11
SNAU219B – June 2017 – Revised March 2020
Copyright © 2017–2020, Texas Instruments Incorporated
Changing Reference Oscillator and Setup
Appendix D
SNAU219B – June 2017 – Revised March 2020
Changing Reference Oscillator and Setup
The reference can be single-ended or differential. To measure the performance of the PLL ONLY,
the reference must have at least this level of performance. We understand that this can be a
challenge at 100-Hz offset:
(1)
A noise source 10 dB down from the PLL noise will contribute to raise the noise by 0.4 dB.
Table 4. Reference Oscillator Requirements
100-MHz REFERENCE MINIMUM REQUIREMENTS FOR A 0.4-dB IMPACT ON PLL INBAND PN
(1)
Offset [Hz]
100
1k
10k
100k
Noise level [dBc/Hz]
–139
–149
–159
–164
There are different options to provide a reference oscillator to LMX2595. Use onboard oscillator, enable
LMK61xx from Reference Pro PCB, or use external oscillator. By default, the EVM is configured for an
external single-ended clock.
Table 5. Reference Clock Input Configuration
INPUT
EXTERNAL CLOCK
CRYSTAL OSCILLATOR
Single-
ended
Differential
(LVDS)
