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(R)
OPA128
Difet (R) Electrometer-Grade OPERATIONAL AMPLIFIER
FEATURES
q q q q q ULTRA-LOW BIAS CURRENT: 75fA max LOW OFFSET: 500V max LOW DRIFT: 5V/C max HIGH OPEN-LOOP GAIN: 110dB min HIGH COMMON-MODE REJECTION: 90dB min q IMPROVED REPLACEMENT FOR AD515 AND AD549
APPLICATIONS
q q q q q q ELECTROMETER MASS SPECTROMETER CHROMATOGRAPH ION GAUGE PHOTODETECTOR RADIATION-HARD EQUIPMENT
DESCRIPTION
The OPA128 is an ultra-low bias current monolithic operational amplifier. Using advanced geometry dielectrically-isolated FET (Difet(R)) inputs, this monolithic amplifier achieves a performance level exceeding even the best hybrid electrometer amplifiers. Laser-trimmed thin-film resistors give outstanding voltage offset and drift performance. A noise-free cascode and low-noise processing give the OPA128 excellent low-level signal handling capabilities. Flicker noise is very low. The OPA128 is an improved pin-for-pin replacement for the AD515.
Difet(R) Burr-Brown Corp.
5 Trim 1k 2k 2k 4 -VCC OPA128 Simplified Circuit Case (Guard) 8 7 +VCC
-In 2 3 +In Noise-Free Cascode 6 Output Trim 1 1k 28k 28k
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/ * FAXLine: (800) 548-6133 (US/Canada Only) * Cable: BBRCORP * Telex: 066-6491 * FAX: (520) 889-1510 * Immediate Product Info: (800) 548-6132
(c)
1986 Burr-Brown Corporation
PDS-653E
Printed in U.S.A. May, 1995
SPECIFICATIONS
ELECTRICAL
At VCC = 15VDC and TA = +25C, unless otherwise noted. Pin 8 connected to ground. OPA128JM PARAMETER INPUT BIAS CURRENT(1) Input Bias Current OFFSET CURRENT(1) Input Offset Current OFFSET Input Offset Voltage Average Drift Supply Rejection VOLTAGE(1) VCM = 0VDC TA = TMIN to TMAX 80 260 120 1 92 78 27 15 2.4 4 4.2 0.22 1013 || 1 1015 || 2 10 80 12 118 10 90 1000 20 90 100 140 120 1 92 78 27 15 2.4 4 3 0.16 1013 || 1 1015 || 2 12 118 10 90 500 10 90 32 140 120 1 92 78 27 15 2.4 4 2.3 0.12 1013 || 1 1015 || 2 12 118 10 90 500 5 90 32 140 120 1 92 78 27 15 2.4 4 3 0.16 1013 || 1 1015 || 2 12 118 500 10 32 V V/C dB V/V nV/Hz nV/Hz nV/Hz nV/Hz Vrms Vp-p fA, p-p fA/Hz || pF || pF V dB VCM = 0VDC, RL 10k VCM = 0VDC, RL 10k CONDITIONS MIN TYP MAX OPA128KM MIN TYP MAX MIN OPA128LM TYP MAX MIN OPA128SM TYP MAX UNITS
150
300
75
150
40
75
75
150
fA
65
30
30
30
fA
NOISE Voltage: fO = 10Hz fO = 100Hz fO = 1kHz fO = 10kHz fB = 10Hz to 10kHz fB = 0.1Hz to 10Hz Current: fB = 0.1Hz to 10Hz fO = 0.1Hz to 20kHz IMPEDANCE Differential Common-Mode VOLTAGE RANGE(4) Common-Mode Input Range Common-Mode Rejection OPEN-LOOP GAIN, DC Open-Loop Voltage Gain FREQUENCY RESPONSE Unity Gain, Small Signal Full Power Response Slew Rate Settling Time, 0.1% 0.01% Overload Recovery, 50% Overdrive(3) RATED OUTPUT Voltage Output Current Output Output Resistance Load Capacitance Stability Short Circuit Current POWER SUPPLY Rated Voltage Voltage Range, Derated Performance Current, Quiescent TEMPERATURE RANGE Specification Operating Storage Junction-Ambient Ambient Temp. Ambient Temp. Ambient Temp. 0 -55 -65 RL = 2k VO = 10VDC DC, Open Loop Gain = +1 10 5
