INA121P - FET-Input Low Power Instrumentation Amplifier DIP-8 | Texas Instruments
N.º da peça: INA121P ✓ Ativo| Qtd. | Preço unitário | Total |
|---|---|---|
| 1 | $9.85 | $9,85 |
| 10 | $8.85 | $88,50 |
| 100 | $7.5 | $750,00 |
| 500 | $6.4 | $3.200,00 |
| 1.000 | $5.65 | $5.650,00 |
INA121P Visão geral
What is an instrumentation amplifier? An instrumentation amplifier is a precision differential amplifier with very high input impedance, high common-mode rejection ratio (CMRR), and user-adjustable gain set by a single external resistor. INAs occupy the hierarchy: instrumentation amplifier -> differential amplifier -> operational amplifier -> analog IC. Compared with a discrete op-amp difference amp, a monolithic INA matches the input stage transistors on the same die, providing inherently high CMRR without precision resistor networks, making it the standard building block for low-level sensor signal conditioning.
The INA121P's versatile three-op-amp topology and small footprint suit general-purpose precision applications. Internal input protection survives ±40V differential or common-mode faults, and gain is set from 1 V/V to 10,000 V/V using one external resistor between pins 1 and 8. Noise is specified at 20 nV/√Hz (f = 1 kHz) with 0.001% nonlinearity, and the bandwidth reaches 600 kHz (G = 100). The 8-pin PDIP through-hole package supports easy breadboarding and hand-repairable designs where surface-mount parts would be impractical.
Architecture-wise, the INA121P uses CMOS FET input stages for sub-picoampere bias current and laser-trimmed thin-film resistors for gain accuracy. The three-op-amp topology delivers fully differential inputs and a single-ended output referenced to pin 5 (REF). Operation from a single supply down to ±2.25V accommodates battery-powered systems, while ±18V supplies support industrial 4-20 mA and ±15V signal chains.
Typical applications include ECG/biomedical front-ends, weigh scales and load-cell bridges, thermocouple and RTD signal conditioning, industrial process-control transducer amplifiers, and audio-frontend microphone preamps requiring high CMRR. The ±4 pA input bias permits direct interface to photodiodes and high-impedance pH/ion-selective electrodes without input-bias compensation networks.
Designers should guard-drive pin 1 and pin 8 (RG) with a buffered reference rather than leaving them floating when gain is set at minimum (1 V/V), and provide 0.1 µF supply bypass capacitors within 5 mm of pins 4 and 7. The 8-pin PDIP's higher thermal resistance (~80 °C/W) limits continuous dissipation above 400 mW, so PCB copper area should be assessed for productionized layouts.
This page synthesizes distributor pricing, drop-in DIP-8 alternatives, and practical design notes not found in the manufacturer datasheet alone.
Alternativas drop-in para INA121P — mesmo encapsulamento, compatível pino a pino. Peças de encapsulamento diferente que exigem retrabalho na PCB são excluídas.
Variantes desta série
Modelos da mesma série compatíveis como drop-in com INA121P (mesmo formato e footprint) — diferindo em Package, Gain Range, Input Bias Current, Input Protection, Number of Channels.
Ferramenta de comparação rápida — selecione peças alternativas para comparação lado a lado:
INA121PAG4
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
INA121PG4
✅ Drop-In📋 Alternativa de referência (fora do catálogo)
INA128PA
✅ Drop-In✓ Em estoque
Consulte o preço
Ver ficha técnica →INA128PA
✅ Drop-In✓ Em estoque
Consulte o preço
Ver ficha técnica →AD620ANZ
✅ Drop-In✓ Em estoque
$6.2 / unidade
Ver ficha técnica →AD620ANZ
✅ Drop-In✓ Em estoque
$6.2 / unidade
Ver ficha técnica →INA121P Classificações máximas e características elétricas
| Amplifier Type | Instrumentation Amplifier (3-op-amp topology) |
| Number of Channels | 1 |
| Input Type | FET / CMOS |
| Input Bias Current | ±4 pA typical |
| Input Offset Voltage | ±200 µV typical |
| Input Offset Drift | ±2 µV/°C typical |
| Input Voltage Noise Density | 20 nV/√Hz at 1 kHz |
| Corrente de repouso | ±450 µA typical |
| Common-Mode Rejection Ratio (CMRR) | 106 dB minimum |
| Bandwidth (-3 dB) | 600 kHz at G = 100 |
| Nonlinearity Error | 0.001% (G = 10) |
| Gain Range | 1 V/V to 10,000 V/V (single external resistor) |
| Supply Voltage Range | ±2.25 V to ±18 V |
| Input Protection | ±40 V differential and common-mode |
| Faixa de temperatura de operação | -40 °C to +85 °C |
| Encapsulamento | 8-Pin PDIP (P) |
| Tipo de montagem | Through-Hole |
| Status RoHS | Compliant |
| Lead-Free Finish | Yes (Matte Tin) |
Configuração de pinos do INA121P
| Pino 1 | RG — Gain-setting resistor pin (one terminal) |
| Pino 2 | IN+ — Non-inverting input |
| Pino 3 | IN- — Inverting input |
| Pino 4 | V- — Negative power supply |
| Pino 5 | REF — Output reference pin (sets output DC level) |
| Pino 6 | OUT — Amplified signal output |
| Pino 7 | V+ — Positive power supply |
| Pino 8 | RG — Gain-setting resistor pin (other terminal) |
Aplicações típicas
INA121P é adequado para 6 aplicaçãos: ECG / Biopotential Front-End, Weigh-Scale / Load-Cell Bridge Amplifier, Thermocouple / RTD Signal Conditioning, Industrial 4-20 mA Loop Read-Back, Photodiode Preamplifier, Audio Microphone Front-End.
