Harmonic level become very high after lmk00101

Roger Lee44

Other Parts Discussed in Thread: LMK00101

Hi Bro,

I find a harmonic problem when using a lmk00101 output as reference source for a VCO (Analog/Hittile's HMC830) then i test the lmk00101 separately.

I use a ocxo(10MHz/5x10(-8)ppm/clipped sine-wave/amplitude 0dBm@10MHz,-50dBm@20MHz,-60dBm@30MHz) connect to lmk00101's CLKin and measure its output leve. After LMK00101 we got a result: +8dBm@10MHz, -28dBm@20MHz,-2dBm@30MHz and the level reach -50dBm@3GHz even at 5GHz band we could see many signals in spectrum analyzer. When add an adjustable attenuator at OCXO output but it make no effect and lmk00101 lost its output at attenuate value reach 20dB.

I guess the lmk00101 do not work properly could many one give me some advice to solve this problem ?

Thanks a lot.

Roger

over 9 years ago

0 Timothy T over 9 years ago

TI__Mastermind 28590 points

Was the CLKin setup for single ended input? I calculate 0 dBm into 50 ohms as ~0.6 V, so this should be within the input limits for single ended

Do you know the slew rate of the clipped sine signal? Is it > than 2 V/ns?

73,
Timothy

0 Alan O over 9 years ago

TI__Mastermind 32575 points

Hello,

The LMK00101 is a high-speed LVCMOS clock buffer. It is not an analog clock buffer, but rather a "limiting" buffer so it's output will always be a square-wave even if the input is a sine-wave. Because the LVCMOS output has fast edge rate, the output spectrum will indeed have harmonics up to high frequencies.

Alan

0 Roger Lee44 over 9 years ago in reply to Alan O

Prodigy 50 points

Thank you Alan,your answer is clear and do any company provide low cost analog clock buffer ?now we using a analog power divider to replace lmk00101.

0 Roger Lee44 over 9 years ago in reply to Timothy T

Prodigy 50 points

Hi Timothy,
yes,it is for single ended input.
Regards to the slew rate i don't have the data and we'll test. Must >2v/ns ?

0 Alan O over 9 years ago in reply to Roger Lee44

TI__Mastermind 32575 points

Here's a 1:4 analog fanout buffer with near unity-gain:
www.ti.com/.../cdc3s04

Alan

Clock & timing

Clock & timing forum

Harmonic level become very high after lmk00101