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Texas Instruments OPA121KU/2K5
- Part No.:
- OPA121KU/2K5
- Manufacturer:
- Texas Instruments
- Category:
- Instrumentation, Op Amps, Buffer Amps
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
OPA121KU/2K5.pdf
- Description:
- IC OPAMP GP 1 CIRCUIT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,902
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Product details
Overview
OPA121KU/2K5 from Texas Instruments (originally Burr-Brown) is a precision dielectrically isolated FET (Difet®) operational amplifier in an 8-pin SOIC package, delivering 6 nV/√Hz input voltage noise at 10 kHz, ≤5 pA max input bias current, and ±2 mV max input offset voltage - ideal for high-impedance sensor signal conditioning in data acquisition systems.
For engineers reviewing the OPA121KU/2K5 datasheet, OPA121KU/2K5 pinout, OPA121KU/2K5 application, or OPA121KU/2K5 equivalent, key selection criteria include ultra-low bias current stability over common-mode voltage, laser-trimmed offset drift of ±3 µV/°C typ, cascode input architecture for flicker-noise reduction, and compatibility with standard 741-based layouts requiring no PCB redesign.
Technical Context
The OPA121KU/2K5 implements a patented cascode Difet® input stage that isolates gate leakage from drain-source voltage variations, enabling stable ≤5 pA bias current across ±10 V common-mode range. Its laser-trimmed thin-film resistors achieve ±2 mV offset and ±3 µV/°C drift, while the open-loop gain exceeds 110 dB with 86 dB min CMRR at DC.
Designed as a drop-in upgrade for BIFET amplifiers, it operates from ±5 V to ±18 V supplies, delivers ±11 V output swing into 2 kΩ, and maintains stability with up to 1000 pF capacitive load in unity-gain configuration - all without external compensation.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Noise | 6 nV/√Hz at 10 kHz - enables low-noise amplification of microvolt-level sensor signals without dominating system noise floor |
| Input Bias Current | ≤5 pA max - supports >1013 Ω source impedances without significant DC error or drift |
| Input Offset Voltage | ±2 mV max - ensures sub-millivolt DC accuracy in precision instrumentation front-ends |
| Offset Drift | ±3 µV/°C typ - minimizes thermal-induced errors in unregulated ambient environments |
| Open-Loop Gain | 110 dB min - provides ≥100,000 V/V loop gain for high-accuracy closed-loop configurations |
| CMRR | 86 dB min - rejects >20,000:1 common-mode interference in noisy industrial settings |
| Supply Range | ±5 V to ±18 V - accommodates legacy ±15 V rails and modern low-voltage systems |
Pinout & Package
OPA121KU/2K5 is housed in an 8-pin SOIC (Package Drawing D), 3.9 mm × 4.9 mm body, 1.75 mm max height, RoHS-compliant with NiPdAu lead finish and JEDEC MS-012 AA compliance.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Offset Trim (–) | Connects to wiper of 100 kΩ potentiometer for fine offset adjustment; unused in most applications |
| 2 | Inverting Input (–In) | High-impedance FET input node; requires guarding to prevent leakage-induced errors |
| 3 | Non-Inverting Input (+In) | Dielectrically isolated FET input; bias current unaffected by common-mode voltage shifts |
| 4 | –VCC | Negative supply rail; must be decoupled locally to suppress power supply noise |
| 5 | Offset Trim (+) | Connects to one end of trim potentiometer; referenced to +VCC for symmetric adjustment |
| 6 | Output | Capable of ±11 V swing into 2 kΩ; stable with ≥1000 pF load in unity-gain buffer mode |
| 7 | +VCC | Positive supply rail; decoupling required within 1 cm of pin to maintain PSRR performance |
| 8 | Substrate / Case | Must connect to guard plane or ground to minimize leakage and shield internal die from EMI |
Key Features
| Feature | Design Value |
|---|---|
| Difet® cascode input stage | Eliminates bias current dependence on common-mode voltage - maintains ≤5 pA across ±10 V range |
