There are some things that you think you know quite well because you learned them in your youth and you understand their principles of operation. Then along comes a link in your morning feed that reminds you of the limits of your knowledge, and you realize that there is a whole new level of understanding to be reached.
You learn how they work, you use them for frequency synthesis, and you know they can do other things like recover noisy clock lines and do FM demodulation. We can easily look at different PLLs with varying parameters, for example their use with a narrowband loop filter to retrieve signals buried in the noise, all through some straightforward code tweaks rather than extensive circuitry. And here I though math made designing the hardware possible, including the hardware necessary to construct SDR equipment.
Software facilitating the marriage of RF hardware and computer hardware. Shit that was started shortly after relatively inexpensive computers made it to the benches of amateur radio operators, and has been maturing ever since. What I'm trying to do is to sample a sinewave and then produce another sinewave which is in-phase with the sampled sinewave.
The sinewave which is going to be produced as the output is already stored in an array and the output from the PLL is produced by shifting the array stored sinewave according to the sampled sinewave. Can anyone help me with some code examples, please? Super Member. I would measure the time between zero crossings at the input and run a timer fast enough to scan all array data in that time. Change the timer overflow interrupt rate as necessary. Even though the pull-in process itself is relatively slow, the PLL will always become locked for an offset within this range.
The lock range is much smaller than the pull-in range; however on the up side, the lock-in process itself is much faster than the pull-in process. Remember that the lock actually implies that for each cycle of the input, there is one and only one cycle of NCO output. Even with a phase lock, both steady phase errors and fluctuating phase errors can be present. In practical applications, the operating frequency range of a PLL is normally restricted to the lock range.
In summary, the hold range and the lock range are the largest and the smallest, respectively, while the pull-in range lies somewhere within the boundaries set by them. Thus, the following inequality holds. Next, we describe two other important quantities which determine the suitability of a PLL for an application. The acquisition time is given by the sum of the time to achieve frequency lock as well as that of the phase lock.
For a PLL in tracking mode i. It makes sense that a wider bandwidth allows a larger amount of noise at the PLL output, thus increasing the tracking error. In conclusion, a good PLL design balances the opposite criteria of fast acquisition time and reduced tracking error.
In the world of hardware radio, PLL designers had to balance these two performance criteria by finding an acceptable compromise. The realm of software radio offers a better solution due to our ability to change the code on the fly which is explained below.
In parallel, a certain algorithm known as a lock detector is run which generates a binary output depending on whether the PLL has acquired lock or not. In other articles, we discuss carrier and timing synchronization procedures in a communications receiver.
These blocks incorporate a PLL as an integral component. We also introduce some of the issues faced during a practical implementation. Most others threw giant equations at me in the 2nd sentence that made me feel like I was sleeping in EE academic lectures.
My application for SPLL is a very low frequency input signal with a lot of amplitude variation. Alternatively would it be practical for K values to be tweaked in realtime in response to changes in my input signal amplitude? Both options, an AGC or varying loop filter coefficients, can be implemented. However, if the signal amplitude variations are fast enough to impact the PLL performance, the AGC option is preferred as compared to tweaking K values.
I have a question regarding the basic operation of a CDR. Is this right? A large loop bandwidth allows high noise power to enter the system and affect the loop performance. The best way is to start with a large loop bandwidth but reduce it step by step while passing through acquisition to tracking mode. Thank you for your reply! There are different types of PLLs in a radio system e. Basically I need to generate a new sinusoid the output that has the exact same phase and frequency as the input.
Sounds simple enough, right? The difficulty is knowing precisely how to execute step 2 to get the output to converge and not blow up that's where all that math from the previous post came in. There's a simple trick to you can use to get really good performance:. From the results we can make a few observations:.
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