OPA660AU [ROCHESTER]
SPECIALTY ANALOG CIRCUIT, PDSO8, PLASTIC, SO-8;
| 型号： | OPA660AU |
| 厂家： | 
Rochester Electronics |
| 描述： | SPECIALTY ANALOG CIRCUIT, PDSO8, PLASTIC, SO-8 光电二极管 |
| 文件： | 总21页 (文件大小：989K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
OPA660
®
OPA660
OPA660
Wide Bandwidth
OPERATIONAL TRANSCONDUCTANCE
AMPLIFIER AND BUFFER
FEATURES
APPLICATIONS
● WIDE BANDWIDTH: 850MHz
● BASE LINE RESTORE CIRCUITS
● VIDEO/BROADCAST EQUIPMENT
● COMMUNICATIONS EQUIPMENT
● HIGH-SPEED DATA ACQUISITION
● WIDEBAND LED DRIVER
● HIGH SLEW RATE: 3000V/µs
● LOW DIFFERENTIAL GAIN/PHASE
ERROR: 0.06%/0.02°
● VERSATILE CIRCUIT FUNCTION
● EXTERNAL IQ-CONTROL
● AGC-MULTIPLIER
● NS-PULSE INTEGRATOR
● CONTROL LOOP AMPLIFIER
DESCRIPTION
● 400MHz DIFFERENTIAL INPUT
The OPA660 is a versatile monolithic component
designed for wide-bandwidth systems including high
performance video, RF and IF circuitry. It includes a
wideband, bipolar integrated voltage-controlled cur-
rent source and voltage buffer amplifier.
AMPLIFIER
200Ω
5
6
+1
VO
8
C
100Ω
R3
390Ω
3
B
The voltage-controlled current source or Operational
Transconductance Amplifier (OTA) can be viewed as
an “ideal transistor.” Like a transistor, it has three
terminals—a high-impedance input (base), a low-
impedance input/output (emitter), and the current
output (collector). The OTA, however, is self-biased
and bipolar. The output current is zero-for-zero dif-
ferential input voltage. AC inputs centered about zero
produce an output current which is bipolar and cen-
tered about zero. The transconductance of the OTA
can be adjusted with an external resistor, allowing
bandwidth, quiescent current and gain trade-offs to
be optimized.
OTA
VI
IQ = 20mA
R1
E
2
R3
G = 1 +
= 3
2R5
RP
82Ω
CP
R5
100Ω
6.4pF
XE
OPA660 DIRECT-FEEDBACK FREQUENCY RESPONSE
20
15
5Vp-p
10
2.8Vp-p
5
The open-loop buffer amplifier provides 850MHz
bandwidth and 3000V/µs slew rate. Used as a basic
building block, the OPA660 simplifies the design of
AGC amplifiers, LED driver circuits for Fiber Optic
Transmission, integrators for fast pulses, fast control
loop amplifiers, and control amplifiers for capacitive
sensors and active filters.
1.4Vp-p
0.6Vp-p
0
–5
–10
–15
–20
0.2Vp-p
–25
–30
The OPA660 is packaged in SO-8 surface-mount,
and 8-pin plastic DIP, specified from –40°C to +85°C.
100k
1M
10M
100M
1G
Frequency (Hz)
International Airport Industrial Park
•
Mailing Address: PO Box 11400, Tucson, AZ 85734
FAXLine: (800) 548-6133 (US/Canada Only)
•
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
© 1990 Burr-Brown Corporation
PDS-1072F
Printed in U.S.A. April, 1995
SBOS007
SPECIFICATIONS
Typical at IQ = 20mA, VS = ±5V, TA = +25°C, and RL = 500Ω, unless otherwise specified.
