liminfoOp-Amp Reference
Free reference guide: Op-Amp Reference
About Op-Amp Reference
The Op-Amp Reference is a searchable guide to operational amplifier circuit configurations, key parameters, popular ICs, active filter designs, and comparator applications. It covers fundamental circuits including inverting amplifier (Gain = -Rf/Rin), non-inverting amplifier (Gain = 1 + Rf/Rin), voltage follower, differential amplifier, instrumentation amplifier (INA128, AD620), summing amplifier, integrator, and differentiator with ASCII circuit diagrams and design equations.
Key parameters documented include CMRR (Common-Mode Rejection Ratio), slew rate, GBW (Gain-Bandwidth Product), input offset voltage, input bias current, and noise density with typical values across popular op-amp families. The IC reference covers LM741, LM358, TL072/TL074, OPA2134, NE5532, and LM324 with complete specifications, pinouts, and application notes.
Active filter designs include 1st-order low-pass, 2nd-order Sallen-Key LPF (Butterworth), high-pass, and band-pass (Multiple Feedback) with cutoff frequency formulas and component calculations. Comparator and application circuits cover basic comparators, Schmitt triggers with hysteresis, constant current sources, and window comparators. Ideal for electronics engineers, audio designers, and EE students.
Key Features
- Eight fundamental op-amp circuit configurations with ASCII diagrams: inverting, non-inverting, follower, differential, instrumentation, summing, integrator, differentiator
- Key parameter reference: CMRR, slew rate, GBW, input offset voltage, input bias current, and noise density with typical values across IC families
- Detailed IC specifications for LM741, LM358, TL072/TL074, OPA2134, NE5532, and LM324 including pinouts and application notes
- Active filter design guide: 1st-order LPF, 2nd-order Sallen-Key Butterworth LPF, HPF, and Multiple Feedback BPF with component calculations
- Comparator circuits: basic comparator, Schmitt trigger with hysteresis formulas, constant current source, and window comparator
- Design equations for every circuit: gain, cutoff frequency, Q factor, bandwidth, and maximum output frequency
- Audio op-amp selection guide comparing THD+N, noise density, and slew rate across NE5532, OPA2134, and TL072
- Practical design tips including DC offset compensation, noise reduction, stability considerations, and impedance matching
Frequently Asked Questions
What is the difference between an inverting and non-inverting amplifier?
An inverting amplifier has gain = -Rf/Rin (output phase-shifted 180 degrees) with input impedance equal to Rin. A non-inverting amplifier has gain = 1 + Rf/Rin (no phase inversion) with very high input impedance. The non-inverting configuration is preferred when high input impedance is needed, such as buffering sensor signals, while the inverting configuration is used when precise gain control through the Rf/Rin ratio is important.
How do I choose between LM741, TL072, and OPA2134?
LM741 (GBW: 1 MHz, SR: 0.5 V/us) is a legacy educational device. TL072 (GBW: 3 MHz, SR: 13 V/us, noise: 18 nV/sqrt(Hz)) is a JFET-input op-amp widely used in audio due to high input impedance and fast slew rate. OPA2134 (GBW: 8 MHz, SR: 20 V/us, noise: 8 nV/sqrt(Hz), THD: 0.00008%) is a premium audio op-amp for hi-fi, DAC outputs, and headphone amplifiers. Choose based on bandwidth, noise, and application requirements.
What is CMRR and why does it matter?
CMRR (Common-Mode Rejection Ratio) measures how well a differential amplifier rejects signals common to both inputs, expressed as 20*log10(Ad/Acm) in dB. Higher CMRR means better noise rejection. Typical values range from 90 dB (LM741) to 120 dB (INA128 instrumentation amplifier). In sensor applications with long cable runs, high CMRR is critical for rejecting electromagnetic interference.
How do I design a 2nd-order Sallen-Key Butterworth low-pass filter?
For a Butterworth response (Q = 0.707, maximally flat passband), use the Sallen-Key topology with R1=R2=R and choose C1/C2 ratio for Q=0.707. With R=10k ohm, C1=22nF, C2=10nF gives Q approximately 0.707 and fc approximately 1.07 kHz. The cutoff frequency formula is fc = 1/(2*pi*sqrt(R1*R2*C1*C2)). The rolloff is -40 dB/decade (2nd order), double that of a 1st-order filter.
What is slew rate and how does it affect audio circuits?
Slew rate (SR) is the maximum rate of output voltage change in V/us. It determines the maximum undistorted sine wave frequency: f_max = SR/(2*pi*Vp). For example, TL072 with SR=13 V/us and Vp=10V gives f_max approximately 207 kHz. In audio circuits, insufficient slew rate causes slew-rate limiting distortion on fast transients. For audio, SR > 5 V/us is generally recommended; OPA2134 at 20 V/us provides comfortable headroom.
When should I use an instrumentation amplifier instead of a differential amplifier?
Use an instrumentation amplifier (INA128, AD620) when you need very high CMRR (100-130 dB), high input impedance on both inputs, and single-resistor gain adjustment. A basic differential amplifier requires precise resistor matching (even 0.1% mismatch degrades CMRR significantly). Instrumentation amplifiers are essential for bridge sensors (load cells, strain gauges), biomedical signals (ECG, EEG), and precision measurement applications.
How does a voltage-controlled constant current source work?
The op-amp constant current source uses feedback to maintain Iload = Vin/Rs regardless of load resistance. The op-amp forces its inverting input to equal Vin (virtual ground principle), so the current through Rs equals Vin/Rs. With Rs=1 ohm and Vin=1V, Iload=1A; with Rs=100 ohm and Vin=5V, Iload=50mA. Applications include LED driving, sensor biasing, and electrochemical cells.
Is this op-amp reference free?
Yes, this reference is completely free with no usage limits, no account required, and no software installation needed. It covers 25+ op-amp circuits, 6 popular ICs, 4 filter topologies, and 3 comparator/application circuits. All data is processed locally in your browser. It is part of liminfo.com's free online electronics engineering tool collection.