(2)
VIN = 10VDC RL 2k
94
128
110
128
110
128
110
128
dB
0.5 0.5
20Vp-p, RL = 2k VO = 10V, RL = 2k Gain = -1, RL = 2k 10V Step Gain = -1
1 47 3 5 10 5
0.5 1
1 47 3 5 10 5
0.5 1
1 47 3 5 10 5
0.5 1
1 47 3 5 10 5
MHz kHz V/s s s s
10
13 10 100 1000 34
10 5
55
10
13 10 100 1000 34
10 5
55
10
13 10 100 1000 34
10 5
55
10
13 10 100 1000 34
55
V mA pF mA
15 5 IO = 0mADC 0.9 18 1.5 5
15 18 1.5 5
15 18 1.5 5
15 18 1.5
VDC VDC mA C C C C/W
0.9
0.9
0.9
+70 +125 +150 200
0 -55 -65 200
+70 +125 +150
0 -55 -65 200
+70 +125 +150
-55 -55 -65 200
+125 +125 +150
NOTES: (1) Offset voltage, offset current, and bias current are measured with the units fully warmed up. Bias current doubles approximately every 11C. (2) Sample tested. (3) Overload recovery is defined as the time required for the output to return from saturation to linear operation following the removal of a 50% input overdrive. (4) If it is possible for the input voltage to exceed the supply voltage, a series protection resistor should be added to limit input current to 0.5mA. The input devices can withstand overload currents of 0.3mA indefinitely without damage. 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.
(R)
OPA128
2
ELECTRICAL (FULL TEMPERATURE RANGE SPECIFICATIONS)
At VCC = 15VDC and TA = TMIN and TMAX, unless otherwise noted. OPA128JM PARAMETER TEMPERATURE RANGE Specification Range INPUT BIAS CURRENT(1) Input Bias Current OFFSET Input Offset Current CURRENT(1) VCM = 0VDC VCM = 0VDC 74 114 2 11 112 1.1 2.2mV 20 80 200 10 80 114 2 11 112 0.6 1mV 10 80 100 10 80 114 2 11 112 0.6 750 5 80 100 10 74 106 5 11 104 18 1.5mV 10 100 pA V V/C dB V/V V dB VCM = 0VDC 2.5 8 1.3 4 0.7 2 43 170 pA Ambient Temp. 0 +70 0 +70 0 +70 -55 +125 C CONDITIONS MIN TYP MAX OPA128KM MIN TYP MAX MIN OPA128LM TYP MAX OPA128SM MIN TYP MAX UNITS
OFFSET VOLTAGE(1) Input Offset Voltage Average Drift Supply Rejection VOLTAGE RANGE(2) Common-Mode Input Range Commmon-Mode Rejection OPEN-LOOP GAIN, DC Open-Loop Voltage Gain RATED OUTPUT Voltage Output Current Output Short Circuit Current POWER SUPPLY Current, Quiescent
VIN = 10VDC RL 2k
10 74
90
125
104
125
104
125
90
122
dB
RL = 2k VO = 10VDC VO = 0VDC
10 5 10
22
10 5 10
22
10 5 10
22
10 5 10
18
V mA mA
I = 0mADC
0.9
1.8
0.9
1.8
0.9
1.8
0.9
2
mA
NOTES: (1) Offset voltage, offset current, and bias current are measured with the units fully warmed up. (2) If it is possible for the input voltage to exceed the supply voltage, a series protection resistor should be added to limit input current to 0.5mA. The input devices can withstand overload currents of 0.3mA indefinitely without damage.
