Clock (Frequency) Synthesizer IP Core

June 17, 2020, anysilicon

A clock synthesizer IP core, also referred to as a frequency synthesizer IP core, is essentially an electronic circuit that is responsible for generating frequencies using a single reference frequency. This means that with the help of a clock synthesizer, an IC design can produce a number of varying output frequencies while only using a single frequency as the reference.


There are a plethora of techniques that can be employed to generate the frequencies, including the likes of frequency multiplication, division, mixing, and even direct digital synthesis. But one of the most commonly employed techniques is the phase locked loop or PLL.


In a phase locked loop, the reference frequency is compared with the feedback frequency by a component known as the phase or frequency detector. The output of this detector is in the form of current pulses which are subsequently integrated and filtered to produce a resultant voltage or signal. The job of this signal is to prompt the voltage controlled oscillator to modify its output frequency to make the average output of the phase detector zero, i.e. keep the phase constant.


The output frequency is fed back into the input section through a frequency divider. This divider is usually a digital counter which is set to a certain value initially and it counts down at each cycle of the clock signal. The original value is reloaded once the counter reaches zero and the state of the output changes. Thus, the job of this negative feedback loop is to keep the output locked to the frequency of the input on the other end which is the reference.


The performance of the clock signal also varies based on multiple parameters. The amount of jitter in the clock signal typically is a good indicator of its quality, and the jitter is controlled by the timing uncertainty. This electric noise can be produced easily in electronic circuits and increases the chances of error and uncertainty in the signal.


Clock and frequency synthesizer IP cores have become extremely critical components of ASICs/ICs as they are able to produce very clean and precise frequencies spanning across a wide range from just a single input signal. The modern applications of click synthesizers are wide and varied. You will find frequency synthesizers IP cores to be frequently used in IC devices such as CPUs, communications ICs, networking ICs and more.


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