Top Benefits of PLL Based Crystal Oscillators

The phase locked loop (PLL) is one of the earliest feedback circuits devised in electronics. Going back 70 to 80 years, the PLL has become the workhorse of timing circuits. Its ability to synchronize to a base frequency, as well as, multiply the frequency to a much higher value provides flexibility and timing accuracy. Let’s take a look at the top 2 benefits:

1. Supply chain agility solves business cycle challenges
Problem: The start of any quartz oscillator (XO) manufacturing begins with the step of growing and cutting the quartz blank. The long lead time associated is unavoidable, often reaching 12 to 16 weeks. Manufacturing cannot begin without accurately knowing the desired oscillation frequency. Each blank must be cut precisely to meet the dimensions required by the end frequency. The result is a long production cycle that requires staging and long range forecasting. Errors in forecasting, sudden upside demand or changes in the output frequency requirements cannot be easily handled within the long lead time window of the quartz process.

Solution: Incorporating a PLL stage within the XO solves this problem. With the use of a PLL, the output frequency can be programmed at the end of manufacturing process, independently of the quartz resonant frequency. A common quartz blank targeting a convenient and often low cost frequency can be shared and staged to address a wide variety of output frequencies. Supply chain agility is achieved by building a bank of unprogrammed quartz blanks that can address large upside demand or changes to the frequency requirements within a short production window of a couple of weeks. In today’s fast changing business landscape, supply chain agility can mean the difference between catching the business or missing the window altogether.

2. High frequency operation improves system performance
Problem: High performance systems benefit from higher frequency reference clocks. However, there is a real frequency limitation to quartz resonators. Blanks designed for higher frequencies, especially above 250MHz, are much thinner than standard lower frequency technology. Thinly cut blanks are fragile, challenging to produce consistently at high volume, and often low yielding. Additionally, quartz blanks that operate up to 1GHz are not manufacturable with today’s technology.

Solution: PLLs solve this problem because they can multiply the base frequency of the quartz to any value. Using a PLL in an oscillator generates high frequencies using standard quartz technology, avoiding thinly cut inverted mesa or other boutique quartz designs. There is no theoretical limit and it comes down to noise performance and power consumption tradeoffs. As silicon circuits improve, the frequency range, power consumption, and noise performance of PLL circuits become more attractive to use within high bandwidth applications such as communications and RF. System designers are able to improve data link integrity and reduce bit error rate in high performance systems while using proven crystal technology.

Many of today’s clock circuits take advantage of the PLL. An XO with a built-in PLL features extended frequency range and improved lead time and manufacturability compared with standard oscillators. With today’s advanced PLL technology, there is practically no tradeoff in noise performance. No system is perfect; even the PLL has some downsides. In this case two stand out the most. First, the PLL introduces its own intrinsic noise into the clock signal. Second, each PLL stage consumes power, possibly increasing overall power requirements and usually also increasing costs. However, the benefits of the PLL based oscillator usually overcome its costs.

Power consumption on most PLL circuits drops with each generation. Supply chain agility that addresses fast moving business cycles and improved overall system performance are two top benefits to use a PLL based XO. With minimal impact to noise and power performance, the PLL based XO presents an excellent value. There is little reason to use other types of oscillators in high performance systems.

About Abracon, LLC
Founded in 1992, and headquartered in Spicewood, Texas, Abracon is a leading global manufacturer of passive and electromechanical timing, synchronization, power, connectivity and RF solutions. Abracon offers a wide selection of quartz timing crystals and oscillators, MEMS oscillators, real time clocks (RTC), Bluetooth modules, ceramic resonators, SAW filters and resonators, power and RF inductors, transformers, circuit protection components and RF antennas and wireless charging coils. The company is ISO9001-2015 certified with design & application engineering resources in Texas and sales offices in Texas, California, China, Taiwan, Singapore, Scotland, Israel, Hungary, UK, and Germany. Abracon’s products are offered through its global distribution network. For more information about Abracon, visit www.abracon.com.