SBAA661 February   2025 LMX1205

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Flicker Noise, Noise Floor, and Total Noise
    1. 1.1 Flicker Noise
    2. 1.2 Noise Floor
    3. 1.3 Total Noise
  5. 2Finding the Slew Rate
    1. 2.1 Finding the Slew Rate With an Oscilloscope
    2. 2.2 Calculating the Slew Rate From Power and Frequency
  6. 3Impact of Slew Rate on Phase Noise
    1. 3.1 Modeling of Input Clock Slew Rate, Inherent Device Noise, and Output Jitter
    2. 3.2 Slew Rate Impact on Flicker Noise and Noise Floor
  7. 4Application of Slew Rate Rules to PLL Synthesizers
    1. 4.1 PLL Flicker Noise
    2. 4.2 PLL Figure of Merit
    3. 4.3 Other Areas in PLLs Where Slew Rate has an Impact on Performance
    4. 4.4 Improving PLL Slew Rate for Better Performance
  8. 5Application of Slew Rate Rules to Data Converters
  9. 6Summary
  10. 7References
  11.   Appendix A: Relating Slew Rate, Power, and Frequency
  12.   Appendix B: Relating Slew Rate, Frequency, Jitter, and Phase Noise
  13.   Appendix C: Equations for Data Converters
    1. 8.1 Relating Sampled Signal Slew Rate to SNR
    2. 8.2 Justification That SNR Decreases 1dB per 1dB With Input Power for Slew Rate Limited Case
  14.   Appendix D: Calculations for Data Converter Example

3.1 Modeling of Input Clock Slew Rate, Inherent Device Noise, and Output Jitter

Understanding the impact of slew rate on phase noise starts with modeling this on a simple buffer as shown in Figure 3-1. This understanding can then be expanded to understand the impact of input clock slew rate for PLLs, data converters, and clock buffers because they all contain an input buffer. The noise modeling starts with the assumption that the input clock has no noise and has some known slew rate. The inherent device noise can be modeled as an rms voltage that adds to the input clock to create an internal resultant signal. The signal then goes through a comparator that squares it up to produce the output signal.

Modeling Impact of Slew Rate on Output Jitter Figure 3-1 Modeling Impact of Slew Rate on Output Jitter