Dapu Microelectronics Voltage Controlled Oscillators (VCXO)

Pull range is the total frequency deviation achievable by varying the control voltage from minimum to maximum. It's specified in ppm (parts per million) relative to the center frequency. Common pull ranges include ±50ppm, ±100ppm, and ±150ppm. Wider pull range provides more frequency adjustment capability but typically results in poorer phase noise and stability. The pull range should be selected based on the expected frequency variation in the system plus margin. For PLL applications, the pull range must accommodate the VCO tuning range plus initial frequency tolerance. Dapu VCXOs offer various pull ranges to meet different application requirements.

Select pull range based on system frequency variation requirements. Contact us for PLL design assistance.

Pull linearity measures how linearly the frequency changes with control voltage. It's typically specified as a percentage deviation from ideal linearity, with <10% being good and <5% being excellent. Good linearity is important for PLL applications because it affects loop stability and lock time. Non-linear VCXOs can cause loop instability or increased phase noise. Dapu VCXOs use high-quality varactor diodes and optimized circuit design to achieve excellent linearity. Linearity is measured across the full control voltage range and specified in the datasheet. For critical PLL applications, request linearity test data.

Select VCXOs with <10% linearity for most PLLs, <5% for critical applications.

VCXO gain (Kvco) is the sensitivity of frequency to control voltage, measured in Hz/V or ppm/V. It's calculated as the frequency change divided by voltage change. Kvco is important for PLL design because it affects loop bandwidth, stability, and lock time. Higher Kvco means more frequency adjustment per volt but can make the PLL more sensitive to noise on the control line. Lower Kvco provides more stable operation but requires larger voltage swings for the same frequency range. Typical Kvco values range from 1kHz/V to 50kHz/V depending on pull range. When designing PLLs, use the actual Kvco from the datasheet for loop filter calculations.

Use higher Kvco for wide tracking range, lower Kvco for noise-sensitive applications. Check datasheet for exact value.

Yes, VCXOs can be used for spread spectrum clock generation by modulating the control voltage with a triangle or random waveform. This spreads the clock energy over a wider frequency range, reducing EMI peaks. The pull range must be sufficient to achieve the desired spread percentage (typically ±0.5% to ±2%). Linearity is important for uniform spreading. The modulation frequency is typically 30-33kHz for FCC compliance. Dapu VCXOs with good linearity are suitable for spread spectrum applications. However, for dedicated spread spectrum applications, consider using spread spectrum oscillators (SSO) which integrate the modulation circuitry.

Use VCXO with external modulation for spread spectrum. Consider dedicated SSO for simpler implementation.

Dapu VCXOs typically have high control voltage input impedance of >100kΩ, sometimes up to 1MΩ depending on the specific model. This high impedance minimizes loading on the control circuit (typically a DAC or op-amp output). The high input impedance means the VCXO control pin draws very little current, typically <1μA. This allows the use of high-impedance loop filters without significant voltage drop. The input is usually DC-coupled and may have internal protection diodes. Check the specific datasheet for exact input impedance values. The high impedance is maintained across the full control voltage range and temperature range.

High input impedance >100kΩ. Compatible with high-impedance control circuits.