INA121P - FET-Input Low Power Instrumentation Amplifier DIP-8 | Texas Instruments
MPN: INA121P ✓ Hoạt độngINA121P Tóm tắt
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.
Bộ thay thế dễ dàng lắp đặt cho INA121P — cùng gói, chân-to-chân tương thích. Các bộ phận yêu cầu hàn PCB bị loại trừ.
Các biến thể trong loạt này
Các mẫu cùng loạt có thể lắp đặt dễ dàng tương thích với INA121P (cùng hình factor và footprint) — khác nhau ở Package, Input Bias Current, Gain Range, Common-Mode Rejection, Gain Setting.
INA121PAG4
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
INA121PG4
✅ Drop-In📋 Tham chiếu thay thế (không có trong danh mục)
INA128PA
✅ Drop-InLiên hệ để biết giá
Xem tài liệu →INA128PA
✅ Drop-InLiên hệ để biết giá
Xem tài liệu →AD620ANZ
✅ Drop-InLiên hệ để biết giá
Xem tài liệu →AD620ANZ
✅ Drop-InLiên hệ để biết giá
Xem tài liệu →INA121P Tỷ lệ tối đa & tính chất điện
| 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 |
| Điện áp yên tĩnh | ±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 |
| Khoảng nhiệt độ hoạt động | -40 °C to +85 °C |
| Hộp | 8-Pin PDIP (P) |
| Kiểu lắp đặt | Through-Hole |
| Trạng thái RoHS | Compliant |
| Lead-Free Finish | Yes (Matte Tin) |
Cấu hình chân INA121P
| Chân 1 | RG — Gain-setting resistor pin (one terminal) |
| Chân 2 | IN+ — Non-inverting input |
| Chân 3 | IN- — Inverting input |
| Chân 4 | V- — Negative power supply |
| Chân 5 | REF — Output reference pin (sets output DC level) |
| Chân 6 | OUT — Amplified signal output |
| Chân 7 | V+ — Positive power supply |
| Chân 8 | RG — Gain-setting resistor pin (other terminal) |
Ứng dụng tiêu biểu
INA121P phù hợp cho 6 Áp dụngs: 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.
Được đề xuất
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.
Được đề xuất
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.
Được đề xuất
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.
Được đề xuất
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.
Được đề xuất
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.
Được đề xuất
Tóm tắt các sản phẩm được đề xuất
Dữ liệu tham khảo kỹ thuật cho INA121P — so sánh, hướng dẫn thiết kế và thông tin tuân thủ.
Hướng dẫn chọn lựa
So sánh với các sản phẩm thay thế
| Tham số | Sản phẩm này | 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) |
Bảo phân biệt quan trọng
- Internal ±40 V input protection (vsINA128P)
- Higher CMRR (106 dB vs ~93 dB) (vsINA128P)
- Higher bandwidth (600 kHz vs 120 kHz) (vsAD620AN)
Ghi chú thiết kế
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.
Thông tin tuân thủ
Per Texas Instruments INA121 product page: RoHS-compliant Pb-free finish, REACH compliant; AED-Q100 not applicable (industrial/medical use, not automotive).
