Datasheet

Mixed Domain Oscilloscopes — MDO4000 Series

Figure 1 – T

ime and Frequency Domain view showing the turn-on of a VCO/PLL.

Channel 1 (

yellow) is probing a control signal that enables the VCO. Channel 2 (cyan)

is probing

the PLL voltage. The SPI bus which is programming the VCO/PLL with the

desired fr

equency is probed with three digital channels and automatically decoded. Notice

Spectrum

Time is placed after the VCO was enabled and coincident with the command

on the SPI

bus telling the VCO/PLL the desired frequency.

Figure2–SpectrumTimeismovedabout 60 µs to the right. At this point, the spectrum

shows that the VCO/PLL is in the process of tuning to the correct frequency (2.400 GHz).

It has made it up to 2.3168 GHz.

Figure3–S

pectrum Time is moved another 120 µs to the right. At this point the spectrum

shows that

the VCO/PLL has actually overshot the correct frequency and gone all the

way to 2.41

64 GHz.

Figur

e4–TheVCO/PLLeventuallysettlesonthecorrect2.400GHzfrequency about

340 µs

after the VCO was enabled.