10 foot quartzcrystal12/15/2023 The mechanical model, Figure 2, and electrical model, Figure 3, are closely aligned. Q: What are the electrical characteristics of the quartz blank?Ī: The crystal material and blank have been intensively studied electrically, mechanically, and thermally for decades, as their performance is so critical in many systems. Understanding these characteristics is critical to a high-performance oscillator circuit, including whether the crystal is used in a series- or parallel-resonant mode. Each arrangement has tradeoffs in terms of complexity, cost, stability, and compatibility with the electrical characteristics of the quartz blank. Q: What types of circuits are used for the oscillator?Ī: There are many topologies in use, among the better known are the Hartley, Pierce, and Colpitts oscillators. Fig 1: The many steps from raw quartz-crystal blank to packaged final unit require precision and perfection. The crystal is used in the feedback loop of the oscillator to constrain the oscillator’s frequency, Figure 1. When subject to a voltage potential, it will begin to vibrate and oscillate at its “fundamental frequency.” It’s a mutual relationship: the electrical circuit supports the mechanical resonance and vice versa. Q: How does a quartz blank become an oscillator?Ī: The quartz blank is used in an oscillator circuit as the resonating element. This principle is used in piezoelectric actuators, small audio speakers, pressure sensors, and numerous other applications. Q: What’s the basic principle of the oscillator based on a quartz crystal?Ī: It is yet another manifestation of the piezoelectric effect, which characterizes a duality: when a crystal (not necessarily quartz) is subject to an electric field (a voltage), its dimension change in reversible action when a crystal is stressed, it produces a small voltage. In contrast, with a synthesized radio, only one master crystal is needed. Some “full-band” radios carried 23 transmit- and 23 receive-channel crystals (a total of 46) to access any and all assigned channels other radios had slots for just two to six crystal pairs, and users would have to physically remove and replace the crystals if they wanted to go to other channels. For example, in the 1970s, Citizen’s Band radio was very popular with 23 full-duplex channels assigned in the 27-MHz band. The development of frequency synthesizers changed the need for and use of crystals. In World War II, having the right crystals was so important that the Army Corp of Engineers has a special team of skilled crystal “grinders” whose sole job was to cut, grind, and tune crystals for the military radio channels, and change them as needed. The former was low cost but inexact the latter was exact but needed many crystals. Before the availability of such tuning, a radio could be tuned one of two ways: either by manual LC tuning using a knob and dial or by a using a crystal to establish each channel frequency. They are used extensively for generating system clocks, as well as establishing a single master frequency in a transmitter and receiver, with all needed carrier channels then derived via a synthesizer. Q: How important are these crystals for determining frequency?Ī: Very, very important. This results in closer-to-perfect crystalline structures, which yield greatly improved, more consistent performance. However, since the 1970s, synthetic quartz crystals have been grown much like silicon ingots (and using many of the same techniques and processes). The quartz was cut along specific crystalline axes and then polished. Although the piezoelectric effect which they exploit (discussed below) was well-known well before that, there was no place for these quartz elements, as radio and electronics did not exist.Ī: For many decades, mined natural quartz was the sole option, much of it from Brazil. Q: For how long have quartz crystals been used in circuits as frequency-setting elements?Ī: Since the early part of the 20 th century. There are alternatives to the quartz-based crystal, such as are MEMS-based resonators which are gaining increasing market share, and very simple LC-resonant “tank” circuits for low-end applications and with low-modest performance objectives. This FAQ will look at the quartz-crystal blank itself, and some of the subtleties and variabilities the crystal can undergo. It’s easy and commonplace to think of the crystal as a simple component, but as with most components, that’s misleading and incorrect there are many aspects to the material itself, and how itis used, regardless of the application and electronics. An oscillator or clock function is key to nearly all electronic circuits, and in most (but not all) cases, the heart of this oscillator circuit is a tiny piece of quartz, called the crystal blank or slab.
0 Comments
Leave a Reply.AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |