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MC13110A Datasheet(PDF) 26 Page - Motorola, Inc |
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MC13110A Datasheet(HTML) 26 Page - Motorola, Inc |
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26 / 68 page  MC13110A/B MC13111A/B 26 MOTOROLA ANALOG IC DEVICE DATA Second Local Oscillator The 2nd LO is a CMOS oscillator. It is used as the PLL reference oscillator and local oscillator for the second frequency conversion in the RF receiver. It is designed to utilize an external parallel resonant crystal. See schematic in Figure 39. Figure 39. Second Local Oscillator Schematic 2nd LO RPI CPI RPO CPO Gm LO2 In LO2 Out Xtal C2 C1 Figure 40. Second Local Oscillator Input and Output Impedance Input Impedance (RPI // CPI) 11.6 k Ω // 2.9 pF Output Impedance (RPO // CPO) 9.6 k Ω // 2.7 pF Figure 41 shows a typical gain/phase response of the second local oscillator. Load capacitance (CL), equivalent series resistance (ESR), and even supply voltage will have and affect on the 2nd LO response as shown in Figures 45 and 46. Except for the standby mode open loop gain is fairly constant as supply voltage increases from 2.5 V. This is due to the regulated voltage of 2.5 V on PLL Vref. From the graphs it can seen that optimum performance is achieved when C1 equals C2 (C1/C2 = 1). Figure 46 represents the ESR versus crystal load capacitance for the 2nd LO. This relationship was defined by using a 6.0 dB minimum loop gain margin at 3.6 V. This is considered the minimum gain margin to guarantee oscillator start–up. Oscillator start–up is also significantly affected by the crystal load capacitance selection. In Figures 42 and 43 the relationship between crystal load capacitance, supply voltage, and external load capacitance ratio (C2/C1), can be seen. The lower the load capacitance the better the performance. Given the desired crystal load capacitance, C1 and C2 can be determined from Figure 47. It is also interesting to point out that current consumption increases when C1 ≠ C2, as shown in Figure 44. Be careful not to overdrive the crystal. This could cause a noise problem. An external series resistor on the crystal output can be added to reduce the drive level, if necessary. 0 6.0 10.235 15 CAPACITOR RATIO (C2:C1) Figure 41. Second LO Gain/Phase @ –10 dBm f, FREQUENCY (MHz) Figure 42. Start–Up Time versus Capacitor Ratio, Inactive to Rx Mode Gain 10.24 MHz Crystal CL = 10 pF RS = 20 Ω VCC = 5.0 V VCC = 3.6 V VCC = 2.3 V VCC = 2.7 V 10 5.0 0 –5.0 –10 –15 –20 –25 5.0 4.0 3.0 2.0 1.0 0 10.24 10.245 Phase 90 67.5 45 22.5 0 –22.5 –45 –67.5 –90 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 10.24 MHz Crystal CL = 10 pF RS = 20 Ω C1 = C2 = 15 pF SECOND LOCAL OSCILLATOR |
Similar Part No. - MC13110A |
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Similar Description - MC13110A |
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