referenced to best fit dB-linear curve.
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user’s own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
®
VCA2612
2
ELECTROSTATIC
DISCHARGE SENSITIVITY
ABSOLUTE MAXIMUM RATINGS
Power Supply (+VS) ............................................................................. +6V
Analog Input ............................................................. –0.3V 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
This integrated circuit can be damaged by ESD. Burr-Brown
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/ORDERING INFORMATION
PRODUCT
PACKAGE
PACKAGE
DRAWING
NUMBER
VCA2612Y
TQFP-48 Surface Mount
355
–40°C to +85°C
A12
"
"
"
"
"
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING
ORDERING
NUMBER(1)
TRANSPORT
MEDIA
VCA2612Y/250
VCA2612Y/2K
Tape and Reel
"
NOTE: (1) Models with a slash (/) are available only in Tape and Reel in the quantities indicated (e.g., /2K indicates 2000 devices per reel). Ordering 2000 pieces
of “VCA2612Y/2K” will get a single 2000-piece Tape and Reel.
®
3
VCA2612
MGS1
MGS2
MGS3
VCAOUTPB
VCAOUTNB
GNDB
46
VCACNTL
VCAOUTPA
47
FBSWCNTL
VCAOUTNA
48
VCAINSEL
GNDA
PIN CONFIGURATION
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
32 VCAINPB
VCAINPA
5
LNPOUTNA
6
LNPOUTPA
7
30 LNPOUTPB
SWFBA
8
29 SWFBB
FBA
9
28 FBB
31 LNPOUTNB
VCA2612
18
19
VBIAS
VCM
20
21
22
23
24
LNPGS3B
17
LNPGS2B
16
LNPGS1B
15
GNDR
14
LNPINPB
13
VDDR
25 LNPINNB
LNPINPA
LNPINNA 12
LNPGS1A
26 COMP2B
LNPGS3A
27 COMP1B
COMP2A 11
LNPGS2A
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
®
VCA2612
4
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
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VDD = 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.
GAIN ERROR vs TEMPERATURE
GAIN vs VCACNTL
65
2.0
MGS = 111
60
55
1.0
Gain Error (dB)
MGS = 101
50
Gain (dB)
1.5
MGS = 110
45
MGS = 100
40
35
MGS = 011
30
MGS = 001
20
0
–0.5
+85°C
–1.5
MGS = 000
15
+25°C
0.5
–1.0
MGS = 010
25
–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
1.5
0.5
1.5
1MHz
1.0
10MHz
Gain Error (dB)
Gain Error (dB)
1.0
–40°C
0
–0.5
5MHz
MGS = 000
MGS = 011
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: CHA to CHB = 3.0V
100
90
90
80
80
70
70
60
60
Units
Units
GAIN MATCH: CHA to CHB = 0.2V
100
50
50
40
40
30
30
20
20
10
10
0
0
–0.5 –0.4 –0.3 –0.2 –0.1 0.0
0.1 0.2
0.3
0.4
0.5
–0.5 –0.4 –0.3 –0.2 –0.1 0.0
Delta Gain (dB)
0.1 0.2
0.3
0.4
0.5
Delta Gain (dB)
®
5
VCA2612
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
GAIN vs FREQUENCY
(VCA and PGA, VCACNTL = 0.2V)
GAIN vs FREQUENCY
(Pre-Amp)
30
5.0
LNP = 25dB
25
3.0
2.0
Gain (dB)
20
Gain (dB)
MGS = 111
MGS = 100
MGS = 011
MGS = 000
4.0
LNP = 22dB
15
LNP = 17dB
10
1.0
0.0
–1.0
–2.0
–3.0
5
–4.0
LNP = 5dB
0
0.1
–5.0
1
10
0.1
100
1
10
Frequency (MHz)
Frequency (MHz)
GAIN vs FREQUENCY
(VCA and PGA, VCACNTL = 3.0V)
GAIN vs FREQUENCY
(VCACNTL = 3.0V)
45
60
LNP = 25dB
MGS = 111
40
LNP = 22dB
50
35
MGS = 100
30
40
Gain (dB)
Gain (dB)
100
25
MGS = 011
20
15
LNP = 17dB
