SYNC Function
X - 48
Function Generators
SYNC Synchronisation function (GX 320 only, contd.)
Example 1:
Generating three phase signals
Connect the three GX 320 generators as shown above (see Connections),
identify a master and 2 slaves and then programme the 3 devices with:
•
the same frequency 1 kHz,
•
the same amplitude 10 Vpp
•
the same offset 0 V
•
the same sine waveform
•
phases 0° (master), +120° and -120°.
Activate the 3 MAIN OUTs.
On an oscilloscope view the output signals from the three devices:
Example 2:
Fourier synthesis
A simple illustration of generator synchronisation is the synthesis of a square
signal using its first harmonics.
The square signal is broken down as follows:
f(x) = 4/
π
(sinx+ sin3x / 3 + sin5x / 5 + sin7x / 7 + ... sinnx / n + ...)
where n is always an odd number.
To synchronise multiple frequencies the values programmed in the DDS must
also be multiple.
We are here faced with the problem of calculation rounding and programming
resolution: it is highly probable that the direct entry on F on the master and n*F
on the slaves will not give synchronous signals.
The DDS is programmed using a 28 bit register and is piloted by a 10 MHz
clock (in the SYNC function).
The DDS frequency resolution for this function is therefore:
10 MHz / 2
28
= 0.037 Hz, which means that for a frequency F entered the
resulting frequency is F
±
18.5 MHz.
The formula relating the user entered frequency to the value programmed in the
DDS is the following:
Val
DDS
= ENT((Frequency
(Hz)
x 2
28
) / DDS 0.5)
with:
ENT( ) function returning the whole part of the value
DDS_Clock = 10 MHz,
adding 0.5 rounds the value.
Channel 1: master (0°)
Channel 2: slave1 (120°)
Channel 3: slave 2 (-120°)