“Choosing the right oscillator usually requires weighing several factors. This article will briefly explain the eight most critical parameters that affect the oscillator. When choosing Electronic components, what are your first considerations? Most likely it is the processor or other core components of the system. A timer may be the last thing that comes to your mind, even though the clock signal is the “heartbeat” on which all signals in the system depend.
Choosing the right oscillator usually requires weighing several factors. This article will briefly explain the eight most critical parameters that affect the oscillator.
When choosing electronic components, what are your first considerations? Most likely it is the processor or other core components of the system. A timer may be the last thing that comes to your mind, even though the clock signal is the “heartbeat” on which all signals in the system depend.
Choosing the correct operating frequency for the application may seem simple, but there are still many factors that affect system performance to consider. So, what are the most important parameters and precautions? The following will give a brief overview of the main parameters of the oscillator and their importance.
The most basic parameter of an oscillator is frequency, which is the repetition rate (period) of the oscillator’s output signal. The frequency is measured in Hertz (Hz), which is the number of cycles per second. At present, SiTime’s oscillators can provide low-power devices with frequencies as low as 1Hz, while also supporting devices up to 725MHz. The frequency of the SiTime oscillator can be programmed within its frequency range, accurate to six decimal places.
2. Frequency stability
Frequency stability is one of the basic performance indicators of an oscillator. The reference rated output frequency is usually measured in parts per million (ppm) or parts per billion (ppb). It represents the deviation of the output frequency from the ideal value caused by external conditions. Therefore, the smaller the stability value, the better the performance.
Different oscillator types may have different external conditions that affect frequency stability, but they usually include temperature changes and initial compensation measured at 25°C. It may also include electrical conditions such as frequency aging, frequency deviation, power supply voltage changes, and output load changes over time.
3. Jitter and phase noise
The importance of phase noise and jitter measured in the time domain is generally considered to be the performance index following the oscillator frequency stability. Phase noise and jitter are directly related to system performance, and will affect parameters such as bit-error-ratio (BER) in serial data systems. Phase noise and jitter are two methods of quantifying clock signal noise. Phase noise is used to measure the clock noise in the frequency domain; jitter is used to measure the influence of noise in the time domain on the clock.
Since jitter and phase noise are the main factors that affect system timing errors, it is necessary to fully consider clock noise when evaluating the total timing budget. This is not a simple matter. Not all oscillator manufacturers specify jitter in the same way. Jitter requirements vary from application to application. The integrated phase jitter measured in the frequency domain has different types of jitter and different integration ranges.
4. Output signal format
The chipset supplier can specify the desired output signal mode for the timing chip. There are two types of output: single-ended or differential. Single-ended oscillators are low cost and easy to implement, but they also have limitations. For example, they are more sensitive to circuit board noise, so they are usually more suitable for frequencies below 166MHz. LVCMOS (Low-voltage CMOS) is the most common single-ended output type, which can swing rail-to-rail.
Relatively speaking, differential signaling is a more expensive option, but with better performance, it is the first choice for high-frequency applications. Since all noise common to differential traces will be eliminated, this mode is less sensitive to external noise and will produce lower jitter and electromagnetic interference (EMI). The most commonly used differential signal types include LVPECL, LVDS, and HCSL.
5. Power supply voltage
The power supply voltage, in volts (V), is the input power required to operate the oscillator. The power supply voltage supplies power to the oscillator through the VDD pin, so it is sometimes referred to as VDD. Standard voltages for single-ended oscillators include 1.8V, 2.5V, and 3.3V. The voltage of modern differential oscillators is usually between 2.5V and 3.3V.
6. Power supply current
The power supply current refers to the maximum operating current of the oscillator, measured in microamps (μA) or milliamps (mA) at the maximum voltage or nominal voltage. The typical supply current is measured under no load.
7. Operating temperature range
The operating temperature range specifies the ambient temperature at which the device is expected to work and must meet the data specifications. The common temperature ranges are: – Commercial grade, automotive grade 4 grade: 0 to +70°C – Commercial extended grade: -20 to +70°C – Industrial grade, automotive grade grade 3: -40 to +85° C-Industrial extended grade, car standard grade 2: -40 to +105°C-car standard grade 1: -40 to +125°C-military grade: -55 to 125°C-car standard grade 0: -40 to 150°C
Oscillators usually use metal, ceramic or plastic packaging technology, and use a variety of industry standard packaging sizes. The arrangement of pads (pins) may vary from supplier to supplier, but the overall size of xy is standardized. Common package sizes for single-ended oscillators that usually have four pins include: – 2016: 2.0 x 1.6 mm – 2520: 2.5 x 2.0 mm – 3225: 3.2 x 2.5 mm – 5032: 5.0 x 3.2 mm – 7050: 7.0 x 5.0 mm
Differential oscillators have six pins, usually in the larger 3225, 5032, and 7050 package sizes.
Some specialized oscillators, such as Oven Controlled Crystal Oscillator (OCXO), use a much larger package size. Usually 25.4 x 25.4mm, ranging from 9.7 x 7.5mm to 135 x 72mm.
Rich packaging types of oscillators
The eight parameters listed in this article are the most commonly used specification parameters when designers choose oscillators. However, depending on the application, there are sometimes many other parameters and functions that need to be considered. These parameters include reducing EMI characteristics, the pulling range of frequency fine-tuning, start-up time and quality/reliability, etc.
For high-performance applications, in addition to ensuring basic frequency stability, other additional stability-related specifications should also be considered. Such as aging, frequency and temperature slope (ΔF/ΔT), thermal hysteresis, Allan deviation, Hadamard Variance, holdover and retrace, etc.