Oscillator Information			Frequency search   MHz

Output:- The oscillator output is a voltage that goes up and down at the oscillator frequency. The waveform is usually either sinewave or logic output, also called square wave. Frequency:-The rate at which the oscillator output goes up and down. Measured in Hertz (Hz) or number of cycles per second. The frequencies are usually high enough that kilohertz (kHz) or megahertz (MHz) are more convenient. Package:-Unless a resistance weld package these Oscillators are not hermetically sealed Stability:-The change in frequency, usually measured in parts per million (ppm). The main causes of frequency change are temperature, supply voltage and ageing (change of frequency with time). Clock oscillators have overall stabilities between 15 and 100 ppm. Clock oscillators are non-adjustable oscillators for general applications where higher stabilities are not required. Precision oscillators have stabilities of 5 ppm. Precision oscillators use crystals with more careful control of the characteristics to achieve temperature stabilities close to the theoretical limit. Adjustment is often provided to allow for ageing. Temperature Compensated Oscillators have stabilities between 5 and 0.3 ppm. Temperature-compensated oscillators have temperature stabilities that are better than the stabilities achieved by the best crystals. The temperature variation of the crystals is predictable, and compensation circuits are fitted to a TCXO that adjust the frequency of the oscillator. The amount of adjustment changes with temperature, and it is designed to cancel out the change of frequency that the crystal exhibits. Compensation of TCXOs can be by passive networks of thermistors and capacitors or by networks that adjust a voltage according to temperature, and the voltage is used to adjust the frequency. The network that adjusts the voltage can be analogue, using thermistors, or it can be digital, using microcomputers. Digitally Compensated Crystal Oscillators, sometimes known as DTCXOs, are made to closely match the non-linear characteristics of a crystal to give the best temperature stability of all compensated oscillators. The digital temperature-compensated crystal oscillator (DTCXO) allows improved temperature compensation over an analogue TCXO by using digital processing rather than the conventional analog compensation network. Each oscillator is individually calibrated and the compensation values are stored as digital information, accurately matched to the individual crystal's characteristics. This is a quick way of accurately matching the compensation to the crystal, to give the best stability when in use. However, it still suffers from the basic TCXO limitations deriving from the need to keep the oscillator tuned to frequency. Also it has small frequency jumps due to the discrete nature of digital compensation. Oven oscillators have stabilities of 0.2 ppm or better. For even better stabilities, the temperature changes that cause the frequency variations have to be eliminated. In Oven oscillators, the crystal and its immediate circuit are fitted into a temperature controlled environment. The temperature of this is always higher than the maximum ambient temperature, and the crystal is chosen to change its frequency as little as possible near this temperature. The resulting stabilities are excellent, at the expense of size, weight, power and warm-up time. Enable function:- This is a feature fitted to some oscillators where a control signal can be applied to the oscillator to make the output go high impedance. The output is usually disabled when the control signal goes low. The crystal is usually left running when the oscillator is disabled so that the oscillator starts immediately when the control signal enables it again. This feature is often used for testing circuits at lower frequencies. Start-up time:- This is the time that starts when the supply voltage is connected to the oscillator and ends when the oscillator starts oscillating. Most oscillators take between 0.5 and 5 ms, but oscillators using crystals at 10 - 100 kHz can take several seconds to start.

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