PHD Modeling
PHD modeling is a black-box, frequency-domain modeling technique. The annotation black box refers to the fact that no knowledge is used nor required concerning the internal circuitry of the DUT. All information needed to construct a PHD model is acquired through externally stimulating the signal ports of a DUT and measuring the response signals. The frequency domain formulation means that the approach is well suited for distributed (dispersive) high-frequency applications. This is true for both the measurement techniques and the modeling approach. Note that these considerations are true for conventional linear S-parameters, which can also be considered as a black-box frequency-domain modeling technique. The advantage of using a black-box approach is that it is truly technology independent. It does not matter whether one is dealing with silicon bipolar technology or compound semiconductor field-effect transistors. Another advantage is that a black-box model, unlike a circuit schematic, can be shared with and used by other people without revealing the details of the internal circuit. In other words, it provides complete and fundamental protection of intellectual property. This characteristic is highly appreciated in a business environment. Of course, with black-box modeling, as with all engineering solutions, there are tradeoffs to consider in practical use conditions. Black-box models are, by definition, only valid for signals that are close to the signals that were used to simulate the DUT to produce the responses used for model identification (extraction). If the model needs to be valid across a wide range of signals, then a wide range of excitation signals is needed and, as a result, the measurement time will be long and the resulting model will be complex.