ECG / Biopotential Front-End
The INA121P's ±4 pA typical FET input bias and 106 dB CMRR per the INA121 datasheet make it well-suited for ECG/EEG front-end amplification where patient-leakage current must stay below 10 µA IEC 60601-1 limits. The on-chip ±40 V input protection survives defibrillator-pulse transients when paired with external gas-discharge and current-limiting resistors, and the 600 kHz bandwidth (G = 100) preserves QRS morphology. Pin 5 (REF) accepts the right-leg-drive driven Common-Mode Voltage for maximum CMRR. Placed between the lead-set and the 24-bit ADC for a digital ECG recorder, the INA121P operates from ±5 V supplies, dissipating only 5.4 mW at typical G = 10 and full bandwidth. The 0.1 µF supply-bypass capacitors within 5 mm of pins 4 and 7 prevent HF pickup on long patient cables.
Recomendado
Weigh-Scale / Load-Cell Bridge Amplifier
For weigh-scale and load-cell signal conditioning, the INA121P's user-programmable gain from 1 V/V to 10,000 V/V accommodates a 1 mV/V full-scale bridge output at full scale weights from 5 kg to 500 kg. The laser-trimmed offset (±200 µV typical) and 0.001% nonlinearity translate directly into ±0.005% full-scale accuracy in commercial kitchen scales and industrial process weighing. Placed between the 350 Ω strain-gauge bridge and the 24-bit ADC, the INA121P's dual-power supply (±12 V) tolerates large common-mode noise from motor drives. Per the datasheet, RG ≈ 50 kΩ / (G − 1) on pins 1 and 8 sets gains like G = 100 (RG = 505 Ω) or G = 500 (RG = 100 Ω, low-side bridge). The 20 nV/√Hz noise floor sets a 0.5 µg resolution at the load cell output.
Recomendado
Thermocouple / RTD Signal Conditioning
The INA121P amplifies J, K, S, or T thermocouple EMF (10 µV to 60 µV per °C) from a far-field cold-junction. The low offset drift (±2 µV/°C) tracks ambient temperature changes without bringing error into the sub-50 µV measurement range, while the FET inputs do not load the thermocouple's high-impedance output. Used with K-type thermocouples on industrial boiler piping, the INA121P runs at G = 100 to provide a 1 V/°C conditioned output (after cold-junction compensation by a separate PT100 amplifier). Per the INA121 datasheet, the wide ±2.25 V to ±18 V supply range accommodates 4-20 mA single-supply retransmissions using a single +24 V industrial rail.
Recomendado
Industrial 4-20 mA Loop Read-Back
The INA121P monitors the 4-20 mA process loop current by sensing the voltage across a precision current-sense resistor; the high CMRR rejects motor-induced common-mode noise picked up on long shielded twisted pairs. ±40 V input protection guards against mis-wiring surges on plant commissioning, per the Texas Instruments datasheet. With R_sense = 250 Ω, G = 10, and ±15 V rails, the INA121P produces 1 V at 4 mA and 5 V at 20 mA for an ADC front-end in a PLC backplane. The 106 dB CMRR typically eliminates the need for an additional isolating amplifier in single-pair sensing, while the FET input reduces ground-loop leakage current below 10 nA.
Recomendado
Photodiode Preamplifier
The INA121P's FET-input stage is ideal for amplifying the photocurrent of a photodiode or small-area PIN detector. The ±4 pA input bias introduces negligible error compared with the photodiode's own dark current, and the FET noise floor of 20 nV/√Hz at 1 kHz imposes an NEP in the low fW/√Hz range for typical UV/visible band detectors. Photodiodes reverse-biased through the input stage see G set in the 10 V/V to 100 V/V range using a single resistor, with the output DC component proportional to the optical power. Per the INA121 datasheet, the 600 kHz bandwidth supports pulsed-laser detection at sub-microsecond response times when RG is reduced to a few hundred ohms.
