Signal Combination

The defining feature of the HPP is that the Plasma Frequency Probe DDS output can be superimposed on the Langmuir Probe DAC output.  This has been implemented with a level shifting op-amp configuration.  This combined signal is then sent to the sensor head and the microprocessor will determine what changes need to be made to the DAC and DDS in order to complete Langmuir Probe voltage sweeps and/or track the plasma resonant frequency.  As discussed previously, there is no clear negative implication for the HPP by combining these features.  There are many positive ramifications however.  For example, the Fast Temperature Probe mode of operation becomes available.  Here, only a very small amplitude AC signal from the DDS is superimposed on a fixed bias output from the DAC.  The science benefits in this case by the ability to make very fast, accurate measurements of the electron temperature.