Contents
What is the purpose of the loop filter in a PLL?
The loop filter removes the unwanted high-frequency components of the error signals. The output of the loop filter (vlf (t) in Figure 23-11) is used to control the output frequency of the VCO and serves as the demodulated output of the PLL FM detector.
What is a digital loop filter?
Abstract: Modern digital telecommunication and audio systems include a Digital Phase Locked Loop (D-PLL) in a form of a device or an algorithm. Wireless infrastructure, broadband wire-line networks and high end audio systems require very high performance PLLs.
How do loop filters work?
The loop filter acts to slow the response down. The narrower the loop bandwidth, i.e. the lower the cut-off frequency of the filter, the slower the response of the loop to responding to changes.
What is a digital phase locked loop?
A phase-locked loop (PLL) is an electronic circuit that controls an oscillator so that it maintains a constant phase angle relative to a reference signal. In communications, the oscillator is usually at the receiver, and the reference signal is extracted from the signal received from the remote transmitter.
Which filter is used in VCO?
passive low pass loop filter
The passive low pass loop filter is used to convert back the charge pump current into the voltage. The output voltage of the loop filter controls the oscillation frequency of the VCO.
What are the applications of phase locked loop?
Applications. Phase-locked loops are widely used for synchronization purposes; in space communications for coherent demodulation and threshold extension, bit synchronization, and symbol synchronization. Phase-locked loops can also be used to demodulate frequency-modulated signals.
What are the characteristics of an ADPLL implementation?
The ADPLL implemented in this work has the characteristics of design flexibility, a wide range of working frequency from 120 MHz to 300 MHz, and a fast response for achieving a locked state. The proposed ADPLL can be easily ported to different processes in a short time.
How are TDC and DCO implemented in adplls?
In typical ADPLLs, a time-to-digital converter (TDC), a digital loop filter, and a DCO replace the PFD, the analog loop filter, the VCO, respectively. Although the TDC can be implemented on FPGA [ 17 ], non-linearity due to signal distribution must be calibrated to an extent, resulting in design complexity.
What kind of filter does a charge pump PLL use?
Conventional charge-pump PLLs have a phase-frequency detector (PFD), charge pump, an analog loop filter, and a VCO. In typical ADPLLs, a time-to-digital converter (TDC), a digital loop filter, and a DCO replace the PFD, the analog loop filter, the VCO, respectively.
How are phase locked loops used in emulation?
This paper demonstrates the design and implementation of an all-digital phase-locked loop (ADPLL) on Field Programmable Gate Array (FPGA). It is useful as an emulation technique to show the feasibility and effectiveness of the ADPLL in the early design stage.