INA121UA - FET-Input Low Power INA | SOIC-8 | Texas Instruments
Référence : INA121UA ✓ Actif| Qté | Prix unitaire | Total |
|---|---|---|
| 1 | $9.2 | $9,20 |
| 10 | $8.15 | $81,50 |
| 100 | $6.4 | $640,00 |
| 500 | $5.55 | $2 775,00 |
| 1 000 | $4.95 | $4 950,00 |
INA121UA Présentation
An instrumentation amplifier is a precision differential amplifier that combines high input impedance, high common-mode rejection ratio (CMRR), and user-settable gain, making it ideal for extracting small differential signals riding on large common-mode voltages. Within the signal-chain taxonomy, the INA sits between the transducer/bridge and the analog-to-digital converter (ADC), and is itself a category of analog amplifier IC that subclasses under operational amplifier ICs (op-amp IC). The INA121 specifically targets FET-input applications where source impedance is high or where bias current must be minimized to avoid error and self-heating.
Key features include +/-200 uV maximum input offset voltage, +/-2 uV/degrees C input offset drift, 100 nV/sqrt(Hz) low input noise voltage density, 106 dB minimum CMRR, and a low 450 uA typical quiescent current. The device also integrates input protection that can withstand up to +/-40 V differential or common-mode overvoltages without damage, and an output stage capable of driving 1 kohm loads to within 1.5 V of either supply rail.
Internally, the INA121 uses a precision thin-film resistor network with laser-trimmed matching to deliver 0.001% maximum nonlinearity at G = 100. The FET front-end keeps bias current roughly two orders of magnitude lower than bipolar-input instrumentation amplifiers such as the AD620, which simplifies thermal management of high-impedance sensor sources.
Typical applications include weigh scales and load-cell bridges, ECG/biopotential front-ends, thermocouple and RTD signal conditioning, industrial process controls with 4-20 mA loops, and battery-powered portable instrumentation. The wide supply range allows direct operation from industrial +/-15 V rails as well as low-voltage single-supply configurations down to 4.5 V total.
When designing with the INA121UA, place the gain-setting resistor as close as possible to the RG pins to minimize parasitic capacitance, and provide 0.1 uF ceramic bypass capacitors within 5 mm of each supply pin. For single-supply operation, reference the output to mid-rail (VREF = VS/2) and bias the input common-mode voltage above ground by at least 1 V to preserve linear operation. Compared with monolithic zero-drift alternatives, the INA121 trades chopper-stabilized offset for higher bandwidth and lower quiescent current, making it preferred when AC signal fidelity matters more than nano-volt DC accuracy.
This page synthesizes distributor pricing, same-brand and cross-brand drop-in alternatives, and practical design notes not found on the manufacturer datasheet front page.
Alternatives de remplacement direct pour INA121UA — même boîtier, compatible broche à broche. Les références à boîtier différent nécessitant une retouche du PCB sont exclues.
Outil de comparaison rapide — sélectionnez des références alternatives pour une comparaison côte à côte :
INA121U
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
INA121UA/2K5
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
INA121U/2K5
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
INA129UA
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
INA128UA
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
INA121UA Valeurs maximales et caractéristiques électriques
| Product Type | Instrumentation Amplifier (FET-input) |
| Number of Channels | 1 |
| Gain Range | 1 V/V to 10,000 V/V (external resistor) |
| Bandwidth (G = 100) | 600 kHz |
| Slew Rate | 0.07 V/us |
| Input Bias Current | ±4 pA (max) |
| Input Offset Voltage | ±200 uV (max) |
| Input Offset Drift | ±2 uV/°C (max) |
| CMRR | 106 dB (min) |
| Nonlinearity (G = 100) | 0.001% (max) |
| Courant de repos | ±450 uA |
| Supply Voltage Range | ±2.25 V to ±18 V (dual) / 4.5 V to 36 V (single) |
| Input Protection | ±40 V differential and common-mode |
| Boîtier | 8-pin SOIC (D) |
| Type de montage | Surface Mount |
| Statut RoHS | Compliant (per DigiKey product page) |
Configuration des broches de INA121UA
| Broche 1 | RG — Gain-setting resistor pin (tie to pin 8) |
| Broche 2 | IN- — Inverting input |
| Broche 3 | IN+ — Non-inverting input |
| Broche 4 | V- — Negative supply |
| Broche 5 | REF — Reference voltage (output baseline) |
| Broche 6 | V+ — Positive supply |
| Broche 7 | OUT — Amplifier output |
| Broche 8 | RG — Gain-setting resistor pin (tie to pin 1) |
Applications typiques
INA121UA convient pour 6 applications: Weigh Scale / Load Cell Bridge Front-End, ECG / Biopotential Front-End, Thermocouple and RTD Signal Conditioning, Photodiode Transimpedance Front-End, Industrial Process Control / 4-20 mA Loop Receiver, Portable / Battery-Powered Instrumentation.
