LMX2595: Input Reference Power

Scott Berger

Part Number: LMX2595
Other Parts Discussed in Thread: LMX2592

What is the recommend input power for the input reference signal (Oscin) for double and single-ended input signal? Assume the 50 ohm input configuration shown in Figure 32 of the datasheet.

over 4 years ago

0 Derek Payne over 4 years ago

TI__Mastermind 34510 points

Hi Scott,

We recommend no more than 2Vpp at the pin (10dBm single-ended, 13dBm differential). However, it depends on what kind of OSCin signal you have. The 10dBm single-ended / 13dBm differential number is for sine-wave input. Sine wave input slew rate scales as a function of input amplitude, so actually the best case for sine wave input is the maximum input power, always. For our own validation we use a 16dBm Wenzel sine-wave OCXO into a 3dB attenuator and a balun. On the other hand, if you have a high slew rate signal like LVDS, LVPECL, or CML at the reference input, the input power becomes less important. Between a 200mVpp signal and a 2Vpp signal with the same slew rate, there is not much difference in noise performance unless there is some concern about noise immunity or amplitude margin.

Regards,

Derek Payne

0 Scott Berger over 4 years ago in reply to Derek Payne

Prodigy 20 points

Hi Derek, Sorry I had the wrong part number. My part is LMX2592 and Table 6.1 of the datasheet shows <1.8 Vpp with Vcc applied and <1Vpp with Vcc = 0. My input is 100 MHz sine wave. So, based on your explanation above, I should have an input close to 1.8Vpp assuming Vcc is applied. Thanks, Scott