OPA660AP, AU
TYP
PARAMETER
CONDITIONS
MIN
MAX
UNITS
OTA TRANSCONDUCTANCE
Transconductance
VC = 0V
VB = 0
75
125
200
mA/V
OTA INPUT OFFSET VOLTAGE
Initial
vs Temperature
vs Supply (tracking)
vs Supply (non-tracking)
vs Supply (non-tracking)
+10
50
60
45
48
±30
mV
µV/°C
dB
dB
dB
VS = ±4.5V to ±5.5V
V+ = 4.5V to 5.5V
V– = –4.5V to –5.5V
55
40
40
OTA B-INPUT BIAS CURRENT
Initial
vs Temperature
vs Supply (tracking)
vs Supply (non-tracking)
vs Supply (non-tracking)
–2.1
5
±5
µA
nA/°C
nA/V
nA/V
nA/V
VS = ±4.5V to ±5.5V
V+ = 4.5V to 5.5V
V– = –4.5V to –5.5V
±750
±1500
±500
OTA OUTPUT BIAS CURRENT
Output Bias Current
vs Temperature
vs Supply (tracking)
vs Supply (non-tracking)
vs Supply (non-tracking)
VB = 0, VC = 0V
±10
500
±10
±10
±10
±20
µA
nA/°C
µA/V
µA/V
µA/V
VS = ±4.5V to ±5.5V
V+ = 4.5V to 5.5V
V– = –4.5V to –5.5V
±25
±25
±25
OTA OUTPUT
Output Current
±10
±4.0
±15
±4.7
25k || 4.2
70
mA
V
Ω || pF
dB
Output Voltage Compliance
Output Impedance
Open-Loop Gain
IC = ±1mA
f = 1kHz
BUFFER OFFSET VOLTAGE
Initial
vs Temperature
vs Supply (tracking)
vs Supply (non-tracking)
vs Supply (non-tracking)
+7
50
60
45
48
±30
mV
µV/°C
dB
dB
dB
VS = ±4.5V to ±5.5V
V+ = 4.5V to 5.5V
V– = –4.5V to –5.5V
55
40
40
BUFFER INPUT BIAS CURRENT
Initial
vs Temperature
vs Supply (tracking)
vs Supply (non-tracking)
vs Supply (non-tracking)
–2.1
5
±5
µA
nA/°C
nA/V
nA/V
nA/V
VS = ±4.5V to ±5.5V
V+ = 4.5V to 5.5V
V– = –4.5V to –5.5V
±750
±1500
±500
BUFFER and OTA INPUT IMPEDANCE
Input Impedance
1.0 || 2.1
4
MΩ || pF
nV/√Hz
BUFFER INPUT NOISE
Voltage Noise Density, f = 100kHz
BUFFER DYNAMIC RESPONSE
Small Signal Bandwidth
Full Power Bandwidth
VO = ±100mV
VO = ±1.4V
VO = ±2.5V
850
800
570
0.06
0.02
–68
3000
25
MHz
MHz
MHz
%
Degrees
dBc
V/µs
ns
Differential Gain Error
Differential Phase Error
Harmonic Distortion, 2nd Harmonic
Slew Rate
3.58MHz, at 0.7V
3.58MHz, at 0.7V
f = 10MHz, VO = 0.5Vp-p
5V Step
Settling Time 0.1%
2V Step
Rise Time (10% to 90%)
VO = 100mVp-p
5V Step
1
1.5
ns
ns
Group Delay Time
250
ps
BUFFER RATED OUTPUT
Voltage Output
Current Output
Gain
IO = ±1mA
±3.7
±10
0.96
±4.2
±15
0.975
0.99
V
mA
V/V
RL = 500Ω
RL = 5kΩ
V/V
Output Impedance
7 || 2
Ω || pF
POWER SUPPLY
Voltage, Rated
Derated Performance
±5
V
V
±4.5
±5.5
Quiescent Current (Programmable, Useful Range)
±3 to ±26
mA
®
OPA660
2
PIN CONFIGURATION
ABSOLUTE MAXIMUM RATINGS
Top View
DIP/SO-8
Power Supply Voltage ......................................................................... ±6V
Input Voltage(1) ........................................................................ ±VS ±0.7V
Operating Temperature ................................................... –40°C to +85°C
Storage Temperature..................................................... –40°C to +125°C
Junction Temperature .................................................................... +175°C
Lead Temperature (soldering, 10s) ............................................... +300°C
IQ Adjust
C
1
2
3
4
8
7
6
5
E
B
V+ = +5V
Out
NOTE: (1) Inputs are internally diode-clamped to ±VS.
1
PACKAGE/ORDERING INFORMATION
PACKAGE
DRAWING TEMPERATURE
V– = –5V
In
PRODUCT
PACKAGE
NUMBER(1)
RANGE
OPA660AP
OPA660AU
8-Pin Plastic DIP
SO-8 Surface-Mount
006
182
–25°C to +85°C
–25°C to +85°C
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
ELECTROSTATIC
DISCHARGE SENSITIVITY
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.
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.
®
3
OPA660
TYPICAL PERFORMANCE CURVES
IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted.
TOTAL QUIESCENT CURRENT vs R
Q
TOTAL QUIESCENT CURRENT vs TEMPERATURE
100
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
30
Nominal
Device
High IQ
Device
10
3.0
1.0
Low IQ
Device
0.6
0.5
100
300
1.0k
RQ — Resistor Value (
3.0k
10k
100
20
–25
0
25
50
75
100
Temperature (°C)
)
Ω
BUFFER AND OTA B-INPUT BIAS CURRENT
vs TEMPERATURE
OTA C-OUTPUT BIAS CURRENT vs TEMPERATURE
0.0
–1.0
–2.0
–3.0
5 Representative
Units
Trim Point
–4.0
–5.0
–40
–20
–0
20
40
60
80
–20
–0
20
40
60
80
100
Temperature (°C)
Temperature (°C)
OTA C-OUTPUT RESISTANCE
vs TOTAL QUIESCENT CURRENT (IQ)
OTA TRANSFER CHARACTERISTICS
60
50
40
30
20
10
5
IQ = 5mA
0
IQ = 10mA
IQ = 20mA
–5
10
0
–10
4
6
8
10
12
14
16
18
–60
–40
–20
0
20
40
60
Total Quiescent Current — IQ (mA)
OTA Input Voltage (mV)
®
OPA660
4
TYPICAL PERFORMANCE CURVES (CONT)
IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted.
