Architectures (Sallen-Key, MFB, state-variable, cascaded biquads, notch, fully-differential, Gm-C/SC, programmable) plus PGAs, FDAs, rectifiers, RMS, TIAs, lock-in, S/H, clamps, anti-alias & reconstruction, calibration hooks, applications, key specs and design tips.
Architectures & Types
Sallen-Key LP/HP
Simple topology; op-amp GBW must be sufficient; Q sensitive to tolerances—great for anti-alias/denoise fronts.
MFB LP/HP
Better Q control with friendly ratios—popular for audio/measurement bandwidth shaping.
State-Variable (BP/LP/HP/Notch)
Multi-response outputs with tunable Q—ideal for tunable BP/notch.
Cascaded Biquads (Butt/Cheb/Bessel/Elliptic)
Build target magnitude/phase for anti-alias or reconstruction.
Precision 50/60 Hz Notch
Twin-T/active notch for deep hum suppression with temp compensation.
Fully-Differential Filters
Controlled common-mode and low distortion for differential chains/ADC fronts.
Gm-C / OTA-Tunable Filters
Electronically tunable f0/Q for variable-BW comms and self-cal AFE.
Switched-Capacitor Filters
Clock-set frequency with accurate on-chip ratios—great in integrated AFEs/acoustics.
Digitally-Programmable Filter IC
I²C/SPI selectable type/frequency/gain for multi-sensor platforms.
Active All-Pass / Phase Equalizer
Group-delay shaping for audio/measurement phase correction.
Signal Conditioning
PGA / Digitally-Programmable Gain
Multi-range matching with step/continuous gain—perfect for DAQ.
FDA / SE↔Differential Converter
Set output common-mode and drive ADCs/differential links.
Precision Rectifier / Peak Hold
Low-threshold distortion with fast holding for envelope/limit detection.
RMS-to-DC Converter
Wide dynamic range; watch distortion and bandwidth—power/acoustic metering.
Log / Antilog Amplifier
Compress/expand across decades with temp compensation for optics/chemistry/acoustics.
V-I / I-V (Transconductor/TIA)
Focus on linearity/accuracy/noise for sensors and electrochemistry.
Charge Amplifier w/ Reset
Piezo/IEPE sensing with ultra-low leakage and drift.
Phase-Sensitive / Lock-In
Narrowband demod to extract signals at very low SNR (optics/chem/ultrasound).
Sample-&-Hold / Track-&-Hold
Large-step linearity and low aperture jitter for pulse/step measurements.
DC Servo / Offset Servo
Remove very-low-freq drift while preserving the passband (audio/instruments).
Remote-Sense / Line-Drop Compensation
Use differential sampling to compensate long-line drops.
Clamp & ESD Front-End
Low-C TVS + current-limit RC to protect without killing bandwidth.
Anti-Alias / Reconstruction Interface
Pair with ADC/DAC—match amplitude/phase and impedance.
Auto-Zero / Calibration Hooks
Relay matrices/digipots/EEPROM for production-grade consistency.
Digipot + Op-Amp Gain Block
Soft-tune gain/threshold/hysteresis for field-adjustable systems.
Programmable EQ / De-Emphasis
Shape passbands and open eyes for high-speed test/interface fronts.
Envelope / Crest-Factor Detection
Overload criteria and dynamic limiting for audio/RF fronts.
Application-Focused
Bridge / Strain Chains
PGA + LP + notch + lock-in to fight noise and temperature drift.
Bio-Potential / Low-Frequency
Ultra-low-noise BP + 50/60 Hz notch with RLD interface.
Ultrasound / ToF Front-End
Tunable BP + detection/envelope + T/H; gated echo thresholds.
Motor / PSU Loop Filters
Anti-alias LP with differential drive—low latency and adequate phase margin.
Audio / Measurement
Butter/Bessel cascades with controlled group delay for hi-fi/transient fidelity.
Comms / RF Baseband
Gm-C/SC tunables with AGC/PGA for multi-standard platforms.
Key Specs & Selection
Noise
en/in, 1/f corner and in-band noise vs source-Z and target SNR.
Linearity & Distortion
THD/SFDR with output swing/drive, CM control for differential stages.
Frequency & Phase
GBW/phase margin, Q vs tolerance, group delay and phase linearity.
Tunability
Digital steps/analog trims, tempco/repeatability and in-field calibration.
Power & Supply
Iq/thermal, single/dual rails, RRIO and dynamic range.
Reliability
EMI/ESD/surge readiness, input protection and temp/aging stability.
Design Hooks
Topology vs. Op-Amp Choice
Sallen-Key needs GBW/output drive; MFB sensitive to input noise/distortion; use FDAs for differential filters.
Tolerance & Q Control
Cap/res accuracy dominates—prefer NP0/C0G, add matched networks or digital self-cal.
Noise & Dynamic Budget
Combine pre/post-filter noise, ADC quantization and ref noise into SNR/ENOB.
AAF vs. Sampling Rate
Pick fc:fs ratio, roll-off order and phase/latency objectives coherently.
SC / Gm-C Caveats
Beware clock feedthrough/folding and switch injection; manage Gm drift/linearity.
Layout & Grounding
Star grounds/guard rings, symmetric diff traces and control thermal/leakage paths.
Protection Front-End
RC limit + low-C TVS; model clamp impact on phase and distortion.
Calibration & Serviceability
Bypass/loopback, temp re-cal and EEPROM’d parameters for field upgrades.
