English 
Chinese In audio system design, a high-quality preamplifier circuit is essential to ensure that the signal from a MEMS microphone is properly conditioned before being sent to an ADC or downstream processor. The core of this preamplifier is the operational amplifier (op-amp)—a component whose performance directly impacts the overall signal fidelity, noise performance, and dynamic range of the system.
This article explores the key specifications to consider when selecting an op-amp for MEMS microphone applications, and how to ensure compatibility with audio chain requirements.
🔗 Explore MEMS microphones from SISTC:
https://sistc.com/product-category/mems-microphone/
Why the Op-Amp Matters in MEMS Mic Designs
MEMS microphones like the ADMP504 or WBC6556 typically output signals with sensitivities around –38 dBV and SNR values between 60–70 dB. To preserve this signal integrity, the op-amp in the preamp stage must add minimal noise, distortion, and phase error—especially across a 20 kHz audio bandwidth.
1. Voltage Noise: The Top Priority
The most critical op-amp spec in this application is input voltage noise density, usually expressed in nV/√Hz. To avoid degrading the microphone’s SNR, the op-amp’s own noise should be 10 dB lower than the mic’s self-noise floor.
📊 Example:
- Microphone noise floor: –103 dBV
- Required op-amp noise floor: ≤ –113 dBV
- Equivalent to: ≤ 15.9 nV/√Hz over 20 kHz
🔎 Analog Devices provides a detailed guide on low-noise op-amp selection for audio, including real-world performance tips.
2. Bandwidth and Slew Rate
To maintain clean reproduction of high-frequency audio content, the op-amp’s slew rate must be high enough to support the fastest voltage transitions. A common design formula is:
Slew Rate ≥ 2 × π × fMAX × VP
Where:
fMAX= 20 kHzVP= Output peak voltage (e.g. 12 V → 8.5 VRMS)
✅ Minimum required slew rate: ~1.5 V/μs
Even though full-scale signals at high frequencies are rare, the op-amp should handle edge cases without inducing slew-induced distortion.
3. THD+N (Total Harmonic Distortion + Noise)
High-performance audio systems demand that op-amp THD+N be minimized to maintain clarity and reduce signal artifacts.
🎯 Recommended:
- THD+N ≤ 0.001% or –100 dB
- Especially important for voice processing, smart audio devices, and high-resolution ADC front ends
TI’s Audio Op Amp Guide offers a deep dive into optimizing op-amps for low THD+N in various audio conditions.
4. Power Efficiency and Application Considerations
In battery-powered MEMS mic applications like TWS earbuds or portable recorders, low-power op-amps are often required. Designers should balance:
- Quiescent current
- Startup time
- Package size
- Voltage rails compatibility (e.g., 1.8V/3.3V systems)
📌 Use low-power precision op-amps for portable devices, and full-bandwidth op-amps for studio or industrial applications.
Example: Design Target Using WBC2718
Assume a MEMS microphone with the following parameters:
- SNR: 65 dB
- Sensitivity: –38 dBV
- Bandwidth: 20 kHz
- Noise floor: –103 dBV
To ensure the preamp adds minimal noise:
- Target op-amp noise: ≤ –113 dBV or ≤ 15.9 nV/√Hz
- Slew rate: ≥ 1.5 V/μs
- THD+N: ≤ –100 dB
🎯 WBC2718, combined with SISTC MEMS microphones like WBC6556, satisfies these conditions and is ideal for high-fidelity, low-noise applications.
Conclusion
Selecting the right op-amp is critical for unlocking the performance of MEMS microphones. From input voltage noise to THD+N and power efficiency, every parameter must align with your application’s goals—whether you’re building smart assistants, conference systems, or industrial acoustic monitors.
🛠️ Visit our MEMS microphone portfolio:
👉 https://sistc.com/product-category/mems-microphone/
🔗 Read more from Analog Devices:
Op-Amps for Precision Audio
🔗 Application tips from TI:
TI Low-Distortion Audio Op-Amps
📞 Need help selecting the right preamp or MEMS mic combo? Contact Us
