![]() ![]() Mathematically, a closed-loop gain of one is required to maintain steady state oscillations. When oscillations are established, only a small amount of energy is needed to compensate for losses in the circuit. The initial oscillations are very weak and it takes time to amplify the signal to the desired magnitude. The frequency that fulfills the Barkhausen condition is amplified the most, because it is in phase with the original signal. When the necessary conditions are met, any disturbance (noise) in the oscillator will cause oscillations to start. This is a necessary, but not sufficient, condition for oscillations to be present. The principle behind the oscillator is a positive feedback loop satisfying the Barkhausen condition: If the closed-loop gain is larger than unity and the total phase lag is 360°, the resulting closed-loop system is unstable and will self-reinforce. Once the oscillator has started, the changing voltage on the terminals of the vibrating crystal is used as the clock signal. ![]() Conversely, a deformation of the crystal will cause a voltage across the terminals. This means an applied electric field will cause the crystal to deform. Quartz crystals and ceramic resonators hold the direct piezoelectric property. This application note will focus on quartz crystals however, the theory presented is also valid for ceramic resonators. This can be more important than precision in frequency for some applications. As will be seen in subsequent chapters, the quality factor for ceramic resonators are lower than for crystal oscillators, which usually results in a faster startup time. They are easier to manufacture and therefore cheaper than quartz crystals, but suffer from inferior precision in the oscillation frequency. This makes crystal oscillators more expensive than RC oscillators.Ĭeramic resonators operate in the same way as crystal oscillators. Producing quartz crystals require very stable temperature and pressure conditions over a few weeks. The most commonly used crystal is the quartz crystal. Due to the molecular composition of the crystal matter and the angle of which the crystal is cut, this type of oscillator is very precise and stable over a wide temperature range. While the internal RC-oscillators will ensure proper operation of the EFM32, EZR32, EFM32 Gemstones, or Wireless Gecko device, some applications require higher accuracy than these can provide.Ĭrystal oscillators use the mechanical vibration of a crystal to generate the clock signal. In addition, an auxiliary 14 MHz RC oscillator (AUXHFRCO) is used for flash programming and debug trace. ![]() The EFM32, EZR32, EFM32 Gemstones, or Wireless Gecko devices provide two internal RC-oscillators, one high frequency RC oscillator (HFRCO) and one low frequency RC oscillator (LFRCO). They come at a low cost and have a shorter startup time than the crystal oscillator, but variations in component values over temperature makes it difficult to precisely determine the oscillation frequency. RC oscillators are built from resistors, capacitors and an inverting amplifier. Several ways of generating such a signal exists, all with different properties that influences cost, size and stability of the clock signal. Oscillator Theory 1.1 What is an Oscillator?Īn oscillator is an electronic circuit which generates a repetitive time-varying signal, which in this context is used to clock communication and the execution of instructions in the EFM32, EZR32, EFM32 Gemstones, or Wireless Gecko microcontroller. Topics covered include oscillator theory and some recommended crystals for these devices.įor simplicity, EFM32 is used throughout this document to represent the existing EFM32 Wonder Gecko, Gecko, Giant Gecko, Leopard Gecko, Tiny Gecko, Zero Gecko, or Happy Gecko MCU series, Wireless Gecko is used to represent the EFR32 Wireless Gecko portfolio devices, and EFM32 Gemstones is used to represent the next-generation Gecko MCUs (Pearl Gecko, Jade Gecko, and future devices).ġ. The EFM32, EZR32, EFM32 Gemstones, or Wireless Gecko devices contain two crystal oscillators: one low speed (32.768 kHz) and one high speed (4-32 MHz, 4-48 MHz, or 38-40 MHz). This application note provides an introduction to the oscillators in EFM32, EZR32, EFM32 Gemstones, or Wireless Gecko devices and provides guidelines in selecting correct components for their oscillator circuits. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |