The M8190A provides a direct mode, which allows sending sample data from the
sample memory directly to the output of the instrument. Additionally, it provides
mechanisms to do IQ modulation internally (highlighted in blue in Figure 4-1). This
includes the interpolation of IQ sample pairs from a low input data rate to the sampling
rate of the instrument, the generation of a carrier frequency by a Numerically Controlled
Oscillator (NCO) and the IQ modulation itself. Control data that is in time aligned to the
sample data allows changing settings, like the NCO configuration, at run-time.
Therefore, it is possible to change the carrier frequency, the phase and an amplitude
multiplier in real time and sequence control. Complex operations, like a frequency
sweep are also possible.
In direct mode, (see Option -14B, -12G) the samples are sent directly to the DAC. IQ
modulation can be implemented by:
Using two channels providing I and Q data separately to an external analog IQ
modulator. This setup is expensive and causes analog distortions.
IQ modulation can be done by software.
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