Datasheet

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Mixed Domain Oscilloscopes

of interest, but never both at the same time. This is because

traditional oscilloscopes only have a single acquisition system

with a single set of user settings such as record length,

sample rate, and time per division that drive all data views.

But with the MDO4000C Series, the spectrum analyzer has its

own acquisition system that is independent, but time corre-

lated, to the analog and digital channel acquisition systems.

This allows each domain to be conﬁgured optimally, providing

a complete time correlated system view of all analog, digital,

and RF signals of interest.

The spectrum shown in the Frequency Domain view is taken

from the period of time indicated by the short orange bar

in the time domain view – known as the Spectrum Time.

With the MDO4000C Series, Spectrum Time can be moved

through the acquisition to investigate how the RF spectrum

changes over time. And this can be done while the oscillo-

scope is live and running or on a stopped acquisition.

The upper half of the MDO4000C Series display shows the Time Domain view of

the analog and digital channels, while the lower half shows the Frequency Domain

view of the spectrum analyzer channel. The orange bar – Spectrum Time – shows

the period of time used to calculate the RF spectrum.

1. Time and Frequency Domain view showing the turn-on of a PLL. Channel 1

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

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

the desired frequency 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 PLL the desired frequency

of 2.400 GHz. Note that the RF is at 2.5564 GHz when the circuit turns on.

2. Spectrum Time is moved about 90 μs to the right. At this point, the spec-

trum shows that the PLL is in the process of tuning to the correct frequency

(2.400 GHz). It has made it down to 2.4924 GHz.

3. Spectrum Time is moved another 160 μs to the right. At this point the spectrum

shows that the PLL has actually overshot the correct frequency and gone all the

way down to 2.3888 GHz.

4. The PLL eventually settles on the correct 2.400 GHz frequency about 320 μs

after the VCO was enabled.