Difference Between DLL and PLL

DLL and PLL ate terms used in electronics. DLL and PLL are types of output signal loops, that we use widely in integrated circuits of electronic gadgets.


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Any gadget that needs a time loop circuit to make it automated or to make efficient uses output signal loops. Both are output signal loops but there are many key differences between the two loops.


The difference between DLL and PLL is that DLL does not have a voltage-controlled oscillator while PLL has. Instead, DLL has a delay line and it can self-regulate its delay line. Also, DLL is preferred over PLL as DLL is less subjected to errors as compared to PLL.


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DLL stands for Delay locked loop. It is a digital circuit that is mostly used in technical gadgets. It is used to change the phase of a clock signal. enhance the output timing of ICs.

It gives periodic waveform consistently, and can be programmed or designed to become fully digital because it can give constant delays or loops every time.

PLL stands for Phase-locked loop. It is a high order system that is widely used in electronic appliances like television and radio, etc. The PLL system generates an output signal and the phase of this output signal is related to the phase of the input signal.

Comparison Table

Parameters of ComparisonDLLPLL
Stands forIt stands for Delay locked loop.It stands for Phase-locked loop.
AccumulationThere is no jitter accumulation.There is jitter accumulation.
Order systemDLL is a first-order system.PLL is of high order system. Most PLLs are of second order.
IntegrationIt is easy to integrate LF in DLL.It is costly and harder to integrate LF in PLL.
StabilityDLL is always stable.PLL can become unstable sometimes.

What is DLL?

Delay locked loop is the full form of DLL, which is a digital circuit. DLL has a voltage-controlled delay line and it can self-regulate the line.

The main component of a DLL is the delay chain which is composed of delay gates that are connected from output to input.

DLL is connected with the clock along with the input of the chain, and the clock is to be negatively delayed. It is like a negative-delay gate placed in the clock path in a digital circuit.

The delay chain at its every stage is connected with a multiplexer. A control circuit updates the selector of the multiplexer automatically.

And it produces the negative delay effect. The DLL gives the negatively delayed clock signal as the output. It also gives a periodic waveform.

DLL uses a variable phase block and it is of the first-order system. A DLL compares the phase of the last output with the input clock and generates an error signal.

Then the integration takes place of this signal and is fed back as the control to all of the delay elements.

DLL is preferred over PLL as it is less likely to show errors and is more stable.

What is PLL?

PLL is short-termed for a phase-locked loop. It is a control system used in integrated circuits. It generates an output signal and the phase of this output signal is related to the phase of the input signal.

The main component in the PLL is a voltage-controlled oscillator (VCO). It consists of a phase detector in a feedback loop as well. PLL uses a variable frequency block.

The oscillator generates a periodic signal that is adjusted to keep the phase of the output and input signal matched. PLL uses a variable frequency block.

It compares the phase of its oscillator with the incoming signal and generates an error signal. This error signal is then integrated and creates a control signal for the VCO.

PLL contains delay elements that are based on a slow clock buffer. The advantage of PLL is that since it is a negative feedback action and gives a frequency if the clock buffer’s evenly matched, the negative feedback action and the reference clock match.

PLL is of high order system, most PLLs are of second order. They are harder to design as compared to DLL and can also become unstable sometimes. PLLs are widely used in electronic gadgets like radio, etc.

Main Differences Between DLL And PLL

  1. The main difference is the name of both the circuits which suggests there are differences between the two terms. DLL is short-termed for Delay Locked Loop. And PLL stands for Phase-Locked Loop.
  2. In DLL, there is no internal voltage-controlled oscillator while PLL has the Voltage-controlled oscillator. Instead, DLL has a delay line.
  3. DLL uses a variable phase block. On the other hand, PLL uses a variable frequency block.
  4. DLL is a first-order, type 1 loop while PLL is a second-order, type 2 loop.
  5. DLL needs a reference clock while PLL does not need it, instead, it generates it.
  6. DLL is preferred over PLL cause it is less likely to have any errors as compared to PLL.
  7. DLL is easier to design than PLL.
  1. https://ieeexplore.ieee.org/abstract/document/641688/
  2. https://ieeexplore.ieee.org/abstract/document/1216154/
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