BUFFER AND OTA B-INPUT OFFSET VOLTAGE
vs TEMPERATURE
BUFFER AND OTA B-INPUT RESISTANCE
vs TOTAL QUIESCENT CURRENT (IQ)
20
15
10
5
4
3
2
1
RINOTA
RINBUF
0
–5
–10
0
–15
–20
–1
–25
0
25
50
75
100
4
6
8
10
12
14
16
18
20
Temperature (°C)
Total Quiescent Current — IQ (mA)
BUFFER SLEW RATE
vs TOTAL QUIESCENT CURRENT (IQ)
BUFFER OUTPUT AND OTA E-OUTPUT RESISTANCE
vs TOTAL QUIESCENT CURRENT (IQ)
4000
3800
3600
3400
3200
3000
2800
2600
2400
40
30
20
Rising Edge
ROUTOTA
Falling Edge
ROUTBUF
10
0
2200
2000
4
6
8
10
12
14
16
18
20
4
6
8
10
12
14
16
18
20
Total Quiescent Current—IQ (mA)
Total Quiescent Current—IQ (mA)
OTA TRANSCONDUCTANCE
vs TOTAL QUIESCENT CURRENT (IQ)
OTA TRANSCONDUCTANCE vs FREQUENCY
1000
150
100
RL = 50Ω
IQ = 20mA 106mA/V
100
IQ = 10mA 66mA/V
IQ = 5mA 40mA/V
50
0
10
1M
10M
1G
100M
Frequency (Hz)
0
2
4
6
8
10
12
14 16
18
20
Total Quiescent Current—IQ (mA)
®
5
OPA660
TYPICAL PERFORMANCE CURVES (CONT)
IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted.
BUFFER FREQUENCY RESPONSE
2.8Vp-p
BUFFER VOLTAGE NOISE SPECTRAL DENSITY
100
20
15
–3dB Point
10
5
1.4Vp-p
0.6Vp-p
0
–5
10
–10
–15
–20
0.2Vp-p
–25
dB
1
100
1k
10k
100k
1M
10M
100M
200k
1M
10M
100M
1G
Frequency (Hz)
Frequency (Hz)
IQ = 20mA RIN = 160Ω RL = 100Ω
BUFFER MAX OUTPUT VOLTAGE vs FREQUENCY
TRANSCONDUCTANCE vs INPUT VOLTAGE
160
10
RQ = 250Ω
RQ = 500Ω
120
80
0
RQ = 1kΩ
RQ = 2kΩ
40
0
0.1
1M
10M
100M
1G
–40
–30
–20
–10
0
10
20
30
40
Input Voltage (mV)
Frequency (Hz)
OTA PULSE RESPONSE
OTA PULSE RESPONSE
+2.5V
+0.625V
0V
0V
–2.5V
–0.625V
Input Voltage = 1.25Vp-p, tR = tF = 1ns, Gain = 4
Output Voltage = 5Vp-p
®
OPA660
6
TYPICAL PERFORMANCE CURVES (CONT)
IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted.
BUFFER LARGE SIGNAL PULSE RESPONSE
BUFFER LARGE SIGNAL PULSE RESPONSE
tR = tF = 3ns, VO = 5Vp-p
(HDTV Signal Pulse) tR = tF = 10ns, VO = 5Vp-p
Network
Analyzer
R6
160Ω
50Ω
50Ω
50Ω
6
+1
5
VI
VO
RIN = 50Ω
50Ω
50Ω
R7
RL = R6 + R7||RIN = 100Ω
tR = tF = 3ns, VO = 0.2Vp-p
Test Circuit Buffer Pulse and Frequency Response
BUFFER DIFFERENTIAL GAIN ERROR
vs TOTAL QUIESCENT CURRENT (IQ)
0.25
BUFFER DIFFERENTIAL PHASE ERROR
vs TOTAL QUIESCENT CURRENT (IQ)
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
RL = 500Ω
VO = 0.7Vp-p
f = 3.58MHz
0.20
RL = 500Ω
VO = 0.7Vp-p
f = 3.58MHz
0.15
0.10
0.05
0
0.01
0
4
6
8
10
12
14
16
18
20
4
6
8
10
12
14
16
18
20
Total Quiescent Current—IQ (mA)
Total Quiescent Current—IQ (mA)
®
7
OPA660
TYPICAL PERFORMANCE CURVES (CONT)
IQ = 20mA, TA = +25°C, and VS = ±5V unless otherwise noted.
