Difet Electrometer-Grade OPERATIONAL AMPLIFIER

Transcription

1 OPA Difet Electrometer-Grade OPERATIONAL AMPLIFIER FEATURES ULTRA-LOW BIAS CURRENT: fa max LOW OFFSET: µv max LOW DRIFT: µv/ C max HIGH OPEN-LOOP GAIN: db min HIGH COMMON-MODE REJECTION: 9dB min IMPROVED REPLACEMENT FOR AD AND AD9 APPLICATIONS ELECTROMETER MASS SPECTROMETER CHROMATOGRAPH ION GAUGE PHOTODETECTOR RADIATION-HARD EQUIPMENT DESCRIPTION The OPA is an ultra-low bias current monolithic operational amplifier. Using advanced geometry dielectrically-isolated FET (Difet ) 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 OPA excellent low-level signal handling capabilities. Flicker noise is very low. The OPA is an improved pin-for-pin replacement for the AD. Difet Burr-Brown Corp. Case (Guard) In +In Trim Trim kω kω Noise-Free Cascode kω kω kω kω +V CC OPA Simplified Circuit V CC International Airport Industrial Park Mailing Address: PO Box Tucson, AZ Street Address: S. Tucson Blvd. Tucson, AZ Tel: () - Twx: 9-9- Cable: BBRCORP Telex: -9 FAX: () 9- Immediate Product Info: () - 9 Burr-Brown Corporation PDS-E Printed in U.S.A. May, 99

2 SPECIFICATIONS ELECTRICAL At V CC = ±VDC and T A = + C unless otherwise noted. Pin connected to ground. OPAJM OPAKM OPALM OPASM PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS INPUT BIAS CURRENT () Input Bias Current OFFSET CURRENT () Input Offset Current V CM = VDC, R L kω ± ± ± ± ± ± ± ± fa V CM = VDC, R L kω fa OFFSET VOLTAGE () Input Offset Voltage V CM = VDC ± ± ± ± ± ± ± ± µv Average Drift T A = T MIN to T MAX ± ± ± ± µv/ C Supply Rejection db ± ± ± ± ± ± ± ± µv/v NOISE Voltage: f O = Hz nv/ Hz f O = Hz nv/ Hz f O = khz nv/ Hz f O = khz nv/ Hz f B = Hz to khz.... µvrms f B =.Hz to Hz µvp-p Current: f B =.Hz to Hz.. fa, p-p f O =.Hz to khz.... fa/ Hz IMPEDANCE Differential Ω pf Common-Mode Ω pf VOLTAGE RANGE () Common-Mode Input Range ± ± ± ± ± ± ± ± V Common-Mode Rejection V IN = ±VDC db OPEN-LOOP GAIN, DC Open-Loop Voltage Gain R L kω 9 db FREQUENCY RESPONSE Unity Gain, Small Signal ().... MHz Full Power Response Vp-p, R L = kω khz Slew Rate V O = ±V, R L = kω. V/µs Settling Time,.% Gain =, R L = kω µs.% V Step µs Overload Recovery, % Overdrive () Gain = µs RATED OUTPUT Voltage R L = kω ± ± ± ± ± ± ± ± V Current V O = ±VDC ± ± ± ± ± ± ± ± ma Resistance DC, Open Loop Ω Load Capacitance Stability Gain = + pf Short Circuit Current ma POWER SUPPLY Rated Voltage ± ± ± ± VDC Voltage Range, Derated Performance ± ± ± ± ± ± ± ± VDC Current, Quiescent I O = madc ma TEMPERATURE RANGE Specification Ambient Temp C Operating Ambient Temp C Storage Ambient Temp C θ Junction-Ambient C/W NOTES: () Offset voltage, offset current, and bias current are measured with the units fully warmed up. Bias current doubles approximately every C. () Sample tested. () Overload recovery is defined as the time required for the output to return from saturation to linear operation following the removal of a % input overdrive. () 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.ma. The input devices can withstand overload currents of.ma 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. OPA