CONNECTION DIAGRAM
Top View Substrate and Case Offset Trim -In 2 8 1 7 +VCC
ORDERING INFORMATION
PRODUCT OPA128JM OPA128KM OPA128LM OPA128SM PACKAGE TO-99 TO-99 TO-99 TO-99 TEMPERATURE RANGE 0C to +70C 0C to +70C 0C to +70C -55C to +125C BIAS CURRENT, max (fA) 300 150 75 150
OPA128
6 Output
PACKAGE INFORMATION
+In 3 4 -VCC 5 Offset Trim PRODUCT OPA128JM OPA128KM OPA128LM OPA128SM PACKAGE TO-99 TO-99 TO-99 TO-99 PACKAGE DRAWING NUMBER(1) 001 001 001 001
ABSOLUTE MAXIMUM RATINGS
Supply ........................................................................................... 18VDC Internal Power Dissipation(1) .......................................................... 500mW Differential Input Voltage .............................................................. 36VDC Input Voltage Range ..................................................................... 18VDC Storage Temperature Range .......................................... -65C to +150C Operating Temperature Range ....................................... -55C to +125C Lead Temperature (soldering, 10s) ............................................... +300C Output Short Circuit Duration(2) ................................................ Continuous Junction Temperature .................................................................... +175C NOTES: (1) Packages must be derated based on CA = 150C/W or JA = 200C/W. (2) Short circuit may be to power supply common only. Rating applies to +25C ambient. Observe dissipation limit and TJ.
NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book.
(R)
3
OPA128
DICE INFORMATION
PAD 1 2 3 4 5 6 7 8 NC FUNCTION Offset Trim -In +In -VCC Offset Trim Output +VCC Substrate No Connection
Substrate Bias: Isolated, normally connected to common.
MECHANICAL INFORMATION
MILS (0.001") Die Size Die Thickness Min. Pad Size 96 x 71 5 20 3 4x4 MILLIMETERS 2.44 x 1.80 0.13 0.51 0.08 0.10 x 0.10 None
OPA128 DIE TOPOGRAPHY
Backing
TYPICAL PERFORMANCE CURVES
At TA = +25C, 15VDC, unless otherwise noted. OPEN-LOOP FREQUENCY RESPONSE 140
Power Supply Rejection (dB)
POWER SUPPLY REJECTION vs FREQUENCY 140 -45 120 100 80 60 -PSRR 40 20 0 1 10 100 1k 10k 100k 1M 10M Frequency (Hz) +PSRR
120 Gain
Voltage Gain (dB)
100 80 60 40 20 0 1 10 100 1k 10k 100k 1M Frequency (Hz) -180 10M Phase Margin 90 O -90
-135
Phase Shift (Degrees)
COMMON-MODE REJECTION vs INPUT COMMON-MODE VOLTAGE 120
Common-Mode Rejection (dB)
Common-Mode Rejection (dB)
COMMON-MODE REJECTION vs FREQUENCY 140 120 100 80 60 40 20 0
110
100
90
80
70 -15
-10
-5
0
5
10
15
1
10
100
1k
10k
100k
1M
10M
Common-Mode Voltage (V)
(R)
Frequency (Hz)
OPA128
4
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25C, +15VDC, unless otherwise noted. BIAS AND OFFSET CURRENT vs TEMPERATURE 100pA
BIAS AND OFFSET CURRENT vs INPUT COMMON-MODE VOLTAGE 10
Normalized Bias and Offset Current
Bias and Offset Current (fA)
SM 10pA IB IOS
1
1pA
100
0.1
10 1 -50 -25 0 25 50 75 100 125 Ambient Temperature (C)
0.01 -15 -10 -5 0 5 10 Common-Mode Voltage (V) 15
GAIN-BANDWIDTH AND SLEW RATE vs TEMPERATURE 4 4 3
GAIN-BANDWIDTH AND SLEW RATE vs SUPPLY VOLTAGE 6
Gain-Bandwidth (MHz)
3
3
Gain-Bandwidth (MHz)
Slew Rate (V/s)
2 + Slew - Slew 1
4
2
2
2
1
1
0 -75 -50 -25 0 25 50 75 100 125 Ambient Temperature (C)
0
0 0 5 10 Supply Voltage (VCC) 15 20
0
SUPPLY CURRENT vs TEMPERATURE 2
140
OPEN-LOOP GAIN, PSR, AND CMR vs TEMPERATURE
PSR, CMR, Voltage Gain (dB)
Supply Current (mA)