Weigh Scale / Load Cell Bridge Front-End
The INA121UA fits weigh-scale front-ends because its ±4 pA input bias current does not load the 350-1000 ohm strain-gauge bridge, preserving the open-circuit voltage that defines scale accuracy. Combined with 106 dB CMRR and 0.001% nonlinearity at G = 100, the INA121UA extracts microvolt-level bridge imbalance at full-scale loads while rejecting the 50/60 Hz line noise on the bridge common-mode voltage. Place RG to set G = 100-500 V/V for typical 10 mV/V full-scale bridge sensitivity, and drive the INA121 output directly into a 16-24 bit sigma-delta ADC reference input.
Recommandé
ECG / Biopotential Front-End
The INA121UA suits ECG and biopotential front-ends because its FET input eliminates the bias-current-cancellation resistors required by bipolar INAs such as AD620, simplifying the patient-isolation interface. Its 106 dB CMRR rejects 50/60 Hz mains pickup on the body-electrode common-mode voltage, while the 100 nV/sqrt(Hz) input noise keeps the trace baseline clean below 0.5 Hz heart-rate frequencies. Configure gain at 1000 V/V (RG = 40 ohm) to amplify the 1 mV ECG signal to a 1 V ADC range; pair with a right-leg drive op-amp for common-mode feedback.
Recommandé
Thermocouple and RTD Signal Conditioning
The INA121UA is appropriate for thermocouple and RTD conditioning because its ±4 pA input bias prevents self-heating of high-impedance sensors and keeps cold-junction compensation error below 0.1 degree C. With ±200 uV offset and ±2 uV/°C drift, the INA121UA delivers enough DC accuracy for type K, J, and T thermocouples across the -200 to +1200 degrees C industrial range. Use G = 100 V/V (RG = 404 ohm) and a precision reference such as the REF5025 for thermocouple reference-junction compensation; the result is a complete 4-20 mA loop-ready temperature transmitter.
Recommandé
Photodiode Transimpedance Front-End
The INA121UA converts photodiode current to voltage in transimpedance configurations because the FET input draws only ±4 pA, leaving the entire photocurrent signal available to develop across the feedback resistor. At G = 1 (RG open), the input behaves as a unity-gain buffer with 600 kHz bandwidth, sufficient for pulse-oximetry and ambient light sensors. For higher gain transimpedance conversion, operate the INA121 in current-to-voltage mode with an external T-network; the result is a wide-dynamic-range optical front-end with picoamp-level sensitivity.
Recommandé
Industrial Process Control / 4-20 mA Loop Receiver
The INA121UA serves as a 4-20 mA current-loop receiver because its ±18 V supply rating tolerates the 24 V industrial rail plus headroom, and its 106 dB CMRR rejects common-mode noise injected by long cable runs. Set gain at 100 V/V (RG = 404 ohm) with a 250 ohm sense resistor to translate 4-20 mA into a 1-5 V output that feeds an ADC or comparator. The ±40 V input protection guards against field-wiring transients and miswiring, a critical robustness feature for factory-floor installations.
