Using two capacitors (0.1µF and 0.01µF) in parallel in a circuit (often seen near power supply pins of ICs or sensors) is a common practice to improve noise filtering and stabilize voltage. Here’s why:
1. The Core Principle: Decoupling & Bypass Capacitors
These capacitors act as "local energy reservoirs" for the IC, providing instant current when needed and filtering out high-frequency noise.
Key Roles:
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Stabilize voltage (prevent dips/spikes when the IC draws sudden current).
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Filter noise (short high-frequency disturbances to ground).
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Prevent oscillations (especially in fast-switching digital ICs).
2. Why Two Different Values?
Each capacitor is optimized for a different frequency range due to their Equivalent Series Inductance (ESI) and impedance characteristics.
| Capacitor | Best At Filtering | Why? |
|---|---|---|
| 0.1µF (100nF) | Mid-high frequencies (1–100MHz) | Low ESL, effective for digital noise (e.g., MCU clock signals). |
| 0.01µF (10nF) | Very high frequencies (>100MHz) | Smaller capacitors have even lower ESL, tackling RF noise. |
Real-World Analogy:
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A 0.1µF cap is like a "large bucket" handling sudden current demands.
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A 0.01µF cap is like a "small sponge" catching tiny, fast noise spikes.
3. Where You’ll See This Combo
A. Near Power Pins of ICs
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Microcontrollers (Arduino, ESP8266)
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Sensors (MPU6050, ADXL345)
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Voltage Regulators (LM7805)
B. High-Speed Digital Circuits
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Clock lines (e.g., crystal oscillators).
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RF/wireless modules (WiFi, Bluetooth).
4. What Happens If You Use Only One?
| Scenario | Risk |
|---|---|
| Only 0.1µF | May miss ultra-high-frequency noise (e.g., RF interference). |
| Only 0.01µF | Insufficient for stabilizing sudden current draws. |
5. Practical Example: MPU6050 Accelerometer
A typical MPU6050 circuit uses 0.1µF + 0.01µF near its VCC pin to:
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Prevent noise from affecting gyro/accel readings.
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Stabilize power during rapid I2C communication.
https://i.imgur.com/JzZQx7m.png
(Note the dual capacitors near the power supply.)
6. Advanced Considerations
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Placement: Place capacitors as close as possible to the IC’s power pins.
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ESR (Equivalent Series Resistance): Lower ESR = better high-frequency performance.
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Tantalum vs. Ceramic: Ceramic (MLCC) caps are preferred for decoupling (low ESL).
7. When Can You Skip the 0.01µF Cap?
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Low-frequency circuits (e.g., temperature sensors).
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Battery-powered devices with minimal noise.
Key Takeaways
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0.1µF handles bulk decoupling (mid-high frequencies).
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0.01µF catches ultra-high-frequency noise (RF/EMI).
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Together, they cover a wider frequency range than a single capacitor.