1.5
130
AOL
1
120 CMR 110 PSR 100
0.5
0 -75 -50 -25 0 25 50 75 100 125 Ambient Temperature (C)
-75
-50
-25
0
25
50
75
100
125
Ambient Temperature (C)
5
OPA128
Slew Rate (V/s)
(R)
TYPICAL PERFORMANCE CURVES (CONT)
At TA = +25C, +15VDC, unless otherwise noted. LARGE SIGNAL TRANSIENT RESPONSE 80 SMALL SIGNAL TRANSIENT RESPONSE
Output Voltage (V)
10
Output Voltage (mV)
5V 0 25 Time (s) 5s 5s
40
0
0
-10
-40
-80 50 0
20mV 2 4 6 Time (s)
1s 8 10
COMMON-MODE INPUT RANGE vs SUPPLY VOLTAGE 15 Common-Mode Voltage (V) 100pA
BIAS CURRENT vs ADDITIONAL POWER DISSIPATION
10pA 10
Bias Current (fA)
KM 1pA
100
5
10 1 0 5 10 Supply Voltage (VCC) 15 20 0 50 100 150 200 250 300 350 Additional Power Dissipation (mW)
0
INPUT VOLTAGE NOISE SPECTRAL DENSITY 1k
30
FULL-POWER OUTPUT vs FREQUENCY
Voltage Density (nV/ Hz)
Output Voltage (Vp-p)
20
100
10
10 1 10 100 1k 10k 100k Frequency (Hz)
0 1k 10k 100k Frequency (Hz) 1M
(R)
OPA128
6
APPLICATIONS INFORMATION
OFFSET VOLTAGE ADJUSTMENT The OPA128 offset voltage is laser-trimmed and will require no further trim for most applications. As with most amplifiers, externally trimming the remaining offset can change drift performance by about 0.3V/C for each 100V of adjusted effort. Note that the trim (Figure 1) is similar to operational amplifiers such as HA-5180 and AD515. The OPA128 can replace many other amplifiers by leaving the external null circuit unconnected.
+VCC 7 6 1 5 4
(1)
The amplifier case should be connected to any input shield or guard via pin 8. This insures that the amplifier itself is fully surrounded by guard potential, minimizing both leakage and noise pickup (see Figure 2).
Non-Inverting Buffer
2 3
8 OPA128 6 Out
2 3 In
8 OPA128 6 Out
In
2
Inverting
TO-99 Bottom View 4 56 7 1 8
OPA128 3
In 2
10mV Typical Trim Range
3 OPA128 6 Out 8 2
3
-VCC
NOTE: (1) 10k to 1M Trim Potentiometer (100k Recommended)
FIGURE 1. Offset Voltage Trim. INPUT PROTECTION Conventional monolithic FET operational amplifiers' inputs must be protected against destructive currents that can flow when input FET gate-to-substrate isolation diodes are forward-biased. Most BIFET(R) amplifiers can be destroyed by the loss of -VCC. Because of its dielectric isolation, no special protection is needed on the OPA128. Of course, the differential and common-mode voltage limits should be observed. Static damage can cause subtle changes in amplifier input characteristics without necessarily destroying the device. In precision operational amplifiers (both bipolar and FET types), this may cause a noticeable degradation of offset voltage and drift. Static protection is recommended when handling any precision IC operational amplifier. GUARDING AND SHIELDING As in any situation where high impedances are involved, careful shielding is required to reduce "hum" pickup in input leads. If large feedback resistors are used, they should also be shielded along with the external input circuitry. Leakage currents across printed circuit boards can easily exceed the bias current of the OPA128. To avoid leakage problems, it is recommended that the signal input lead of the OPA128 be wired to a Teflon standoff. If the input is to be soldered directly into a printed circuit board, utmost care must be used in planning the board layout. A "guard" pattern should completely surround the high impedance input leads and should be connected to a low impedance point which is at the signal input potential.