30
LNP = 5dB
20
MGS = 000
10
10
5
0
0
0.1
1
10
100
0.1
1
Frequency (MHz)
GAIN vs FREQUENCY
(LNP = 22dB)
100
OUTPUT REFERRED NOISE vs VCACNTL
1800
60
VCACNTL = 3.0V
1600
RS= 50Ω
MGS = 111
50
1400
Noise (nv/√Hz)
VCACNTL = 1.6V
40
Gain (dB)
10
Frequency (MHz)
30
20
1200
1000
800
600
MGS = 011
400
10
200
VCACNTL = 0.2V
0
0
0.1
1
10
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
100
VCACNTL (V)
Frequency (MHz)
®
VCA2612
6
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
INPUT REFERRED NOISE vs VCACNTL
INPUT REFERRED NOISE vs RS
10.0
RS= 50Ω
MGS = 111
Noise (nV√Hz
Noise (nV/√Hz)
24
22
20
18
16
14
12
10
8
6
4
2
0
1.0
MGS = 011
0.1
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
1
10
VCACNTL (V)
100
1000
RS (Ω)
NOISE FIGURE vs RS
(VCACNTL = 3.0V)
11
NOISE FIGURE vs VCACNTL
30
10
25
8
Noise Figure (dB)
Noise Figure (dB)
9
7
6
5
4
3
2
20
15
10
5
1
0
0
100
1000
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
RS (Ω)
VCACNTL (V)
LNP vs FREQUENCY
(Differential, 2Vp-p)
LNP vs FREQUENCY
(Single-Ended, 1Vp-p)
–45
–45
–50
–50
Harmonic Distortion (dBc)
Harmonic Distortion (dBc)
10
–55
3rd Harmonic
–60
–65
–70
–75
–55
2nd Harmonic
–60
–65
–70
–75
3rd Harmonic
2nd Harmonic
–80
–80
0.1
1
10
100
0.1
Frequency (MHz)
1
10
100
Frequency (MHz)
®
7
VCA2612
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
HARMONIC DISTORTION vs FREQUENCY
(Differential, 2Vp-p, MGS = 000)
HARMONIC DISTORTION vs FREQUENCY
(Differential, 2Vp-p, MGS = 011)
–40
–40
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–50
–55
–60
–65
–70
–75
–80
–85
–55
–60
–65
–70
–75
–80
–90
0.1
1
–30
10
0.1
Frequency (Hz)
HARMONIC DISTORTION vs FREQUENCY
(Differential, 2Vp-p, MGS = 111)
HARMONIC DISTORTION vs FREQUENCY
(Single-Ended, 1Vp-p, MGS = 000)
–45
10
–40
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–45
Harmonic Distortion (dBc)
–40
1
Frequency (MHz)
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–35
Harmonic Distortion (dBc)
–50
–85
–90
–50
–55
–60
–65
–70
–75
–50
–55
–60
–65
–70
–75
–80
–85
–80
–90
0.1
1
10
0.1
Frequency (MHz)
HARMONIC DISTORTION vs FREQUENCY
(Single-Ended, 1Vp-p, MGS = 011)
HARMONIC DISTORTION vs FREQUENCY
(Single-Ended, 1Vp-p, MGS = 111)
–55
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–35
Harmonic Distortion (dBc)
–50
10
–30
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–45
1
Frequency (MHz)
–40
Harmonic Distortion (dBc)
VCACNTL = 0.2V, H2
VCACNTL = 0.2V, H3
VCACNTL = 3.0V, H2
VCACNTL = 3.0V, H3
–45
Harmonic Distortion (dBc)
Harmonic Distortion (dBc)
–45
–60
–65
–70
–75
–80
–85
–40
–45
–50
–55
–60
–65
–70
–75
–80
–90
–85
0.1
1
10
0.1
Frequency (MHz)
®
VCA2612
1
Frequency (MHz)
8
10
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
HARMONIC DISTORTION vs VCACNTL
(Differential, 2Vp-p)
HARMONIC DISTORTION vs VCACNTL
(Single-Ended, 1Vp-p)
–45
–45
MGS = 000, H2
MGS = 011, H2
MGS = 111, H2
MGS = 000, H3
MGS = 011, H3
MGS = 111, H3
–55
–60
–65
–70
–75
–55
–60
–65
–70
–75
–80
–80
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)
