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MC10E197 Fiches technique(PDF) 5 Page - ON Semiconductor |
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MC10E197 Fiches technique(HTML) 5 Page - ON Semiconductor |
5 / 16 page MC10E197 2–5 MOTOROLA ECLinPS and ECLinPS Lite DL140 — Rev 4 Idle Mode In the absence of data or when the drive is writing to the disk, PLL servoing is accomplished by pulling the read enable line (RDEN) low and providing a reference clock via the REFCLK pins. The condition whereby RDEN is low selects the Phase/Frequency detector (Figure 1) and the 10E197 is said to be operating in the “idle mode”. In order to function as a frequency detector the input waveform must be periodic. The pump up and pump down pulses from the Phase/Frequency detector will have the same frequency, phase and pulse width only when the two clocks that are being compared have their positive edges aligned and are of the same frequency. As with the data phase detector, by using suitable external filter circuitry, a VCO input control signal can be generated by inverting the pump down signal, summing the inverted signal with the pump up signal and averaging the result. The polarity of this control signal is defined as zero when all positive edges of both clocks are coincident. For the case in which the frequencies of the two clocks are the same but the clock edges of the reference clock are slightly advanced with respect to the VCO clock, the control clock is defined to have a positive polarity. A control signal with negative polarity occurs when the edges of the reference clock are delayed with respect to those of the VCO. If the frequencies of the two clocks are different, the clock with the most edges per unit time will initiate the most pulses and the polarity of the detector will reflect the frequency error. Thus, when the reference clock is high in frequency than the VCO clock the polarity of the control signal is positive; whereas a control signal with negative polarity occurs when the frequency of the reference clock is lower than the VCO clock. Phase-Lock Loop Theory Introduction Phase lock loop (PLL) circuits are fundamentally feedback systems used to synchronize the frequency of an oscillator to an incoming signal. In addition to frequency synchronization, the PLL circuitry is designed to minimize the phase difference between the system input and output signals. A block diagram of a feedback control system is shown in Figure 1. where: A(s) is the product of the feed-forward transfer functions. Figure 1. Feedback System Xi(s) Xo(s) A(s) β(s) + – Xe(s) R β(s) is the product of the feedback transfer functions. The transfer function for this closed loop system is Xo(s) Xi(s) = A(s) 1 + A(s) β(s) Typically, phase lock loops are modeled as feedback systems connected in a unity feedback configuration ( β(s)=1) with a phase detector, a VCO (voltage controlled oscillator), and a loop filter in the feed-forward path, A(s). Figure 2 illustrates a phase lock loop as a feedback control system in block diagram form. LOOP FILTER F(s) Fi Fo PHASE DETECTOR Kf VCO Ko s Figure 2. Phase Lock Loop Block Diagram The closed loop transfer function is: Xo(s) Xi(s) = K φ Ko s F(s) Ko s 1 + K φ F(s) where: K φ= the phase detector gain. Ko= the VCO gain. Since the VCO introduces a pole at the origin of the s-plane, Ko is divided by s. F(s) = the transfer function of the loop filter. The 10E197 is designed to implement the phase detector and VCO functions in a unity feedback loop, while allowing the user to select the desired filter function. Gain Constants As mentioned, each of the three sections in the phase lock loop block diagram has an associated open loop gain constant. Further, the gain constant of the filter circuitry is composed of the product of three gain constants, one for each filter subsection. The open loop gain constant of the feed-forward path is given by Kol = K φ * Ko * K1 * Kl * Kd eqt. 1 and obtained by performing a root locus analysis. Phase Detector Gain Constant The gain of the phase detector is a function of the operating mode and the data pattern. The 10E197 provides data |
Numéro de pièce similaire - MC10E197 |
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Description similaire - MC10E197 |
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