BOARD LAYOUT FOR INPUT GUARDING Guard top and bottom of board. Alternate: use Teflon(R) standoff for sensitive input pins.
Teflon(R) E.I. Du Pont de Nemours & Co.
FIGURE 2. Connection of Input Guard. Triboelectric charge (static electricity generated by friction) can be a troublesome noise source from cables connected to the input of an electrometer amplifier. Special low-noise cable will minimize this effect but the optimum solution is to mount the signal source directly at the electrometer input with short, rigid, wiring to preclude microphonic noise generation. TESTING Accurately testing the OPA128 is extremely difficult due to its high level of performance. Ordinary test equipment may not be able to resolve the amplifier's extremely low bias current. Inaccurate bias current measurements can be due to: 1. Test socket leakage 2. Unclean package 3. Humidity or dew point condensation 4. Circuit contamination from fingerprints or anti-static treatment chemicals 5. Test ambient temperature 6. Load power dissipation
BIFET(R) National Semiconductor Corp.
(R)
7
OPA128
500 Guard 2 3
9.5k +15V 8 7 OPA128 4 5 1 pH Probe RS 500M 50mV Output 100k -15V Offset Trim 6 1VDC Output
CF RF
10pF 1011
2 3 Q 100pF 1011
8 OPA128 6 Output eO
e O = - Q/C F Low Frequency Cutoff = 1/(2 RF CF) = 0.16Hz
FIGURE 3. High Impedance (1015) Amplifier.
FIGURE 4. Piezoelectric Transducer Charge Amplifier.
IB 100fA -In 3 2 OPA128 6 Gain = 100 CMRR 118dB RIN 1015
RF 10k
2
25k
25k
5
RG 202
RF 10k
3
25k Burr-Brown INA105 Differential Amplifier 1
6
Output
2 3 OPA128 6
25k
+In
Differential Voltage Gain = 1 + 2RF /RG
FIGURE 5. FET Input Instrumentation Amplifier for Biomedical Applications.
10pF
(1)
10k
1M 1N914 2 3 Input OPA606 6
(1) (1)
2 3
8 OPA128 6
Output
1N914 NOTE: (1) Reverse polarity for negative peak detection.
2N4117A
1000F Polystyrene
Droop 100V/s
FIGURE 6. Low-Droop Positive Peak Detector.
(R)
OPA128
8
<1pF to prevent gain peaking.
1010 Silicon Detector Corp. SD-020-11-21-011 +15V 0.1F 8 7 OPA128 3 0.01F 1010 -15V Circuit must be well shielded. 4 6 Output 5 x 10 9 V/W
Current Input 1000M 2 3 OPA128 8 VO = -1V/nA 6 Output 18k 2k
Guard 2
0.1F
FIGURE 7. Sensitive Photodiode Amplifier.
FIGURE 8. Current-to-Voltage Converter.
+5V 2
109
Biased Current Transducer
OPA128 3 8
6
3 4 5 10 11 12 +15V 7 5 6 4 REF101 1 8 +5V
INA101HP 14
1 Output
VO = 1mV/pA
FIGURE 9. Biased Current-to-Voltage Converter.
(R)
9
OPA128

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