INTERMODULATION DISTORTION
(Differential, 2Vp-p, f = 10MHz)
INTERMODULATION DISTORTION
(Single-Ended, 1Vp-p, f = 10MHz)
–5
–5
–15
–15
–25
–25
–35
–35
Power (dBm)
Power (dBm)
MGS = 000, H2
MGS = 011, H2
MGS = 111, H2
MGS = 000, H3
MGS = 011, H3
MGS = 111, H3
–50
Harmonic Distortion (dBc)
Harmonic Distortion (dBc)
–50
–45
–55
–65
–45
–55
–65
–75
–75
–85
–85
–95
–95
–105
–105
9.96
9.98
10
10.2
9.96
10.4
0
9.98
10
10.2
10.4
Frequency (MHz)
Frequency (MHz)
–1dB COMPRESSION vs VCACNTL
0
3rd-ORDER INTERCEPT vs VCACNTL
–5
–5
–10
–10
IP3 (dBm)
PIN (dBm)
–15
–15
–20
–25
–20
–25
–30
–35
–30
–40
–35
–45
–40
–50
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)
®
9
VCA2612
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
OVERLOAD RECOVERY
(Differential, VCACNTL = 3.0V, MGS = 111)
PULSE RESPONSE (BURSTS)
(Differential, VCACNTL = 3.0V, MGS = 111)
Output
500mV/div
Output
1V/div
Input
10V/div
Input
1V/div
200ns/div
200ns/div
GAIN RESPONSE
(Differential, VCACNTL Pulsed, MGS = 111)
CROSS TALK vs FREQUENCY
(Single-Ended, 1Vp-p, MGS = 011)
0
–10
Output
500mV/div
Cross Talk (dB)
–20
Input
2V/div
VCACNTRL = 1.5V
–30
–40
–50
VCACNTRL = 0V
–60
–70
VCACNTRL = 3.0V
–80
–90
100ns/div
0.1
1
10
Frequency (MHz)
CMRR vs FREQUENCY
(LNP only)
0
0
–10
–10
–20
–20
–30
VCACNTL = 0.2V
–40
CMRR (dB)
CMRR (dB)
CMRR vs FREQUENCY
(VCA only)
VCACNTL = 1.4V
–50
–60
–30
–40
–50
–60
–70
–70
–80
VCACNTL = 3.0V
–90
0.1
1
–80
10
100
0.1
Frequency (MHz)
10
Frequency (MHz)
®
VCA2612
1
10
100
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VDD = 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.
GROUP DELAY vs FREQUENCY
ICC vs TEMPERATURE
80
79.5
Group Delay (ns)
78.5
78
77.5
77
76.5
76
–40
–25
–10
5
20
35
50
65
80
95
VCACNTL = 3.0V
VCACNTL = 0.2V
1
10
Temperature (°C)
100
Frequency (MHz)
PSRR vs FREQUENCY
–45
–40
–35
–30
PSRR (dB)
ICC (mA)
79
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
–25
–20
–15
–10
–5
0
5
10
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
Frequency (Hz)
®
11
VCA2612
THEORY OF OPERATION
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.
The VCA2612 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.
1kΩ
External
InA
Channel A
Input
LNP
Input
Signal
VCA
PGA
To VCA
47nF
Channel A
Output
1kΩ
VCM
Analog
Control
VCA
Control
Channel B
Input
LNP
VCA
Maximum
Gain
Select
PGA
MGS
FIGURE 2. Recommended Signal Coupling.
VCA—OVERVIEW
Channel B
Output
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 VCA2612.
External
InB
FIGURE 1. Simplified Block Diagram of the VCA2612.
LNP—OVERVIEW
The LNP input may be connected to provide active-feedback
signal termination, achieving lower system noise performance 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 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 44µs time constant (3.6kHz 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.
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
VCA Attenuation (dB)
0
–24
–45
Maximum Attenuation
Control Voltage
FIGURE 3. Swept Attenuator Characteristic.
