Circuit noise generation and method of suppressing noise
Circuit noise refers to any unwanted signal in an electronic system that is not the intended signal. Initially, noise was understood as the random signals produced by audio devices such as radios. However, over time, the concept expanded beyond just sound-related disturbances. For instance, signals causing white lines on a screen or interference from power supply fluctuations are also considered noise. In essence, any signal present in the circuit other than the desired one can be classified as noise, regardless of whether it affects the circuit's performance.
Noise and interference are often confused, but they are distinct concepts. Noise is an actual signal, while interference is the negative impact that this noise has on the circuit’s operation. Not all noise causes interference, especially in digital circuits where small voltage spikes may exist without disrupting logic operations. When noise becomes significant enough to affect circuit performance, it is referred to as interference voltage. The ability of a circuit or device to withstand noise without failure is known as its immunity.
The sources of noise in electronic circuits are typically associated with digital components and power supplies. Digital circuits generate electromagnetic radiation and coupling noise, which can interfere with adjacent circuits. Power supplies, particularly switching types, introduce high-frequency harmonics and ripple, contributing to noise. To reduce noise, engineers use techniques like proper grounding, differential signaling for analog signals, decoupling capacitors, shielding, and separating analog and digital sections.
Designing low-noise preamplifiers requires careful component selection and understanding of noise sources. Operational amplifiers (op-amps) play a key role, and their specifications—such as input offset voltage, common-mode rejection ratio, power supply rejection ratio, and bandwidth—must align with the application’s requirements. For example, high-gain systems demand precision op-amps with low noise characteristics. The choice of power supply and output swing capabilities also influences noise performance.
Noise in op-amps comes from four main sources: thermal noise, flicker noise, shot noise, and popcorn noise. Thermal noise is related to resistance and temperature, while flicker noise dominates at lower frequencies. Shot noise arises from current carriers, and popcorn noise, though rare, is caused by semiconductor contamination. Bipolar and CMOS input op-amps differ in their noise characteristics, with CMOS amplifiers generally having lower noise currents but higher sensitivity to temperature.
In designing a microphone preamplifier for PDAs, engineers must consider factors like microphone type, output level, impedance, frequency range, and noise specifications. A typical ceramic microphone might have an output of 200 µVpp, an impedance of 2.2 kΩ, and a frequency range of 100 Hz to 4 kHz. Calculating the equivalent input noise (EIN) helps determine the total noise contribution and ensures the signal-to-noise ratio meets design goals.
A well-designed preamplifier circuit minimizes noise by using low-noise op-amps, proper filtering, and optimal layout. Components like capacitors and resistors must be chosen carefully to avoid introducing additional noise. Real-world designs often require iterative adjustments to achieve the desired performance, especially when dealing with analog circuits where noise behavior is more complex and less predictable than in digital systems.
Understanding and managing noise is essential for achieving reliable and high-quality electronic systems. Whether working on audio equipment, communication devices, or industrial control systems, noise reduction strategies are crucial for maintaining signal integrity and overall performance.
Redundant Power Supply Series,Full Modular Redundant Power,800W Redundant Power Supplies,Redundant Server Power Supply 2000W
Boluo Xurong Electronics Co., Ltd. , https://www.greenleaf-pc.com