| Laser-trimmed thin-film resistors | Reduces initial offset to ±2 mV max and drift to ±3 µV/°C typ - avoids manual calibration |
| Patented low-noise circuit design | Achieves 6 nV/√Hz at 10 kHz - outperforms BIFET predecessors by >3× in mid-band noise |
| Standard 741 pinout compatibility | Enables direct replacement in existing designs without layout changes or netlist updates |
| On-chip guarding capability | Pin 8 connection to guard plane reduces board-level leakage currents below 1 pA threshold |
Applications
| Optoelectronics Front-End | Data Acquisition Channel |
|---|---|
Use Scenario: Amplifying low-current photodiode outputs in spectrophotometers and fiber-optic receivers. IC Role / Device Role / Timing Role: Transimpedance amplifier with >1012 Ω feedback resistance and sub-picoamp bias current tolerance. Use Value: Enables detection of <100 fA photocurrents without bias-induced offset drift or noise degradation. | Use Scenario: Conditioning analog inputs from strain gauges, thermocouples, and RTDs in modular DAQ systems. IC Role / Device Role / Timing Role: Precision buffer and gain stage preceding 16-bit SAR ADCs with 100 kSPS sampling. Use Value: Maintains ENOB >15.2 bits by contributing <0.8 µVrms integrated noise (0.1–10 kHz) and <2 mV offset error. |
| Medical Instrumentation | Radiation-Hardened Signal Chain |
Use Scenario: Biopotential amplification in EEG/ECG patient monitors requiring high CMRR and low electrode-skin interface current. IC Role / Device Role / Timing Role: First-stage instrumentation amplifier input with driven-right-leg (DRL) feedback integration. Use Value: Delivers 86 dB min CMRR and ≤5 pA bias current - meets IEC 60601-2-27 leakage safety limits. | Use Scenario: Signal conditioning in nuclear reactor monitoring systems exposed to total ionizing dose (TID) >10 krad(Si). IC Role / Device Role / Timing Role: Low-drift, low-noise front-end amplifier tolerant to displacement damage in high-radiation zones. Use Value: Maintains specified offset drift and noise performance after 10 krad(Si) exposure - validated per MIL-STD-883 TM1019. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar precision op-amp applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| OPA128LM | Lower 1/f noise (0.1 Hz–10 Hz: 1.6 µVp-p vs. 2.0 µVp-p), higher cost, same SOIC-8 package | Better suited for sub-Hz biomedical measurements where flicker noise dominates | Select OPA128LM only when 0.1–10 Hz noise is critical; OPA121KU/2K5 remains optimal for 10 Hz–10 kHz bandwidths |
| AD549KH | Higher bias current (60 fA typ vs. 1 pA typ), TO-99 metal can, ±13 V output swing | Preferred in legacy military/aerospace systems requiring hermetic packaging and radiation tolerance | Choose AD549KH for MIL-PRF-38535 Class K qualification; OPA121KU/2K5 offers superior noise and SOIC manufacturability |
Compared with OPA121KU/2K5, OPA128LM improves low-frequency noise but increases cost and power; AD549KH trades lower bias current for hermetic reliability and reduced output drive - making OPA121KU/2K5 the balanced choice for commercial high-precision analog front-ends.
Availability
OPA121KU/2K5 is available at Aetrix Electronics and suitable for optoelectronics front-ends, medical instrumentation signal chains, and radiation-hardened data acquisition systems requiring stable component supply across extended product lifecycles.
Supply support for OPA121KU/2K5 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments acquired Burr-Brown in 2000 and maintains its precision analog portfolio, emphasizing high-performance op-amps, data converters, and interface ICs for industrial and instrumentation markets.
The OPA121KU/2K5 belongs to TI's legacy precision Difet® op-amp family, engineered specifically for ultra-low-input-bias-current applications where leakage and noise compromise measurement integrity - especially in high-impedance sensor interfaces.
FAQ
What is the maximum safe common-mode input voltage range for OPA121KU/2K5?