3 ELECTRICAL (FULL TEMPERATURE RANGE SPECIFICATIONS) At V CC = ±VDC and T A = T MIN and T MAX unless otherwise noted. OPAJM OPAKM OPALM OPASM PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS TEMPERATURE RANGE Specification Range Ambient Temp C INPUT BIAS CURRENT () Input Bias Current V CM = VDC ±. ± ±. ± ±. ± ± ± pa OFFSET CURRENT () Input Offset Current V CM = VDC... pa OFFSET VOLTAGE () Input Offset Voltage V CM = VDC ±.mv ±mv ± ±.mv µv Average Drift ± ± ± ± µv/ C Supply Rejection db ± ± ± ± ± ± ± ± µv/v VOLTAGE RANGE () Common-Mode Input Range ± ± ± ± ± ± ± ± V Commmon-Mode Rejection V IN = ±VDC db OPEN-LOOP GAIN, DC Open-Loop Voltage Gain R L kω 9 9 db RATED OUTPUT Voltage R L = k ± ± ± ± V Current V O = ±VDC ± ± ± ± ma Short Circuit Current V O = VDC ma POWER SUPPLY Current, Quiescent I = madc ma NOTES: () Offset voltage, offset current, and bias current are measured with the units fully warmed up. () 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.ma. The input devices can withstand overload currents of.ma indefinitely without damage. CONNECTION DIAGRAM Top View Offset Trim In ABSOLUTE MAXIMUM RATINGS +In Substrate and Case OPA V CC Supply... ±VDC Internal Power Dissipation ()... mw Differential Input Voltage... ±VDC Input Voltage Range... ±VDC Storage Temperature Range... C to + C Operating Temperature Range... C to + C Lead Temperature (soldering, s)... + C Short Circuit Duration ()... Continuous Junction Temperature... + C NOTES: () Packages must be derated based on θ CA = C/W or θ JA = C/W. () Short circuit may be to power supply common only. Rating applies to + C ambient. Observe dissipation limit and T J. +V CC Offset Trim ORDERING INFORMATION TEMPERATURE BIAS CURRENT, MODEL PACKAGE RANGE max (fa) OPAJM TO-99 C to + C ± OPAKM TO-99 C to + C ± OPALM TO-99 C to + C ± OPASM TO-99 C to + C ± PACKAGE INFORMATION PACKAGE DRAWING MODEL PACKAGE NUMBER () OPAJM TO-99 OPAKM TO-99 OPALM TO-99 OPASM TO-99 NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix D of Burr-Brown IC Data Book. OPA

4 DICE INFORMATION PAD FUNCTION Offset Trim In +In V CC Offset Trim +V CC Substrate NC No Connection Substrate Bias: Isolated, normally connected to common. MECHANICAL INFORMATION OPA DIE TOPOGRAPHY MILS (.") MILLIMETERS Die Size 9 x ±. x. ±. Die Thickness ±. ±. Min. Pad Size x. x. Backing None TYPICAL PERFORMANCE CURVES T A = + C, ±VDC, unless otherwise noted. OPEN-LOOP FREQUENCY RESPONSE POWER SUPPLY REJECTION vs FREQUENCY Voltage Gain (db) Gain Ø Phase Margin 9 9 Phase Shift (Degrees) Power Supply Rejection (db) PSRR +PSRR k k k M M k k k M M COMMON-MODE REJECTION vs INPUT COMMON-MODE VOLTAGE COMMON-MODE REJECTION vs FREQUENCY Common-Mode Rejection (db) 9 Common-Mode Rejection (db) Common-Mode Voltage (V) k k k M M OPA

5 TYPICAL PERFORMANCE CURVES (CONT) At T A = + C, +VDC unless otherwise noted. pa BIAS AND OFFSET CURRENT vs TEMPERATURE BIAS AND OFFSET CURRENT vs INPUT COMMON-MODE VOLTAGE Bias and Offset Current (fa) pa pa SM I B I OS Normalized Bias and Offset Current.. Ambient Temperature ( C) Common-Mode Voltage (V) GAIN-BANDWIDTH AND SLEW RATE vs TEMPERATURE GAIN-BANDWIDTH AND SLEW RATE vs SUPPLY VOLTAGE Gain-Bandwidth (MHz) Slew Rate (V/µs) Gain-Bandwidth (MHz) + Slew Slew Slew Rate (V/µs) Ambient Temperature ( C) Supply Voltage (±V CC ) SUPPLY CURRENT vs TEMPERATURE OPEN-LOOP GAIN, PSR, AND CMR vs TEMPERATURE Supply Current (ma).. PSR, CMR, Voltage Gain (db) PSR A OL CMR Ambient Temperature ( C) Ambient Temperature ( C) OPA

