What is a Phase Detector?
A phase detector provides information on the phase difference between different signals. In many common applications in the telecommunications market, a phase detector is incorporated into a receiver side clock and data recovery (CDR) unit. In these cases, the phase detector is utilizes to determine the phase different between the incoming data signal and the sampling clock signal. Linear phase detectors find themselves in test laboratory equipment and telecommunications products.
What does a Phase Detector do?
To ensure a low bit error rate (BER), it is best to sample the data right in the middle of the bit with the clock. A linear phase detector will provide an error signal that is equal to the amount of distance the clock signal is from the center of the data bit. The further away the clock’s sampling edge is away from the center of the bit, the larger the error signal is. This error signal is then processed by the clocking circuitry that usually includes a voltage controlled oscillator (VCO). The VCO’s frequency is either sped up (push the sampling edge earlier in the bit) or slowed down (push the sampling edge later in the bit) briefly to adjust to phase of the sampling clock correctly to minimize the error signal from the phase detector. Without a phase detector, there is no easy way to center a clock signal in the middle of a data bit.
What are some applications of Phase Detectors?
Another common application of a phase detector is in a phase locked loop (PLL). The purpose of a PLL is to phase and frequency lock a local VCO to an incoming or reference clock signal. Similar to a CDR, the PLL uses a phase detector to measure the phase difference between the local clock and the reference clock signal. Any difference results in an error signal that is then fed back to the VCO so it can make the proper adjustments. Delay locked loops (DLLs) also leverage the advantages of phase detectors.
A few examples of ADSANTEC’s Phase Detectors:
ADSANTEC currently supports two linear phase detector IC products. Both are meant to measure the phase difference between input clock and data. For both ICs, the data input contains equalization capabilities while the clock input has a frequency doubling feature. Not only do both phase detectors determine the phase difference between both input data and clock signals, but they also have edge detection capabilities. The ASNT8120-KMC works up to 28.6Gb/s while the ASNT8121-KMC can operate to data rates up to 34Gb/s.