Pay attention to certain parameters, the design engineer can choose the oscillator suitable for the application
---- Countless electronic circuits and applications today require precise timing or clock reference signals. Crystal clock oscillators are extremely suitable for many applications in this area.
----The clock oscillator has a variety of packages, and it is characterized by a variety of electrical performance specifications. There are several different types:
Voltage controlled crystal oscillator (VCXO), temperature compensated crystal oscillator (TCXO), oven crystal oscillator (OCXO),
And digitally compensated crystal oscillator (DCXO). Each type has its own unique properties.
----Consideration of frequency stability----
One of the main characteristics of the crystal oscillator is the stability within the operating temperature, which is an important factor in determining the price of the oscillator. stable
The higher the performance or the wider the temperature range, the higher the price of the device.
----Design engineers must carefully determine the actual needs of a particular application, and then specify the stability of the oscillator. Overvalued
It means to spend more money.
----For applications requiring frequency stability of ±20ppm or above, ordinary crystal oscillators without compensation can be used. For Cheng
For stability of ±1 to ±20ppm, TCXO should be considered. For stability below ±1ppm, OC should be considered
XO or DCXO.
Other parameters that must be considered are output type, phase noise, jitter, voltage stability, load stability, power consumption, packaging
Form, shock and vibration, and electromagnetic interference (EMI). The crystal oscillator can be HCMOS/TTL compatible, ACMOS compatible,
ECL and sine wave output. Each output type has its unique waveform characteristics and uses. Should pay attention to three-state or complementary loss
Requirements. Symmetry, rise and fall times, and logic levels are also specified for certain applications. Many DSPs
And communication chipsets often require strict symmetry (45% to 55%) and fast rise and fall times (less than 5ns).
----Phase noise and jitter----
The phase noise measured in the frequency domain is a true measure of short-term stability. It can measure within 1Hz of the central frequency and
Usually measured to 1MHz.
----The phase noise of the oscillator improves at frequencies far from the center frequency. TCXO and OCXO oscillators and their
It uses the fundamental or harmonic crystal oscillator with the best phase noise performance. Use PLL synthesizer to generate output
Frequency oscillators generally exhibit inferior phase noise performance than those using non-phase-locked loop technology.
----Jitter is related to phase noise, but it is measured in the time domain. The jitter expressed in picoseconds can be an effective value or peak
-The peak value is measured. Many applications, such as communication networks, wireless data transmission, ATM and SONET, require strict
Grid mixing index. It is necessary to pay close attention to the jitter and phase noise characteristics of the oscillators used in these systems.
----The influence of power supply and load----
The frequency stability of the oscillator is also affected by the fluctuation of the oscillator power supply voltage and the fluctuation of the oscillator load. Correct choice of oscillation
The device can minimize these effects. The designer should verify the performance of the oscillator under the recommended supply voltage tolerance and load. Do not
It can be expected that an oscillator rated to drive 15pF will perform well when driving 50pF. When exceeding the recommended power supply voltage
Oscillators that work under will also show bad waveforms and stability.
----For devices that require battery power, power consumption must be considered. The introduction of 3.3V products must be developed under 3.3V
As an oscillator. ----The lower voltage allows the product to operate at low power. Most of the surface mount oscillators on the market today
Work under 3.3V. Many through-hole oscillators using traditional 5V devices are being redesigned to work at 3.3V
Similar to other electronic components, clock oscillators also use increasingly smaller packages. For example, M3L/M5L from M-tron
The series surface mount oscillators are now available in a 3.2×5.0×1.0mm package. Generally, smaller devices are larger than larger ones
Surface mount or through hole packaged devices are more expensive. Small packages often have to compromise between performance, output selection and frequency selection
The actual application environment of the oscillator requires careful consideration. For example, high vibration or shock levels can cause problems for the oscillator.
----In addition to possible physical damage, vibration or shock can cause erroneous actions at certain frequencies. Externally induced
Disturbance can cause frequency jitter, increase the amount of noise, and intermittent oscillator failure. ----For those who require special EMI compatibility
Application, EMI is another priority issue. In addition to adopting appropriate PCB layout technology, it is important to choose
Choose the clock oscillator that provides the smallest amount of radiation. Generally speaking, oscillators with slower rise/fall times perform better
----For frequencies below 70MHz, it is recommended to use an HCMOS oscillator. For higher frequencies, ECL can be used
Type oscillator. ECL type oscillators usually have the best total noise rejection, even at lower frequencies from 10 to 100 MHz.
At low rates, the ECL type is also slightly better than other types of oscillators