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As the core component of the audio system, the power amplifier is responsible for amplifying weak audio signals to a power sufficient to drive the speaker. In traditional analog amplifiers and modern digital amplifiers (such as Class D amplifiers), crystal oscillators play a vital role as the core components of frequency control and clock synchronization.
一、The basic principle of crystal oscillators
Crystal oscillators are frequency control components based on the piezoelectric effect, and their core is quartz crystals. Crystal oscillators are clock frequency devices made using the piezoelectric effect of quartz crystals. They play an important role in digital circuits and are known as the "heart" of frequency references in electronic systems.
二、The core role of crystal oscillators in power amplifiers
1. Clock source for digital signal processing (DSP)
Modern power amplifiers generally use digital signal processing technology (such as DSP equalization, frequency division, dynamic compression, etc.), which requires strict timing control.
Sampling rate synchronization: The analog-to-digital conversion (ADC) and digital-to-analog conversion (DAC) of audio signals rely on the clock signal provided by the crystal oscillator to ensure accurate sampling rates (such as 44.1kHz, 48kHz, etc.) and avoid sound quality degradation caused by jitter.
Algorithm execution timing: The operating clock of the DSP chip is provided by the crystal oscillator to ensure the real-time performance of algorithms such as filtering and noise reduction, and prevent audio signal processing delays.
2. PWM modulation control of Class D amplifiers
In high-efficiency Class D amplifiers, audio signals need to be converted into high-frequency switching signals through pulse width modulation (PWM).
Carrier frequency stability: The crystal oscillator provides a reference frequency (usually hundreds of kHz to several MHz) for the PWM modulator to ensure the stability of the switching frequency. Frequency drift may cause electromagnetic interference (EMI) or increase switching losses.
Harmonic distortion suppression: Accurate PWM clocks can reduce switching timing errors, reduce total harmonic distortion (THD), and improve the purity of sound quality.
3. System control and communication interface
Microcontroller (MCU) clock: The control logic of the amplifier (such as volume adjustment, input switching, and protection circuits) requires MCU coordination, and the crystal oscillator provides the main clock for the MCU to ensure the real-time performance of instruction execution and interrupt response.
Digital audio interface synchronization: For amplifiers that support digital inputs such as S/PDIF, I2S or HDMI, the crystal oscillator ensures that the data stream is synchronized with the clock of the host device to avoid data loss or noise.
4. Clock synchronization of wireless transmission module
In Bluetooth/WiFi amplifiers, the crystal oscillator provides a reference frequency for the RF module to ensure the accuracy of wireless signal modulation, reduce the bit error rate (BER), and ensure the continuity of audio transmission.
三、 Key parameters for crystal oscillator selection
In order to meet the performance requirements of the amplifier, the following parameters should be considered when selecting the crystal oscillator:
1. Frequency accuracy: usually required within ±10ppm (one millionth), and high-end devices require ±2ppm.
2. Temperature stability: Temperature compensated crystal oscillator (TCXO) or oven controlled crystal oscillator (OCXO) can cope with ambient temperature changes.
3. Phase noise: Low phase noise (such as 150dBc/Hz @10kHz offset) can reduce high-frequency interference.
4. Load capacitance matching: It needs to match the circuit design to avoid frequency offset.
四、Recommended amplifier selection scheme
In digital audio, the phase noise of the clock frequency will affect the jitter function of the DAC and cause the deterioration of the sound source. In order to accurately reproduce the high-resolution sound source, the sampling frequency is the audio master clock signal provided by the quartz crystal oscillator outside the audio device.
Common crystal frequencies are: 11.2896MHZ, 12.288MHZ, 22.5792MHZ, 24.576MHZ, 45.1584MHZ, 49.152MHZ.
YXC YSO110TR series is recommended, with a frequency stability of ±10ppm, a frequency range of 1-125MHZ, and is compatible with multiple voltages: 1.8-3.3V, an operating temperature of -40~+85°, and the series specifications are as follows:
