Welcome to ChipSun Technology Co.,Ltd. 

86-755 8345 8798 sales@chinachipsun.com
EN
|CN

The knowledge of the VCXO

Voltage-Controlled Crystal Oscillators (VCXOs) commonly utilize AT-cut quartz resonators. By incorporating an adjustable component into the oscillation circuit, they achieve the function of adjusting the oscillation frequency in response to a control voltage. VCXOs are mainly applied in frequency modulation (FM) and phase-locked loop (PLL) technologies, communication systems, navigation equipment, radar, and consumer electronics. Key characteristics include excellent transmission performance, strong anti-interference capability, low power consumption, high frequency stability (±5×10⁻⁶), and low phase noise.

Working Principle of VCXOs

The working principle of VCXOs is based on the piezoelectric effect—applying pressure to a crystal changes its electrical properties, thereby altering the crystal’s oscillation frequency. The specific mechanism is as follows:
  1. Oscillation Circuit: Composed of a crystal, capacitors, and transistors. The crystal is the core component, exhibiting both mechanical and electrical oscillation characteristics.
  2. Mechanical Oscillation: The crystal undergoes physical vibration (mechanical oscillation) when stimulated.
  3. Electrical Oscillation: The crystal’s mechanical vibration induces electrical oscillation—charge displacement occurs within the crystal under the influence of an internal electric field, generating electrical oscillation.
  4. Feedback Effect: The oscillated signal is amplified through feedback and fed back to the crystal via its piezoelectric effect, sustaining oscillation and enabling signal output.

Typical Application Scenarios and Technical Adaptations of VCXOs

  1. Telecommunications and Broadband Communication Systems
    • Application Scenarios: Clock synchronization modules in 5G/4G base stations, SDH/SONET optical transmission equipment, xDSL broadband modems;
    • Technical Adaptations: VCXOs require a pull range of ±100ppm~±200ppm to compensate for frequency offsets in transmission links (e.g., clock drift caused by fiber dispersion or signal attenuation). Additionally, a linearity of ≤5% is required to ensure fast PLL locking.
  2. Video Transmission and Display Systems
    • Application Scenarios: HDMI 2.1 video transmitters, signal processing units for 4K/8K UHD TVs, video synchronization modules in security surveillance cameras;
    • Technical Adaptations: Video signal transmission demands strict frame synchronization. VCXOs must support frequency fine-tuning within ±50ppm~±100ppm to compensate for clock deviations during video encoding/decoding, preventing frame stuttering or tearing;
    • Key Requirements: Output frequency must match the video pixel clock (e.g., 27MHz@1080P, 148.5MHz@4K) with phase noise ≤-115dBc/Hz@10kHz offset to ensure noise-free video signals.
  3. Test and Measurement Instruments
    • Application Scenarios: Clock reference modules in oscilloscopes, signal generators, spectrum analyzers, and frequency counters;
    • Technical Adaptations: Test equipment requires high-precision frequency calibration. VCXOs need a narrow pull range of ±20ppm~±50ppm, frequency stability ≤±10ppm (-40℃~85℃), and linearity ≤3% to ensure test signal frequency accuracy error < 0.1%.
  4. Industrial Control and Internet of Things (IoT)
    • Application Scenarios: Industrial Ethernet (Profinet, EtherCAT) controllers, time synchronization units in IoT gateways, data acquisition modules for smart sensors;
    • Technical Adaptations: Industrial environments experience large temperature fluctuations. VCXOs must feature a wide operating temperature range (-40℃~105℃) and a pull range of ±100ppm~±500ppm to compensate for frequency drift caused by ambient temperature changes.
Back To Top