Texas Instruments OPA121KUG4

Overview

OPA121KUG4 from Texas Instruments (originally Burr-Brown) is a precision dielectrically isolated FET (Difet®) operational amplifier in an 8-pin SOIC package. It delivers ultra-low input bias current (5 pA max), low voltage noise (6 nV/√Hz at 10 kHz), low offset (2 mV max), low drift (3 µV/°C typ), and high open-loop gain (110 dB min), making it ideal for high-impedance sensor interfacing in medical instrumentation and precision data acquisition.

For engineers reviewing the OPA121KUG4 datasheet, OPA121KUG4 pinout, OPA121KUG4 application, or OPA121KUG4 equivalent, key selection criteria include guaranteed low bias current over temperature, laser-trimmed offset stability, cascode input architecture for flicker-noise reduction, and compatibility with standard 741-based layouts requiring minimal redesign.

Technical Context

The OPA121KUG4 employs a patented cascode Difet® input stage that isolates gate leakage paths and minimizes sensitivity to common-mode voltage shifts - enabling stable 5 pA bias current across ±10 V input range. Its laser-trimmed thin-film resistors achieve ±2 mV offset and ±3 µV/°C drift, while the internal guard structure referenced to Pin 8 (substrate) suppresses PCB leakage currents.

This amplifier operates from ±5 V to ±18 V supplies, delivers ±11 V output swing into 2 kΩ, and maintains 110 dB open-loop gain and 86 dB CMRR at DC - all within its specified 0°C to +70°C ambient operating range. The SOIC-8 package supports surface-mount assembly with JEDEC Level-3 moisture sensitivity rating.

Key Specifications

Pinout & Package

OPA121KUG4 is housed in an 8-pin SOIC (Small Outline Integrated Circuit) package per JEDEC MS-012 variation AA, with 1.27 mm lead pitch and 1.75 mm maximum height. Pin 1 is marked by a beveled corner or dot; the package is RoHS-compliant with NiPdAu lead finish and MSL Level-3 rating (260°C peak, 168 hr floor life).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision FET op-amp applications.

Compared with OPA121KUG4, OPA128LM offers superior bias current but lacks SMT compatibility and increases board area and assembly cost, while ADA4530-1ARZ provides integrated guarding at the expense of higher flicker noise and reduced slew rate - making OPA121KUG4 the optimal balance of manufacturability, noise, and precision for commercial-grade instrumentation.

Availability

OPA121KUG4 is available at Aetrix Electronics and suitable for medical instrumentation, precision data acquisition, and test equipment requiring stable component supply across extended production lifecycles.

Supply support for OPA121KUG4 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 Corporation in 2000 and maintains its precision analog portfolio, including legacy Difet® technology. TI is a global semiconductor leader focused on analog and embedded processing solutions.

The OPA121KUG4 belongs to TI's precision operational amplifier product line, designed specifically for high-impedance, low-noise signal conditioning in instrumentation, medical, and industrial measurement systems where bias current and offset stability are critical.

FAQ

What is the maximum guaranteed input bias current for OPA121KUG4 over temperature?

The OPA121KUG4 guarantees ≤10 pA maximum input bias current at +25°C and ≤250 pA over its full operating temperature range of –25°C to +85°C. This specification reflects worst-case device behavior under rated conditions and is validated per the manufacturer's production test flow - ensuring consistent performance in high-impedance sensor interfaces where leakage must remain below 100 fA/V.

Does OPA121KUG4 require external offset trimming in typical applications?

No, the OPA121KUG4 uses laser-trimmed thin-film resistors to achieve ±2 mV maximum input offset voltage at +25°C, 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 across temperature - though doing so may increase drift by ~0.3 µV/°C per 100 µV adjusted offset, as documented in the original Burr-Brown application note.

How should Pin 8 (Substrate) be connected for optimal noise performance in OPA121KUG4?

For optimal noise and leakage performance, Pin 8 of the OPA121KUG4 must be connected to a low-impedance guard plane at the same potential as the input signal reference - typically circuit ground or the non-inverting input guard trace. This connection fully surrounds the die with equipotential shielding, minimizing surface leakage currents and EMI pickup. Leaving Pin 8 floating or connecting it to a noisy node degrades input bias stability and increases measured offset drift.

Is OPA121KUG4 compatible with single-supply operation?

The OPA121KUG4 is specified for dual-supply operation (±5 V to ±18 V) and does not support true single-supply operation due to its input common-mode range extending only to ±11 V - insufficient to accommodate rail-to-rail input near ground or VCC. While it may function with asymmetric supplies (e.g., +15 V/–5 V), full-spec performance requires both positive and negative rails. For single-supply designs, consider TI's OPA377 or OPA189 families instead.

What is the recommended layout practice to prevent leakage errors with OPA121KUG4?

To prevent leakage errors, route the OPA121KUG4's input traces over a continuous guard plane connected to Pin 8, isolate them with solder-mask-defined clearance (>10 mil), and avoid conformal coating over high-impedance nodes. Use Teflon standoffs if through-hole mounting is unavoidable. Clean flux residues thoroughly using IPA and verify insulation resistance >10¹³ Ω - because even 1 pA leakage across a PCB trace equals 50% of the OPA121KUG4's max bias current spec.