HARMONIC DISTORTION vs FREQUENCY
HARMONIC DISTORTION vs FREQUENCY
–30
–40
–50
–60
–30
–40
–50
–60
RL = 150Ω
VO = 0.5Vp-p
IQ = 20mA
RL = 500Ω
IQ = 20mA
3f
2Vp-p
3f
0.5Vp-p
2f
2f
2Vp-p
3f
2f
0.5Vp-p
–70
–80
–70
–80
Measurement Limit
20M
Measurement Limit
20M
10M
40M
60M
100M
10M
40M
60M
100M
Frequency (Hz)
Frequency (Hz)
APPLICATIONS INFORMATION
The OPA660 operates from ±5V power supplies (±6V
maximum). Do not attempt to operate with larger power
supply voltages or permanent damage may occur.
The buffer output is not current-limited or protected. If the
output is shorted to ground, currents up to 60mA could flow.
Momentary shorts to ground (a few seconds) should be
avoided, but are unlikely to cause permanent damage. The
same cautions apply to the OTA section when connected as
a buffer (see Basic Applications Circuits, Figure 6b).
Inputs of the OPA660 are protected with internal diode
clamps as shown in the simplified schematic, Figure 1. These
protection diodes can safely conduct 10mA, continuously
(30mA peak). If input voltages can exceed the power supply
voltages by 0.7V, the input signal current must be limited.
(7)
+VCC = +5V
VI
VO
B
E
C
(5)
(6) (3)
(2)
(8)
Bias
Circuitry
BUFFER
OTA
100Ω
50kΩ
–VCC = –5V
(4)
IQ Adj.
(1)
RQ (ext.)
FIGURE 1. Simplified Circuit Diagram.
®
OPA660
8
BUFFER SECTION—AN OVERVIEW
QUIESCENT CURRENT CONTROL PIN
The buffer section of the OPA660 is an open-loop buffer
consisting of complementary emitter-followers. It uses no
feedback, so its low frequency gain is slightly less than unity
and somewhat dependent on loading. It is designed prima-
rily for interstage buffering. It is not designed for driving
long cables or low impedance loads (although with small
signals, it may be satisfactory for these applications).
The quiescent current of the OPA660 is set with a resistor,
RQ, connected from pin 1 to V–. It affects the operating
currents of both the buffer and OTA sections. This controls
the bandwidth and AC behavior as well as the
transconductance of the OTA section.
RQ = 250Ω sets approximately 20mA total quiescent current at
25°C. With a fixed 250Ω resistor, process variations could
cause this current to vary from approximately 16mA to 26mA.
It may be appropriate in some applications to trim this resistor
to achieve the desired quiescent current or AC performance.
TRANSCONDUCTANCE
(OTA) SECTION—AN OVERVIEW
The symbol for the OTA section is similar to a transistor.
Applications circuits for the OTA look and operate much
like transistor circuits—the transistor, too, is a voltage-
controlled current source. Not only does this simplify the
understanding of applications circuits, but it aids the circuit
optimization process. Many of the same intuitive techniques
used with transistor designs apply to OTA circuits as well.
Applications circuits generally do not show resistor, RQ,
but it is required for proper operation.
With a fixed RQ resistor, quiescent current increases with
temperature (see typical performance curve, Quiescent Current
vs Temperature). This variation of current with temperature
holds the transconductance, gm, of the OTA relatively con-
stant with temperature (another advantage over a transistor).
The three terminals of the OTA are labeled B, E, and C. This
calls attention to its similarity to a transistor, yet draws
distinction for clarity.
It is also possible to vary the quiescent current with a control
signal. The control loop in Figure 3 shows a 1/2 of a REF200
current source used to develop 100mV on R1. The loop
forces 100mV to appear on R2. Total quiescent current of the
OPA660 is approximately 85 • I1, where I1 is the current
made to flow out of pin 1.
While it is similar to a transistor, one essential difference is
the sense of the C output current. It flows out the C terminal
for positive B-to-E input voltage and in the C terminal for
negative B-to-E input voltage. The OTA offers many advan-
tages over a discrete transistor. The OTA is self-biased,
simplifying the design process and reducing component
count. The OTA is far more linear than a transistor.
Transconductance of the OTA is constant over a wide range
of collector currents—this implies a fundamental improve-
ment of linearity.
Internal
Current Source
Circuitry
OPA660
V+
BASIC CONNECTIONS
100Ω
1/2 REF200
50kΩ
Figure 2 shows basic connections required for operation.
