Equation 7 shows the complete loop transfer function for the lock condition. Equation 6 gives the basic loop transfer function. Schematic of charge pump and loop filter.Ĭomplete Phase-Lock Loop (PLL) Figure 4 illustrates a complete phase-lock loop comprising phase detector, charge pump, loop filter, VCO and feedback frequency divider (if required). Equations 4 and 5 give the transfer function of the charge pump filter and filter network impedance.įigure 3.
#Battery pulse charging with pll series
At the lock condition the phase detector presents a series of equal, minimum duration, pulses on both inputs to the charge pump. Phase differences at the phase detector input produce dissimilar pulse widths on the phase detector "up" and "down" outputs, causing the loop filter voltage to pump up or down as directed. This arrangement uses a matched current source and sink together with switches, which direct the currents into and out of the loop filter. Ideal response of the MAX9382 phase/frequency detector.Ī typical charge pump and passive loop filter arrangement is shown in Figure 3. The MAX9382 phase/frequency detector.įigure 2. Equations 1, 2 and 3 show the phase/frequency detector transfer functions when the input frequencies are equal (loop lock condition) and when the inputs are at different frequencies (loop-out-of-lock).įigure 1. Figure 2 shows the average (DC) value of the MAX9382 outputs as a function of input phase difference. This behavior greatly improves the loop ability to lock to out-of-band signals. When the two inputs are at dissimilar frequencies, the MAX9382 acts as a frequency detector with the time averaged value of the outputs being a function of the input frequency difference. These outputs are the "up" and "down" signals required to control the loop filter charge pump.
The MAX9382 converts the input phase difference into a series of variable width pulses on two outputs. One of the key parameters of the MAX9382 is a guaranteed minimum short pulse duration that eliminates the dead-band behavior often associated with charge pump-based loop filter designs.
The MAX9382 is a phase/frequency detector that has been designed specifically for use with charge pump-based loop filters. A popular implementation of these phase-locked loops is one that uses charge pump based loop filter designs. Phase-locked loops are used extensively within the telecommunications industry for frequency multiplication, data extraction and re-timing purposes.
0 kommentar(er)
