CDCLVC1104: About evaluation environment of CDCLVC1104

Hi Ozawa-san

Figures 11 and 12 measure an important parameter for all buffers called additive jitter. It is basically the measure of the noise added to a clean reference clock as it gets distributed by the buffer to several receivers in the application. In order to make this measurement, you will need

1) A low noise reference source (ideally with a noise floor better than the buffer that you are trying to measure the performance of)

2) A phase noise analyzer (such as Agilent 5052 as shown in the datasheet)

Frequency domain analysis of jitter on a reference clock is typically measured on an instrument like the Agilent 5052. This equipment has lower noise floor than even the most state of the art real time oscilloscopes. The measurements are therefore precise and repeatable.

The reference clock (source) phase noise is first measured. The integrated jitter within 12 kHz - 20 MHz integration band (offset from carrier) is calculated and displayed by the equipment. Next this reference is injected into the buffer under test and the output clock from the buffer is routed into the phase noise analyzer for computing the integrated phase jitter over the same integration bandwidth (12 kHz - 20 MHz). The square root of the difference of squares of the output integrated RMS jitter from the device under test and reference source jitter is then calculated and is a measure of the additive jitter of the buffer. The lower this number the better the performance of the buffer. For true performance of the buffer under test, it is crucial to use a very clean reference clock.

Regards

Arvind Sridhar