 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LMK61E0M-SIAR Datasheet(PDF) 11 Page - Texas Instruments |
|
|
||||||||||||||||||||||||||||||
LMK61E0M-SIAR Datasheet(HTML) 11 Page - Texas Instruments |
|
|
11 / 47 page  11 LMK61E0M www.ti.com SNAS692 – JANUARY 2017 Product Folder Links: LMK61E0M Submit Documentation Feedback Copyright © 2017, Texas Instruments Incorporated Feature Description (continued) 8.3.5 Integrated Oscillator The integrated oscillator in LMK61E0 features programmable load capacitances that can be set for the device to either operate at exactly its nominal oscillation frequency or operate at a fixed frequency offset from its nominal oscillation frequency. This is done by programming R16 and R17. More details on frequency margining are provided in Fine Frequency Margining. 8.3.6 Reference Divider and Doubler The reference path has a divider and frequency doubler. The reference divider can be bypassed by programming R24[0] = 0 or can be set to divide-by-4 by programming R24[0] = 1. Enabling the divider results in a lower comparison frequency for the PLL and would result in a 6 dB increase in the in-band phase noise at the output of the LMK61E0 but would result in a finer frequency resolution at the output for every bit change in the numerator of fractional feedback divider. The reference doubler can be enabled by programming R34[5] = 1. Bypassing the divider allows for a higher comparison rate and improved in-band phase noise at the output of the LMK61E0. Enabling the doubler allows a higher comparison frequency for the PLL and would result in a 3 dB reduction in the in-band phase noise at the output of the LMK61E0. Enabling the doubler also results in higher reference and phase detector spurs which will be minimized by enabling the higher order components (R3, C3) of the loop filter and programming them to appropriate values. Disabling the doubler would result in a finer frequency resolution at the output for every bit change in the numerator of the fractional feedback divider and higher in-band phase noise on the device output than when the doubler is enabled. However, the reference and phase detector spurs would be lower on the device output than when the doubler is enabled. 8.3.7 Phase Frequency Detector The Phase Frequency Detector (PFD) of the PLL takes inputs from the reference path and the feedback divider output and produces an output that is dependent on the phase and frequency difference between the two inputs. The input frequency of the PFD is equal to the 50 MHz reference frequency doubled if the reference doubler is enabled and then divided by 4 if the reference divider is enabled. The feedback frequency to the PFD must equal the reference path frequency to the PFD for the PLL to lock. 8.3.8 Feedback Divider (N) The N divider of the PLL includes fractional compensation and can achieve any fractional denominator (DEN) from 1 to 4,194,303. The integer portion, INT (valid range 1-4095), is the whole part of the N divider value and the fractional portion, NUM / DEN, is the remaining fraction. INT, NUM, and DEN are programmed in R25/R26, R27/R28/R29, and R30/R31/R32, respectively. The total programmed N divider value, N, is determined by: N = INT + NUM / DEN. The output of the N divider sets the PFD frequency to the PLL. The feedback frequency to the PFD must equal the reference path frequency to the PFD for the PLL to lock. In DCXO mode, the NUM registers can be re-programmed MSB first and LSB last to update the output frequency without glitches or spikes. 8.3.9 Fractional Engine The delta signal modulator is a key component of the fractional engine and is involved in noise shaping for better phase noise and spurs in the band of interest. The order of the delta sigma modulator is selectable between integer mode and third order, for fractional PLL mode, and can be programmed in R33[1:0]. Dithering can be programmed in R33[3:2] and should be disabled for integer PLL mode and set to weak for fractional PLL mode. 8.3.10 Charge Pump The PLL has charge pump slices of 1.6 mA, to be used when PLL is set to fractional mode, or 6.4 mA, to be used when PLL is set to integer mode. These slices can be selected by programming R34[3:0]. When PLL is set to fractional mode, a phase shift needs to be introduced to maintain a linear response and ensure consistent performance across operating conditions and a value of 0x2 should be programmed in R35[6:4]. When PLL is set to integer mode, a value of 0x0 should be programmed in R35[6:4]. |
Similar Part No. - LMK61E0M-SIAR |
|
Similar Description - LMK61E0M-SIAR |
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