These connections are not shown in subsequent circuit
diagrams. Power supply bypass capacitors should be located
as close as possible to the device pins. Solid tantalum
capacitors are generally best. See “Circuit Layout” at the end
of the applications discussion and Figure 26 for further
suggestions on layout.
100µA
1kΩ
R1
1
4
I1
–VCC
425Ω
R2
IQ ≈ 85 • I1
= 85 • (100µA)
= 20mA
R1
R2
1/2
OPA1013(1)
NOTE: (1) Requires input common-mode range and
output swing close to V–, thus the choice of OPA1013.
RQ = 250Ω sets roughly
IQ 20mA
≈
+5V(1)
1
2
3
4
8
7
6
5
470pF
FIGURE 3. Optional Control Loop for Setting Quiescent
Current.
RQ
250Ω
10nF
+
RB
With this control loop, quiescent current will be nearly
constant with temperature. Since this differs from the tem-
perature-dependent behavior of the internal current source,
other temperature-dependent behavior may differ from that
shown in typical performance curves.
2.2µF
1
Solid
Tantalum
(25Ω to
200Ω)
10nF
–5V(1)
RB
470pF
(25Ω to 200Ω)
+
2.2µF
The circuit of Figure 3 will control the IQ of the OPA660
somewhat more accurately than with a fixed external resis-
tor, RQ. Otherwise, there is no fundamental advantage to
Solid
Tantalum
NOTE: (1) VS = ±6V absolute max.
FIGURE 2. Basic Connections.
®
9
OPA660
using this more complex biasing circuitry. It does, however,
demonstrate the possibility of signal-controlled quiescent
current. This may suggest other possibilities such as AGC,
dynamic control of AC behavior, or VCO.
+5V
4.7kΩ
Internal
Current Source
Circuitry
Figure 4 shows logic control of pin 1 used to disable the
OPA660. Zero/5V logic levels are converted to a 1mA/0mA
current connected to pin 1. The 1mA current flowing in RQ
increases the voltage at pin 1 to approximately 1V above the
–5V rail. This will reduce IQ to near zero, disabling the
OPA660.
0/5V
2N2907
OPA660
Logic In
5V: OPA660 On
100Ω
50kΩ
BASIC APPLICATIONS CIRCUITS
IC
1
4
Most applications circuits for the OTA section consist of a
few basic types which are best understood by analogy to a
transistor. Just as the transistor has three basic operating
modes—common emitter, common base, and common col-
lector—the OTA has three equivalent operating modes com-
mon-E, common-B, and common-C. See Figures 5, 6, and 7.
RQ
250Ω
IC = 0: OPA660 On
C ≈ 1mA: OPA660 Off
I
–5V
FIGURE 4. Logic-Controlled Disable Circuit.
V+
RB
RL
8
VO
C
VO
100Ω
Non-Inverting Gain
VOS
3
B
VI
OTA
≈
0
RL
Inverting Gain
VOS several volts
VI
E
2
≈
RE
RB
RE
V–
(a) Common-Emitter Amplifier
(b) Common-E Amplifier
Transconductance varies over temperature.
Transconductance remains constant over temperature.
FIGURE 5. Common-Emitter vs Common-E Amplifier.
V+
RL
RL
RE
8
V+
G = –
≈ –
1
RL
C
RE
+
100Ω
gm
G
VOS
1
≈
≈
3 B
VI
OTA
0
VO
Non-Inverting Gain
E
2
VI
VOS several volts
≈
VO
VO
8
RE
VO
C
Inverting Gain
OS ≈ 0
RL
100Ω
G
VOS
1
≈
B
3
RE
V
(b) Common-C Amplifier
(Buffer)
OTA
RE
0.7V
≈
E
2
VI
1
G =
≈ 1
1
(a) Common-Base
Amplifier
V–
1 +
RE
g
m ¥ RE
(a) Common-Collector Amplifier
(Emitter Follower)
VI
1
gm
RO
=
(b) Common-B Amplifier
FIGURE 6. Common-Collector vs Common-C Amplifier.
FIGURE 7. Common-Base vs Common-B Amplifier.
®
OPA660
10
A positive voltage at the B, pin 3, causes a positive current
to flow out of the C, pin 8. Figure 5b shows an amplifier
connection of the OTA, the equivalent of a common-emitter
transistor amplifier. Input and output can be ground-refer-
enced without any biasing. Due to the sense of the output
current, the amplifier is non-inverting. Figure 8 shows the
amplifier with various gains and output voltages using this
configuration.
It is recommended to use a low value resistor in series with
the B OTA and buffer inputs. This reduces any tendency to
oscillate and controls frequency response peaking. Values
from 25Ω to 200Ω are typical.