®
VCA2612
Maximum Attenuation
12
PGA OVERVIEW AND OVERALL DEVICE
CHARACTERISTICS
The VCA2612 includes a built-in reference, common to
both channels, to supply a regulated voltage for critical areas
of 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 cross-talk.
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, 45) dB.
The “GAIN vs VCACNTL” curve on page 5 shows the
composite gain control characteristic of the entire VCA2612.
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.
Further details regarding the design, operation and use of
each circuit block are provided in the following sections.
LOW NOISE PREAMPLIFIER (LNP)—DETAIL
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, low
distortion performance with very high input impedance.
Normally, low noise circuits exhibit high power consumption due to 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.
The differential gain of the LNP is given in Equation (1):
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 (46dB) to
59µs at the lowest gain (25dB).
R 
Gain = 2 •  L 
 RS 
(1)
VDD
RL
93Ω
Q2
RL
93Ω
–Out
To Bias
Circuitry
Q9
+Out
Buffer
Buffer
Q8
Q3
RS1
105Ω
RS2
34Ω
Q4
+IN
LNPGS1
Q7
–IN
LNPGS2
RS3
17Ω
Q10
LNPGS3
Q1
Q5
Q6
To Bias
Circuitry
FIGURE 4. Schematic of the Low Noise Pre-Amplifier (LNP).
®
13
VCA2612
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
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.
NOISE (nv/√Hz)
2260
1650
1060
597
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 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
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.)
Figure 5 shows 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):
(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 VCA2612 will vary as
a function of gain. Table II shows the typical input-and
output-referred noise densities of the entire VCA2612 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 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.
R IN =
RF
(1 + A)
(3)
where RF is the feedback resistor (supplied externally between 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 of
®
VCA2612
Output-Referred
1.54
1.59
1.82
4.07
The LNP is capable of generating a 2Vp-p differential
signal. The maximum signal at the LNP input is therefore
2Vp-p 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.
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 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).
2 R S1R L + 2 R FIX R L – Gain • R S1R FIX
Gain • R S1 – 2 R L
Input-Referred
25
22
17
5
TABLE II. Noise Performance for MGS = 111 and VCACNTL = 3.0V.
TABLE I. Pin Strappings of the LNP for Various Gains.
R EXT =
LNP GAIN (dB)
14
VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB
♦
14
RF
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
Noise Figure (dB)
RS
A
RIN
RIN =
Active Feedback
RF
1+A
= RS
×
10
8
6
4
2
RS
0
0
A
100
200
RS
300
400
500
600
700
800
Source Impedance (Ω)
FIGURE 7. Noise Figure for Conventional Termination.
Conventional Cable Termination
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. Referring again to the input resistance calculation of
Equation (3), and considering that the gain term “A” falls
off below 3.6kHz, 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.
FIGURE 5. Configurations for Active Feedback and Conventional Cable Termination.
two (6dB) before being re-amplified by the “A” gain setting.
This avoids the extra 3dB degradation due to the square-root
effect described above, the key advantage of the active
termination technique.
As mentioned above, the 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 VCA2612 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.
RF
VCA NOISE = 3.8nV√Hz, LNP GAIN = 20dB
9
♦
8
Noise Figure (dB)
7
×
6
VCM
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
5
4
3
1MΩ
44pF
CL
Buffer
RS
44pF
2
1
Buffer
Gain
Stage
0
0
100
200
300
400
500
600
700
1MΩ
800
Source Impedance (Ω)
VCM
FIGURE 6. Noise Figure for Active Termination.
FIGURE 8. Low Frequency LNP Time Constants.
®
15
VCA2612
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 (non-inverting
for high impedance plus inverting for negative feedback
reasons) results in excessive phase lag and stability problems when the loop is closed. The VCA2612 uses a patented
architecture that achieves these requirements, with the additional benefits of low power dissipation and differential
signal handling at both input and output.
equal increment of the VCACNTL control voltage. Figure 9
shows 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 piecewiselinear 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.
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 in 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.
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 Maximum Gain Setting
(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 shown in Figure
9. In the simplified diagram of Figure 10, 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 subelement 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.