6 TYPICAL PERFORMANCE CURVES (CONT) At T A = + C, +VDC unless otherwise noted. LARGE SIGNAL TRANSIENT RESPONSE SMALL SIGNAL TRANSIENT RESPONSE Voltage (V) Voltage (mv) V µs mv µs Time (µs) µs Time (µs) COMMON-MODE INPUT RANGE vs SUPPLY VOLTAGE pa BIAS CURRENT vs ADDITIONAL POWER DISSIPATION Common-Mode Voltage (±V) Bias Current (fa) pa pa KM Supply Voltage (±V CC ) Additional Power Dissipation (mw) k INPUT VOLTAGE NOISE SPECTRAL DENSITY FULL-POWER OUTPUT vs FREQUENCY Voltage Density (nv/ Hz) Voltage (Vp-p) k k k k k k M OPA

7 APPLICATIONS INFORMATION OFFSET VOLTAGE ADJUSTMENT The OPA 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.µv/ C for each µv of adjusted effort. Note that the trim (Figure ) is similar to operational amplifiers such as HA- and AD. The OPA can replace many other amplifiers by leaving the external null circuit unconnected. +V CC The amplifier case should be connected to any input shield or guard via pin. This insures that the amplifier itself is fully surrounded by guard potential, minimizing both leakage and noise pickup (see Figure ). In Non-Inverting OPA Out In Buffer OPA Out Inverting TO-99 Bottom View OPA FIGURE. Offset Voltage Trim. V CC () ±mv Typical Trim Range NOTE: () kω to MΩ Trim Potentiometer (kω Recommended) 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 amplifiers can be destroyed by the loss of V CC. Because of its dielectric isolation, no special protection is needed on the OPA. 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 OPA. To avoid leakage problems, it is recommended that the signal input lead of the OPA 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. In OPA Out FIGURE. 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 OPA 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:. Test socket leakage. Unclean package. Humidity or dew point condensation. Circuit contamination from fingerprints or anti-static treatment chemicals. Test ambient temperature. Load power dissipation BIFET National Semiconductor Corp. BOARD LAYOUT FOR INPUT GUARDING Guard top and bottom of board. Alternate: use Teflon standoff for sensitive input pins. Teflon E.I. Du Pont de Nemours & Co. OPA

8 Ω 9.kΩ C F pf ph Probe R S MΩ mv Guard +V VDC OPA Offset Trim kω V Q pf R F Ω OPA Ω e O = Q/C F e O Low Frequency Cutoff = /( π RF C F ) =.Hz FIGURE. Piezoelectric Transducer Charge Amplifier. FIGURE. High Impedance ( Ω) Amplifier. I B fa In OPA Gain = CMRR db R IN Ω R F kω kω kω R G Ω R F kω kω +In OPA kω Burr-Brown INA Differential Amplifier Differential Voltage Gain = + R F /R G FIGURE. FET Input Instrumentation Amplifier for Biomedical Applications. pf kω Input FIGURE. Low-Droop Positive Peak Detector. () N9 OPA () N9 NOTE: () Reverse polarity for negative peak detection. MΩ () NA µf Polystyrene OPA Droop µv/s OPA

9 <pf to prevent gain peaking. Ω Silicon Detector Corp. SD----.µF Guard Ω +V.µF OPA.µF x 9 V/W Current Input MΩ kω kω OPA V O = V/nA V Circuit must be well shielded. FIGURE. Sensitive Photodiode Amplifier. FIGURE. Current-to-Voltage Converter. +V 9 Ω Biased Current Transducer OPA +V INAHP REF +V V O = mv/pa FIGURE 9. Biased Current-to-Voltage Converter. 9 OPA