OP27 — Low-Noise Precision High-Speed Operational Amplifier

Overview

The OP27 is an industry-standard precision, low-noise operational amplifier manufactured by Analog Devices (originally designed by Precision Monolithics Inc. / PMI). Available in an 8-pin DIP-8 through-hole and SOIC-8 surface-mount package, it combines ultra-low input noise voltage ( $3.0\text{ nV}/\sqrt{\text{Hz}}$ at $1\text{ kHz}$ ), exceptional DC precision ( $10\ \mu\text{V}$ input offset voltage, $0.2\ \mu\text{V}/^\circ\text{C}$ drift), and an $8.0\text{ MHz}$ gain bandwidth product.

Unlike high-speed uncompensated amplifiers that require minimum gains of 5 (such as the OP37), the OP27 is internally frequency-compensated for unity-gain stability ( $A_V = 1$ ). It is a benchmark component in high-end audio preamplifiers, precision strain gauge / bridge amplifiers, thermocouple sensors, low-frequency medical instrumentation (EEG/ECG front ends), and high-resolution 16-bit to 24-bit ADC driver buffers.

Quick reference


Op-Amp Channels	1 (Single Precision Op-Amp)
Package	8-pin DIP / SOIC-8
Supply Voltage Range	$\pm 4.0\text{ V}$ to $\pm 18.0\text{ V}$ (Dual) / $+8.0\text{ V}$ to $+36.0\text{ V}$ (Single)
Input Voltage Noise ( $e_n$ )	$3.0\text{ nV}/\sqrt{\text{Hz}}$ typ ( $3.8\text{ nV}/\sqrt{\text{Hz}}$ max) at $1\text{ kHz}$
Low-Frequency Noise ( $0.1\text{Hz} \dots 10\text{Hz}$ )	$80\text{ nV}_{p-p}$ typical
Input Offset Voltage ( $V_{OS}$ )	$10\ \mu\text{V}$ typ ( $25\ \mu\text{V}$ max for E grade)
Gain Bandwidth Product (GBW)	$8.0\text{ MHz}$
Slew Rate ( $SR$ )	$2.8\text{ V}/\mu\text{s}$
Stability	Unity Gain Stable ( $A_V \ge +1$ )

Pinout (DIP-8 / SOIC-8 Package)

text

             ┌───┴───┐
     VO-TRIM 1│ 1   8 │ VO-TRIM
         -IN 2│       │ 7 V+
         +IN 3│  OP27 │ 6 OUT
          V- 4│       │ 5 NC
             └───────┘

Pin	Name	Type	Description
1, 8	`VO-TRIM`	Analog Input	Offset voltage nulling pins (Connect across $10\text{ k}\Omega$ trim pot wiper to $V+$ if trimming)
2	`-IN`	Analog Input	Inverting signal input
3	`+IN`	Analog Input	Non-inverting signal input
4	`V-`	Power	Negative power supply rail (e.g. $-15\text{ V}$ or $0\text{ V}$ )
5	`NC`	No Connect	No internal connection
6	`OUT`	Analog Output	Op-amp output
7	`V+`	Power	Positive power supply rail (e.g. $+15\text{ V}$ )

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Input Offset Voltage	$V_{OS}$	—	10	25	µV	$T_A = 25^\circ\text{C}, V_S = \pm 15\text{V}$ (E Grade)
Offset Voltage Temp Drift	$TCV_{OS}$	—	0.2	0.6	µV/°C	$-40^\circ\text{C} \le T_A \le +85^\circ\text{C}$
Input Bias Current	$I_B$	—	$\pm 10$	$\pm 40$	nA	$V_{CM} = 0\text{V}$
Input Offset Current	$I_{OS}$	—	7	35	nA	$V_{CM} = 0\text{V}$
Input Noise Voltage Density	$e_n$	—	3.0	3.8	nV/√Hz	$f = 1\text{ kHz}$
Gain Bandwidth Product	$GBW$	—	8.0	—	MHz	$f = 100\text{ kHz}, A_{VO} \ge 10^6$
Slew Rate	$SR$	1.7	2.8	—	V/µs	$R_L \ge 2\text{ k}\Omega, C_L = 15\text{ pF}$
Common-Mode Rejection	$CMRR$	114	126	—	dB	$V_{CM} = \pm 11\text{V}$
Power Supply Rejection	$PSRR$	110	120	—	dB	$V_S = \pm 4.5\text{V} \dots \pm 18\text{V}$
Quiescent Supply Current	$I_S$	—	3.0	4.0	mA	$V_O = 0\text{V}$

Typical circuits

Precision Ultra-Low-Noise AC Preamplifier

text

                 +15V
                  │
                [Pin 7: V+]
  Signal In ───[ C1: 10µF ]───► [Pin 3: +IN]
                                   OP27
                                [Pin 6: OUT] ────┬────[ C2: 10µF ]───► Amplified Out
                                [Pin 4: V-]      │
                                  │            [ Rf: 9.9kΩ 0.1% ]
                                 -15V            │
                ┌────────────────────────────────┴───► [Pin 2: -IN]
                │
              [ Rg: 100Ω 0.1% ]
                │
              [ Cg: 47µF Bipolar ]
                │
               GND

Voltage Gain: $A_V = 1 + \frac{R_f}{R_g} = 1 + \frac{9.9\text{ k}\Omega}{100\ \Omega} = 100\times\ (+40\text{ dB})$ .

Common mistakes

Using high resistor values with bipolar inputs: Because the OP27 is a bipolar input op-amp, its input noise current is $0.4\text{ pA}/\sqrt{\text{Hz}}$ . Using feedback resistors $> 10\text{ k}\Omega$ will cause the resistor thermal Johnson noise and input current noise to dominate over the op-amp's ultra-quiet $3\text{ nV}/\sqrt{\text{Hz}}$ voltage noise. Keep source/feedback resistances below $2\text{ k}\Omega$ .
Confusing OP27 with OP37: OP27 is unity-gain compensated ( $A_V \ge 1$ stable); OP37 is decompensated for higher speed ( $63\text{ MHz}$ GBW, $17\text{ V}/\mu\text{s}$ slew rate) but is unstable at gains below 5.
Missing supply decoupling: Low-noise precision op-amps require clean local power. Place $0.1\ \mu\text{F}$ ceramic and $10\ \mu\text{F}$ tantalum bypass capacitors directly between Pin 7 ( $V+$ ) / Pin 4 ( $V-$ ) and Ground.

Notes

Pin-Compatible Modern Equivalents: OPA227 (Texas Instruments / Burr-Brown), LT1007 (Linear Technology), AD797 (Ultra-low 0.9nV noise).

Interface	Single Op-Amp Terminals (+IN, -IN, OUT, V+, V-, OFFSET NULL)
Package	8-pin DIP / SOIC-8