Figure 7 shows the Common-B amplifier. This configura-
tion produces an inverting gain, and a low impedance input.
This low impedance can be converted to a high impedance
by inserting the buffer amplifier in series.
Just as transistor circuits often use emitter degeneration,
OTA circuits may also use degeneration. This can be used to
reduce the effect that offset voltage and offset current might
otherwise have on the DC operating point of the OTA. The
E-degeneration resistor may be bypassed with a large ca-
pacitor to maintain high AC gain. Other circumstances may
suggest a smaller value capacitor used to extend or optimize
high-frequency performance.
CIRCUIT LAYOUT
The high frequency performance of the OPA660 can be
greatly affected by the physical layout of the circuit. The
following tips are offered as suggestions, not dogma.
•
Bypass power supplies very close to the device pins. Use
a combination between tantalum capacitors (approxi-
mately 2.2µF) and polyester capacitors. Surface-mount
types are best because they provide lowest inductance.
The transconductance of the OTA with degeneration can be
calculated by—
•
•
•
•
Make short, wide interconnection traces to minimize
series inductance.
1
gm
=
1
gm
+ RE
Use a large ground plane to assure that a low impedance
ground is available throughout the layout.
Figure 6b shows the OTA connected as an E-follower—a
voltage buffer. The buffer formed by this connection per-
forms virtually the same as the buffer section of the OPA660
(the actual signal path is identical).
Do not extend the ground plane under high impedance
nodes sensitive to stray capacitance.
Sockets are not recommended because they add signifi-
cant inductance.
RL1
20
VO
15
10
–3dB Point
Network
Analyzer
8
2.8Vp-p
RIN
50Ω
5
1.4Vp-p
3
OTA
0
RL2
600mVp-p
–5
100Ω
rE
–10
–15
–20
–25
–30
R1
RL = RL1 + RL2 || RIN
200mVp-p
V
2
I
RL
1
gm
G =
, rE =
RE
RE + rE
1
At IQ = 20mA rE
RL
=
= 8Ω
300k
1M
10M 100M
Frequency (Hz)
1G
3G
125mA/V
G =
at IQ = 20mA
Ω
RE + 8
IQ = 20mA R1 = 100Ω RE = 51Ω RL = 50Ω Gain = 1
20
15
10
5
20
15
–3dB Point
5Vp-p
–3dB Point
2.8Vp-p
10
2.8Vp-p
1.4Vp-p
5
1.4Vp-p
0
0
–5
600mVp-p
200mVp-p
–5
600mVp-p
200mVp-p
–10
–15
–20
–25
–30
–10
–15
–20
–25
–30
300k
1M
10M
100M
1G
3G
100k
1M
10M
100M
1G
Frequency (Hz)
Frequency (Hz)
IQ = 20mA R1 = 100Ω RE = 51Ω RL = 100Ω Gain = 2
IQ = 20mA R1 = 100Ω RE = 51Ω RL = 500Ω Gain = 10
FIGURE 8. Common-E Amplifier Performance.
®
11
OPA660
•
•
Use low-inductance components. Some film resistors are
trimmed with spiral cuts which increase inductance.
•
•
A resistor (25Ω to 200Ω) in series with the buffer and/or
B input may help reduce oscillations and peaking.
Use surface-mount components—they generally provide
the lowest inductance.
Use series resistors in the supply lines to decouple mul-
tiple devices.
OPA660 CURRENT-FEEDBACK
20
56Ω
R2
5Vp-p
C1
15
5
6
VO
+1
10
5
2.8Vp-p
1.4Vp-p
8
C
0
3 B
OTA
–5
0.6Vp-p
E
2
–10
–15
–20
0.2Vp-p
200Ω
R1
–3dB Point
100M
47Ω
R4
–25
–30
R5
VI
22Ω
R4
R5
G = 1 +
10
≈
100k
1M
10M
1G
Frequency (Hz)
Ω
RQ = 250 (IQ ≈ 20mA)
I
Q = 20mA R1 = 47Ω R2 = 56Ω R4 = 200Ω R5 = 22Ω Gain = 10
FIGURE 9. Current-Feedback Amplifier.
FIGURE 10. Current-Feedback Amplifier Frequency
Response, G = 10.
C1
100pF
20Ω
20Ω
5
6
+1
VIN
VOUT
OPA650
R2
100kΩ
D1
D2
25Ω
D1, D2 = 1N4148
RQ = 1kΩ
R1
40.2Ω
• The OTA amplifier works as a current conveyor
(CCII) in this circuit, with a current gain of 1.
• R1 and C1 set the DC restoration time constant.
CCII
8
2
C
E
• D1 adds a propagation delay to the DC restoration.
• R2 and C1 set the decay time constant.
B
3
20Ω
FIGURE 11. DC Restorer Circuit.