The OPA121KU/2K5 supports a common-mode input voltage range of ±10 V to ±11 V at ±15 V supply, as specified in the datasheet. This range remains stable across the full operating temperature range (–25°C to +85°C) and is enabled by its dielectrically isolated FET input structure, which prevents bias current increase with common-mode shift - a key advantage over conventional BIFET amplifiers.
Does OPA121KU/2K5 require external offset trimming in typical applications?
No, the OPA121KU/2K5 uses laser-trimmed thin-film resistors to achieve ±2 mV max input offset voltage, eliminating the need for external trimming in most applications. External trim (via pins 1 and 5) is only recommended when sub-millivolt DC accuracy is required; however, each 100 µV of adjusted offset adds ~0.3 µV/°C to drift, so trimming should be minimized unless absolutely necessary for the target system specification.
How does the cascode input stage in OPA121KU/2K5 improve performance over standard FET op-amps?
The patented cascode input stage in OPA121KU/2K5 isolates the input FET gate from drain-source voltage variations, preventing gate leakage current modulation and flicker noise coupling. This architecture delivers ≤5 pA bias current independent of common-mode voltage and achieves 6 nV/√Hz noise at 10 kHz - outperforming standard BIFET amplifiers by >3× in mid-band noise and maintaining bias stability across ±10 V input range.
Can OPA121KU/2K5 drive capacitive loads without oscillation?
Yes, the OPA121KU/2K5 is internally compensated for unity-gain stability and can safely drive up to 1000 pF capacitive loads in voltage-follower configuration without external compensation. This capability is verified in the datasheet's "Load Capacitance Stability" specification and confirmed by transient response testing showing clean settling with no ringing - essential for driving ADC input filters or long cables in data acquisition systems.
What is the thermal resistance (θJA) of OPA121KU/2K5 in its SOIC package?
The OPA121KU/2K5 in SOIC-8 (Package Drawing D) has a junction-to-ambient thermal resistance (θJA) of 150°C/W, as documented in TI's packaging addendum. This value assumes standard JEDEC 2-layer board conditions (1 inch2 copper pad); actual thermal performance improves with enhanced PCB copper area or thermal vias, enabling reliable operation at full ±15 V supply and 4.5 mA quiescent current without exceeding the 175°C max junction temperature.
OPA121KU/2K5 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- Difet®
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Amplifier Type:
- General Purpose
- Number of Circuits:
- 1
- Output Type:
- -
- Slew Rate:
- 2V/µs
- Gain Bandwidth Product:
- 2 MHz
- -3db Bandwidth:
- -
- Current - Input Bias:
- 1 pA
- Voltage - Input Offset:
- 500 µV
- Current - Supply:
- 2.5mA
- Current - Output / Channel:
- 10 mA
- Voltage - Supply Span (Min):
- 10 V
- Voltage - Supply Span (Max):
- 36 V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
OPA121KU/2K5 FAQ
1.How can I place an order for OPA121KU/2K5 through Aetrix?
Please submit a Request for Quotation (RFQ) for OPA121KU/2K5 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for OPA121KU/2K5 reliable?
The price and inventory of OPA121KU/2K5 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for OPA121KU/2K5 is usually 5 days.
3.What payment methods are accepted for OPA121KU/2K5?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for OPA121KU/2K5 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for OPA121KU/2K5?
OPA121KU/2K5 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your OPA121KU/2K5 order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for OPA121KU/2K5?
For technical support, including OPA121KU/2K5 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your OPA121KU/2K5 requirements.
6.How does Aetrix verify that OPA121KU/2K5 is sourced from the original manufacturer or authorized distributors?
All OPA121KU/2K5 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that OPA121KU/2K5 meets industry standards.
7.What is the process for return or replacement of OPA121KU/2K5?
All OPA121KU/2K5 units undergo pre-shipment inspection (PSI). If there is an issue with OPA121KU/2K5, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The OPA121KU/2K5 part is unused and in its original packaging.
Return procedure for OPA121KU/2K5:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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