SNAA411 September   2024 CDCLVC1102 , CDCLVC1103 , CDCLVC1104 , CDCLVC1110 , CDCLVD1204 , LMK00301 , LMK00304 , LMK00306 , LMK00308 , LMK01801 , LMK04832 , LMK1C1102 , LMK1C1103 , LMK1C1104 , LMK1C1106 , LMK1C1108 , LMK1D1204 , LMK1D1208 , LMX2485 , LMX2491 , LMX2572 , LMX2592 , LMX2594 , LMX2595 , LMX2820

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Generic Clock Tree
  5. 2Sine Wave Slew Rate Requirement
  6. 3Current Approach vs Clock Buffer
  7. 4Clock Buffer Implementation
    1. 4.1 Clock Buffer Common Input Stages
    2. 4.2 Choosing Between Internal or External DC Bias
    3. 4.3 Single Ended or LVCMOS Signal
    4. 4.4 Differential Inputs
  8. 5Performance Improvements, Results With Clock Buffer
    1. 5.1 FSWP Phase Noise Analyzer Measurements Case
    2. 5.2 TI LMX2820 Noise Improvements With Sine to Square Wave Clock Buffer
      1. 5.2.1 LMX2820 Phase Noise and RMS Jitter Results Summary
  9. 6Sine to Square Wave Clock Buffer Comparison
    1. 6.1 LMK1C110x Additive Noise vs Others
  10. 7Summary
  11. 8References

6 Sine to Square Wave Clock Buffer Comparison

Since our previous findings shows that low noise clock buffers can help improve the phase noise performance when doing the sine to square conversion. In this section, we provide a comparison of different clock buffers from TI and other vendors to use as a reference for sine to square conversion.

We used 10MHz sine wave input at 10dBm input power level for all the buffers under the same conditions. LMK1C110x shows the lowest total phase noise among all the buffers in the comparison. Table 6-1 provides additive phase noise numbers when using the direct sine wave input to each buffer as this is the main use case in actual systems when sine to square wave conversion is needed.

Since the equipment can suffer from slew rate issues described in FSWP Phase Noise Analyzer Measurements Case, cascaded configuration is used for actual additive phase noise modeling of LMK1C110x and other devices in the later sections.

Sine to Square Wave Buffer Comparison Figure 6-1 Sine to Square Wave Buffer Comparison
Table 6-1 Additive Jitter Comparison with Sine Wave 10MHz, 10dBm
Parameter LMK1C110x CDCLVP120x COMP.LVCMOS COMP.LVDS Unit
Source RMS Jitter (10Hz - 1MHz) 117.084 117.084 117.084 117.084 fs
Total RMS Jitter (10Hz - 1MHz) 150.321 457.152 210.055 271.11
Additive RMS Jitter (10Hz - 1MHz) 94.274 441.904 174.397 244.524
Source RMS Jitter (10Hz - 1MHz) 107.832 107.832 107.832 107.832
Total RMS Jitter (12kHz - 1MHz) 145.478 452.119 204.935 266.091
Additive RMS Jitter (12kHz - 1MHz) 97.653 439.071 174.271 243.263