VO
+3
8
5
6
+1
8
C
C
IO
3
B
VI
150Ω
OTA
+IN
3
B
RL
RE + rE
OTA
RL
150Ω
G =
≈
E
2
E
2
50Ω
Tuning Coil
Magnetic Head
Driver Transformer
RE
42Ω
RE
Ω
RQ = 250 (IQ ≈ 20mA)
2
E
FIGURE 13. Cable Amplifier.
3
B
–IN
OTA
C
8
FIGURE 12. High Speed Current Driver (bridge combina-
tion for increased output voltage capability).
®
OPA660
12
C8
0.5...2.5pF
+5V
–5V
R6
47kΩ
R8
27kΩ
Offset
Trim
R2
10kΩ
+5V
2.2µF
C3
+5V
1
C3
2.2µF
R3
100Ω
7
R1
R4
150Ω
R5
3
100Ω
47Ω
RC5
8
4
BUF600
150Ω
OTA
4
VI
6
5
2
1
VO
C3
2.2µF
+1
5
RQ
250Ω
C3
R2
100Ω
2.2µF
–5V
–5V
Propagation Delay Time = 5ns
Rise Time = 1.5ns
D1
D2
DMF3068A
FIGURE 14. Comparator (Low Jitter).
+5V
22Ω
22Ω
Q1
+IB
Q2
IO = IO1 + IO2
IO1
IO1
8
8
C
C
1kΩ
180Ω
3
B
3 B
OTA
OTA
VI
Diode
E
E
2
2
Q1, Q2: 2N3906
RE
50Ω
RE
50Ω
180Ω
FIGURE 15. High Speed Current Driver.
®
13
OPA660
8
C
33pF
200Ω
180Ω
5
6
3
B
+1
VO
OTA
VI
47Ω
8
27pF
C
E
2
780Ω
50Ω
3
B
OTA
VI
Network
Analyzer
VO
VO
f–3dB
E
2
±100mV
±300mV
±700mV
±1.4V
351MHz
374MHz
435MHz
460MHz
443MHz
620Ω
820Ω
RE
50Ω
RIN
50Ω
1µF
50kΩ
±2.5V
1
1
2gm
G =
≈ 1; RO =
+5V
–5V
1
1 +
2gm • (RE + RIN
)
FIGURE 16. Voltage Buffer with Doubled-Output Current.
FIGURE 17. Integrator for ns-pulses.
+5V
2.2pF
10nF
R9
240Ω
+5V
R3
51Ω
7
8
22pF
R6
150Ω
OPA660
10nF
1
3
5
+VI
–VI
R10
150Ω
R11
51Ω
R6
150Ω
VO
OTA
4
8
BUF601
+1
5
R7
51Ω
1
4
6
2
R8
43Ω
10nF
R16
560Ω
Rg
10nF
G = ––––––––– = 4
R8 + rE
2.2µF
–5V
C5
18pF
rE = 1/gm
2.2µF
–5V
FIGURE 18. 400MHz Differential Amplifier
–10
–20
–30
–40
–50
–60
–70
10
0
without C5
–10
–20
–30
with C5
IQ = 20mA, G = +4V/V
300k
1M
10M
100M
1G
3G
Frequency (Hz)
FIGURE 19. CMRR and Bandwidth of the Differential Amplifier
®
OPA660
14
C
E
3
B
C
E
TRANSFER CHARACTERISTICS
R2M
2
6
5
B
B
B
R3
R1M
1
+
VO
VI
s2C1C2R1M R3 + sC1 R2
R1
F(p) =
=
s2C1C2R1M R2M + sC1 R1M
1
R2
+
R2S
R1S
R3S
C
E
C
E
VI
7
1
Lowpass
Highpass
Bandpass
R2 = R3 = ∞
B
C2
B
C
E
R
R
R
1 = R2 = ∞
1 = R3 = ∞
C1
R2M
Band Rejection
Allpass
2 = ∞, R1 = R3
R1
R1 = R1S, R2 = –R2S, R3 = R3S
R1M
VO
C
E
8
B
C
E
C
E
4
B
RB
R3S
RB
RB
R1S
R2S
FIGURE 20. High Frequency Universal Active Filter.
120Ω
5
6
+1
VLUMINANCE
8
C
150Ω
3
B
OTA
E
2
665Ω(1)
340Ω(1)
1820Ω(1)
200Ω
VRED
VGREEN
VBLUE
RQ = 500Ω (IQ ≈ 20mA)
NOTE: (1) Resistors shown are 1% values that
produce 30%/59%/11% R/G/B mix.
FIGURE 21. Video Luminance Matrix.
