＞ Introduction to voltage-controlled crystal oscillator
VCXO (Voltage Controlled Crystal Oscillator) is a type of quartz crystal oscillator. Its full name is voltage-controlled crystal oscillator. It is a crystal oscillator that inserts a varactor diode in series with a crystal resonator. The capacitance of the diode changes according to the external voltage, so that the output frequency can change according to the load capacitance characteristics of the crystal resonator.
· Composition and principle
VCXO is mainly composed of a quartz resonator, a varactor diode and an oscillation circuit. Its working principle is to change the capacitance of the varactor diode by controlling the voltage, thereby "pulling" the frequency of the quartz resonator to achieve the purpose of frequency modulation. VCXO is mostly used for phase-locked technology and frequency negative feedback modulation.
· Features of voltage-controlled crystal oscillator
VCXO is composed of a quartz crystal oscillator (i.e., a resonator and an oscillation circuit) with a very high quality factor. The quality of the crystal, the cutting orientation, the structure of the crystal oscillator and the circuit form jointly determine the performance of the oscillator. Voltage-controlled crystal oscillators have the following characteristics:
＞ Important parameters of voltage-controlled crystal oscillators
How to choose a suitable VCXO voltage-controlled crystal oscillator is mainly considered from the following 9 parameter dimensions.
①Nominal frequency
Nominal frequency refers to the center output frequency of the voltage-controlled crystal oscillator (VCXO) under standard operating conditions (such as the control voltage is the middle value, normal temperature, rated power supply voltage). It is the reference frequency of the VCXO, usually determined by the internal quartz crystal resonator.
②Frequency stability (key parameter)
Refers to the allowable deviation from the nominal frequency within the specified operating temperature range, expressed in ppm (parts per million). Generally speaking, the higher the stability or the wider the temperature range, the higher the price.
③Power supply voltage
Commonly used are 1.8V, 2.5V, 3.3V, 5V, etc., among which 3.3V is widely used.
④ Output mode
Different outputs (CMOS, CML, TTL, PECL, LVPECL, LVDS, HCSL, etc.) are used according to the needs. Each output type has its unique waveform characteristics and uses. Attention should be paid to the requirements of tri-state or complementary output.
⑤ Operating temperature
Normal operating temperature -40~+85℃, storage temperature -55~+125℃, some special occasions such as aerospace military have more stringent requirements on temperature.
⑥ Phase noise and jitter
Phase noise and jitter are both indicators to measure the "purity" of the output clock: they describe how large the random or deterministic deviation of the signal is outside the ideal period. The smaller the value, the cleaner the clock and the lower the system bit error rate.
1) Phase noise (Phase Noise)
Definition: In the frequency domain, how wide is the "skirt" of the signal spectrum.
Unit: dBc/Hz (noise power per Hz bandwidth relative to carrier power).
2) Jitter
Definition: In the time domain, the time deviation between the real edge and the ideal edge (statistical value).
Unit: ps (picoseconds).
Phase noise is the noise power distribution in the frequency domain, which affects the signal spectrum purity; jitter is the clock edge uncertainty in the time domain, which determines the timing accuracy. The two are essentially two ways of expressing the same phenomenon, but the optimization methods are different (such as low-noise power supply to improve phase noise, PCB layout to reduce jitter).
⑦Pull range
It is a parameter for voltage-controlled crystal oscillators. The crystal oscillator with voltage control function is (VCXO). The frequency deviation range of the oscillation frequency is variable by applying an external control voltage (1.65±1.35V), which indicates the ratio of the change frequency (increase or decrease) to the center frequency. The range is generally ±50ppm~±200ppm. Depends on the structure of the VCXO and the selected crystal.
⑧Package size
Similar to other electronic components, quartz oscillators also use increasingly smaller packages. Typically, smaller devices are more expensive than larger surface mount or through-hole packaged devices. Therefore, small packages often have to compromise between performance, output selection, and frequency selection.
⑨ Aging rate
When all other conditions remain constant, the frequency of the oscillator will still drift over time. This long-term drift is caused by the slow change of the crystal element and other components of the oscillation circuit, that is, the frequency change caused by the crystal oscillator over time. It can be expressed in daily aging (ppb/day) and annual aging (ppm/year).
＞ YXC voltage-controlled crystal oscillator selection recommendation
· CMOS voltage-controlled crystal oscillator
☆ YSV310PR series
Product features:
* CMOS output
*10~250MHz frequency range can be programmed arbitrarily
*Wide pulling range: ±50ppm (min.)
*Low jitter: 1.0ps typ.
*Fast delivery, flexible delivery time
*Packaging: 3.2x2.5mm, 5.0x3.2mm, 7.0x5.0mm
*Applied to solar photovoltaic, lithium battery, 10 GB Ethernet, SONET, SATA, SAS, Fiber Channel, etc.
☆ YSV311PJ series
Product features:
*Programmable voltage-controlled crystal oscillator
*Multiple voltage options (1.8V, 2.5V, 3V, 3.3V)
*15~250MHz wide frequency range arbitrarily programmable
*CMOS output
*Wide traction range: ±200ppm typ.
*Ultra-low jitter: 0.15ps typ.
*Package: 5.0x3.2mm, 7.0x5.0mm
· Differential voltage-controlled crystal oscillator
☆ YSV220PR series
Product features:
*Voltage-controlled differential crystal oscillator VCXO
*10~1500MHz ultra-wide frequency range arbitrarily programmable
*Multiple voltage options (2.5V, 3.3V)
*Wide traction range
*Rich output types (LVDS, LVPECL)
*Fast delivery, flexible delivery time
*Package: 3.2x2.5mm, 5.0x3.2mm, 7.0x5.0mm
☆ YSV221PJ Series
Product Features:
*15~2100MHz ultra-wide frequency range, programmable
*Multiple voltage options (1.8V, 2.5V, 3.3V)
*Wide pull range: ±200ppm typ.
*Rich output types (LVDS, PECL, HCSL, CML)
*Ultra-low jitter: 0.163ps typ.
*Package: 5.0x3.2mm, 7.0x5.0mm
Tips: Xiao Yang will give you a selection formula
"First determine the frequency point, then determine the adjustable range; small package saves space, large package has low phase noise; digital uses CMOS, high speed uses differential." Remember it?
