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In electronics, a delay-locked loop (DLL) is a pseudo- digital circuit similar to a phase-locked loop (PLL), with the main difference being the absence of an internal voltage-controlled oscillator, replaced by a delay line.
A DLL can be used to change the phase of a clock signal (a signal with a periodic 
Another way to view the difference between a DLL and a PLL is that a DLL uses a variable phase (=delay) block, whereas a PLL uses a variable frequency block.
A DLL compares the phase of its last output with the input clock to generate an error signal which is then integrated and fed back as the control to all of the delay elements.
The integration allows the error to go to zero while keeping the control signal, and thus the delays, where they need to be for phase lock. Since the control signal directly impacts the phase this is all that is required.
A PLL compares the phase of its oscillator with the incoming signal to generate an error signal which is then integrated to create a control signal for the voltage-controlled oscillator. The control signal impacts the oscillator's frequency, and phase is the integral of frequency, so a second integration is unavoidably performed by the oscillator itself.
In the Control Systems jargon, the DLL is a loop one step lower in order and in type with respect to the PLL, because it lacks the 1/
In electronics, a delay-locked loop (DLL) is a pseudo- digital circuit similar to a phase-locked loop (PLL), with the main difference being the absence of an internal voltage-controlled oscillator, replaced by a delay line.
A DLL can be used to change the phase of a clock signal (a signal with a periodic waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time.David Crecraft, David Gorham, ''Electron ...
), usually to enhance the ''clock rise''-to-''data output valid'' timing characteristics of integrated circuits (such as DRAM devices). DLLs can also be used for clock recovery (CDR). From the outside, a DLL can be seen as a negative delay gate placed in the clock path of a digital circuit.
The main component of a DLL is a delay chain composed of many delay gates connected output-to-input. The input of the chain (and thus of the DLL) is connected to the clock that is to be negatively delayed. A multiplexer is connected to each stage of the delay chain; a control circuit automatically updates the selector of this multiplexer to produce the negative delay effect. The output of the DLL is the resulting, negatively delayed clock signal.
Another way to view the difference between a DLL and a PLL is that a DLL uses a variable phase (=delay) block, whereas a PLL uses a variable frequency block.
A DLL compares the phase of its last output with the input clock to generate an error signal which is then integrated and fed back as the control to all of the delay elements.
The integration allows the error to go to zero while keeping the control signal, and thus the delays, where they need to be for phase lock. Since the control signal directly impacts the phase this is all that is required.
A PLL compares the phase of its oscillator with the incoming signal to generate an error signal which is then integrated to create a control signal for the voltage-controlled oscillator. The control signal impacts the oscillator's frequency, and phase is the integral of frequency, so a second integration is unavoidably performed by the oscillator itself.
In the Control Systems jargon, the DLL is a loop one step lower in order and in type with respect to the PLL, because it lacks the 1/