Recomendado
Audio Microphone Front-End
Studio-grade condenser microphones and instrument preamps benefit from the INA121P's low input-bias, low noise, and 106 dB CMRR per TI datasheet — pushing the noise floor below the microphone's own thermal noise in the 20 Hz to 20 kHz band. Three-op-amp topology preserves a fully balanced input through 100 mV to 10 V full-scale microphone signals. The INA121P with G = 100 (RG = 505 Ω) and dual ±15 V supply provides ample swing for a follow-on 24-bit audio ADC. Unlike portable mobile-amp ICs, the discrete INA121P does not impose 3 V supply limits and tolerates 48 V phantom-power feed faults on pins 2 and 3 within the integrated ±40 V protection window.
Recomendado
Resumo dos produtos recomendados
Dados de referência de engenharia para INA121P — comparação, orientação de projeto e informações de conformidade.
Guia de seleção
Comparação com alternativas
| Parâmetro | Este produto | INA121PAG4 | INA121PG4 | INA128P | AD620AN | AD620ANZ |
|---|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Analog Devices | Analog Devices |
| Package | 8-PDIP (P) | 8-PDIP (P) — same | 8-PDIP (P) — same | 8-PDIP (P) — same | 8-PDIP (N) — same footprint | 8-PDIP (N) — same footprint |
| Input Bias Current | ±4 pA typical | ±5 pA typical | 0.5 nA typical | |||
| Input Offset Voltage | ±200 µV typical | ±200 µV typical | ±30 µV max (typical ~10 µV) | |||
| CMRR | 106 dB minimum | ~93 dB | 100 dB minimum (G = 10) | |||
| Bandwidth (-3 dB, G=100) | 600 kHz | 200 kHz | 120 kHz | |||
| Supply Voltage Range | ±2.25 V to ±18 V | ±2.25 V to ±18 V | ±2.3 V to ±18 V | |||
| Input Protection | ±40 V (internal) | Not internal — external clamp needed | ±15 V (external recommended) | |||
| Quiescent Current | ±450 µA typical | ±350 µA typical | 0.9 mA typical (single +V) |
Principais diferenciais
- Internal ±40 V input protection (vs INA128P)
- Higher CMRR (106 dB vs ~93 dB) (vs INA128P)
- Higher bandwidth (600 kHz vs 120 kHz) (vs AD620AN)
Notas de projeto
Place 0.1 µF supply-bypass capacitors within 5 mm of V+ (pin 7) and V- (pin 4) on the Texas Instruments INA121, and add a 10 µF tantalum in parallel for ±15 V industrial rails where switching regulators raise common-mode noise. Per the datasheet, inadequate supply decoupling on long lead lengths can cost 10-20 dB of CMRR at 60 Hz. The pin 5 REF should be tied directly to mid-supply (0 V on dual supplies) with a low-impedance buffer, not via the signal-source return path.
The 8-pin PDIP package has θJA ≈ 80 °C/W (JEDEC still-air) per the INA121 datasheet. Estimated: at full supply ±18 V and static short-circuit on the output (worst-case), the device dissipates approximately 1.2 W, which would give a ΔT of 96 °C above 25 °C — well under the 150 °C junction limit. However, the more realistic continuous-load scenario of G = 100 with 1 mA output current only dissipates a few mW, leaving thermal management non-critical. Provide PCB copper ≥100 mm² if a target surface-mount version is later selected.
For sensor conditioning, route the INA121P inputs (pins 2 and 3) as a guarded parallel pair with trace widths ≤0.2 mm and a ground shield pin 5 (REF) act as both DC reference and shield drain. Keep the gain-setting resistor RG between pins 1 and 8 within 5 mm to minimize stray-capacitance leakage at high gain (G = 100 to G = 10000). Per TI's INA121 datasheet, stray capacitance at RG above 3 pF limits bandwidth to below 100 kHz — so the RG location is more critical than the input trace.
Do not exceed the absolute maximum common-mode input voltage of |V+| +40 V on pins 2/3 without the input protection foldback, per the INA121 datasheet. Avoid using the INA121P below ±2 V total supply — the laser-trim circuitry is only characterized above ±2.25 V. Most production failures come from omitting the REF pin 5 connection, which forces the output stage into saturation; tie REF directly to analog ground even if not used for active cancellation. Final layout tip: do not connect a bypass capacitor from REF to ground — leave REF floating or buffered, never RC-grounded.
Informações de conformidade
Per Texas Instruments INA121 product page: RoHS-compliant Pb-free finish, REACH compliant; AED-Q100 not applicable (industrial/medical use, not automotive).
