Agilent Technologies 93000 SOC Series Training Manual page 89

N OT E
Sampling Technique
The following figure shows the undersampling technique of the
sampler:
Master Clock
(Digital clock domain)
Phase Lock
Master Clock
(Analog clock domain)
Tin
Tin
Ts
Sample
Ts = K x Tin + Ts_e
(K =2)
Measuring a Periodic Signal Using Undersampling
In the sampler, the sampling period (Ts) is slightly different (Ts_e)
from a multiple of the input signal period (Tin), that is
Ts = K × Tin + Ts_e. (Ts_e is called the equivalent sampling
period.)
To perform coherent sampling by using the undersampling
technique, the following equivalent sampling period requires for
the signal period:
Npoints × Ts_e = Mcycles_e × Tin
where Npoints is the number of sampled data points and
Mcycles_e is the number of captured signal cycles (not input
cycles). Npoints and Mcycles_e should be mutually prime, that is,
they have no common divisor other than 1.
To obtain a very short equivalent sampling period (Ts_e), the
sampling period (Ts) must be freely selectable. This can be achieved
by using a different master clock from the one for the signal to be
captured (the analog clock domain master clock and digital domain
master clock).
Lesson 1 – Analog Modules
Digital I/O Channels
Sampler
Tin Tin
Ts_e
Ts_e
Ts
Clock
Data
DUT
Trigger
Analog Out
Tin Tin
Ts_e
Ts
89