Recommandé
Portable / Battery-Powered Instrumentation
The INA121UA suits battery-powered instruments because its ±450 uA quiescent current is roughly half that of bipolar INAs, extending run-time on 9 V or Li-ion cells. The wide ±2.25 V to ±18 V supply lets the device operate from a single 5 V USB rail as well as dual ±15 V industrial supplies without re-design. Pair the INA121 with a low-power ADC like the ADS1115 for a sub-1 mW precision data-acquisition front-end that fits in a handheld multimeter or wireless sensor node.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour INA121UA — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | INA121U | INA121UA/2K5 | INA121U/2K5 | INA129UA | INA128UA |
|---|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments |
| Package | SOIC-8 (D) | SOIC-8 (D) - same | SOIC-8 (D) - same | SOIC-8 (D) - same | SOIC-8 (D) - same | SOIC-8 (D) - same |
| Input Stage | FET (JFET) | FET (JFET) - same | FET (JFET) - same | FET (JFET) - same | Bipolar | Bipolar |
| Input Bias Current (max) | ±4 pA | ±4 pA | ±4 pA | ±4 pA | ~25 nA | ~5 nA |
| Bandwidth (G = 100) | 600 kHz | 600 kHz | 600 kHz | 600 kHz | 200 kHz | 200 kHz |
| Input Offset Voltage (max) | ±200 uV | ±200 uV | ±200 uV | ±200 uV | ±50 uV | ±50 uV |
| Quiescent Current (typ) | ±450 uA | ±450 uA | ±450 uA | ±450 uA | ±700 uA | ±700 uA |
| Supply Voltage Range | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.25 V to ±18 V |
| Approx. 1k Price (USD, 2026-10-08) | 4.95 | 4.95 | 4.95 | 4.95 | 3.50 | 4.20 |
Principaux différenciateurs
- Lowest input bias current in the INA1xx SOIC-8 family (vs INA129UA)
- Higher small-signal bandwidth at G = 100 (vs INA128UA)
- Wider supply voltage range (vs AD620 (Analog Devices))
- Pin-compatible with most TI SOIC-8 INA family members (vs INA126UA)
Notes de conception
Estimated gain calculation for the INA121UA: with RG open, G = 1; with RG = 40 kohm, G = 2; with RG = 404 ohm, G = 100. Placing RG more than 5 mm from pins 1 and 8 introduces parasitic resistance and capacitance that cause gain error at high gains (>100) and may induce peaking above 100 kHz. Use a tight layout and a 1% metal-film resistor for best DC accuracy. Do not float pin 5 (REF); tie it to mid-rail for dual supply, or to a buffered half-supply for single supply.
Place 0.1 uF ceramic bypass capacitors within 5 mm of pins 4 (V-) and 6 (V+) of the INA121UA, plus a 10 uF tantalum or aluminum bulk cap at the supply entry point. The gain-setting resistor RG (between pins 1 and 8) should be the closest component to the SOIC-8 package and routed with short traces to minimize loop area. Use a single ground plane and route the IN- and IN+ traces as a differential pair with matched length and impedance; avoid running them parallel to noisy digital lines.
The INA121UA input stage tolerates up to ±40 V differential or common-mode overvoltage without damage, per the TI datasheet, but sustained overvoltage increases input bias current and can degrade long-term reliability. For ESD-sensitive end-product applications (e.g., ECG patient-connected), add external TVS diodes such as SMAJ5.0CA at the inputs. Source impedance above 10 Gohm can cause thermal noise and pickup; consider adding a 1 Mohm discharge resistor at each input to define the input impedance in floating applications.
Single-supply operation of the INA121UA requires a mid-rail reference on pin 5 (REF) to bias the output into the ADC input range. Use a low-impedance buffer such as the OPA2333 to drive REF, with a 0.1 uF ceramic local bypass. The INA121UA draws ±450 uA quiescent current typical; for battery-powered applications, gate the supplies with a low-leakage load switch to reduce idle current below 1 uA. The wide ±2.25 V to ±18 V supply range also allows direct connection to a +/-15 V industrial rail without LDO regulation.
Informations de conformité
RoHS and lead-free compliance per DigiKey product page (272057). Industrial temperature grade; not AEC-Q100 qualified for automotive use.