VOLTAGE-CONTROLLED ATTENUATOR (VCA)—DETAIL
The VCA is designed to have a “dB-linear” attenuation
characteristic, i.e. the gain loss in dB is constant for each
RS
OUTPUT
INPUT
Q1A
Q1B
Q2A
Q2B
Q3A
Q3B
Q4A
Q4B
Q5A
VCM
A1
A2
A3
A4
B1
B2
PROGRAMMABLE ATTENUATOR SECTION
FIGURE 10. Programmable Attenuator Section.
®
VCA2612
16
A5
Q5B
Attenuator
Input
RS
A1 - A10 Attenuator Stages
Attenuator
Output
QS
Q1
VCM
A1
Q2
A2
C1
A3
C2
V1
Q3
A4
C3
V2
Q4
V4
Control
Input
Q6
A5
C4
V3
Q5
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
–4.5dB
0.3V
3V
Control Signal
FIGURE 9. Piecewise Approximation to Logarithmic Control Characteristics.
®
17
VCA2612
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.
OVERLOAD RECOVERY CIRCUITRY—DETAIL
produce low-distortion outputs as large as 1Vp-p singleended (2Vp-p differential). Therefore the maximum input
signal for linear operation is 2Vp-p divided by the LNP
differential gain setting. Clamping circuits in the LNP ensure that larger input amplitudes will exhibit symmetrical
clipping and short recovery times. The VCA itself, being
basically a voltage divider, is intrinsically free of overload
conditions. However, the PGA post-amplifier is vulnerable
to sudden overload, particularly at high gain settings. Rapid
overload recovery is essential in many signal processing
applications such as ultrasound imaging. A special comparator circuit is provided at the PGA input which detects
overrange signals (detection level dependent on PGA gain
setting). When the signal exceeds the comparator input
threshold, the VCA output is blocked and an appropriate
fixed DC level is substituted, providing fast and clean
overload recovery. The basic architecture is shown in Figure
11. Both high and low overrange conditions are sensed and
corrected by this circuit.
With a maximum overall gain of 70dB, the VCA2612 is
prone to signal overloading. Such a condition may occur in
either the LNP or the PGA depending on the various gain
and attenuation settings available. The LNP is designed to
Figures 12 and 13 show typical overload recovery waveforms with MGS = 100, for VCA • PGA minimum gain
(0dB) and maximum gain (36dB), respectively. LNP gain is
set to 25dB in both cases.
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 (i.e., low gain
settings), the impedance will approach the series resistor
value of approximately 135Ω.
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 VCA2612 devices may be connected in parallel
with no significant loading effects.
From VCA
Output
PGA
Comparators
Gain = A
Selection
Logic
E = Maximum Peak Amplitude
–
E E
A A
FIGURE 11. Overload Protection Circuitry.
VCACNTL = 3.0V, DIFFERENTIAL, MGS = 100
VCACNTL = 0.2V, DIFFERENTIAL, MGS = 100
Output
1V/div
1V/div
Output
Input
Input
200ns/div
200ns/div
FIGURE 12. Overload Recovery Response For Minimum Gain.
FIGURE 13. Overload Recovery Response For Maximum Gain.
®
VCA2612
18
PGA POST-AMPLIFIER—DETAIL
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.
Figure 14 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 (= 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.
MGS
VCA GAIN min to max
SETTING VCACNTL = 0V to 3V
000
001
010
011
100
101
110
101
DIFFERENTIAL
PGA GAIN
VCA • PGA GAIN
min to max
24dB
27dB
30dB
33dB
36dB
39dB
42dB
45dB
0dB to 24dB
0dB to 27dB
0dB to 30dB
0dB to 33dB
0dB to 36dB
0dB to 39dB
0dB to 42dB
0dB to 45dB
–24dB to 0dB
–27dB to 0dB
–30dB to 0dB
–33dB to 0dB
–36dB to 0dB
–39dB to 0dB
–42dB to 0dB
–45dB to 0dB
TABLE III. MGS Settings.
VDD
To Bias
Circuitry
Q1
RL
Q11
Q12
Q9
RL
+Out
–Out
Q3
Q8
VCM
RS1
VCM
Q13
RS2
Q4
+In
Q7
–In
Q14
Q2
Q10
Q5
Q6
To Bias
Circuitry
FIGURE 14. Simplified Block Diagram of the PGA.
®
19
VCA2612