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7B991RPFI Datasheet(PDF) 8 Page - Maxwell Technologies |
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7B991RPFI Datasheet(HTML) 8 Page - Maxwell Technologies |
8 / 17 page 8 All data sheets are subject to change without notice ©2002 Maxwell Technologies. All rights reserved. Programmable Skew Clock Buffer (PSCB) 7B991 09.23.02 Rev 4 BLOCK DIAGRAM DESCRIPTION Phase Frequency Detector and Filter These two blocks accept inputs from the reference frequency (REF) input and the feedback (FB) input and generate correction information to control the frequency of the Voltage-Controlled Oscillator (VCO). These blocks, along with the VCO, form a Phase-Locked Loop (PLL) that tracks the incoming REF signal. VCO and Time Unit Generator The VCO accepts analog control inputs from the PLL filter block and generates a frequency that is used by the time unit generator to create discrete time units that are selected in the skew select matrix. The operational range of the VCO is determined by the FS control pin. The time unit (t U) is determined by the operating frequency of the device and the level of the FS pin as shown in Table 1. Skew Select Matrix The skew select matrix is comprised of four independent sections. Each section has two low-skew, high-fanout driv- ers(xQ0, xQ1), and two corresponding three-level function select (xF0, xF1) inputs. Table 9 below shows the nine pos- sible output functions for each section as determined by the function select inputs. All times are measured with respect to the REF input assuming that the output connected to the FB input has 0t U selected. TABLE 8. 7B991 FREQUENCY RANGE SELECT AND t U CALCULATION 1 1. For all three state inputs. HIGH indicates a connection to V CC. LOW indicates a connection to GND, and MID indicates an open connection. Internal termination circuitry holds an unconnected input to V CC/2. FS 2,3 2. The level to be set of FS is determined by the “normal” operating frequency (f NOM) of the VCO and Time Unit Generator (see Logic Block Diagram). Nominal frequency (f NOM) always appears at 1Q0 and the other outputs when they are operated in their undivided modes (See Table 9). The frequency appearing at the REF and FB inputs will be f NOM when the output connected to FB is undivided. The frequency appearing at the REF and FB inputs will be f NOM/2 or fNOM/4 when the part is configured for a frequency multiplication by using a divided output as the FB input. 3. When the FS pin is selected HIGH, the REF input must not transition upon power-up until V CC has reached 4.3V. fNOM (MHZ)t U = 1/fNOM X N WHERE N = APPROXIMATE FREQUENCY (MHZ) AT WHICH t U = 1.0 ns MIN MAX LOW 15 30 44 22.7 MID 25 50 26 38.5 HIGH 40 80 16 62.5 |
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