GW Instek GFG-3015 - Manual (Page 54)

p. 50 GFG-3015
(6) Amplitude and DC offset
The Amplifier of GFG-3015 is similar to lineally multiplier (EL4451). The amplitude
of this amplifier varies with the different control voltage.
The control voltage comes from the Amplitude of the D/A converter. The MPU
puts a specific value to the D/A converter which will generate a corresponding
voltage to main output Amplifier, from which, user will get different output
amplitude.
The procedure of the amplitude setting is similar to that of DC offset setting,
except that there is another D/A converter (Offset adjust D/A) to change the DC
offset of output amplifier.
(7) Modulation Function
The GFG-3015 provides two different kinds of modulation functions, one is
Amplitude modulation and the other is Frequency modulation.
The instrument has another internal independent function generator which can
generate Sine, Triangle, and Square waveform with the frequency range from
0.01Hz to 10kHz, and the symmetry and amplitude of waveform are adjustable.
The full function generator is used to make the source for modulation even trigger
function.
The detailed principles of modulation is as follows:
1. Amplitude Modulation
The AM function block is for general purpose of the Amplitude modulation
circuit (MC1496), including a carrier signal input, an audio signal input and a
modulation output. The output amplitude of carrier signal is decided by the
audio signal.
The carrier signal is obtained from the main waveform (can select Sine,
Triangle and Square), and the audio signal is obtained from a internal
independent of function generator.
Set all the parameters of Amplitude modulation by selecting the Waveform
(modulation source), the Amplitude (Span), the Frequency (Rate) and the
Duty (Symmetry) of the generator.
The output of AM function block is to correct AM waveform and pass the
output amplifier, the ATT, and the output through the Main Output terminal.
The function includes the internal modulation and the external modulation with
the same operation procedure, except that the modulation signal source is
obtained from the external MOD input terminal.
2. Frequency Modulation
The principles of the VCF have been described previously, the voltage varies
with the different frequency, and the signal obtained from the internal
independent function generator is put to the main frequency D/A, then the
frequency of the VCF will be according to this signal.
Set all the parameters of the Frequency modulation by selecting the
Waveform (modulation source), the Amplitude (Span), the Frequency (Rate)
and the Duty (Symmetry) of the generator.
The output of VCF will become FM function waveform and pass the waveform
choice, the output amplifier, the ATT, and the output through the Main Out
terminal.
This function includes internal modulation and external modulation with the
same operation procedure. The only difference with external modulation is
that the modulation signal source will come from external MOD input terminal.