®
15
OPA660
VO INT
8
290Ω
+VO
3
OTA
10Ω
15nF
2
IN6263
IN6263
220Ω
+5V
220Ω
+5V
180Ω
8
7
100Ω
7
–VO
6
5
1µF
100Ω
180Ω
VI
+1
6
5
3
OTA
+1
1
4
1.2kΩ
4
1.2kΩ
2
20kΩ
–5V
12kΩ
–5V
220Ω
390Ω
+
–
5kΩ
Offset Trim
33pF
FIGURE 22. Signal Envelope Detector (Full-Wave Rectifier).
Network
Analyzer
120Ω
200Ω
5
6
+1
VO
8
R2
R4
VO
f–3dB
50Ω
RIN
C
R6
68Ω
R3
±100mV
±300mV
±700mV
±1.4V
331MHz
362MHz
520MHz
552MHz
490MHz
100Ω
3
B
OTA
390Ω
VI
IQ = 20mA
R1
E
±2.5V
2
RP
R5
82Ω
100Ω
R3
2
+
R5
CP
R3
G =
= 1 +
6.4pF
1
2R5
R5
+
2 • gm
XE
FIGURE 23. Direct-Feedback Amplifier.
®
OPA660
16
OPA660 DIRECT FEEDBACK
5Vp-p
20
15
Gain = 3, tR – tF = 2ns, VI = 100mVp–p
10
2.8Vp-p
1.4Vp-p
5
+150mV
0V
0
0.6Vp-p
0.2Vp-p
–5
–10
–15
–20
–25
–30
–150mV
100k
1M
10M
100M
1G
Frequency (Hz)
0
5
10 15 20 25 30 35 40 45 50
Time (ns)
R
1 = 100Ω R2 = 120Ω R3 = 390Ω R4 = 200Ω
R5 = 100Ω R6 = 68Ω IQ = 20mA Rp = 82Ω Cp = 6.4pF
FIGURE 25. Direct-Feedback Amplifier Small-Signal Pulse
Response.
FIGURE 24. Frequency Response Direct-Feedback Amplifier.
Network
Analyzer
180Ω
VO
Gain = 3, VI = 2Vp-p, tR = tF = 2ns
8
R2
R1
50Ω
RIN
R3
C
56Ω
160Ω
+3V
OTA
VI
3
B
IQ = 20mA
E
2
0V
VO
f–3dB
R4P
R4
51Ω
±100mV
±300mV
±700mV
±1.4V
351MHz
374MHz
435MHz
460MHz
443MHz
75Ω
C4P
–3V
5.6pF
±2.5V
FIGURE 27. Forward Amplifier.
40 45 50
0
5
10 15 20 25 30 35
Time (ns)
SPICE MODELS
FIGURE 26. Direct-Feedback Amplifier Large-Signal Pulse
Response.
Computer simulation using SPICE models is often useful
when analyzing the performance of analog circuits and sys-
tems. This is particularly true for video and RF amplifier
circuits, where parasitic capacitance and inductance can have
a major effect on circuit performance. SPICE models are
available from Burr-Brown.
OPA660 OTA FORWARD AMPLIFIER
20
5Vp-p
15
2.8Vp-p
1.4Vp-p
10
5
0
0.6Vp-p
0.2Vp-p
–5
–10
–15
–20
–25
–30
100k
1M
10M
100M
1G
Frequency (Hz)
IQ = 20mA R1 = 160Ω R4 = 51Ω
R2 = 180Ω R3 = 56Ω R4p = 75Ω C4p = 5.6pF
FIGURE 28. Frequency Response Forward Amplifier.
®
17
OPA660
FIGURE 29. Evaluation Circuit Silk Screen and Board Layouts.
R6
R5
470Ω
160Ω
6
5
+1
BUF Out
BUF In
R7
56Ω
R2
24Ω
OTA Out
8
RQC
820Ω
R1
100Ω
+5V
–5V
C
R3
51Ω
3 B
1
OTA
OTA In
470pF 470pF
E
2
10nF 10nF
2.2µF 2.2µF
R4
51Ω
C2
3.3nF
C1
2.2µF
1N4007
7
4
FIGURE 30. Evaluation Circuit Diagram.
®
OPA660
18
PACKAGE OPTION ADDENDUM
www.ti.com
9-Jun-2008
PACKAGING INFORMATION
Orderable Device
Status (1)
Package Package
Pins Package Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3)
Qty
Type
PDIP
SOIC
SOIC
Drawing
OPA660AP
OPA660AU
OBSOLETE
OBSOLETE
OBSOLETE
P
D
D
8
8
8
TBD
TBD
TBD
Call TI
Call TI
Call TI
Call TI
Call TI
Call TI
OPA660AU/2K5
(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.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check
http://www.ti.com/productcontent for the latest availability information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements
for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered
at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and
package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS
compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame
retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder
temperature.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is
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to Customer on an annual basis.
Addendum-Page 1
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